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ABSTRACT: Dominance, aggression and predator avoidance were compared among farmed, sea-ranched and wild juvenile masu salmon Oncorhynchus masou in laboratory experiments. Domesticated fish (farmed and sea-ranched), which had been exposed to artificial selection, were not dominant against wild fish in pairwise contests, nor did they show greater aggressiveness. Farmed fish did show greater feeding than wild fish. Under chemically simulated predation risk, farmed fish were more willing to leave cover and feed than wild fish, indicating reduced predator avoidance in the farmed fish. Our results indicate that selection for fast growth (domestication) in masu salmon favors fish that respond to food quickly and ignore predation risk. 相似文献
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Abstract. The protozoan Balantidium ctenopharyngodonis is a: common intestinal commensal of two-summer and older grasscarp, hut it may occasionally become pathogenic under the influence of certain predisposing factors. Outbreaks of enteritis complicated by excess multiplication of balantidia occurred among the two-summer and three-summer grasscarp stock in two pond farms during the autumn and winter. Fishes in the terminal stage of disease showed hyperaemia and inflammation of the mucosa over the entire gut. In the posterior 10–12 cm of the gut a dense creamy exudate coated the mucosa. Large numbers of balantidia were found in the exudate and between the mucosal folds there were excoriations, the size of a pin-head, obviously caused by the parasites. Histological examination revealed a loss of superficial epithelium and ulcerations in the grooves between folds. 相似文献
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