472 



FISH BREEDING. 



Although pond-culture may prove a remedy for a deficient supply of food- 

 fish in places distant from natural sources, and although it may also greatly 

 improve the yield of small natural lakes, yet the only efficient method for pre- 

 venting the exhaustion of the food-supply from our inland waters is Fish-breed- 

 ing on a large scale commensurate with the rate of artificial depletion due to 

 the fisheries. 



It has been noted above that great differences are observable between differ- 

 ent species of fish as to the number of eggs deposited by them. It might be- 

 supposed that those species which are characterized by great fertility would 

 eventually crowd out the less fertile species, but observation teaches that the lat- 

 ter are able to hold their own, a greater proportion of eggs arriving at maturity, 

 generally because the young are exposed to fewer dangers. In fact in any body 

 of water there is a certain natural balance of life, liable to slow natural changes, 

 to which the rate of reproduction is in the case of each species closely adjusted. 

 Artificial interference with this balance en a grand scale of the character of our 

 fisheries must inevitably lead to depletion of the species sought after, for the 

 rate of reproduction being already adjusted to natural conditions cannot at once 

 alter to suit the new artificial condition. If, however, i\\e proportion of eggs- 

 arriving at maturity can be artificially increased on a scale commensurate with 

 the rate of depletion, then the danger of exhausting the fish-supply will be 

 thereby obviated. This is the object of the artificial breeding of fish ; it is evi- 

 dently only possible with those species where the natural conditions of the devel- 

 opment of the eggs are such that only a small proportion of them attain maturity 

 and it consists in the artificial hatching out of such eggs, and the care of the fry 

 till such time as they may be safely introduced into the waters to be stocked. 



Many of the earliest experiments in this direction are due to the energy of 

 Mr. Samuel Wilmott, of Newcastle, Ont., who, stimulated by the rapid disappear- 

 ance of the Atlantic Salmon from Lake Ontario, endeavoured thus to prevent it. 

 Much of the apparatus employed is also due to this gentleman's ingenuity, and 

 has, during his official connection with the Fish-culture operations of th& 

 Dominion Government, undergone improvements which have led to highly suc- 

 cessful results. 



The earlier apparatus consisted of shallow hatching trays, over which a 

 steady current of water was allowed to flow ; these permitted readily the extrac- 

 tion of the dead eggs, the decomposition of which interfered with the development 

 of their neighbours. Now glass incubating jars are in use which allow of an easy 

 inspection of the progress of development, with better aeration by a constant 

 current of water running through them. These are employed successfully for 

 Whitefish, Lake Trout and other Salmonidse, and are also used for the propaga- 

 tion of Shad by the U. S. Government. The jars are cylindrical with a hemi- 

 sphsrical bottom ; a metal cover, with two holes |-inch in diameter for in-and out- 

 flow tubes, is screwed water-tight on the mouth by means of a rubber collar. 

 Half-inch rubber tubing connects the inflow tubes with the constant water-sap- 

 ply, the pressure of which may vary with different kinds of eggs, but for the 

 Salmonidae a fall of six feet from a tank provided with a ball-cock (in the event 

 of the water-pressure being high) suffices. The amount required per diem varies ;, 

 for Whitefish eggs 4,000 gallons a day is ample. 



