Systematics of Agricultural Animals and Aquaculture

1.1. Introduction: What Are “Agricultural Animals” from the Standpoint of Systematics

Agricultural animals are not a taxonomic but an economic category. It includes species that humans deliberately breed to obtain food, raw materials, draft power, and also to perform other functions — guarding, herding, sport, and decorative. From a systematic standpoint, these species are distributed across several classes and orders of the phylum Chordata, as well as across the phyla Mollusca and Arthropoda, and even across the kingdom Bacteria (cyanobacteria used in aquaculture). It is precisely this mismatch between economic and taxonomic logic that constitutes the main methodological problem to be mastered from the very beginning.

Traditionally, in animal husbandry courses, agricultural animals are treated as a single group, contrasted with “wild” animals. However, from the standpoint of biological systematics, such an grouping is artificial: cattle (Bos taurus) and, for example, the oyster (Crassostrea gigas) are not close relatives, yet both are involved in agricultural production. Therefore, within the discipline “Systematics and Taxonomy of Organisms of the Agrosphere,” we must clearly distinguish two approaches:

1. Phylogenetic approach — reflects real kinship relationships between organisms, based on common ancestors and molecular data.

2. Economic approach — groups organisms by their practical use, ignoring kinship.

The task of this lecture is to show how these two approaches relate to each other, and why it is equally important for a practitioner (animal scientist, veterinarian, fish farmer) to master both.

1.2. Diversity of Species Used in Animal Husbandry and Aquaculture

The number of species involved in agricultural production is relatively small compared with the total number of described animal species. According to estimates, out of approximately 1.5 million described animal species, only a few dozen have been domesticated in the full sense of the word (Clutton-Brock, 1999). At the same time, the main efforts of animal husbandry are concentrated on a very narrow set of taxa.

Among vertebrates, these are primarily:

• Mammals (class Mammalia): cattle, sheep, goats, pigs, horses, donkeys, camels, llamas, alpacas, rabbits, nutria, chinchillas, dogs, cats.
• Birds (class Aves): chickens, turkeys, ducks, geese, guinea fowl, quails, ostriches, pigeons.
• Ray-finned fishes (class Actinopterygii): carp, salmon, trout, tilapia, catfish, sturgeons, eels, and many others.
• Reptiles and amphibians: on a limited scale — crocodiles, turtles, frogs.

Among invertebrates:

• Mollusks (phylum Mollusca): oysters, mussels, scallops, sea scallops, cephalopods (squid, octopus — mainly fishery, but cultivation work is underway).
• Arthropods (phylum Arthropoda): shrimp, crabs, crayfish, lobsters, spiny lobsters.
• Echinoderms: sea urchins, sea cucumbers (trepang).
• Cyanobacteria and algae: spirulina, kelp, nori, gracilaria (Stickney, 2022; Wickins & Lee, 2002).

As we can see, even within aquaculture we go beyond the phylum Chordata: mollusks and arthropods belong to different phyla, and spirulina belongs to prokaryotes altogether. This once again emphasizes that “agricultural animals” is a purely applied category.

1.3. Importance of Accurate Species Identification for Practice

Accurate species identification is not an academic exercise but an urgent necessity for a specialist in the agrosphere. Let us consider several aspects.

Breeding and selection. Different species have different chromosome numbers, different ages of sexual maturity, and different mating systems. An error in species identification can lead to unsuccessful crossing attempts or to the production of infertile offspring. For example, the mule (a hybrid of donkey and horse) is infertile, whereas hybrids of cattle and yak (dzo) produce fertile females but infertile males (Clutton-Brock, 1999; Jones & Bartlett, 2015). These patterns follow directly from the taxonomic affiliation of the parents.

Veterinary medicine. Disease agents are often species-specific. For example, the African swine fever virus affects only pigs and wild boars, but not cattle. Vaccines and therapeutic drugs are developed taking into account the host species. In addition, different species have different sensitivities to the same toxins and drugs. Accurate identification makes it possible to choose the correct treatment and prevention scheme.

Feeding. Nutrient requirements differ not only between species but also between breeds and lines within a species. For example, ruminants (cattle, sheep, goats) use microbial fermentation in the forestomach, whereas pigs and poultry are monogastric animals with a different digestive strategy. An error in species identification can lead to incorrect ration formulation and economic losses (Scanes, 2020; Wickins & Lee, 2002).

Quarantine and biosecurity. When animals are moved across borders, veterinary services are guided by lists of species prohibited or restricted for import. For example, the import of live oysters from areas unfavorable for certain diseases is prohibited. In aquaculture, there is a practice of certifying “specific pathogen free” (SPF) lines (Wickins & Lee, 2002; Stickney, 2022).

Aquaculture. The choice of a cultivation object requires accurate knowledge of its biology: temperature optimum, salinity, feeding spectrum, growth rate. Moreover, hybridization and polyploidy (for example, obtaining triploid oysters) require accurate identification of parental species and control of offspring ploidy (Stickney, 2022; Gosling, 2015).

Thus, systematics provides the conceptual apparatus without which competent practical activity is impossible.

1.4. The Problem of Mixing Taxonomic and Economic Categories

One of the most common errors in agricultural literature is the mixing of taxonomic ranks with economic categories. Let us consider the basic concepts.

Species (species) — a biological category. It is a set of populations capable of interbreeding and producing fertile offspring, but reproductively isolated from other such sets. A species is an objective unit of living nature, existing independently of humans. For example, Bos taurus is the species of cattle (humpless), Bos indicus is the species of zebu (humped cattle), Ovis aries is the species of domestic sheep, Capra hircus is the species of domestic goat (Clutton-Brock, 1999; Jones & Bartlett, 2015).

Breed — an economic category. It is a group of animals within a species, created by humans through artificial selection and possessing stable hereditary traits (productivity, exterior, coat color, temperament). A breed has no status in biological nomenclature and cannot be designated by a trinomial name. For example, Holstein, Simmental, and Shorthorn are breeds of cattle, but all of them belong to the species Bos taurus. Similarly, White Leghorn, Rhode Island Red, and Cornish are breeds of chickens of the species Gallus gallus domesticus (Scanes, 2020).

Line — an intra-breed group obtained through targeted selection and often maintained by inbreeding. Lines can be “closed” (not allowing the introduction of outside blood) and used in heterosis crosses. Example: broiler chicken lines, pig lines in hybridization systems (Scanes, 2020).

Hybrid — the result of crossing two different species, breeds, or lines. In animal husbandry, the following are distinguished:

• Interspecific hybrids: mule (donkey × horse), dzo (cow × yak), zebroid (zebra × horse), sturgeon hybrids.
• Interbreed hybrids (crosses): broiler chicken crosses, pig hybrids.
• Intra-breed hybrids (line crosses).

It is important to understand: a hybrid is not a taxonomic category but the result of a specific crossing, which can be described in terms of the parental forms.

Polyploidy — a phenomenon in which an organism has more than two sets of chromosomes. In aquaculture, triploids are widely used (for example, oysters, salmon) to obtain sterile, fast-growing individuals. A triploid is not a species or a breed, but a genetic modification within a species (Stickney, 2022; Gosling, 2015).

Thus, mixing these categories leads to confusion: for example, the statement “Holstein breed is a species” is incorrect; it is correct to say “the Holstein breed belongs to the species Bos taurus.” Similarly, “broiler” is not a taxon but a product of crossing lines.

2.1. Introduction: The Place of Agricultural Animals in the System of the Organic World

Agricultural animals, as we established in the previous chapter, are an economic rather than a taxonomic category. To understand their biological characteristics, breeding possibilities, feed requirements, and susceptibility to diseases, it is necessary to clearly understand their phylogenetic position — that is, their place on the evolutionary tree of life.

The overwhelming majority of agricultural animals belong to the phylum Chordata — chordates, and to the subphylum Vertebrata — vertebrates (Pough, 2013). The exception is aquaculture objects among invertebrates: mollusks (oysters, mussels, scallops), arthropods (shrimp, crabs, crayfish), and echinoderms (sea urchins, sea cucumbers), as well as cyanobacteria (spirulina) and algae (kelp, nori). However, in this section we will focus specifically on vertebrates, since they form the basis of animal husbandry and a significant part of aquaculture (Stickney, 2022; FAO, 2007).

2.2. Phylum Chordata: The General Framework

The phylum Chordata unites animals characterized by four key features that appear at least at one stage of the life cycle (Hickman, 2004; Pough, 2013):

1. Notochord — a dorsal stiffening rod, an elastic cord located along the dorsal side of the body.

2. Dorsal hollow nerve cord — a nervous system that forms as a tube above the notochord.

3. Pharyngeal slits — paired openings in the pharyngeal wall, in vertebrates transformed into gills or their derivatives.

4. Post-anal tail — a muscular tail located behind the anus.

Modern chordates are divided into three subphyla (Pough, 2013):

• Urochordata — tunicates (ascidians, salps, appendicularians). Marine filter feeders, not used in agriculture.
• Cephalochordata — cephalochordates (lancelets). Marine animals with no agricultural significance.
• Craniata (Vertebrata) — craniates, or vertebrates. It is to this subphylum that the overwhelming majority of agricultural animals belong.

Thus, agricultural animals are a branch of vertebrates, which in turn is divided into a number of large evolutionary lineages.

2.3. Subphylum Vertebrata: General Characteristics

Vertebrates differ from other chordates by the presence of (Pough, 2013; Hickman, 2004):

• A cranium protecting the brain.
• A vertebral column — a series of bony or cartilaginous elements replacing the notochord in adults.
• A three-part brain (forebrain, midbrain, hindbrain).
• Paired sense organs — eyes, olfactory capsules, inner ear.
• A heart consisting of chambers (in ancestral forms — two, in more advanced — three or four).
• Bone or cartilage tissue in the skeleton.
• Neural crest — embryonic tissue giving rise to many structures of the head and peripheral nervous system.

Vertebrates are traditionally divided into two large groups: Agnatha (jawless) and Gnathostomata (jawed). Agricultural animals belong exclusively to jawed vertebrates.

2.4. Agnatha: Jawless Vertebrates

Jawless vertebrates include modern lampreys (Petromyzontiformes) and hagfishes (Myxiniformes), as well as a number of extinct groups (Pough, 2013; Nelson, 2016). These animals lack jaws, paired fins, and true bones. They are not objects of agriculture, but they are important for understanding vertebrate evolution: it was from ancient jawless vertebrates that jawed vertebrates arose.

Lampreys and hagfishes are a paraphyletic group (Pough, 2013). Lampreys are ectoparasites of fish, hagfishes are scavengers. Their study helps to understand the origin of jaws, which in evolution arose from the first gill arch.

2.5. Gnathostomata: Jawed Vertebrates

Jawed vertebrates constitute the overwhelming majority of modern vertebrates. They are characterized by the presence of jaws, paired limbs (fins or legs), three semicircular canals in the inner ear, and a number of other features (Pough, 2013). Jawed vertebrates are divided into two large trunks: Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes). Bony fishes, in turn, include Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes), from the latter of which terrestrial vertebrates — tetrapods — arose (Pough, 2013; Nelson, 2016).

2.6. Tetrapoda: Four-Limbed Vertebrates

Tetrapods are vertebrates with two pairs of limbs (or their derivatives). The key event in their evolution was the transition to land, associated with the development of lungs, cutaneous respiration, strengthening of the skeleton, and the appearance of the five-toed limb (Pough, 2013). In agriculture, tetrapods are represented by amphibians (limited), reptiles (limited), birds, and mammals.

2.7. Key Evolutionary Events and Their Significance for Agriculture

Understanding phylogeny allows us to see which evolutionary acquisitions underlie the biology of agricultural animals.

1. Transition to land (tetrapods). It led to the development of lungs, cutaneous respiration, and strengthening of the skeleton. Agricultural animals are terrestrial or secondarily aquatic (fish, some reptiles). For terrestrial animals, strong limbs, efficient respiration, and protection from desiccation are important.

2. Amniotic egg (amniotes). It allowed reproduction on land. Amniotes are reptiles, birds, and mammals. In birds and reptiles, the egg is covered with a shell; in mammals, development is intrauterine. This determines different breeding strategies: incubation of eggs in birds, gestation in mammals.

3. Warm-bloodedness (endothermy). It developed independently in birds and mammals. It provides a high metabolic rate, activity, and resistance to temperature fluctuations. This allows agricultural animals to live in different climatic zones, but requires high feed costs.

4. Mammary glands (mammals). They allow feeding offspring with milk, which increases survival. In agriculture, milk productivity is one of the key traits.

5. Heterodonty and differentiation of teeth (mammals). Different teeth for different functions (incisors, canines, premolars, molars). This is related to the type of feeding: herbivores, carnivores, omnivores. It determines feed rations.

6. Four-chambered stomach (ruminants). It allows efficient digestion of plant food with the help of microorganisms. This is the basis for feeding cattle, sheep, and goats.

7. Hybridization and polyploidy in aquaculture. They are used to obtain fast-growing, sterile, or disease-resistant forms (Stickney, 2022; Gosling, 2015).

2.8. The Place of Agricultural Animals in the Phylogenetic Tree

To summarize: agricultural animals are distributed across several large branches of vertebrates:

• Actinopterygii (ray-finned fishes) — the main objects of aquaculture.
• Sarcopterygii → Tetrapoda → Amphibia (limited), Reptilia (limited), Aves (birds), Mammalia (mammals).

At the same time, invertebrate aquaculture objects (mollusks, arthropods) are outside vertebrates, in other phyla of the animal kingdom (Stickney, 2022; Wickins & Lee, 2002).

3.1. Introduction: The Place of Mammals in Animal Husbandry

Mammals (class Mammalia) are a group of vertebrates that has given humanity the greatest number of domesticated species and still remains the basis of animal husbandry in most countries of the world. It is among mammals that cattle, sheep, goats, pigs, horses, camels, rabbits, as well as fur-bearing animals and working dogs are found (Clutton-Brock, 1999; FAO, 2007). According to the Food and Agriculture Organization of the United Nations, mammals provide a significant part of world production of meat, milk, wool, and leather raw materials (FAO, 2007).

From a systematic standpoint, agricultural mammals are distributed across several orders, which we will consider sequentially: Artiodactyla (even-toed ungulates), Perissodactyla (odd-toed ungulates), Lagomorpha (lagomorphs), Rodentia (rodents), and Carnivora (carnivores). This order reflects both phylogenetic kinship and economic importance of the groups.

3.2. Order Artiodactyla — Even-Toed Ungulates

Even-toed ungulates are the largest and economically most important order of agricultural mammals. Its name reflects a key feature: the axis of the limb passes between the third and fourth digits, which bear the main load (Pough, 2013; Jones & Bartlett, 2015). The first digit is absent in modern forms, and the lateral digits (second and fifth) are reduced to varying degrees. In the most advanced representatives (ruminants), a “cannon bone” develops — the fusion of the third and fourth metapodials, which provides strength and specialization of the limb for fast running (Jones & Bartlett, 2015).

Modern systematics of even-toed ungulates has undergone significant changes due to molecular data. In particular, cetaceans (Cetacea) turned out to be closer to hippopotamuses than to other even-toed ungulates, so the clade Cetartiodactyla is now used (Jones & Bartlett, 2015; Pough, 2013). However, for the purposes of agricultural systematics, it is convenient to consider the traditional groups within Artiodactyla: Bovidae, Cervidae, Suidae, Camelidae.

3.3. Order Perissodactyla — Odd-Toed Ungulates

Odd-toed ungulates are characterized by the axis of the limb passing through the third digit, which bears the main load. The lateral digits are reduced. This order includes horses, donkeys, zebras, as well as tapirs and rhinoceroses (Jones & Bartlett, 2015; Pough, 2013).

In agriculture, odd-toed ungulates are represented mainly by the family Equidae — equids.

3.4. Order Lagomorpha — Lagomorphs

Lagomorphs are rabbits, hares, and pikas. They differ from rodents by the presence of a second pair of upper incisors located behind the first, as well as by features of digestion (coprophagy) (Jones & Bartlett, 2015; Pough, 2013).

The domestic rabbit (Oryctolagus cuniculus) descends from the wild European rabbit inhabiting the Iberian Peninsula. Domestication began in Ancient Rome, where rabbits were kept in enclosures (leporaria) for meat (Clutton-Brock, 1999). Later, in the Middle Ages, monks began breeding rabbits in cages, which led to the appearance of numerous breeds.

Rabbits are bred for meat, hides, and down. There are more than 100 rabbit breeds in the world (FAO, 2007). Rabbit farming is developed in China, Italy, France, Spain, Russia, and other countries.

3.5. Order Rodentia — Rodents

Rodents are the most numerous order of mammals. In agriculture, they are represented mainly by fur-bearing animals: nutria (Myocastor coypus), chinchilla (Chinchilla lanigera), muskrat (Ondatra zibethicus) (Jones & Bartlett, 2015; FAO, 2007). These animals are bred for valuable fur.

Nutria originates from South America and has been acclimatized in many countries of Europe and Asia. Chinchilla is a native of the Andes, bred on farms for exceptionally soft and warm fur. Muskrat is a North American rodent, also acclimatized in Eurasia.

In addition, rodents (mice, rats) are used as laboratory animals in biomedical research (Jones & Bartlett, 2015).

3.6. Order Carnivora — Carnivores

Carnivores are an order of mammals including dogs, cats, bears, mustelids, viverrids, etc. In agriculture, carnivores are represented mainly by dogs and cats, as well as fur-bearing animals (mink, fox, arctic fox) (Jones & Bartlett, 2015; Clutton-Brock, 1999).

3.7. Importance of Mammal Systematics for Animal Husbandry

The systematics of mammals has direct practical significance:

1. Breeding and selection. Knowledge of phylogenetic relationships makes it possible to predict the success of crossing, assess genetic diversity, and plan heterosis crosses. For example, crossing Bos taurus and Bos indicus produces fertile offspring, whereas crossing with yak produces only partially fertile offspring (Clutton-Brock, 1999; FAO, 2007).

2. Veterinary medicine. The species-specificity of diseases determines the strategy of vaccination and treatment. For example, the African swine fever virus affects only pigs and wild boars, but not cattle (FAO, 2007).

3. Feeding. The type of digestion (ruminant, monogastric, omnivorous) determines the composition of rations. Knowledge of systematic affiliation allows correct selection of feeds and additives.

4. Quarantine. When animals are moved across borders, veterinary services are guided by taxonomic lists prohibiting or restricting the import of certain species.

5. Conservation of genetic resources. Accurate identification of breeds and lines is necessary for preserving the biodiversity of agricultural animals (FAO, 2007).

4.1. Introduction: The Place of Birds in Systematics and Agriculture

Birds (class Aves) are a group of warm-blooded egg-laying vertebrates characterized by feathers, a beak, the absence of teeth, a high metabolic rate, and complex behavior (Gill, 2019). In modern phylogenetic systematics, birds are considered part of the clade Archosauria, the sister group to crocodiles, and their closest extinct relatives are dinosaurs (Pough, 2013; Gill, 2019). Traditionally, birds are separated into a distinct class, which is convenient for practical purposes, including the systematics of agricultural animals.

Poultry farming is one of the most dynamically developing branches of animal husbandry. According to FAO, world production of poultry meat has exceeded the production of beef and mutton, yielding only to pork (Scanes, 2020; FAO, 2007). Birds provide humanity with eggs, meat, feathers, down, and are also used for decorative and sporting purposes.

From a systematic standpoint, agricultural birds belong to several orders: Galliformes (gallinaceous birds), Anseriformes (waterfowl), Columbiformes (pigeons and doves), and Struthioniformes (ostriches). Let us consider them sequentially.

4.2. Class Aves: General Characteristics

Key features of birds significant for agriculture:

• Feather cover — provides thermal insulation, aerodynamics, and protection.
• Beak — horny, without teeth, the shape of which reflects the type of feeding.
• Warm-bloodedness (endothermy) — high and constant body temperature (40–44 °C), high metabolic rate.
• Egg-laying — large eggs with a dense shell, requiring incubation.
• Complex behavior — social structure, parental care, ability to learn.
• High digestive efficiency — fast metabolism, presence of a crop, muscular stomach, and ceca.

These features determine the requirements for keeping, feeding, and breeding birds (Scanes, 2020; Gill, 2019).

4.3. Order Galliformes — Gallinaceous Birds

Gallinaceous birds are the most important order of agricultural birds. It includes the family Phasianidae (pheasants), to which chickens, turkeys, guinea fowl, quails, and pheasants belong, and the family Numididae (guinea fowl). Characteristic features: dense build, strong legs adapted for scratching the ground, short wings, large eggs, and precocial development of chicks (Gill, 2019; Scanes, 2020).

4.4. Order Anseriformes — Waterfowl

Waterfowl are the second most important order of agricultural birds. It includes the family Anatidae (ducks, geese, swans). Characteristic features: aquatic lifestyle, webbed feet, broad beak with lamellae for filtering, dense plumage with down, and large eggs (Gill, 2019; Scanes, 2020).

4.5. Order Columbiformes — Pigeons and Doves

Columbiformes include pigeons and doves. The domestic pigeon (Columba livia domestica) descends from the rock dove. It was domesticated in ancient times and used for postal communication, meat, and decorative purposes (Gill, 2019; Scanes, 2020). Meat breeds of pigeons (for example, King, Carneau) are bred for delicacy meat. Pigeon breeding is developed in Europe, the USA, and China.

4.6. Order Struthioniformes — Ostriches

Struthioniformes are large flightless birds. The African ostrich (Struthio camelus) is the largest modern representative. Ostrich domestication began in South Africa in the 19th century, initially for feathers, and later for meat, hides, and eggs. Ostrich farming is developed in South Africa, Namibia, Zimbabwe, Australia, Europe, and Russia (Scanes, 2020; Gill, 2019). Ostrich meat is considered dietary, and the hide is valued in the leather industry.

4.7. Features of the Systematics of Poultry Breeds and Crosses

In poultry farming, as in animal husbandry, it is necessary to strictly distinguish taxonomic and economic categories.

• Species — a biological category. For example, Gallus gallus is the species of red junglefowl, including domestic breeds.
• Breed — an economic category created by humans. For example, White Leghorn, Cornish, Plymouth Rock are chicken breeds.
• Cross (hybrid) — the result of crossing specialized lines. Industrial poultry farming uses four-line crosses possessing heterosis (Scanes, 2020).
• Line — an intra-breed group maintained by inbreeding.

It is important to understand that a breed has no taxonomic status and cannot be designated by a trinomial name. For example, “chicken of the White Leghorn breed” is correct; “Gallus gallus domesticus legorn” is incorrect.

4.8. Importance of Bird Systematics for Poultry Farming

Accurate systematics of birds is necessary for:

1. Breeding and selection. Knowledge of phylogenetic relationships makes it possible to predict the success of crossing, plan heterosis crosses, and assess genetic diversity.

2. Veterinary medicine. The species-specificity of diseases (for example, avian influenza, Newcastle disease) determines the strategy of vaccination and quarantine.

3. Feeding. Different bird species have different nutrient requirements. For example, chickens and turkeys require different rations.

4. Quarantine. When birds are moved across borders, veterinary services are guided by taxonomic lists.

5. Conservation of genetic resources. Accurate identification of breeds and lines is necessary for preserving the biodiversity of agricultural birds (FAO, 2007).

5.1. Introduction: The Place of Ray-Finned Fishes in Aquaculture

Ray-finned fishes (class Actinopterygii) are the most numerous group of vertebrates, numbering more than 30,000 species (Nelson, 2016). It is among them that almost all the most important objects of world aquaculture are found. According to FAO, in 2018 world aquaculture production reached 82.1 million tons, of which 54.3 million tons were fish (Stickney, 2022; FAO, 2020). Ray-finned fishes provide humanity with valuable protein, omega-3 fatty acids, vitamins, and minerals.

From a systematic standpoint, ray-finned fishes belong to the class Actinopterygii, which together with the class Sarcopterygii (lobe-finned fishes) forms the superclass Osteichthyes (bony fishes) (Nelson, 2016; Pough, 2013). Unlike cartilaginous fishes (Chondrichthyes), ray-finned fishes have a bony skeleton, an operculum, a swim bladder (or its derivatives), and usually thin scales (Helfman, 2009; Nelson, 2016).

In this chapter we will consider the most important orders of ray-finned fishes cultivated in aquaculture: Salmoniformes, Cypriniformes, Perciformes, Siluriformes, Acipenseriformes, and also briefly touch on other groups. We will separately discuss hybridization and polyploidy, as well as other aquaculture objects (mollusks, crustaceans, algae).

5.2. Order Salmoniformes — Salmonids

Salmonids are one of the commercially most valuable orders. It includes the family Salmonidae (salmonids), to which salmon, trout, char, whitefish, and grayling belong (Nelson, 2016; Helfman, 2009). Characteristic features: adipose fin, absence of spiny rays in the fins, presence of pyloric caeca, and the ability for anadromous migrations (in many species) (Helfman, 2009).

Most important aquaculture objects:

• Atlantic salmon (Salmo salar) — the main object of marine aquaculture in Norway, Chile, Scotland, and Canada. It is grown in cages and net pens. World production exceeds 2 million tons (Stickney, 2022; FAO, 2020).
• Rainbow trout (Oncorhynchus mykiss) — the most widespread object of freshwater aquaculture. It is bred in ponds, tanks, and cages. It is used for sport fishing and commercial cultivation (Stickney, 2022).
• Coho salmon (Oncorhynchus kisutch), chinook salmon (O. tshawytscha), chum salmon (O. keta) — Pacific salmon bred in North America, Japan, and Russia. They are used for sea ranching (Stickney, 2022).
• Chars (Salvelinus spp.) — Arctic char (S. alpinus) and other species bred in cold-water farms.

Salmon farming is one of the most dynamically developing branches of aquaculture. However, it faces problems: spread of diseases (infectious salmon anemia), parasites (sea lice), and genetic pollution of wild populations during escapes (Stickney, 2022).

5.3. Order Cypriniformes — Cyprinids

Cypriniformes are the largest order of freshwater fishes, including more than 4,000 species. In aquaculture, the family Cyprinidae (carps and minnows) is of greatest importance (Nelson, 2016; Helfman, 2009). Characteristic features: absence of teeth on the jaws (teeth located in the pharynx), presence of the Weberian apparatus (in otophysans), usually two or three rows of pharyngeal teeth (Helfman, 2009).

Most important aquaculture objects:

• Carp (Cyprinus carpio) — one of the oldest objects of cultivation (China, more than 2,000 years ago). Bred in ponds, cages, and tanks. World production — more than 4 million tons (Stickney, 2022; FAO, 2020). Breeds: mirror, leather, scaly, Ukrainian, Parsi, etc.
• Grass carp (Ctenopharyngodon idella) — a herbivorous fish used for controlling aquatic vegetation and as a commercial fish. Bred in China, Russia, and Central Asia (Stickney, 2022).
• Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) — filter feeders feeding on phytoplankton and zooplankton. Widely bred in polyculture with carp (Stickney, 2022).
• Crucian carp (Carassius auratus) — silver crucian carp (C. gibelio) and gold crucian carp (C. carassius). Bred in China, Russia, and Eastern Europe.
• Bream (Abramis brama), tench (Tinca tinca), ide (Leuciscus idus) — secondary objects of pond aquaculture.

Cypriniformes are the basis of freshwater aquaculture in China, India, Southeast Asia, and Eastern Europe. They are unpretentious, fast-growing, disease-resistant, and tolerate low oxygen content well (Stickney, 2022; Helfman, 2009).

5.4. Order Perciformes — Perch-Like Fishes

Perciformes are the largest order of fishes, including more than 10,000 species. In aquaculture, the families Cichlidae, Moronidae, Sparidae, Scombridae, Latidae, etc., are of greatest importance (Nelson, 2016; Helfman, 2009).

Most important aquaculture objects:

• Tilapia (Oreochromis spp., Tilapia spp.) — native to Africa and the Middle East. Bred in warm fresh and brackish waters. World production — more than 4.5 million tons (Stickney, 2022; FAO, 2020). Nile tilapia (O. niloticus) is the main species. Tilapia is unpretentious, fast-growing, disease-resistant, but sensitive to low temperatures.
• European perch (Perca fluviatilis) and pikeperch (Sander lucioperca) — valuable predatory fishes bred in Europe, Russia, and Kazakhstan. Used for commercial cultivation and stocking of water bodies (Stickney, 2022).
• European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) — the main objects of marine aquaculture in the Mediterranean. Bred in cages and tanks (Stickney, 2022).
• Barramundi (Lates calcarifer) — a valuable aquaculture object in Australia and Southeast Asia. Grows quickly and reaches large sizes (Stickney, 2022).
• Tuna (Thunnus spp.) — mainly a fishery species, but cultivation work is underway (bluefin tuna, T. thynnus). Cultivation is based on catching young individuals and fattening them in cages (Stickney, 2022).

Perciformes are the most important group of marine and warm-water aquaculture. They occupy upper trophic levels, require protein feeds, but have high growth rates and are valued on the market (Stickney, 2022).

5.5. Order Siluriformes — Catfishes

Siluriformes are a large order including more than 3,000 species. Characteristic features: absence of scales, presence of barbels, spiny rays in the fins (in many), and the ability to breathe atmospheric air (in some) (Nelson, 2016; Helfman, 2009).

Most important aquaculture objects:

• Channel catfish (Ictalurus punctatus) — the main aquaculture object in the USA. Bred in ponds, tanks, and cages. World production — more than 500,000 tons (Stickney, 2022).
• North African catfish (Clarias gariepinus) — an African catfish bred in Africa, Asia, and Europe. Resistant to low oxygen content, fast-growing, unpretentious (Stickney, 2022).
• Pangasius (Pangasianodon hypophthalmus) — the main aquaculture object in Vietnam. Exported to the USA, Europe, and Russia. World production — more than 1.5 million tons (Stickney, 2022; FAO, 2020).
• African catfish (Heterobranchus longifilis), Indian catfish (Clarias batrachus) — secondary objects.

Siluriformes are an important group of warm-water aquaculture. They are omnivorous, fast-growing, disease-resistant, and tolerate high stocking densities well (Stickney, 2022; Helfman, 2009).

5.6. Order Acipenseriformes — Sturgeons and Paddlefishes

Acipenseriformes are an ancient group of fishes that have retained a number of primitive features: cartilaginous skeleton, absence of vertebrae, heterocercal caudal fin, and spiracle (Nelson, 2016; Helfman, 2009). It includes the families Acipenseridae (sturgeons) and Polyodontidae (paddlefishes).

Most important aquaculture objects:

• Russian sturgeon (Acipenser gueldenstaedtii), Siberian sturgeon (A. baerii), beluga (Huso huso), sterlet (A. ruthenus), sevruga (A. stellatus) — bred for meat and caviar (black caviar). Sturgeon farming is developed in Russia, Iran, China, the USA, and Europe (Stickney, 2022; FAO, 2020).
• Paddlefish (Polyodon spathula) — a filter feeder bred in the USA, Russia, and China.
• Sturgeon hybrids (for example, bester — a hybrid of beluga and sterlet) possess increased viability and grow quickly (Stickney, 2022).

Sturgeon farming is an important branch of aquaculture aimed at conserving endangered species and obtaining valuable products. However, sturgeons grow slowly, mature late, and require clean water (Stickney, 2022).

5.7. Other Groups of Cultivated Fishes

In addition to the listed orders, representatives of other groups are used in aquaculture:

• Anguilliformes — European eel (Anguilla anguilla), Japanese eel (A. japonica). Bred in Japan, China, and Europe. The difficulty of breeding is associated with a long larval period and migrations (Stickney, 2022).
• Pleuronectiformes — plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), halibut (Hippoglossus hippoglossus). Bred in Europe, Canada, and Japan (Stickney, 2022).
• Mugiliformes — mullet (Mugil cephalus). Bred in the Mediterranean, Egypt, Israel, and Southeast Asia (Stickney, 2022).
• Characiformes — arapaima (Arapaima gigas), tambaqui (Colossoma macropomum). Bred in South America (Stickney, 2022).
• Cyprinodontiformes — guppies, swordtails, mollies (aquarium fishes). Bred for decorative purposes (Stickney, 2022).

5.8. Hybridization and Polyploidy in Fish Farming

Hybridization and polyploidy are important tools of genetic improvement in aquaculture (Stickney, 2022; Gosling, 2015).

• Hybridization — crossing different species, breeds, or lines. It is used to obtain heterosis (hybrid vigor), increase viability, growth rate, and disease resistance. Examples: sturgeon hybrids (bester), tilapia hybrids, carp and crucian carp hybrids (Stickney, 2022).
• Polyploidy — an increase in the number of chromosome sets. Triploids (3n) are sterile, which allows energy to be directed to growth rather than reproduction. Tetraploids (4n) are used to obtain triploids by crossing with diploids (2n). Polyploidy is widely used in oyster farming (Crassostrea gigas), but is also used for salmonids, cyprinids, and sturgeons (Stickney, 2022; Gosling, 2015).
• Gynogenesis — development of offspring only from maternal heredity. Used to obtain inbred lines (Stickney, 2022).

5.9. Other Aquaculture Objects (Brief Overview)

Aquaculture is not limited to fishes. Important objects include:

5.10. Importance of Systematics for Aquaculture

Accurate systematics of fishes and other aquaculture objects is necessary for:

1. Choice of cultivation objects. Different species have different requirements for temperature, salinity, feeds, and growth rate. An error in identification can lead to failure.

2. Breeding and selection. Knowledge of phylogenetic relationships makes it possible to predict the success of hybridization, plan heterosis crosses, and assess genetic diversity.

3. Veterinary medicine. The species-specificity of diseases (for example, viral hemorrhagic septicemia of salmonids, white spot disease of shrimp) determines the strategy of vaccination, treatment, and quarantine.

4. Feeding. Nutrient requirements differ between species. For example, salmonids require high-protein feeds with high fat content, while cyprinids require less calorie-dense feeds.

5. Quarantine and biosecurity. When aquatic organisms are moved across borders, veterinary services are guided by taxonomic lists prohibiting or restricting the import of certain species.

6. Conservation of genetic resources. Accurate identification of breeds, lines, and hybrids is necessary for preserving the biodiversity of aquaculture objects (FAO, 2007; Stickney, 2022).

6.1. Introduction: Why It Is Important to Distinguish Categories

In previous chapters we have repeatedly emphasized that agricultural animals are an economic, not a taxonomic, category. Now it is time to examine in detail how the basic concepts used by systematists and practitioners relate to each other: species, subspecies, breed, line, cross, hybrid. Mixing these categories is one of the most common errors not only in educational literature but also in practical activity: when preparing veterinary documents, registering breeding animals, importing and exporting across borders, and developing feed rations (Clutton-Brock, 1999; FAO, 2007).

The purpose of this chapter is to give a clear definition of each category, show their subordination, and illustrate them with examples from animal husbandry, poultry farming, and aquaculture.

6.2. Species (species) — A Biological Category

Species is the basic unit of biological classification. According to the Biological Species Concept (BSC), a species is a set of populations whose individuals are capable of interbreeding and producing fertile offspring, but are reproductively isolated from other such sets (Mayr, 1970; Hickman, 2004; Pough, 2013). A species is an objective category: it exists in nature independently of whether humans know about it or not.

Criteria of a species:

1. Reproductive isolation — individuals of different species do not interbreed in nature or produce infertile (or partially infertile) offspring.

2. Morphological unity — individuals of one species are similar in structure, but this is not an absolute criterion (cryptic species exist).

3. Genetic unity — a common gene pool, a characteristic set of chromosomes.

4. Ecological unity — a common ecological niche.

5. Geographic distribution — the range of the species.

In animal systematics, a species is designated by a binomial name: genus name + species epithet. For example:

• Bos taurus — cattle (humpless).
• Bos indicus — zebu (humped cattle).
• Ovis aries — domestic sheep.
• Capra hircus — domestic goat.
• Sus scrofa domesticus — domestic pig.
• Equus caballus — domestic horse.
• Gallus gallus domesticus — domestic chicken.
• Salmo salar — Atlantic salmon.
• Cyprinus carpio — carp.
• Oreochromis niloticus — Nile tilapia.

It is important to understand that some domestic forms are considered subspecies (for example, Sus scrofa domesticus — a subspecies of wild boar Sus scrofa), while others are considered separate species (for example, Bos taurus and Bos indicus are considered separate species, although they are capable of interbreeding) (Clutton-Brock, 1999; Jones & Bartlett, 2015).

6.3. Subspecies (subspecies) — A Geographic Category

Subspecies is a geographically isolated set of populations within a species, differing in stable morphological characters. A subspecies is designated by a trinomial name: genus name + species epithet + subspecies epithet (Hickman, 2004; Pough, 2013).

Examples:

• Felis silvestris lybica — Near Eastern wildcat, ancestor of the domestic cat.
• Canis lupus familiaris — domestic dog (subspecies of the wolf Canis lupus).
• Bos primigenius primigenius — Eurasian aurochs, ancestor of cattle.
• Bos primigenius namadicus — Indian aurochs, ancestor of zebu.

Subspecies is the lowest category that can be included in a formal Linnaean name. Below subspecies, formal taxonomic categories are not used; other terms (breed, line, ecotype, etc.) are used to describe intraspecific diversity (Clutton-Brock, 1999).

6.4. Breed (breed) — An Economic Category

Breed is a group of domestic animals of one species, created by humans through artificial selection and possessing stable hereditary traits that distinguish it from other groups of the same species (Clutton-Brock, 1999; FAO, 2007; Scanes, 2020).

FAO definition of breed:

“A breed is either a subspecific group of domestic livestock with definable and identifiable external characteristics that enable it to be separated by visual appraisal from other similarly defined groups within the same species, or a group for which geographical and/or cultural separation from phenotypically similar groups has led to acceptance of its separate identity” (FAO, 1999).

Key features of a breed:

1. Artificial origin — the breed was created by humans, not by nature.

2. Stable heredity — traits are transmitted from generation to generation.

3. Uniformity — individuals of the breed are similar in exterior, productivity, and temperament.

4. Distinctiveness — the breed differs from other breeds of the same species.

5. Common gene pool — the breed has a common origin and is bred in relative isolation.

A breed has no taxonomic status and cannot be designated by a trinomial name. One cannot say “Bos taurus holsteinicus” — this is incorrect. Correct: “Holstein breed of cattle of the species Bos taurus.”

Examples of breeds:

There are more than 800 breeds of cattle, more than 1,000 breeds of sheep, more than 300 breeds of horses, and more than 400 breeds of dogs in the world (FAO, 2007). Such diversity is the result of long-term selection under different climatic, economic, and cultural conditions.

6.5. Line (line) — An Intra-Breed Category

Line is a group of animals within a breed obtained through targeted selection and often maintained using inbreeding. Lines can be “closed” (not allowing the introduction of outside blood) and used in heterosis crosses (Scanes, 2020; FAO, 2007).

Examples:

• Broiler chicken lines (crosses “Ross,” “Cobb,” “Hubbard”).
• Pig lines in hybridization systems (for example, lines of Landrace and Large White breeds).
• Cattle lines in improvement programs (for example, lines of the Holstein breed).

A line is an even narrower category than a breed. It has no formal taxonomic status and cannot be designated by a trinomial name.

6.6. Cross (cross) and Hybrid (hybrid)

Cross is the result of crossing two or more specialized lines, breeds, or species. In poultry and pig farming, four-line crosses possessing heterosis are widely used (Scanes, 2020). For example, broiler chicken crosses are obtained by crossing four lines: two lines of the paternal form and two lines of the maternal form.

Hybrid is a broader concept. The following are distinguished:

1. Interspecific hybrids — the result of crossing different species:

• Mule (donkey × horse) — infertile.
• Hinny (horse × donkey) — infertile.
• Dzo (cow × yak) — females fertile, males infertile.
• Bester (beluga × sterlet) — fertile.
• Tilapia hybrids — fertile.
• Zebroid (zebra × horse) — infertile.

2. Interbreed hybrids — the result of crossing different breeds:

• Pig hybrids (for example, Large White × Landrace).
• Sheep hybrids (for example, Merino × Romanov).

3. Intra-breed hybrids — the result of crossing lines within a breed.

It is important to understand: a hybrid is not a taxonomic or economic category in the strict sense, but the result of a specific crossing. A hybrid can be described in terms of the parental forms: “hybrid of beluga and sterlet,” “hybrid of Holstein and Simmental breeds.”

6.7. Polyploidy and Other Genetic Modifications

In aquaculture, polyploids are widely used — organisms with an increased number of chromosome sets (Gosling, 2015; Stickney, 2022):

• Triploids (3n) — sterile, which allows energy to be directed to growth rather than reproduction. Used in oyster farming (Crassostrea gigas), salmon farming, and carp farming.
• Tetraploids (4n) — used to obtain triploids by crossing with diploids (2n).

A polyploid is not a species, breed, or hybrid. It is a genetic modification within a species. For example, the triploid oyster Crassostrea gigas is the same species as the diploid one, but with a changed chromosome number.

Gynogenesis — development of offspring only from maternal heredity. Used to obtain inbred lines (Stickney, 2022).

Transgenic organisms — organisms into whose genome genes of other species have been introduced. For example, transgenic Atlantic salmon with a growth hormone gene. In some countries, transgenic organisms are prohibited for commercial breeding (Stickney, 2022).

6.8. The Problem of Identifying Breeds by Morphological and Molecular Markers

Breed identification is a complex task, since breeds are not always clearly delineated. There are:

1. Morphological markers — exterior, coat color, horn shape, ears, body type. Traditionally used in pedigree animal husbandry. However, morphological traits may be similar in different breeds, and significant variability may be observed within a breed.

2. Molecular markers — DNA markers (microsatellites, SNPs, mitochondrial DNA). They make it possible to assess genetic diversity, degree of kinship, and identify breeds and lines. For example, microsatellite analysis is used to confirm the origin of breeding animals, identify hybrids, and assess genetic diversity (FAO, 2007; Gosling, 2015).

3. Protein markers — allozymes, blood groups. Used before the widespread introduction of DNA technologies.

Problems of identification:

• Genetic closeness of breeds — some breeds are genetically very close and difficult to distinguish.
• Hybridization — interbreed hybrids may combine traits of both breeds.
• Lack of clear standards — in different countries and associations, breed standards may differ.
• Cryptic species — there are species that are morphologically similar but genetically distinct.

Modern practice requires an integrated approach: a combination of morphological, molecular, and documentary (pedigree) methods of identification.

6.9. Examples of Mixing Categories and Their Consequences

Let us consider several typical errors.

Error 1: “A breed is a species.”

Incorrect: “The Holstein breed is a species.”

Correct: “The Holstein breed belongs to the species Bos taurus.”

Error 2: “A hybrid is a breed.”

Incorrect: “The mule is a breed.”

Correct: “The mule is an interspecific hybrid of donkey and horse.”

Error 3: “A cross is a breed.”

Incorrect: “A broiler is a breed.”

Correct: “A broiler is a product of crossing specialized lines.”

Error 4: “A triploid is a species.”

Incorrect: “The triploid oyster is a separate species.”

Correct: “The triploid oyster is a genetic modification within the species Crassostrea gigas.”

Consequences of such errors:

• Incorrect preparation of veterinary documents.
• Errors in breeding work.
• Incorrect identification during quarantine.
• Economic losses due to incorrect choice of breeding objects.

7.1. Introduction: Systematics as a Practical Tool

In previous chapters we examined the phylogenetic position of the main groups of agricultural animals, their systematics, and the relationship between taxonomic and economic categories. It may seem that all this is academic exercise far removed from the daily work of an animal scientist, veterinarian, or fish farmer. This is a profound misconception. Accurate species and breed identification is not a luxury but an urgent necessity, without which effective and safe work in the agrosphere is impossible (Clutton-Brock, 1999; FAO, 2007).

In this chapter we will consider five key areas where correct identification is crucial: breeding, veterinary medicine, feeding, quarantine, and aquaculture. In each of them we will show how systematic knowledge directly influences practical decisions and economic results.

7.2. Breeding: Crossing, Genetic Diversity, Heterosis

Breeding agricultural animals is a targeted activity to improve productive and breeding qualities. It is based on knowledge of genetic patterns, which, in turn, are inextricably linked with systematics.

7.3. Veterinary Medicine: Species-Specific Diseases, Vaccination, Treatment

Veterinary medicine is another area where accurate species identification is critically important. Disease agents are often species-specific, and different animal species have different sensitivities to pathogens, different immune responses, and different treatment schemes.

7.4. Feeding: Nutrient Requirements, Feed Rations

Feeding is the basis of productivity of agricultural animals. Nutrient requirements differ not only between species but also between breeds, lines, and sex-age groups within a species. Accurate identification allows correct formulation of rations and avoidance of economic losses.

7.5. Quarantine: Prohibition of Import of Certain Species, Disease Control

Quarantine is a set of measures aimed at preventing the introduction and spread of infectious animal diseases. Accurate species identification is the basis of quarantine measures.

7.6. Aquaculture: Choice of Cultivation Objects, Disease Resistance, Growth Rate

Aquaculture is one of the most dynamically developing branches of agriculture. Accurate systematics is especially important here, since aquaculture objects are extremely diverse — from fishes to mollusks and crustaceans.

7.7. Additional Aspects: Conservation of Biodiversity and Sustainable Development

Accurate identification is important not only for practical needs but also for preserving biodiversity. Many local breeds and wild relatives of agricultural animals are under threat of extinction. Their conservation requires accurate identification and monitoring (FAO, 2007).

For example:

• Wild relatives of cattle — aurochs (extinct), gaur, banteng, yak. Their conservation is important for genetic diversity (FAO, 2007).
• Wild relatives of sheep and goats — mouflon, bezoar goat, argali. They can be sources of genes for disease resistance (FAO, 2007).
• Wild relatives of salmonids — Atlantic salmon, brown trout, char. Their conservation is important for maintaining genetic diversity and disease resistance (Stickney, 2022).

Sustainable development of aquaculture also requires accurate identification: it is necessary to avoid the introduction of alien species that can harm local ecosystems and to use local species adapted to the conditions of the region (FAO, 2020; Stickney, 2022).

8.1. Summary of the Material Covered

We are completing the introductory section of the lecture “Systematics of Agricultural Animals and Aquaculture.” Over seven chapters we have traveled from the general principles of systematics to specific groups of agricultural animals, from phylogenetic trees to practical issues of breeding, veterinary medicine, feeding, and quarantine. It is time to look back and gather together the key ideas that should remain in the listener’s memory.

The first chapter laid the foundation: agricultural animals are not a taxonomic but an economic category. It unites species from different classes and phyla, from mammals and birds to fish, mollusks, crustaceans, and even cyanobacteria. We emphasized that accurate identification of species and breeds is not an academic exercise but an urgent necessity for the practitioner.

The second chapter examined the phylogenetic position of the main groups of vertebrates. We traced the path from chordates to vertebrates, from jawless to jawed, from cartilaginous fishes to bony fishes, from ray-finned and lobe-finned fishes to tetrapods. We saw that key evolutionary events — the transition to land, the amniotic egg, warm-bloodedness, and mammary glands — underlie the biological characteristics of agricultural animals.

The third chapter was devoted to mammals — the main class of animal husbandry. We considered the orders Artiodactyla (cattle, sheep, goats, pigs, camels), Perissodactyla (horses, donkeys), Lagomorpha (rabbits), Rodentia (nutria, chinchillas), and Carnivora (dogs, cats, fur-bearing animals). We saw how phylogenetic position determines the type of digestion, reproductive strategy, and housing requirements.

The fourth chapter introduced us to birds — the second most important group of agricultural animals. We considered the orders Galliformes (chickens, turkeys, guinea fowl, quails, pheasants), Anseriformes (ducks, geese), Columbiformes (pigeons), and Struthioniformes (ostriches). We discussed the features of breeds and crosses, as well as the importance of systematics for poultry farming.

The fifth chapter was devoted to ray-finned fishes — the most important aquaculture objects. We considered the orders Salmoniformes (salmon, trout), Cypriniformes (carp, grass carp, silver carp), Perciformes (tilapia, perch, pikeperch), Siluriformes (catfishes), Acipenseriformes (sturgeons), and others. We discussed hybridization and polyploidy, and also briefly touched on other aquaculture objects — mollusks, crustaceans, and algae.

The sixth chapter examined in detail the relationship between taxonomic and economic categories: species, subspecies, breed, line, cross, hybrid, polyploid. We showed that mixing these concepts leads to practical errors, and discussed methods of breed identification by morphological and molecular markers.

The seventh chapter answered the question of why correct species identification is important. We considered five key areas: breeding, veterinary medicine, feeding, quarantine, and aquaculture. In each of them we showed how systematic knowledge directly influences practical decisions and economic results.

8.2. Main Conclusions of the Lecture

Let us formulate the main conclusions that should be mastered upon completion of this section.

Conclusion 1. Agricultural animals are an artificial category.

They are distributed across different taxa and do not form a single phylogenetic group. Therefore, when working with them, it is always necessary to indicate their exact taxonomic position: species, subspecies, breed, line.

Conclusion 2. Phylogeny determines biology.

Evolutionary history determines the fundamental characteristics of animals: type of digestion, mode of reproduction, thermoregulation, and susceptibility to diseases. Understanding phylogeny allows predicting these characteristics and taking them into account in practice.

Conclusion 3. Species is a biological category, breed is an economic category.

A species exists in nature independently of humans. A breed is created by humans through artificial selection. Mixing these categories is unacceptable. One cannot say “a breed is a species” or “a hybrid is a breed.”

Conclusion 4. Accurate identification is critically important.

An error in determining species or breed can lead to:

• failure in breeding (infertile offspring, loss of heterosis);
• incorrect treatment (ineffective or toxic drug);
• incorrect feeding (nutrient deficiency, economic losses);
• introduction of dangerous diseases (quarantine violation);
• ecological problems (introduction of alien species).

Conclusion 5. Systematics is a practical tool.

It is not an abstract science but the basis for decision-making in animal husbandry, poultry farming, fish farming, veterinary medicine, feed production, and environmental protection.

Conclusion 6. The diversity of agricultural animals is the result of long evolution and selection.

Domestication occurred independently in different regions and at different times. This explains the diversity of breeds and their adaptations to local conditions. Preserving this diversity is the key to sustainable agricultural development.

Conclusion 7. Aquaculture is a dynamically developing branch requiring accurate systematics.

Aquaculture objects are extremely diverse: fish, mollusks, crustaceans, algae, cyanobacteria. The choice of cultivation objects, hybridization, polyploidy, and quarantine — all this requires accurate identification.

8.3. Connection with Subsequent Material

This lecture is introductory to the module “Microorganisms of the Agrosphere: Bacteria, Archaea, Fungi, Oomycetes.” The question may arise: why did we start with animals rather than microorganisms? The answer is simple: the systematics of animals provides visual and familiar material for mastering the general principles of taxonomy, which will then be applied to microorganisms.

In subsequent lectures of the module we will consider:

• Bacteria and Archaea — prokaryotic organisms playing a key role in soil processes, animal digestion, feed production, and bioremediation.
• Fungi — eukaryotic organisms used in feed production, biocontrol, cheese making, and also causing mycoses in animals and plants.
• Oomycetes — pseudofungi, including causative agents of dangerous plant diseases (late blight, downy mildew) and animal diseases.

The principles mastered using the example of animals — species, breed, line, hybrid, polyploidy, phylogenetic position, accurate identification — will be fully applicable to microorganisms as well, taking into account their specificity (for example, the absence of breeds in the traditional sense, but the presence of strains, clones, and serotypes).

8.4. Practical Recommendations for a Specialist in the Agrosphere

Concluding the lecture, let us give several practical recommendations that may be useful in daily work.

1. Always clarify the taxonomic position of the animal. Do not limit yourself to the economic name (“cow,” “pig,” “chicken”). Indicate the species, and if necessary — breed, line, cross.

2. Use reliable sources of information. When identifying species and breeds, refer to authoritative databases: FAO DAD-IS, Integrated Taxonomic Information System (ITIS), FishBase, World Register of Marine Species (WoRMS).

3. Apply an integrated approach. Combine morphological, molecular, and documentary methods of identification. Do not rely only on external features.

4. Take species-specificity into account. When developing rations, vaccination schemes, and therapeutic measures, always consider the biological characteristics of the specific species.

5. Comply with quarantine requirements. When moving animals across borders, strictly follow veterinary rules based on taxonomic affiliation.

6. Conserve genetic resources. Support local breeds possessing unique adaptations. Their loss is irreplaceable.

7. Improve your qualifications. Systematics is a dynamically developing science. New molecular data constantly refine phylogeny and taxonomy. Follow the scientific literature.

8.5. Closing Remarks

Agricultural animals are an amazing diversity of forms created by nature and transformed by humans. They originate from different orders and classes, but are united by one thing — their economic value for humanity. Systematics helps us correctly identify these species and breeds, understand their biological characteristics, and predict their behavior and productivity.

Accurate identification is the basis of effective animal husbandry and aquaculture. It underlies breeding, veterinary medicine, feeding, quarantine, and biodiversity conservation. Without it, neither scientific progress nor sustainable agricultural development is possible.