39 



blunt-nosed minnows often are not of usable size until 

 July of their second season. In extreme cases of over-- 

 crowding, the fish will not grow to maximum size even 

 with plenty of food available. 



Grading of Fish 



Periodic grading or sorting of fish throughout the 

 growing season will reduce the number of small fish that 

 have to be held through the winter and will result in 

 greater production of desirable bait-size minnows. 



The most practicable method suggested for grading 

 minnows, with the least amount of injury to the fish 

 involved, is by the use of a mechanical grader, similar 

 to those used in trout culture, consisting of a wooden 

 box containing a bottom of tubular grating. These 

 tubes of light-wei ght metal, having a diameter of about 

 1/4 inch, extend across the bottom, producing a sieve- 

 lil^e structure. By regulating the spacing between the 

 tubes, certain sizes of minnows can be retained in the 

 box or allowed to pass through. If the minnows are to 

 be graded into several sizes, several grading boxes 

 will be necessary, one for each size-group in minnows 

 desired. 



AQUATIC VEGETATION 



Plants are necessary in minnow ponds for food, 

 spawning locations, shelter of fry from predatory 

 adults, and reduction of predation by birds and snakes. 

 Algae of the unicellular and filamentous types are 

 easily controlled plants that will supply these needs. 

 Though suitable also for some of these functions, 

 submerged plants should not be encouraged because they 

 are difficult to control and may take over the whole 

 pond at the expense of fish production. Too many 

 plants will choke the pond to the extent that an oxygen 

 depletion may occur on hot, still nights. Submerged 

 plants often completely cover the shore feeding and 

 nesting areas and make them unsuitable for the fish. 

 A heavy growth of plants uses up a large percentage of 

 the pond fertility in a form that is not available to 

 the fish as food, and a pond choked with weeds is 

 extremely difficult to harvest. 



There are three methods of controlling submerged 

 vegetation in ponds. The most practical is by heavy 

 fertilization. A pond that is subject to weed trouble 

 should be fertilized early in the season so that a heavy 



