REPORT OF COMMISSIONER OF FISH AND FISHERIES. CXXIII 



animals suitable for bass food, and also in small vegetable and animal 

 organisms on which the flsli food subsists. The more abundant forms 

 included species of Cyclops, Daphnla, Alona, Scapholeberis, Amoeba, 

 Hydra, Bothrimonus, several genera of infusoria, nematodes, Volvox, 

 Spirogyra, Micrasterias, Euglena, and some other alg.T. The stomach 

 contents of the young bass from the same ponds showed that cladocera 

 were being principally consumed. One small-mouth bass 4 days old 

 contained 10 specimens of Cyclops, Daphnia, and other cladocera; one 2 

 days old had 8 specimens of the same animals; three large-mouth bass 

 a few days old had been subsisting on Baphnia. 



The possible use of iinely powdered cereals as food for young white- 

 fish has from time to time been suggested. At Putin Bay, Ohio, station 

 in 1897 Superintendent Stranahau fed wheat shorts to about 2,000,000 

 whitetish fry contained in tanks. They at first api)eared to thrive, but 

 by May 7 had all died, and specimens were forwarded to Washington 

 for examination. In nearly every case the alimentary tract was well 

 filled with granules of wheat starch, and it was apparent that the fry 

 readily took the food. The nutritive value to fish, however, of such a 

 substance is doubtful, and an examination of the condition of the gran- 

 ules in the hind gut, as compared with those in the anterior part of the 

 alimentary canal, showed no evidence that they had undergone diges- 

 tion to the slightest degree. The assimilative powers of the very short 

 intestinal canal of the whitefish fry are not sufficiently active to utilize 

 raw vegetable material of this nature. It is possible, however, that by 

 cooking the shorts and diluting them with other food they may prove 

 of service in rearing young whitefish. 



Study of rainhow trout and steelhead trout in aquaria. — In the month 

 of April, 1897, the aquaria at Washington contained a large number of 

 artificially hatched rainbow trout (*SV<imo irideus) and steelhead trout 

 {Salmo gairdneri). The fish were 4 inches in length and 12 months old, 

 the rainbow trout having been hatched from eggs of domesticated fish 

 at the Wytheville (Va.) station, and the steelheads from eggs of wild 

 fish obtained at Fort Gaston (Cal.) station. Comparing the fish as 

 they appeared in the aquaria, the rainbow trout were relatively shorter 

 and deeper, darker in coloration, with more numerous spots, especially 

 on the caudal fin ; the under parts were darker, the middle of the side 

 more rosy; the pectoral, ventral, and anal fins were darker, the white 

 edges being made i)rominent by contrast. The rainbow trout have the 

 spots on the back larger and more numerous. In the steelhead the 

 spots on the top of head are very much smaller and more numerous. 

 Comparative measurements showed no differences except that the 

 rainbow is somewhat deeper than the steelhead (depth 4:^ in rainbow, 

 4.^ in steelhead). The scales in the lateral line are rather larger in the 

 rainbow and the origins of the dorsal and anal fins are more anterior. 



Flsli parasites and diseases. — About May 15, 1897, a very destructive 

 disease appeared among fresh-water fishes iu the aquaria at Washing- 

 ton. The onset of the attack was very rapid, and in a short time spread 



