The purpose of this study was to investigate the effect of density of fish on the rate of avoidance learning in a schooling fish. Naive adult zebra fish (Brachydanio rerio) were trained in a two-way aquatic shuttlebox, in Isolation, in groups of two, or in groups of five. The number of trials to reach progressively more exacting levels of performance (I, 2, 3, ... ,9 consecutive correct avoidance responses on 2 successive days), was used to quantify the rate of learning for individuals in the three groups. Using this measure, individuals in groups of five reached any given level of performance in fewer trials than individuals tested alone, which in turn reached the progressive criteria in fewer trials than individuals tested in pairs. In addition, the mean latency of response to the conditioned stimulus for individuals in groups of five was significantly lower than for individuals tested alone or in groups of two by Day 3 of the experiment. The rate of learning in zebra fish schools at these densities may be due to either a balance between imitation learning and conflict-inhibition among the fish or the elicitation of different behavioral responses by shock, depending upon environmental stimuli.
This study investigates the role of female color, size, and dominance, and the influence of early color experience in mate selection by male Convict cichlids, Cichlasoma nigrofasciatum. Dark wild-type male fish were reared by dark parents in dark schools (dark homogenous group), and by mixed dark and white parents in mixed schools (dark mixed group), until sexual maturity. Correspondingly a white homogenous group and a white mixed group were also established. Each male was then allowed to choose a mate among two dark (mixed group) and two white (mixed group) females. Males tended to spawn more often with dark females and always spawned with dominant females. Female size is positively correlated with female dominance and this may be either as a cause or as an effect of female dominance. Early color experience appears to be unimportant in male mate selection.
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