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CHAPTER I. 



ARTIFICIAL PEOPAGATION. 



THE commonest and most obvious method of attempting to increase the supply of a 

 valuable fish is to hatch its eggs. The young when hatched may be disposed of in one 

 of two ways. They may be kept in captivity and regularly supplied with food until 

 large enough to be valuable, or they may be set free in the natural haunts of the 

 species so as to replenish its numbers. The question of the best way to increase the 

 supply of soles will be fully discussed subsequently. At present I shall describe my 

 own experiments on the artificial propagation of the species. 



In the case of a number of species of valuable marine food-fishes there is no great 

 difficulty in obtaining large numbers of eggs from the fish, fertilising and hatching 

 them. The eggs become ripe at the spawning period, and it is perfectly easy to tell 

 whether the eggs of a given species are ripe or not. The number of eggs which ripen 

 at one- time varies in different species. In some, as the herring, nearly all the eggs 

 become ripe simultaneously. When the eggs are ripe they can be squeezed out of the 

 ovary by gently squeezing the abdomen of the fish with the fingers and thumb. They 

 run out in a continuous stream, and no blood or membranes escape with them : if the 

 eggs are not ripe no eggs escape unless considerable pressure is applied, and when they 

 are forced out they are accompanied by blood and by membranes containing blood' 

 vessels. When the eggs in the ovary all ripen simultaneously, or nearly so, as in the 

 herring, the ovaries can be entirely emptied by gentle pressure. In all fishes that I 

 have examined, the number of eggs ripe at the same time increases after the .spawning 

 has commenced, so that the ovaries after a certain number of eggs have been shed 

 contain ripe eggs only and can be entirely emptied. In the cod family the ripening of 

 the eggs goes 011 very gradually, so that only a portion of the eggs in the ovaries of a 

 female can be pressed out at one time. The eggs of the sole ripen gradually at first, 

 but after spawning has commenced and some of the eggs have been shed the rest all 

 ripen simultaneously. The eggs also seem to be shed as soon as they are ripe. These 

 are the conclusions I form from my experience, which is that I have usually met with 

 soles whose ovaries were either full of unripe eggs and yielded very few which were 

 ripe, or else were quite empty, all the eggs having been shed. 



I commenced my experiments on the sole in 1888. At my first attempt, which wa,s 



