lxiv . BREEDING AND STERILITY. 



seem that the various sizes, modes of deposit, and numbers of fish eggs, must 

 be on some definite plan, not a chance medley, destitute of any order and 

 deficient of any scheme. We observe, as in many other forms of life, that 

 the more voracious class, as sharks and rays, have fewer young than the 

 herring and the mackerel, that fish which give the most eggs take the least 

 care of their offspring, and, until the contrary is proved, we are justified 

 in assuming that where the most numerous eggs or young are produced by 

 a species, there the greatest destruction occurs, and finally that fish have 

 only sufficient ova for the purpose of compensating for normal loss.* 



But even when fishes' eggs have been deposited in order that they 

 should hatch it does not follow that it is only necessary to place them in a 

 hatching box, and then turn salt-water over marine ones and fresh-water over 

 those of our streams and lakes. The precautions to be taken by the fish culturist 

 I do not propose alluding to here, but certain physical phenomena are very 

 important. 



Some fishes are sterile from various causes. Thus the common eel, a 

 catadromous form, or one which breeds in the. sea but passes its life in fresh- 

 waters, is believed only to deposit ova once during' its lifetime, and then- 

 either dies or returns to the 'rivers, and is sterile for the remainder of its 

 life. It has been observed that among the Salmonidce sterile forms are seen, 

 but which are believed to be only temporarily so, as for one or two seasons. 



Fish may also be sterile consequent on disease. Thus I have seen in a 

 mackerel the oviduct occluded due to disease having set up inflammation, 

 and occlusion of the outlet of the oviduct, and thus the preceding year's 

 eggs have been retained and formed a large tumour. 



Eggs themselves, of course, may fail in •hatching, due to sterility or 

 deficiency of fecundation, injurious surroundings, as by being carried by floods 

 and currents into unsuitable places, or consequent upon the effects of disease, 

 while shocks given to them during incubation produce monstrosities and if 

 severe, death. While fishes' eggs are more or less circular or oval, and of 

 varying colours, being pea-green in some sheat-fishes or siluroids, and among 

 the Salmonidce they may be coral-red, yellow, or pure white, the herrings 

 usually have a slight pink tinge ; those of the sprat are colourless. 



I have already remarked that fishes' eggs before they are fertilized have 

 a small orifice or micropyle into which the spermatazoon enters, but it is 

 evident in sea fishes that if the egg floats at the surface and the milt is 

 beneath, the chances of fertilization must be diminished, unless some means 

 are taken to obviate this. Also that there must exist some mechanical 

 reason why fish eggs float in some forms, and sink in others. Of course, the 



* As a rule fish -hatched from small ova are feebler than those from large ova, and Ryder 

 remarks " some species leave the egg with the throat perforated and other forms do not." The shad 

 cannot swallow at the time of hatching. . 



