196 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



In still another specimen I found both the dermal and flesh spicules 

 of a fresh -water sponge and the remains of a portion of a tracheal tube 

 of an insect. 



A more exhaustive examination of the fish, which I did not care to 

 sacrifice to any great extent, would have shown that in feeding they 

 had probably laid the entire fauna and flora of the pond under contri- 

 bution; at any rate, the foregoing list shows that there was no want of 

 variety in the make-up of the bill of fare consumed by these young Cyp- 



rinoids. 



\ 



X. — EXPERIMENTS IN SUPPLYING THE PROPER FOOD FOR LARVAL 



SHAD. 



It was suggested to me by Professor Baird in 1880 to try to discover 

 the kind of food upon which the young shad normally feeds, and if pos- 

 sible to collect or breed the food in quantities large enough to afford a 

 supply of nutriment for the larvae. My investigations upon the intes- 

 tinal contents of the adults during that season taught me approxi- 

 mately what I might expect to find to be the food of the young. Inves- 

 tigations which I conducted in the latter part of the season of 1880, 

 upon the young which had been kept for fourteen days at the navy- 

 yard at Washington by Mr. F. K. Clark, showed that my surmises had 

 been correct. As already discussed in my paper, published in this 

 Bulletin, entitled "On the Protozoa and Protophytes as the Primitive 

 Source of the Food of Fishes," the young shad, under favorable conditions, 

 soon prey upon other minute organisms. The mouth is not open widely 

 enough immediately after hatching to take food, nor can the mouth be 

 opened and closed at this time, but by the time the yelk sac is fairly 

 absorbed, or in four to five days after hatching, the young fish will al- 

 ready take food, as observed by us this season in the aquaria at the 

 central station. At first the mouth is on the under side of the head, 

 and it is only after the jaws and gill-arches have grown longer that the 

 mouth is widely enough open to seize food with the four conical, hooked 

 teeth with which the lower jaw is armed; this condition of development 

 is attained when the yelk sac has been mostly absorbed. 



It was a problem with me for some time as to how the food of the 

 young shad, which consists mostly of Copepoda, Ostracoda, &c, was 

 to be got in sufficient quantity to make artificial feeding a success. 

 Knowing the favorable conditions which existed in the carp ponds in 

 Washington for the multiplication of these crustaceans, I took a fine 

 net to the ponds and found a locality where I could skim them out from 

 water, amongst dense growths of Anacharis, by the many thousands. 

 The skimming was continued until a large number of Copepoda and 

 Daplmiidoe were obtained, which were turned out amongst the young- 

 fish into the collectors used by Colonel McDonald in connection with his 

 hatching-jar. The young shad in the collector aquarium, having vast 

 numbers of their favorite food all about them, which could not escape 



