ix. 3 FEEDING HABITS 251 



ing Crustacea and insects on land, using the pectoral fins as levers, 

 provided with special anterior and posterior muscles. 



Fishes that live in situations from which they are likely to be carried 

 away develop suckers. Thus in the gobies, found between tide-marks, 

 the pelvic fins form a sucker. The cling-fishes (Lepadogaster) are another 

 group with the same habit. The remoras have developed a sucking- 

 plate from the first dorsal fin and by means of this they attach them- 

 selves to sharks and other large fish. In order to catch their food they 

 leave the transporting host, though they also feed on its ectoparasites. 



3. Structure of mouth and feeding-habits of bony fishes 



Although perhaps the majority of fishes are carnivorous, there are 

 species with all sorts of other methods of feeding. The more active 

 predators have strong jaws and sharp teeth, such as those of the pike 

 (Esox), cod (Gadus), and very many others. The teeth on the edge of 

 the jaw serve to bite and catch the prey, those on the walls of the 

 pharynx to prevent its escape if, as is often the case, it is swallowed 

 whole. The teeth can often be first lowered to allow entrance of the 

 prey and then raised to prevent its exit (e.g. in Lophius). In connexion 

 with this habit the walls of the oesophagus and even stomach are 

 often composed of striped muscle, capable of quick and powerful 

 contraction. 



Many carnivorous fishes are very fierce. For instance, the blue fish 

 (Potnatomas) of the Atlantic move in shoals, cutting up every fish 

 they meet, making a trail of blood in the sea. The barracuda (Sphy- 

 raena) of tropical waters may attack man. They are said to chase 

 shoals of fish into shallow waters and to keep them there to serve for 

 food as required. 



Other fishes feed on invertebrates and are then usually bottom- 

 feeders. Thus the plaice (Pleurojiectes) has developed chisel-like teeth 

 on the jaws and flattened crushing teeth in the pharynx; it feeds 

 largely on molluscs. The Labridae (wrasses) also have blunt teeth 

 and eat molluscs and crabs. The sole {Soled) has a weaker dentition 

 and eats mostly small Crustacea and worms. Fish such as the herring 

 {Chipea) that live on the minute organisms of the plankton have small 

 teeth and weak mouths, but are provided with a filtering system of 

 branched gill-rakers, making a gauze-like net, comparable with the 

 filtering system found in basking sharks (p. 181), paddle-fish (p. 234), 

 and whale-bone whales (p. 669). 



Herbivorous and coral-eating fishes have crushing teeth similar to 

 those of the mollusc-eaters; indeed, many forms with such dentition 



