ZOOLOGY OF CHORDATES STUDY GUIDE - Zakharenko M.O. - 2015

CHAPTER 3. INFRAPHYLUM JAWED VERTEBRATES GNATHOSTOMATA

3.4. Class Bony Fishes Osteichthyes

Bony Fishes inhabit virtually all Water bodies across the globe. This is the most numerous Class of vertebrate and chordate animals. The class of Bony Fishes comprises over 20,000 species grouped into 451 families and 51 orders.

Class Bony Fishes - Osteichthyes

Subclass Lobe-finned Fishes - Sarcopterygii

Superorder Crossopterygians - Crossopterygomorpha

Superorder Lungfishes - Dipneustomorpha

Subclass Ray-finned Fishes - Actinopterygii

Superorder Ganoidei - Ganoidomorpha

Despite their vast morphological and taxonomic diversity, all bony fishes share distinctive features that set them apart from cartilaginous fishes. The Structural Organization of bony fishes will be examined using the superorder of teleost fishes from the subclass of ray-finned fishes as an example, which account for more than 90% of currently living fish species.

The Skeleton of bony fishes is ossified to varying degrees, being of dermal or chondral origin.

The body is covered with cosmoid, ganoid, or bony scales.

In the vast majority of species, the interbranchial septa are reduced, and the gill filaments are located directly on the gill arches.

The gill apparatus is covered by an operculum.

Secondary jaws are formed by the Maxilla and premaxilla dermal bones.

The Brain is enclosed on all sides by a neurocranium composed of dermal roofing bones.

A swim bladder is present, serving as an important hydrostatic organ.

Fertilization in most bony fishes is external, and the eggs are small.

The body of bony fishes, much like that of cartilaginous ones, is divided into the HEAD, trunk, and tail. The boundary between the head and trunk is marked by the gill cleft, while the boundary between the trunk and tail is the anus (Fig. 69).

Fig. 69. External anatomy of bony fishes

The Mouth in bony fishes is located at the anterior end of the head, which is why these fishes are termed terminal-mouthed, in contrast to the subterminal-mouthed cartilaginous sharks (Fig. 70).

Fig. 70. Mouth shapes in bony fishes: 1 - superior; 2 - inferior; 3 - terminal; 4 - protrusible; 5 - funnel-shaped

The Skin of bony fishes is thin and permeated with A large number of mucous glands (Fig. 71).

Fig. 71. Structure of fish skin

1 - goblet mucous Cells; 2 - main epidermal layer; 3 - dermis; 4 - granular cells;

5 - rod-like cells; 6 - nerves; 7 - Blood Vessels; 8 — epidermis

The body is covered with bony scales. In almost all teleost fish, scales are represented by two forms: cycloid and ctenoid (Fig. 72).

Fig. 72. Scales of bony fish

A - ctenoid scale (perch), B - cycloid scale (roach): 1 - annual rings

In some fish, the body is covered with bony plates (scutes), as in sturgeons. Sometimes scales develop into wing-like outgrowths.

Like cartilaginous fish, they possess paired appendages (fins) and a mouth with gripping jaws, which may bear Teeth. The gill arches with attached gill filaments are hidden under a common operculum, leaving only a single external gill slit on each side. The nostrils are paired. The Inner ear contains three semicircular canals. The hydrostatic organ—the swim bladder—develops as a dorsal outgrowth of the Esophagus (in lungfish, a 'lung' develops as a ventral outgrowth). The skeleton contains Bone tissue, and the scales are also bony.

The Axial Skeleton of bony fish is formed by bony vertebrae and is divided into only two regions: trunk and caudal (Fig. 73).

Fig. 73. Skeleton of a fish (perch):

1 - Skull bones; 2-4, 7, 10, 11 - fin bones; 5 - urostyle; 6 - caudal vertebrae; 8 - trunk vertebrae;

9 - Ribs; 12 - opercula; 13 - upper and lower jaws

As in most fish, the vertebral centra are biconcave (amphicoelous type). Remnants of the notochord may persist both between the vertebral centra and within them (Fig. 74).

Fig. 74. Cytology/practical/54.html">Longitudinal section of a portion of the fish Vertebral Column: 1 - neural spine; 2 - Spinal Cord; 3 - vertebral centrum;

4 - notochord; 5 - hemal spine

Notable Features of the vertebrae include the following: the first 4 trunk vertebrae lack ribs, and the first 2 caudal vertebrae do not yet have closed ventral arches. The body of the final caudal vertebra is elongated upward into a rod-like structure called the urostyle. The posterior vertebrae are modified in connection with The formation of the caudal fin: they are flattened, and the upper and particularly the lower arches transform into plates. A typical trunk vertebra consists of a cylindrical centrum and its processes (Fig. 75).

Fig. 75. Trunk (A) and caudal (B) vertebrae of a bony fish: 1 - pit in the center of the vertebra; 2 - neural arch;

3 - neural canal; 5 - ribs; 6 - neural spine; 7 - transverse process; 8 - hemal arch;

9 - hemal canal; 10 - hemal spine

The centrum is deeply concave at both the anterior and posterior ends and features a small opening through which the reduced notochord passes. The upper processes enclose the spinal canal laterally, fusing above it to form the neural spine (Fig. 76).

Fig. 76. Fish vertebra:

1 - vertebral centrum; 2 - neural spine; 3 - ribs; 4 - notochord remnants; 5 - spinal cord; 6 - dorsal aorta; 7 - left and right Veins

In contrast to the cartilaginous SKULL OF A shark, the skull of a carp is composed of bones of both cartilaginous (chondral) and dermal (membrane) origin (Fig. 77).

Fig. 77. Skull skeleton of bony fish.

1 - angular; 2 - articular; 3 - basioccipital; 4 - basisphenoid; 5 - copula; 6 - dentary; 7 - lateral ethmoid;

8 - ectopterygoid; 9 - entopterygoid; 10 - exoccipital; 11 - frontal; 12 - hyomandibula; 13 - hyoid;

14 - ossified ligament; 15 - lateral cuneiform; 16 - middle olfactory, 17 - posterior pterygoid, 18 - maxillary, 19 - nasal;

20 - orbitosphenoid; 21 - parietal; 22 - palatine; 23 - premaxillary; 24 - parasphenoid; 25 - quadrate; 26 - supraoccipital;

27 - accessory; 28 - Vomer; 29-33 - otic bones; I- V - gill arches

In the carp skull, just like in the shark skull, two main regions are distinguished: the axial or neural (forming the braincase) and the visceral. The BONES OF THE neural skull region are accordingly grouped into the occipital, otic, orbital, and olfactory regions. Compared to that of sharks, the visceral skeleton of teleost fishes is significantly more complex due to the enlargement of individual Cartilage ossifications and the presence of numerous dermal bones. Novel evolutionary structures in the visceral skull of teleosts include secondary jaws and the operculum. Cyprinid fishes possess a specialized pharyngeal apparatus used for grinding plant food (Fig. 78).

Fig. 78. Pharyngeal apparatus in cyprinid fishes (A)

1 - grinding pad; 2 - pharyngeal bones. Types of pharyngeal teeth in cyprinid fishes (B):

1 - uniserial; 2 - biserial; 3 — triserial

In the paired fins of certain primitive bony fishes, as in cartilaginous fishes, basal and radial elements are present (Fig. 79).

Fig. 79. Pectoral fins of bony fishes (A - biserial, B, C - uniserial):

1 - basals; 2 - radials; 3 — lepidotrichia

The Skeleton of the median fins has the following structure (Fig. 80).

Fig. 80. Skeleton of median fins in cyclostomes (A), sharks (B), sturgeons (C), and bony (D) fishes

1 - notochord; 2 - vertebral centra; 3 - neural spines; 4 - dermal rays; 5 - internal skeleton rays

Their arrangement can be biserial (radials on both sides of the row of basal elements—as in Neoceratodus and fossil lungfishes) or uniserial (radials on only one side—as in lobe-finned fishes). Other bony fishes lost their basals during the course of evolution. Radials are also absent in the pelvic fins. The free membrane of both paired and median fins is supported by lepidotrichia, which in some fishes are modified into strong, sharp spines. The embedded part of the median fin skeleton is formed by ventrally tapering cartilaginous or bony rays known as pterygiophores (Fig. 81).

Fig. 81. Skeleton (A) and rays (B) of the median dorsal fin: 1 - fin rays (lepidotrichia); 2 - pterygiophores.

B - fin rays: 1 - unbranched soft; 2 - unbranched segmented; 3 - branched; 4 - spiny, smooth;

5 - spiny, serrated; 6 - unbranched, unsegmented, rigid, stiff.

The Pectoral Girdle consists of the primary pectoral girdle, formed by the scapula and coracoid (small bones playing The Role of lost basals), and a much more massive secondary girdle attached to the chondrocranium. The Pelvic Girdle is represented only by a single unpaired bone plate.

The caudal fin of bony fish larvae has a symmetrical structure (its axis is formed by the notochord), which is referred to as protocercal. In sturgeons, much like in cartilaginous fishes, the tip of the tail turns upward while the ventral lobe expands, forming an uneven-lobed, heterocercal fin. In most teleosts, the ventral lobe is even larger; externally, the fin appears symmetrical, but THE VERTEBRAL COLUMN extends into the upper lobe—a homocercal type of structure.

In some lungfishes, lobe-finned fishes, and teleosts, the axial skeleton straightened out again during ontogeny, making the upper and lower lobes secondarily symmetrical; this type of structure is called diphycercal (Fig. 82). In the homocercal caudal fin, the ventral lobe is supported by hypurals—elongated and flattened neural spines of the posterior vertebrae.

Fig. 82. Caudal fins of fishes

A - heterocercal tail of elasmobranchs and sturgeons; B - diphycercal tail of bichirs;

C - homocercal tail of teleosts; 1 - dermal rays (elactotrichia or lepidotrichia); 2 - neural processes;

3 - haemal processes; 4 - radial; 5 — hypurals

Based on the cleft of their lobes, caudal fins are divided into the following types (Fig. 83).

Fig. 83. Types of caudal fins

1 - semilunar (tuna), 2 - forked (herring), 3 - emarginate (salmon),

4 - truncate (cod), 5 - rounded (burbot), 6 - pointed (viviparous blenny)

The Internal Structure of fish is fully adapted to an aquatic lifestyle (Fig. 84).

Fig. 84. Internal anatomy of a female perch:

1 - esophagus; 2 - Stomach; 3 - intestine; 4 - pyloric caeca of The Stomach; 5 - Liver; 6 - Gallbladder; 7 - swim bladder;

8 - atrium; 9 - ventricle; 10 - Spleen; 11 - gills; 12 - Kidneys; 13 - Urinary Bladder; 14 — Ovary

The Digestive System of teleost fish varies considerably in ADAPTATION TO A diverse diet. The digestive tract is divided into three sections: the foregut, which includes the Oral Cavity, Pharynx, and esophagus; the midgut, comprising the stomach, Small Intestine, and digestive glands (liver and Pancreas); and the hindgut, represented by the Large Intestine. Cyprinids, gobies, and certain members of other families lack a stomach. At the beginning of the intestine, various orders of teleost fish may form pyloric appendages that increase the absorptive surface area (ranging from a single appendage in loaches to several hundred in salmonids). The length of the digestive tract in carnivorous fish is generally shorter than in "peaceful" (herbivorous or omnivorous) species, especially herbivores. The intestine terminates in the anus, and only lungfish possess a cloaca. Early-branching systematic groups retain a spiral valve in the intestine (Fig. 85).

Fig. 85. Spiral valve in the intestine of a cartilaginous ganoid fish (A) and pyloric

appendages of the stomach in a teleost fish (B):

1 - esophagus, 2 - stomach, 3 - pyloric caeca, 4 — intestine

The Respiratory system of fish is represented by gills, which are located on the first to fourth gill arches. Interbranchial skin folds are reduced (remnants persist in sturgeons). Rows of gill filaments are paired along the bones of the arches, fusing at their bases (Fig. 86).

Fig. 86. Respiratory system of teleost fish:

A - direction of water flow; B - gill rakers of planktivores; C - carnivorous fish:

1 - gill arches; 2 - gill rakers; 3 - gill filaments

Gill Arteries run along the arches and branch into the filaments, forming a capillary network. The arches are concealed beneath the opercula (gill covers). In some fish, an additional hemibranch may be present on the inner surface of the operculum. Blood flows through the capillaries in the direction opposite to the water current. This countercurrent exchange allows fish to extract 46 to 82% of dissolved oxygen from the water passing through the gills, eliminate over 90% of carbon dioxide from the capillary blood, and maintain water-salt balance alongside The excretion of metabolites. The integument also participates in gas exchange (typically accounting for 4 to 30% of total gas exchange; up to 85% in loaches and certain other species).

The Heart lies near the head, just ventral to the last pair of gill arches. As in all fish, the heart of a carp consists of two chambers: an atrium and a ventricle. The thin-walled sinus venosus, capable of autonomous contraction, directly adjoins the atrium; the conus arteriosus is absent, replaced by a non-pulsatile bulbus arteriosus (Fig. 87).

Fig. 87. Diagram of the fish heart: A - selachian; B - cartilaginous ganoid; C — teleost fish

1 - ventral aorta; 2 - conus arteriosus; 3 - ventricle; 4 - atrium; 5 - sinus venosus.

The conus arteriosus is absent, but there is an arterial bulbus of the aorta, from which the ventral aorta extends, branching into four pairs of afferent gill arteries.

Oxygen-rich blood collects in the efferent gill arteries, which empty into the roots of the dorsal aorta.

The dorsal aorta branches into numerous arterial vessels that supply blood to all Internal Organs. In the head region, the aortic roots form the cephalic arterial circle. Venous blood from the caudal region travels via the unpaired caudal vein, which divides into two branches passing through the kidneys. Unlike cartilaginous fish, teleosts form a renal portal system only in the left Kidney. Subsequently, blood flows forward through the posterior cardinal veins, merging at the heart level with the anterior cardinal veins, which carry blood from the head. This union forms the paired Cuvierian ducts, which empty into the sinus venosus. Blood from the intestine enters the liver via the HEPATIC PORTAL VEIN, forming a hepatic portal system. From the liver, blood flows through the hepatic vein into the sinus venosus (Fig. 88).

Fig. 88. STRUCTURE OF THE Circulatory system in a teleost fish:

1 - sinus venosus; 2 - atrium; 3 - ventricle; 4 - bulbus arteriosus; 5 - ventral aorta; 6 - gill vessels; 7 - anterior cardinal veins; 8 - jugular vein; 9 - Cuvierian ducts; 10 - caudal vein; 11 - renal veins; 12 - renal portal system; 13 - posterior cardinal veins; 14 - renal portal system (duplicate entry in original); 15 - hepatic vein; 16 - kidneys; 17 - intestine; 18 - liver

The excretory system of teleost fish is represented by mesonephric (trunk) kidneys (Fig. 89). The kidneys lie closely appressed to the vertebral column. Ureters, which are homologues of the Wolffian ducts, run along the inner portion of the kidneys. Emerging from the kidneys, the ureters unite into an unpaired duct that terminates on the urogenital papilla with a distinct opening. Both urinary ducts empty into the urinary bladder. The anterior portion of the perch kidney is modified into a lymphoid organ.

Fig. 89. Excretory ducts of the Urogenital System in a male pike:

1 - kidney; 2 - Ureter; 3 - urinary bladder; 4 - external urinary opening; 5 - Testis; 6 - vas deferens;

7 - external urinary opening; 8 - intestine; 9 - anus

Water-Salt METABOLISM in freshwater fish (hypotonic environment) involves the elimination by the kidneys of a significant amount of water that continuously penetrates through the skin, gills, and with food (Fig. 90).

Fig. 90. Excretion and osmoregulation in freshwater teleosts (A), elasmobranchs (B), and marine teleosts (C)

Salt content in tissues and blood is replenished through reabsorption in the renal tubules, active uptake in the gills, and ingestion with food. Marine fish (hypertonic environment) lose water through the skin, gills, urine, and feces. To replenish their body's water content, they drink seawater (40-200 ml per 1 kg of fish body weight per day), eliminating excess salts via specialized cells in the gill filaments. Diadromous fish are capable of rapid physiomorphological adaptations to meet the demands of water-salt balance.

The reproductive organs of teleost fish are closely connected with the excretory system. The Gonads of the male appear as two elongated bodies (Fig. 91).

Fig. 91. Diagram of the urogenital organs in teleost fish: A - male; B - female

1 - kidney; 2 - urogenital sinus; 3 - testis;

4 - vas deferens; 5 - Wolffian duct; 6 - urogenital opening; 7 - ovary; 8 - oviduct;

9 - genital opening; 10 - urogenital opening.

Compared to that of a shark, The Nervous system of the perch is characterized by a smaller Forebrain, the absence of Nervous Tissue in its roof, and the lack of a longitudinal partition dividing the forebrain cavity (Fig. 92).

Fig. 92. Nervous system of teleost fish:

1 - olfactory bulb, 2 - Cerebellum, 3 - optic chiasm, 4 - Diencephalon, 5 - epiphysis (Pineal Gland), 6 - Pituitary Gland (hypophysis), 7 - optic tectum (optic lobes), 8 - Midbrain, 9 - Medulla Oblongata, 10 - spinal cord, 11 - forebrain, I–X - Cranial Nerves

Sense Organs are represented by organs of Vision, smell, taste, Hearing, and the lateral line system (Fig. 93).

Fig. 93. Sense organs of teleost fish

The primary role in food acquisition belongs to the visual organ, which possesses A number of adaptations to the aquatic environment: the lens is spherical, the cornea is flat—resulting in a small anterior chamber—and the sclera is cartilaginous (Fig. 94).

Fig. 94. Structure of the teleost fish eye:

1 - Optic nerve; 2 - ganglion cells; 3 - layer of rods and cones; 4 - retina; 5 - lens; 6 - cornea; 7 - vitreous body

The vascular tunic (choroid) features a falciform process, which is a Connective Tissue fold attached to the lens. By contracting, this process pulls the lens away from the cornea, thereby increasing the distance between them while decreasing the distance between the lens and the retina (the accommodation phenomenon). Visual acuity in the perch is relatively low (a few meters), which is due to the poor light transmission of water. The Organ of Hearing is represented by the inner ear, located within a bony capsule (Fig. 95).

Fig. 95. Labyrinth of the inner ear of the European minnow with otoliths:

1, 2, 3 - anterior, horizontal (external), and posterior semicircular canals; 4, 5, 6 - otoliths; 7 - ampullae

The cavity of the membranous labyrinth, as in sharks, is filled with fluid known as endolymph. Inside it, apart from small otoliths, there are three large otoliths. Studying the concentric layers on cross-sections of the otoliths provides insight into the fish's age. The Olfactory Organ is structurally similar to that of cartilaginous fish. The ORGAN OF TASTE is represented by microscopic taste buds located within the oral cavity.

A specialized organ is the lateral line (Fig. 96).

Fig. 96. Lateral line organs of teleost fish:

1 - lateral line pore in a scale; 2 - longitudinal lateral line canal; 3 - sensory cells; 4 - nerves

In fact, the lateral line is not an essential element of the mechanoreceptive (seismosensory) system; it is merely the most prominent one. The obligate components are the subepidermal head canals that open to the exterior via short branches (Fig. 97).

Fig. 97. Mechanoreceptive system (lateral line organs) of a perch:

1 - nostrils; 2 - supraorbital canal; 3 - infraorbital canal; 4 - hyomandibular canal; 5 - supratemporal canal;

6 - parietal canal; 7 - superficial pores; 8 - trunk (lateral) canal; 9 - brain

Clusters of sensitive ciliated cells, innervated by the Vagus nerve, are located along the walls of the canals. Lateral line organs are capable of detecting vibrations at frequencies up to 500 Hz. The seismosensory system is of particular importance to fish inhabiting turbid waters.