20 U. S. BUREAU OF FISHERIES. 
WATER BEETLES IN RELATION TO POND CULTURE. 
The home fishpond is a subject of continued interest among farm- 
ers and others who value 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 plants 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 through 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 larvee and adults of 
the three beetle genera, Hydrophilus, Dytiscus, and Cybister, destroy 
small fish under normal conditions. The larve of Dineutes are 
known to have killed and eaten fish fry under certain abnormal con- 
ditions. The larve of three other genera (Acilius, Graphoderes, and 
Hydrocharis) are suspected of being capable of committing similar 
depredation. 
On the other hand, both beetle larvee 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 
harmless. 
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 harmful 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 fishpond 
is sure to be stocked with them as soon as it 1s 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 abruptly 
raising and lowering the water in the pond at intervals of a week 
or 10 days during their breeding season in July and August. 
STUDIES OF SALMONIDA: IN RELATION TO FISH CULTURE. 
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 
