22G BULLETIN OF THE UNITED STATES FISH COMMISSION. 



chopped form for the food of large fish. A few barrels of salted alewives have been 

 used, and if well soaked out and chopped they are readily eaten by the larger fish 

 and can be fed to fry, but are less satisfactory with the latter, and like fresh fish they 

 break up to such an extent that they are only to be regarded as one of the last resorts. 



Fresh-water mussels have been occasionally gathered in the lake close to the station 

 when there has been a scarcity of food. Those employed belong almost wholly to a 

 species of Unio, which abounds over a considerable area of soft bottom, under a depth 

 of 2 to 10 feet of water. Many were taken with a boat dredge; more were scooped up 

 with long-handled dip nets of special construction. Finally a wide, flat dredge was 

 made, to be drawn by a windlass on the shore and manipulated by means of poles 

 from a large boat. When needed for food the mussels were opened with knives — a 

 great task — and chopped. The meat is readily eaten by all fishes, and appears to form 

 an excellent diet. Being more buoyant than any other article tried, it sinks slower 

 in the water and gives the fish more time to seize it before it reaches the bottom, a 

 consideration of considerable practical importance. The labor involved in dredging 

 and shelling is a serious drawback, but were the colonies of unios sufficiently extensive 

 or their reproduction rapid enough to warrant expenditure of time in experimenta- 

 tion, improved methods might be devised, which would put this food-source on a 

 practicable basis. 



During the seasons of 1880 and 1888 some use was made of mosquito larvae. Near 

 the station is an extensive swamp where these insects breed in great numbers. From 

 the pools of water the larvae were daily collected by means of a set of strainers spe- 

 cially devised for this use. Barrels filled with water were also disposed in convenient 

 places near the rearing troughs, and were soon swarming with larvae from the eggs 

 deposited by the mosquitoes on the surface of the water. When near the completion 

 of their growth, which was only some ten days after the deposit of the eggs, the larvae 

 (or pupa') were strained out and fed to the fish. No kiud of food has been used at 

 this station that has been more eagerly devoured, and so far as our observation has 

 gone no other food has contributed more to the growth of the fish; indeed, I am 

 inclined to put them at the head in both respects. It was found, however, that the 

 time expended in collecting them was out of all proportion to the quantity of food 

 secured, and pending opportunity for further experiment their use was discontinued. 

 I think it quite possible that an arrangement might be devised whereby the greater 

 part of the labor might be saved. Perhaps a series of breeding tanks arranged in 

 proximity to the fish troughs, into which the water containing the larvae might be 

 drawn when desirable by the simple opening of faucet, would solve the problem. 



Various methods of serving the food have been tried, but at present everything is 

 given with a spoon. The attendant carries the food with the left hand — in a 2-quart 

 dipper if chopped meat, in a larger vessel if maggots — and, dipping it out with a 

 large spoon, strews it the whole length of the trough, being careful to put the greater 

 portion at the head, where the fish nearly always congregate. Finely chopped food, 

 for very young fish, is slightly thinned with water before feeding. At one time the 

 finest food was fed through perforations in the bottom of a tin dish; the food was 

 placed in the dish, which was dipped into the water a little and shaken till enough of 

 the food had dropped out of the perforations; this practice was laid aside because it 

 was thought that the food was too much diluted. In feeding maggots it was, at first, 



