aspects of fish biology form and function

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295a the actual locomotor organs they function to stabilise and manoeuveur the fish. The median fins (dorsal and anal) prevent rolling and yawing in the vertical axis while the paired fins (pectoral and ventral) prevent the fish pitching horizontally. Turning is achieved chiefly by the pectoral and ventral fins with body movements also playing some part. The pectoral fins are nearly always used for braking; however, some fish simply reverse their primary locomotory apparatus, e.g. the leather- jacket (Parika scaber) reverses the direction of the undulations of the dorsal and anal fins. For most fish the shape and size of the pectoral fins, especially the caudal fin, is a good index of speed, agility and mode of life (figure 5). Fish with large square-cut or rounded tail fins as seen in most reef fish are usually comparatively slow swimmers, but are capable of sudden bursts of speed. A deeply forked and lunate tail, a narrow caudal peduncle and small sickle-shaped pectoral fins are typical of the fast-swimming pelagic fishes, e.g. the carangids, the tuna and. mackerel and the snoek (Thrysites atun) . The midwater planktivorous fish (e.g. two-spot demoiselles, Chromis dispilus and butterfly perch, Caesioperca lepidoptera) have deeply forked tails and long oval pectoral fins, allowing great manoeuverability. Hole dwelling and weed dwelling fish such as the eels and syngnathids (seahorses and pipefish) have the caudal and pectoral fins reduced in size and efficiency, and consequently are poor swimmers. These fish also usually lack pelvic fins. Fins also serve functions other than locomotion and may be modified accordingly (figure 5). The dorsal and anal fins are capable of being erected or depressed and are frequently used during aggressive or courting displays. The spines and rays arfe supplied with muscles for this purpose. The spines also provide the fish with some protection against predators. These fins often also complement a fish' s camouflage. For example, the long trailing fins of the butterfish (Odax pullus) and the crested weedfish (Cristiceps aurantiacus) resemble"the weed in which the fish live. Many modifications are associated with seeking and obtaining food. The lower rays of the pectoral fins can be drawn out and may form long finger-like projections which act as tactile or sensory organs for detecting food, e.g. red gurnard [Chelodonichthys kumu) and porae [Chelodactylus douglasi). The first spine of the dorsal fin is greatly extended in the anglerfish (Lophiformes) to form a 'line and bait 1
structure used attract prey. kingfish (Seriola grandis) gurnard (Chelodonichthys kumu) long-snouted pipefish (Stigmatopora macropterygia) butterfish {Odax pullus) 296a two-spot demoiselle (Chromis eagle ray dispilus) (My liobatus tenuicaudatus) porae (Cheilodactylus douglasi) mottled blenny (Forsterygion Q^'Sr^a®^ varium) Figure 5: Various conditions of the dorsal, pectoral and ventral fins. The pelvic fins of the bottom dwelling fish such as the tripterygiids and blue cod (Parapercis colias) are reduced and thickened to act as props for the fish resting on the substratum. The lower rays of the pectoral fins are usually unbranched and thickened. Some bottom living fish of shallow turbulent waters are able to cling, grasp or anchor themselves to the substratum to prevent being buffeted against the rocks. The hiwihiwi (Chironemus marmoratus) has the lower pectoral
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 11 and 12: 298a georgianus), or a series of fi
Page 13 and 14: 300a The lips of fishes' mouths are
Page 15 and 16: 302a skin may be thick and leathery
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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