Innate and Acquired Behavior Affecting the Aggregation of Fishes

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Abstract
Fright induced by a wide variety of visual, mechanical and chemical stimuli induce the formation of temporary schools in Brachydanio refio, but any one stimulus soon loses its potency. Attempts at training Brachydanio to aggregational behavior by a punishment technique led to fighting instead of schooling. Individuals of Brachydanio reared from the egg in isolation joined an aggregation: at once, but individuals removed from a group to isolation and Subsequently returned showed considerable; hesitancy. Moving targets of any shape were moved toward, up to a ciertain size, beyond which they were retreated from, followed by a gathering at the point where last'' seen. Any such stimulus soon lost its potency. On being given a choice of background between yellow and gray, Carassius of either matching color avoided the yellow, although in the case of the yellow fish, they became very conspicuous. Groups of Carassius of like-colored phenotypes were more cohesive than groups in which one fish was of an odd color, on either matching or contrasting backgrounds, as measured by their aggregation pattern. Isolation of Carassius for a period of 6 months modified the normal aggregating behavior pattern and the fish appeared unusually sensitive to stimuli formerly ineffective. Phenotypically uniform groups of Carassius closely approximated the distribution indicated by the reciprocal of binomial distribution as contrasted with blind specimens which approached binomial distribution. Mixed groups of blind and seeing Carassius approximated the reciprocal of the mean of binomial distribution and its reciprocal. Mixed groups of differing phenotypes of Carassius and groups of previously isolated Carassius and Brachydanio did not approach any evident simple mathematical expression. The implications inherent in the above results are discussed in reference to other items in fish aggregations and schools and speculations bearing thereon.