GENERAL FACTS ABOUT SEA FISH 



49 



fish has practically assumed the general characters of the adult, 

 all further changes are for the most part in size or colour. 

 In fact, the metamorphoses are to all intents and purposes at an 

 end, though in some fishes there may be further change in the 

 length of the fins, together with other trifling alterations of 

 like nature. The size of an adult fish is, unlike that of a beast 

 or bird, no exact or reliable index to its maturity or reproduc- 

 tive powers, for it appears to continue growing almost 

 indefinitely, so long as the supply of food is maintained. We 

 have already seen how the eggs of some fishes sink, while those 

 of others float ; but these two categories, instead of, as would 

 seem, being abruptly demarcated, show a large series of 

 gradations. Some of the sinking eggs, for instance, are only a 

 little heavier than the sea-water, and are in consequence {e.g. 

 the eggs of the wolf-fish, Anarrhicas) easily disturbed by under- 

 currents ; while others, like those of the herring, are not only 

 much heavier, but also adhesive, so that they develop where 

 they are deposited. Some of the floating eggs, again, having 

 a low specific gravity when shed, rise rapidly in the water, 

 while others rise much more slowly. Dead eggs of the buoyant 

 kind sink ; but healthy, buoyant eggs from the deeper water out- 

 side may likewise sink if suddenly introduced into the less 

 dense braclcish water of estuaries, yet without at once sufi^ering 

 destruction. The oil-globule, which is found in many eggs of 

 different families of fishes, such as those of the hake [Merluccius) 

 and ling [Molva) among the cod family, and those of the brill 

 and turbot {Rhombus) among flat-fish, also in those of the red 

 and grey gurnards {'Trigia), of the bass {Labrax), of the 

 mackerel {Scomber), and of many other fishes, may possibly have 

 the object of keeping the egg floating with one end uppermost — 

 acting, in fact, as a float. On the other hand, the eggs of the 

 sole {Solea) and others of the same genus, as well as those of the 

 lumpsucker {Cyclopterus) and stickleback {Gasterosteus), have a 

 number of oil-globules so generally distributed that they could 

 not serve to float any particular part of the egg uppermost 



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