aspects of fish biology form and function

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291a e.g. the tropical triggerfish (Balistidae). The bright colours of most cleanerfish (e.g. the crimson cleaner, Suezichthys sp.) are thought to advertise the presence of the cleaner to other fish. ' I Colour patterning may also enable individuals to recognise other members of their own species, which is particularly important for mating and territorial defence. Many species display bright colour patches during courtship displays or aggressive encounters. These may be found on the dorsal, anal or caudal fins and are only revealed when the fins are extended during a display, e„g. the bright blue spot on the first dorsal fin of the tripterygiid Gilloblennius decemdigitatus, and the yellow and black markings on the caudal fin of the male leatherjacket {Parika scaber). The black angeifish (Parma alboscapularis) ? turns on 1 a white shoulder spot while courting, spawning and defending its territory. Colouration often differs between the sexes, particularly in those species that pair spawn and indulge in courtship displays. The male is usually more brightly coloured than the female. These differences may be apparent throughout the entire year, as seen in the labrid group, or may only occur during the breeding season. Male tripterygiids, for example, change from their normal drab colouring to contrasting or bright colours during the breeding season. In most pair spawning fish male colouration intensifies during the spawning season. Some species exhibit differences in colouring between adults and juveniles. The juvenile black angeifish is entirely different in appearance from the adult, with its bright yellow body which is marked with bright blue dots and streaks. Other examples may simply reflect a difference in habitat between adults and juveniles. For example, juvenile paketi {Pseudolabrus celidotus) and leatherjackets [Parika scaber) are usually the colour of the seaweed in which they shelter and the adult colouration is assumed when they leave this habitat. Colour patterns are generally consistent within a species or a group such as males, females and juveniles. However, there is enough variation to allow recognition of individual fish for behavioural studies. The pattern and shape of different lines and spots, and even body scars are usually used. Teleosts are able to change their colours rapidly, and in some\ cases completely. Colour change is achieved by expansion or contraction of certain chromatophores, which effectively reduces or increases the
292a concentration of that colour. Expansion "of the chromatophores usually darkens the fish whereas contraction makes them pale. A fish gains considerable protective advantage in being able to change colour intensity to match that of its surrounding environment. For example, the cobble blenny (Forsterygion capito) is almost white with a black lateral stripe when found in sediment or sandy areas, but on the the darker background of rocks and cobbles it changes to a mottled greenish-black on the back and sides with the dark stripe being almost obliterated. The parore {Givella tricuspidata) changes colour at night when it rests on the substratum. This can also be observed during the day with pink rnaomao (Caprodon longimanus) which changes from the almost uniform pink colouring it exhibits while swimming in midwater to a pale pink with large white blotches while resting on the bottom. Rapid colour changes are also observed during aggressive encounters or courtship displays. During aggressive interactions both fish may darken considerably in colour. Where there is a definite dominant/ subordinant situation the dominant fish is usually dark whereas the other fish is considerably paler than normal. Courting males will often temporarily display very dark or intense colours. Fins and locomotion Fish are propelled through the water by their fins, body movements or a combination of the two. Four basic swimming methods can be observed (figure 4) . (1) Anguilliform: Segments of the body musculature alternatively contract and relax throwing the body into an S-shaped curve. A series of undulations pass the full length of the body, the main thrust coming from the action of the tail or tail fin against the surrounding water. Swimming efficiency is greatly increased if the tail is laterally compressed. This is the typical method of locomotion of the eels (Anguilliformes) and can also be seen in the ungainly movements of the cod, e.g. Lotella rhacinus. (2) Carangiform: The body undulations which produce movement are confined to the rear third of the fish's body. The tail provides the main source of locomotive power. Most pelagic fish and reef fish swim in this manner. The carangids are the typical examples, e.g. kingfish (Seriola grandis).
Page 1 and 2: 288a ASPECTS OF FISH BIOLOGY FORM A
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 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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