Studies on incidence mechanism and prevention of injury caused by fish themselves

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1. Fish injury should be avoided from the view points of prevention for infection, disease and production quality. Studies were conducted using rainbow trout reared by self-feeder under various conditions of light intensity, trigger switch depth, feeding method, and food regime. Following results were obtained.2. Trigger depth had no significant effect on size heterogeneity, mortality feed wastage, feed conversion ratio (FCR) or the incidence of caudal and dorsal fin splitting and fin erosion. Dorsal fin splitting decreased with time in upper trigger but not in lower trigger fish. Caudal fin erosion increased with time in upper and lower bigger fish.3. Feed regime had no significant effect on the incidence of fin splitting or fin erosion to the caudal upper, caudal lower or dorsal fins, and the incidence of fin splitting did not change over time, irrespective of feed regime. Interestingly, the 1-meal regime significantly hindered recovery from dorsal fin erosion, whilst caudal fin erosion to the upper caudal lobe significantly increased with time in the 1-meal and free access regime.4. The incidence of dorsal, but not caudal, fin damage was significantly greater in hand-fed fish. Dorsal fin damage decreased with time in self-fed but not hand-fed fish. Caudal fin damage decreased with time in both self-fed and hand-fed fish, although there was only a non-significant trend for recovery in self-fed fish.5. In the above experiments, most individuals displayed darker body color when they were damaged in their dorsal and/or caudal fin. The darker body color seemed to be originated from the stress due to damages. Then, image analysis of body color was made to obtain relative value of brightness in local area of lateral body changing with the degree of stress. This experiment of image analysis for non-contact and -invade method made possible to measure fish stress.