aspects of fish biology form and function

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303a cod family, Gadidae. The spiny rayed fishes usually have ctenoid scales * Occasionally both ctenoid and cycloid scales are found on the same fish. Scales vary widely in size, from the minute scales of the mackerels (e.g. Scomber australasicus) to the large scales of the labrids (e.g. the pigfish, Bodianus oxycephalies) and the pomacentrids (e.g. the black angelfish, Parma alboscapularis). The eels (e.g. the yellow moray, Gyrrmothorax prasinus) have tiny well separated scales which are deeply embedded in the skin. ,In other species the scales lie very close to the surface of the skin and are easily rubbed off (e.g. goatfish Upeneichthys porosus). Scales may be modified in various ways. The scales of the porcupine fish (Allomy cterus whitleyi) are strong spines, the roots of which are in contact with one another thus giving the fish extra protection. Those of the leatherjacket (Parikā scaber) have become reduced and coalesced to form a tough sandpapery skin. The scutes, or keeled scales, of many fast- swimming fish such as the carangids, give extra strength to the narrow caudal peduncle and also act as stabalizers. In the syngnathids (seahorses and pipefish) the scales have been replaced by a series of jointed bone-like rings. A series of pored scales, or in some cases notched scales (e.g. many tripterygiids), the lateral line scales, form an external line which extends from behind the fish f s head along each side of the body down to the tail. The number and type of the scales and the shape of this line are often used in fish classification. The lateral line may run straight along the midline of the sides, or may be curved to follow either the contour of the back or belly. Usually the lateral line runs continuously to the tail but it also may be interrupted or incomplete. Fish usually possess only one lateral line; however some have several lines of pored scales (e.g. rockfish, Acanthoclinus quadridactylus) or a branched lateral line (e.g. the gemfish, Rexea solandri) . Others such as the clupeioids, clingfish and yellow-eyed mullet {Aldrichetta forsteri) have no external lateral line at all. In most fish the mucous glands in the skin secrete a protective coating of slime over the scales. This acts as a barrier to the entry of parasites, bacteria, fungi and other disease organisms, and it also reduces friction as the fish moves through the water and amongst seaweeds. Weed dwelling fish such as the marblefish (Aplodactylus meandratus) are
304a noticeably slippery, whereas several midwater swimming fish do not produce mucous and are rough and sandpapery to feel (e.g. slender roughy, Hoplostethus elongatus, and pink rnaomao, Caprodon longimanus) . Spines are usually associated with protection. They are found in the fins, especially the dorsal fin, on the opercular and preopercular bones (e.g. the redbanded perch, Ellerkeldia huntii, and the two-spot demoiselle, Chromis dipilus) , on the tail (e.g. the stingrays and eagle rays) or all over the body (e.g. the porcupine fish, Allomyctevus whitleyi) The effectiveness of their protection is greatly increased by the association of poison glands with the spines , as in the rays and red scorpionfish (Scorpaena cardinalis) . The senses Fish possess the senses of smell, touch, taste, sight, and electroreception. The.degree of development of the sense and associated- structures is often related to the fish ! s mode of life or habitat. SMELL: The olfactory organs in fishes, the nostrils, are essentially a deep pit lined with sensory tissue. Most fish have two pair, one situated on each side of the snout, excluding the pomacentrids which usually have only one set of nostrils. The nostrils are never used for breathing in fishes as they are in the terrestrial vertebrates. The sense of smell plays and important part in finding food in some species, especially the sharks which have poor sight. TOUCH: Cells sensitive to touch are found all over the body. Some fish may also have special feelers to aid in the search for food, for example the elongated lower pectoral fin rays of the porae (Cheilodaotylus douglasi) and the red gurnard (Chelodonichthys kurrru) . SIGHT: hearing organs Fish eyes are very like our own in that there is a sensitive screen (the retina) at the back of the eye and a lens which projects an image onto that screen. However, unlike the human eye the iris does not expand
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 and 14: 300a The lips of fishes' mouths are
Page 15: 302a skin may be thick and leathery
Page 20 and 21: 307a Production of sound, light and
Page 22 and 23: 309a opens to the exterior through

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