V 



Factors Controlling \ 



^The Development of Tropical Aquarium FisKes 



REV. FREDERICK R. WEBBER 



Chicago Aquarium Society 



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When we see a fish small in size, poor 

 in color, scrubby in appearance and de- 

 ficient in physical vigor, we know at once 

 that something is wrong. What then are 

 the factors that control and influence the 

 proper development of fishes in the 

 aquarium ? We will try to mention a few 

 of them, bearing in mind that we speak 

 from the viewpoint of aquarists. A fish 

 in an aquarium is under unnatural condi- 

 tions, even at best. Certain rules, draw- 

 backs and other unfavorable conditions 

 must be kept in mind. With fishes bred 

 in the aquarium, the factors commonly 

 concerned are these : 



Food Supply. — No one will deny that 

 the character of the food has much to do 

 with perfect coloring, and size, too, in 

 our specimens. Authorities who write 

 with conviction tell us that the bright 

 color in fishes is due to deposits of certain 

 light-reflecting spicules, or iridocytes, on 

 the scales. The character of the irido- 

 cytes effecting the color. If the spicules 

 are of one type, and present in the deep 

 layers of the skin, the color will be dull. 

 But if these light-reflecting spicules are 

 also present on the scales, their peculiar 

 formation will cause them to act as 

 prisms, breaking the light rays falling on 

 them, and producing iridescent colors. 

 Then we also have the colors due to pig- 

 ment in the skin. The rapid changes in 

 color in some fishes are due to the con- 

 traction and expansion of the pigment 

 cells. It is through this action that cer- 

 tain fishes, the flounders, for example, 

 are enabled to assume a color arrange- 

 ment simulating the bottom on which they 

 may be resting. 



Experiments made in certain European 

 countries have proven beyond doubt that 

 fishes fed on living foods develop these 

 exterior spicules. Daphne, Cyclops and 

 related organisms are rich in the sub- 

 stances producing them. Dr. Francis 

 Ward tells of experiments tried in neigh- 

 boring fish ponds. In certain ponds the 

 fishes were reared on Daphne and 

 Cyclops; in other ponds prepared foods 

 were used. In every case the "flea-fed" 

 fishes were more brilliiantly colored. 

 Moral: Feed "fleas" if you can get them. 



Parental Forms. — The coloration 

 and size of the parents has more or less 

 to do with good coloration and size in the 

 offspring. Scrubs usually produce scrubs. 

 While the tendency is not inherited abso- 

 lutely, a fish born of scrubby parents is 

 predisposed toward that condition. It is 

 therefore well to weed out all the poor, 

 undersized, imperfect specimens. 



Temperature. This is an important 

 factor. A fish reared in a small, poorly- 

 heated aquarium will be deficient in size 

 and color. The color-cells of the tropical 

 fish will not develop under sub-normal 

 temperature conditions. According to 

 the evolutionist, a fish should gradually 

 adapt himself to his environment, but this 

 theory is disposed over eons of time, and 

 not merely through one generation or a 

 dozen. We all know what low tempera- 

 tures will do for our fishes. Tropical 

 specimens have never yet been known to 

 become reconciled to chilly tanks, the 

 temperature less than the average to 

 which they are subjected in their native 

 haunts. If one would have fine, healthy. 



