American Fisheries Society. 101 



PRACTICAL HINTS ON FISH CULTURE. 



BY DK. JAMES A. HENSIIALL. 



In the conduct of any operation the smallest matters are 

 often the most important, and too much care and stndy can not 

 be devoted to seemingly unimportant details. Very often, also, 

 the simplest devices give better practical results than those of 

 more elaborate and complicated structure. 



In fish culture, especially, is this true, and the more we en- 

 deavor to follow the methods of Xature, and rely on the simplest 

 means to that end, the greater will likely be our success. There- 

 fore, while the following suggestions may embody nothing not 

 already known to some or all fish culturists, they are none the less 

 true and worthy of consideration. 



AERATIXG SCREENS. 



To begin with the ovum or egg — air is just as necessary to 

 the well-being and development of the embryo as water. In the 

 running water of streams there is air enough for the necessary 

 aeration or oxygenation of the embryo, but in spring water, as it 

 issues from the ground, there is very little, if any, free air. 



In fish hatcheries air is furnished usually by a horizontal 

 aerating screen at the head of the trough, being simply a wooden 

 frame with a bottom of perforated tin or zinc. This is all right 

 in theory, but in practice I have found that the small holes in 

 the sheet of tin, being cut very smoothly, do not permit a flow of 

 water through each and every hole as one might suppose. A film 

 or diaphragm of water is thrown over many or most of the holes, 

 preventing the water from passing through, under the pressure 

 of water usual in most hatcheries. Under these circumstances 

 there may not be sufficient air furnished to the ova or fry, as the 

 case may be. At all events it is well to give them the benefit of 

 the doubt. 



After being convinced of the inefficiency of the aerating 

 screen as usually made, I devised one that fully meets all require- 

 ments. It is constructed as follows : xV piece of soft roofing tin 

 of the desired size is marked with lines an inch apart, both ways 



