CHAPTER XIV 

 BREEDING 



Reproductive organs. Fertilisation. Ancient theories of spawning. Spawn- 

 ing of Cod, Plaice, Herring, etc. Number of eggs produced. Spawning 

 of Salmon. Of Sea Lamprey. Breeding habits of Fresh-water Eel. 

 Of Cyprinids, 



The reproductive organs or gonads of fishes are of two kinds, 

 ovaries in the female and testes or milt in the male, the former 

 being popularly known as hard roes, the latter as soft roes. In 

 most fishes these are elongate in shape, paired, and more or 

 less intimately associated with the kidneys. The ovaries are 

 pinkish or yellow in colour, granular in texture, and usually 

 lie just below and behind the air-bladder when this is present 

 (Fig. 103). As the breeding season approaches, the ovaries 

 become much enlarged, fill a considerable part of the body 

 cavity, and the separate eggs are plainly visible. The eggs may 

 pass from the ovary to the exterior by way of a passage known 

 as the oviduct, opening either by a special aperture or by one 

 which it shares with the excretory duct, but in a large number of 

 fishes no oviducts are developed, and the eggs simply drop into the 

 main body cavity, passing out through pores in the body wall. 

 The testes have much the same position as the ovaries, but are 

 much smaller, paler in colour, and to the naked eye have a 

 creamy rather than a granular texture. A narrow duct leads 

 from each testis to the genital aperture. Occasionally, indi- 

 viduals are found in which both male and female organs are 

 fully developed, this condition having been recorded in such 

 well-known species as the Cod {Gadus), Herring (Clupea), and 

 Mackerel {Scomber). Such individuals are clearly abnormal, 

 but certain perch-like fishes are invariably hermaphrodite, and, 

 further, are capable of self-fertilisation. 



The act of reproduction, by which a new life is brought into 

 being, will be associated by most people with such activities as 

 courtship and pairing of male and female individuals, and with 

 actual union of the two sexes. In fishes, however, such pairing 

 is the exception rather than the rule, and in the majority of 

 Bony Fishes the relations of the sexes at the breeding season 



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