30 MAINTAINING FISHES 



there are significant phylogenetic diflFerences. It is 

 well to break the group into a number of subdivi- 

 sions, namely: clupeids, cyprinids, cyprinodontids, and 

 percoids. Selection of representatives from this large 

 group constitutes a rather complex problem. 



Clupeids 



We know more, perhaps, about maintaining 

 trout {Salmo gairdner, S. trutta, Salvelinus fontinalis) 

 in captivity than about any other group of fishes. 

 Various pubhc agencies have done a great deal of re- 

 search on their care and culture. Their environmental 

 and nutritional requirements are known and rates of 

 growth and other standards of comparison are avail- 

 able. Trout have some attributes which make them 

 especially suited to experimental use. They are easily 

 obtained from private, state, and federal hatcheries, 

 and with plenty of fresh, cold water may be main- 

 tained in very dense populations. They feed readily 

 upon nonHving foods including liver and heart as well 

 as recently available pelleted food. On the negative 

 side, trout require temperatures of about 60° F. and 

 are best maintained in running water. To work with 

 trout, one should have an abundance of spring or well 

 water. Further, large trout require rather elaborate 

 facihties. 



Mud minnows (Umbra limi and U. pygmaea) in- 

 habit small ponds and back waters, and are especially 

 abundant in permanent swamps. They occur in the 

 wild in the Mississippi drainage, Great Lakes drain- 

 age and Atlantic coastal areas. In nature they feed 

 upon aquatic invertebrates. They would very likely 

 utilize earthworms or tenebrionid larvae. As experi- 



