140 American Fisheries Society 



little current as practicable. Where a long trough is used for 

 a collecting tank the screen may be lengthwise instead of 

 crosswise, thus giving vastly more surface and correspond- 

 ingly less current through it at any point. 



Advantage may be taken of other impulses also to keep 

 fish away from the screens. Trout fry shun the light and 

 will seek the middle of the trough if that part is dark. Pike- 

 perch fry are very active from the first and seek the light 

 and may be attracted aw 7 ay from the screens by a bright 

 sp< >t elsewhere. In ponds young bass seek, the current and 

 struggle to pass screens and it should be practicable to take 

 advantage of this fact and collect them without need of sein- 

 ing the whole pond or any considerable part of it. By a 

 suitable arrangement of ponds and pools and adjustment of 

 screens of different mesh the young fish might be collected 

 and separated not only from the brood fish but from those 

 of the same season but different size. Fear is a great help 

 to a small fish in the business of getting through a small 

 hole. If desirable to hold young fish in the breeding ponds, 

 it may be best to reduce or cut off the overflow. This is 

 sometimes the only practicable way, since a screen fine 

 enough to stop the smallest fish will be sure to clog and over- 

 flow or to catch the young fish attempting to pass it. This 

 point is especially urged. Reduce the inflow until there is 

 little or no overflow. 



It may be claimed that the food for the young fish is 

 brought to them in the water-supply and the inference drawn 

 that the greater the flow through the pond the more food 

 there will be in it. If this were true, it evidently would not 

 do to cut off the supply. But it seems reasonably certain 

 that fish food is produced in greatest abundance in quiet, 

 warm water. Within limits such water will answer for 

 young Salmonidse and it suits bass exactly. A temperature 

 of 70° F. is warm enough for adult trout and salmon, but the 

 young will bear 83° F. Adult bass will seek cooler water 

 when the temperature reaches 90°, but 92° does not ap- 

 pear harmful. 



