COLORATION 



223 



as the fish grows up, may be regarded perhaps as vestiges of a 

 coloration which was characteristic of the ancestors of these 

 fishes and which is repeated as a passing phase during early 

 life. In many fishes, again, the two sexes exhibit differences in 

 coloration, particularly in those forms which pair at the breeding 

 season and indulge in some sort of courtship {cf, p. 299). The 

 difference in colour may be noticeable at all seasons, or may 

 be developed in the male only and make its appearance as 

 the time for breeding approaches, the colours afterwards 

 vanishing and leaving the two sexes once more alike. It is of 

 interest to note that, although species with dimorphic coloration 



:<^f^ 





Fig. 89. 



Angler (Lophius piscatorius), X \. 



are as common among marine fishes as in fresh-water forms, 

 nuptial colours rarely occur in marine species. 



Finally, some types of coloration seem to be of the nature of 

 *' warning colours," a signal to would-be enemies that their 

 possessors are dangerous, either by virtue of their poisonous 

 flesh or on account of the possession of venomous spines and the 

 like. The brilliant hues of such poisonous tropical forms as 

 the Trigger-fishes (Balistidae), Trunk-fishes (Ostraciontidae), and 

 Globe-fishes {Tetrodo?itidae) , probably partake of this nature, 

 and act as danger signals to predaceous fishes that have learnt 

 to associate a particular type of coloration with unpalatable 

 qualities, thus operating to the mutual advantage of both 

 parties. One or two species of Serpent Eels {Ophichthyidae) of the 

 South Seas have a banded coloration similar to that of the 



