102 Reproduction, Competition, and Predation 



operations. Most of this work has been done in Asia and Europe, where 

 fish are raised for food or display. These fish are usually not exposed to 

 "wild" conditions; when they escape to compete with wild fish, they 

 either die or revert to their original wild type as the European carp has 

 done in this country. 



Fish that have been raised in hatcheries for many years have probably 

 been subjected to unintentional as well as intentional selection. Hatchery 



RED-EAR SUNFISH 



R-B Fj HYBRID^ 



Figure 5.4. Hybrid sunfish produced by fertilizing eggs of one species with 

 milt from a different one. In this experiment, fish were limited to green sunfish, 

 bluegills, and red-ear sunfish. Hybrids showed characteristics intermediate be- 

 tween those of parents but were usually heavier-bodied. Males were more 

 abundant than females in most hybrid combinations. [From Childers, W. F., 

 and Bennett, G. W., INHS Biol. Notes, 46 ( 1961 ) ] 



personnel may consciously choose the heaviest-bodied and fastest-growing 

 fish for egg production; at the same time they may unconsciously select 

 the fish that are most easily handled, e.g., those that have lost most of 

 their "wildness." This type of selection has made hatchery trout somewhat 

 less desirable than wild fish ^^ for sport fishing and has reduced their 

 ability to survive under "wild" conditions. 



Attempts at selection for improving species of warm-water fishes ap- 

 parently have accomplished little. However, artificial selection may be 

 operative in heavily-fished, isolated small lakes and ponds that receive 



