154 How to obtain it. 



judicious crossing of races and varieties is an absolute necessity if 

 successful fish farming is to be carried on. An accepted theory 

 amongst biologists is that though the reproductive cells as a rule 

 vary considerably in size between one genus and another, it is less 

 marked in the species, and disappears (especially in the male 

 element) in the varieties. 



An expert can often tell at a glance whether a fish is ripe or 

 not. There are signs which it is difficult to describe, such as the 

 appearance of the organs, the looseness of the ova in the fish, and 

 a general appearance of ripeness, which can only be detected by 

 long practice. No force should be used in expelling the eggs. If 

 they do not flow freely on the hand being very gently passed over 

 the belly of the fish they are not ripe. Of course a slight pressure 

 is necessary, but far more depends upon proper handling. The 

 hand or thumb should be kept behind the eggs, and not allowed 

 to run over or in front of them. In taking the milt a knowledge 

 of the situation of the glands is useful. They are much lower 

 down than the ovaries of the female, and instead of using the 

 hand, the milt may be easily obtained by an adroit use of the 

 thumb and forefinger. The weather has much influence on the 

 spawning of fish. A mild day, preceded by a warm rain, will 

 make the fish lively, and they will spawn freely ; but a hard frost, 

 or snow in the water, will retard the shedding of the ova, and 

 consequently, on a fish farm, preparations are often made accord- 

 ingly. We know, as a rule, before commencing, how the fish will 

 yield their ova. 



When the eggs have had the milt on them long enough, they 

 are easily washed in the spawning dishes, by pouring off a part of 

 the water, adding more that is fresh and clean, and continuing the 

 operation some six or seven times, when the eggs should be clean. 

 Be quite sure that they are so, and should there be any doubt 

 about it give them another wash. At the Solway Fishery, where 

 eggs are dealt with in large quantities, the contents of a dozen or 

 a score of spawning dishes are emptied into a well-charred wooden 

 tank, through which a current of water flows, and are left there for 

 half-an-hour or more, when they are found to be perfectly clean. 



(Fig- 13)- 



One of these tanks will wash a hundred thousand eggs at a 



