THE PUBLIC AQUARIUM 297 



excessively fat, and these were believed to have been overfed. One of 

 the weak points in the mana<»:ement of all aquariums is the matter of 

 feeding. The food of aquatic animals in captivity undoubtedly 

 should be varied as much as possible. Efforts should be made to sup- 

 ply them with some of their natural foods, whicli include virtually 

 all of the small aquatic fauna. Crabs, crayfish, shrimps, clams, mus- 

 sels, snails, whelks, and squid are all of great value in varying the 

 otherwise monotonous rations of the aquarium. The extensive studies 

 of Prof. S. A. Forbes have shown the great variety of invertebrates 

 consumed by fresh-water fishes. Among these are included Entomo- 

 straca, aquatic worms, and insects, on which young fishes subsist 

 chiefly. 



In feeding alligators, crocodiles, and sharks, fish may be supplied 

 without being headed or. if fresh, without being eviscerated. For- 

 merly it was difficult to maintain a tank of dogfish or dog sharks for 

 more than a few months, imtil it was discovered that they really 

 needed more bonj'^ material in their food. They are noAv fed largely 

 on the heads and skeletal portions of fish, from which the fleshy parts 

 are roughly trimmed in the feed room, with the gratifying result that 

 the length of life in these fishes is measured by years instead of 

 months. 



OTHER MATTERS OF CARE 



The necessity of pure water, abundant swimming space, and careful 

 feeding have already been considered, but there are other necessities 

 to be provided for w^hich often are overlooked. 



Fishes in captivity suffer from prrasites, some of which can be 

 guarded against. Parasitic Avorms attached to the gills are respon- 

 sible for the loss of many angel and butterfly fishes in captivity. Ex- 

 perience has shown the desirability of keeping sand in a corner of 

 the fish tank. Many fishes have the habit of sucking fine sand into 

 the mouth and throwing it out through the gills, an act that appar- 

 ently contributes to the cleansing of the gills. Fishes in captivity 

 may often be seen making quick motions against the bottom of the 

 tank to rub their sides or other parts of the body, and manj^ fishes 

 settle down at times into the sand, showing little more than their 

 eyes. It is the habit of some fishes, like flounders and skates, to hide 

 in this manner for hours while watching for their prey. Others 

 do it for short periods, perhaps merely for temporary comfort. Some 

 of the small tropical wrasses seek the sand in the evening and remain 

 hidden through the night. Fresh-water turtles are benefited by hav- 

 ing sand to hide in. Formerly it was difficult to keep soft-shelled 

 turtles in captivity, but experiment showed that they were fond of 

 burying themselves in sand. Two buckets of clean sand were poured 

 into one corner of the tank, into which these mud-loving turtles could 

 burrow for the purpose of cleaning themselves and hiding when at 

 rest. They were very active, frequently chasing each other about 

 the tank and occasionally climbing out on a floating log. These are 

 the most active of all our native turtles. They took to the sand quite 

 naturally, darting into it, and with a few quick movements covering 

 themselves completely. Frequently the entire lot would be under the 

 sand, their small heads and long slim nocks alone protruding. Since 

 these changes were made the turtles have fed freely and none of the 



