ii2 MARVELS OF FISH LIFE 



acquiring the appearance of the adult, now enters upon 

 the stage- of adolescence. 



This change from the transparent post-larval stage 

 to that in which the fish assumes the shape and silvery- 

 appearance of the adult, does not call for our special 

 attention among round fishes, such as the cod, the 

 haddock, and the mackerel. Among flat fish, however, 

 such as the plaice, the sole and the turbot, a remark- 

 able transformation occurs during the post-larval 

 stage. 



Flat-fish larvae begin by swimming near the surface 

 in an upright position like the larvae of other fishes. 

 Next, they flatten from side to side, and gradually 

 approach the bottom, to end up by lying on their right 

 or left sides, as the case may be. 



If no alteration occurred in the position of the eyes 

 when the young fish had settled on the bottom, one eye 

 would be buried in the sand. To prevent this during 

 the transformation of the larval flat fish, the cranium 

 in the region of the orbit rotates on its longitudinal axis 

 until the two eyes lie in a vertical plane, the eye from 

 the underside being above the other. Not infrequently 

 it is stated that the eye from the underside travels 

 round the head, but this is incorrect for, as explained, 

 it is the cranium that rotates, and the relative position 

 of the eyes does not alter. 



Plaice, soles, flounders, dabs, lemon soles and halibut, 

 after they have flattened, all lie on their left side, while 

 turbot and brill lie on their right side. 



