Homotypic and Heterotypic Conditioning in Relation to Survival and Growth of Certain Fishes

Abstract

Young Amtiurus melas show better survival in an artificial pond water made in once-distilled water when this medium has been conditioned by having Carassius or other Ameiurus live in it than they do in unconditioned (control) water. The homotypically conditioned medium allows slightly longer survival for Ameiurus than does the heterotypically conditioned one tested. Similarly, young C. auratus survive longer in these conditioned media than in the uneontaminated controls, except that with goldfish the 2 types of water were equally effective in promoting survival. Although introduced Cu and Al ions, in concs. comparable with those found in once-distilled water, produced no deaths, Cu contamination of the water is suspected of being the toxic agent, the activity of which is greatly decreased or nullified by conditioning. Al in some form may also be related to the observed toxicity. Very low concs. of both metallic ions were present in the once-distilled water. An otherwise similar artificial pond water, based on water redistilled in a tin-lined still, was not toxic, and positive growth was given by assay fish, even in the. control medium. As in earlier expts., goldfish grew in length more rapidly in the conditioned water than in uneontaminated, but otherwise similar, control media. They maintained wt. slightly better in bullhead- than in goldfish-conditioned water. Extracts from the surfaces of bullheads and of goldfishes have essentially similar protective and growth-promoting powers when used in equal cones. Water with the same conditioning coefficients contained less amino X following bullhead, as contrasted with goldfish-conditioning. Differences in oxidizable organic matter in the 2 types of conditioned media are smaller and less consistent than are the variations produced by changing the diet of the conditioning fish. With the concs. used in these expts., all observed effects of conditioned water were, on the average, either neutral or favorable in their effects on fish survival, wt. maintenance, or growth. There is a brief discussion of causal factors.