aspects of fish biology form and function

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301a The fish eaters (piscivores) usually possess strong flat, closely set teeth, which may be acutely sharp and pointed and ideally suited for capturing and holding live fish (e.g. the snoek, Thrysites atun). However, some piscivores such as the kingfish (Seriola grandis) have relatively fine brush-like teeth. These still meet the requirements of grasping and holding struggling prey. Others like the blue cod (Parapercis colias) have surprisingly small teeth, or even toothless mouths; however, thev have sharp well developed pharyngeal teeth. Invertebrate feeders and herbivores exhibit a vast array of teeth, the type dependinq on the food they eat. Small pointed cone-shaped teeth at the front of the jaw are used to pick invertebrates from the substratum. Some species also possess blunt molar-like teeth further back on the jaw (the sparids e.g. Chrysophrys auratus) , or in the throat (the labrids, e.g. banded wrasse, Pseudolabrus fucicola) to crush hard shells. The herbivores usually have bands of small notched teeth in the jaws and some have a series of chisel-like incisors for cutting or scraping algae from the rocks. The teeth of the plankton eaters are small and feeble, or may be absent altogether. These fish typically possess elaborate structures known as gill filaments, which strain the microscopic organisms out of the water they take into their mouths before it passes over the gills. These double rows of stiff, interlocking appendages are situated on the inner marqins of the gill arch (see figure 9). In most fish they exist as bony knobs but in the planktivorous fish they are long, numerous and closely set with many secondary and tertiary branches. Generally the teeth are single structures. However in several groups, the teeth in the jaws are fused together. The teeth of the parrotfish (scarids) are fused to form a beak for cutting off pieces of coral and seaweed. In other groups the fused teeth form a single or double plate in each jaw as in the families Diodontidae and Tetradontidae. These plates are sharp at the edge and also provide a broad crushing surface within. Skin9 scales and spines . Fish have a skin composed of two layers. The outer layer, or epidermis, is composed of cells which are constantly being warn away and replaced by new ones developing at the base. Underneath is the dermis, a thick laver of connective tissue, muscle fibres and mucous glands. Fish also have an outer covering of scales. When these are absent the
302a skin may be thick and leathery (e.g. sunfish, Mold mold) or thickly coated with mucous (e.q. clinqfish) for protection. The form of the scales, spines and other related structures varies considerably and provides an important character for classification. The sharks have a primitive type of scale. Their placoid scales are tooth-like structures, each consistinq of a central spine coated with enamel and with an intermediate layer of dentine. These scales do not increase in size as the fish qrows; instead, new scales are continually beinq added. The teleosts are covered with thin bony scales that overlap each other like the tiles on the roof of a house. The scales increase in size as the fish grows. These may have a comb-like serrated rear margin (ctenoid scales) or a smooth rear margin (cycloid scales) (figure 8) A few fishes, the. sturgeons (Acipenseridae) and some garfishes (Exocoetidae), possess ganoid scales. These are hard thick bony scales which fit against each other like the bricks of a wall, and often form ridges of armour along the back and sides of the fish. Figure 8: The different types of scales In general, teleosts with softrayed fins have cycloid scales, for example members of the orders Salmoniformes and Antheriniformes and the
Page 1 and 2: 288a ASPECTS OF FISH BIOLOGY FORM A
Page 4 and 5: 291a e.g. the tropical triggerfish
Page 6: 293a (3) Labriform: Some fish, part
Page 9 and 10: structure used attract prey. kingfi
Page 11 and 12: 298a georgianus), or a series of fi
Page 13: 300a The lips of fishes' mouths are
Page 17 and 18: 304a noticeably slippery, whereas s
Page 20 and 21: 307a Production of sound, light and
Page 22 and 23: 309a opens to the exterior through

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