597.5 382 



591.16 



II. 



Some Effects of Pelagic Spawning-habit on 

 the Life-histories of Teleostean Fishes.' 



FOR the last few years several naturalists at home and abroad have 

 freely bestowed their time and labour upon the study of the eggs 

 and young stages of teleostean fishes, and, as a result, there are now 

 only one or two species the ontogeny of which is not known. We 

 thus have to hand a long series of memoirs in which the eggs and 

 larvae of these fishes are figured and minutely described, at all stages 

 in their career, and it is now made evident that our commonest food- 

 fishes go through a remarkable series of anatomical changes before 

 arriving at the adult condition. Intimately connected with this 

 metamorphosis is the change of environment of the young fish during 

 its career ; and although at present we know less about this part of 

 the life-history, an increase of our knowledge promises to furnish even 

 more important results, in every way, than the facts of structural 

 change. 



This is not the place to discuss how far the structural features 

 are connected with, or determined by, the environmental factors; but 

 we may note, in passing, that teleostean fishes and their ontogeny 

 offer a very advantageous field for the investigation of this general 

 biological problem. A brief survey of what we know concerning the 

 environmental history of two of our common fishes may illustrate this 

 point. In the case of the plaice, the eggs, pelagic and buoyant, are 

 laid in enormous numbers at a varying distance from shore. Tossed 

 about just below the surface, they are carried by currents here and 

 there, eventually inshore, at least in the case of the majority. The 

 larva, some time after hatching and after absorbing its yolk-sac (when it 

 has reached the post-larval stage), migrates downwards to the bottom 

 and then takes up its station close inshore. As growth proceeds, the 

 young fish slowly moves off seawards till the adult stage is reached. 

 In the case of the herring, on the other hand, the eggs (demersal) are 

 laid comparatively near inshore in masses, adhering to any object at 

 the sea-bottom ; and the larvae, on hatching, tarry awhile at the 

 bottom. In a few days, however, they, with an unerring instinct, 

 migrate upwards into the surface-water and move offshore. Later 



1 This paper, in more extended form, was read before Section D of the British 

 Association, September, 1896. 



