20 U. S. BUREAU OF PISHERIES. 



WATER BEETLES IN RELATION TO POND CULTURE. 



The home fishpond is a subject of continued interest among farm- 

 ers and others who vahie the additional table food made available 

 or the means of recreation provided. There must be a great deal in 

 a pond besides fish; otherwise the fish would starve. There must be 

 small animals which serve as food to fish and still smaller animals 

 and i)lants which serve as food for them. Some things in a pond are 

 desirable, others objectionable in varying degree. The fishpond is, 

 indeed, not a simple thing, but a very elaborate complex, the scien- 

 tific unraveling of which is necessary before the best plans of pond 

 management can be known. The unraveling of the complex can be 

 accomplished eventually only by tracing particular threads, that is, 

 by centering attention at one time upon a particular group or species 

 of the inhabitants of the water. An instance of such special studies 

 carried thi'ough to a point where helpful practical conclusions are 

 derived is afforded by the investigation of water beetles conducted at 

 the Fairport station. 



Dr. C B. Wilson has made a comprehensive study of the role beetles 

 play in pondfish culture. He has found that larvse and adults of 

 the three beetle genera, Hydrophilus, Dytiscus, and Cybister, destroy 

 small fish under normal conditions. The larvae of Dineutes are 

 known to have killed and eaten fish fry under certain abnormal con- 

 <litions. The larva) of three other genera (Acilius, Graphoderes, and 

 Ilydrocharis) are suspected of being capable of committing similar 

 depredation. 



On the other hand, both beetle larvae and adults are eaten freely 

 by the young of nearly all our common food and game fishes after 

 the latter attain a length of 25 to 40 millimeters. This is just as true 

 of the seven genera mentioned above as of the others that are 

 li a mil ess. 



Practically speaking, only the young fish of the year are menaced 

 by beetles. Fish a year or more old are large enough to feed on the 

 beetles and are almost never attacked by the latter. Consequently 

 beetles are really luirmful only in breeding ponds, and even in those 

 places, as everywhere else, they contribute materially to the available 

 food supply for the fish. 



Adult beetles migrate and travel so constantly that every fishpoml 

 is sure to be stocked with them as soon as it is completed, and yet 

 the beetles of two ponds side by side are likely to differ radically in 

 numbers and variety. If they occasion trouble in one pond, the 

 temporary removal of the fish to another pond will usually prove an 

 effectual remedy. Beetles may also be kept in check by abrujitly 

 raising and lowering the water in the pond at intervals of a week 

 or 10 days during their breeding season in July and August. 



STl DIES OF SALMONH).!; IN RELATION TO FISH CULTl RK. 



In a previous report reference in detail was made to the investi- 

 gations by Dr. W. C. Kendall of rainbow and steelhead trout and 

 of some hitherto unrecognized anatomical characters of trout which 

 seemed to have a direct bearing upon fish-cultural practices. It is 

 worthy of note that the results.of the latter investigation were deemed 

 of such value by independent persons that the report upon them was 



