THE LIFE-HISTORIES OF FISHES 157 



All marine and fresh-water fishes have definite 

 breeding or spawning seasons. Generally these are 

 in the first half of the year. The cod, haddock, 

 whiting, gurnard, and most flat fishes spawn 

 between the beginning of February and the end 

 of May in British waters ; but the sole spawns 

 towards midsummer, and the mackerel which, 

 however, is somewhat variable in this respect is 

 also a late spawner. Herring, on the other hand, 

 may spawn at any time, and indeed these fishes 

 may be found spawning in some part of the British 

 seas all round the year. In many places there 

 are two distinct herring spawning periods, a 

 spring period and an autumn period, and there 

 are also two distinct fisheries. This curious 

 condition has recently been established for the 

 cod also. 1 But in these latter cases it is quite 

 improbable that the same fish spawns twice in 

 the year. It is most probably a case of two 

 distinct " races " or " schools " of herring or cod, 

 one spawning in the spring and the other in 

 the autumn. 



As a very general rule, marine fishes are 

 enormously prolific. The eggs laid annually by 

 the females of many species are to be numbered 

 by the million. Fulton first determined approxi- 

 mately how many ova were produced by each, and 

 the following table gives the average numbers of 



1 Fulton, Publications de circonstance, No. 8 : Conseil permanent 

 international pour 1'exploration de la mer, Copenhagen, 1904. 



