BREEDING 



281 



to 



seventeenth century, insisted on "spontaneous generation 

 explain the propagation of certain fishes ! 



With regard to the time at which spawning takes place, this 

 varies somewhat in different species, and naturally occurs at 

 different seasons in various parts of the world. As far as our 

 northern food-fishes are concerned, the majority breed in the 

 first half of the year, the spawning season of the Plaice (Pleuro- 

 nectes) extending from January to April, that of the Cod (Gadus) 

 in the North Sea from February to May, and of the Sole {Soled) 



Reproductive and excretory organs of a typical Bony Fish (female) ; A. with 



oviducts continuous with the ovaries ; b. with oviducts separated from the 



ovaries. (After Rey.) 



from April to July. As was pointed out in the last chapter, 

 each race of Atlantic Herring (Clupea harengus) has its own 

 spawning season, and some deposit their eggs close to the shore 

 in winter or spring, others in deeper water during the summer or 

 autumn. By the spawning period or breeding season of a 

 particular species or race is meant that period during which 

 some individuals may be found to possess ripe ova or sperms, 

 and this may last only for a few days or extend o\er as many 

 weeks or even months. 



As the time for spawning approaches the fish congregate in 

 huge shoals in suitable localities, and on some grounds they may 



