112 Reproduction, Competition, and Predation 



food for bluegills or at least produce enough additional plankton to allow 

 some survival of bass. 



Even with a high rate of survival of stocked fish, corrective stocking 

 will not eflFectively improve a fish population unless the number of fish 

 stocked per acre is large enough to approach that found in "superior" 

 populations of these same fish.-^ However, this is not always easy to 

 achieve. Thus, if bass fry were stocked at the rate of 100 per acre into a 

 population of stunted bluegills and the survival rate of the bass was 75 

 per cent ( a very unlikely assumption ) , they soon might grow large enough 

 to feed upon the smaller bluegills, reducing food competition among 

 the bluegills and thus facilitating the growth of the larger ones to useful 

 sizes. However, in most instances of bass-fry stocking, the evidence in- 

 dicates a low survival of the bass fry. Thus, the larger the young fish are 

 allowed to grow before they are stocked from a hatchery, the better are 

 their chances of survival. The problem here is that hatchery production 

 of large fingerlings as compared to fry might be 1 to 1000, so that the 

 fingerling production of the hatcheries of an entire state might be able to 

 stock only a relatively small number of ponds at the rate of 100 large 

 fingerlings per acre. 



The kinds of warm-water fishes that are prone to overpopulate and 

 stunt in certain waters often may be introduced successfully into existing 

 fish populations with the release of only a few adults. Under severe com- 

 petition, these adults are incapable of producing a substantial population 

 in one or two years, but after three or more years, these fish may appear 

 in large numbers. Bluegills, red-ear sunfish, green sunfish, white crappies, 

 and black bullheads have all been observed to increase in this manner 

 after a small number of individuals were introduced into a dominant 

 population of other fishes. 



Corrective stocking is always more dependable where a part of the 

 population has been removed by poisoning or through mechanical means 

 (seining, etc.). Tliis procedure reduces the standing crop of fish to a 

 point below the carrying capacity of the water and leaves food and space 

 for the fish that are introduced. 



Corrective stocking should not be attempted unless a source of fish is 

 available for introducing a large enough number of a given species to 

 approach the carrying capacity of the water for that species, e.g., 100 bass 

 per acre, 300 to 1000 bluegills per acre, etc. 



Stocking to Improve a Food Chain 



This type of stocking is done in an attempt to improve the production of 

 game fish in an existing fish population by increasing the forage for these 

 game fish. The introduction of the threadfin shad into large southern 



