Ontogeny of feeding behaviour in hatchery-reared rainbow trout, Salmo gairdneri Richardson

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Abstract
Development of feeding behavior in young rainbow trout, S. gairdneri, from swim-up to day 57 after hatch at 8.5.degree. C is described relative to food type (live Artemia salina or dry trout ration) and water flow (current or no current). Earliest signs of feeding behavior appear during the process of swim-up at days 27-29, with the movement of the eyes to fixate particles and the beginning of a snap response which intensifies within 2 days. Initially the alevins are nonselective between food and inert targets, but by about day 25 at the test temperature they become able to discriminate food from nonfood items, and show a marked increase in exogenous feeding activity. The timing, which will differ at different rearing temperatures, coincides approximately with final absorption of the visible yolk sac and follows disappearance of the oesophageal plug by about 10 days. This may be the best time to initiate artificial feeding of hatchery-reared alevins, with the fish showing a preference for ingestion of live food (shrimp nauplii) over dry rations. Despite evident behavioral differences in current and no-current conditions, this factor had little effect on timing or ultimate success of 1st feeding. Failure of some alevins to begin feeding, or feed adequately for survival, is associated with the agonistic behavior of more aggressive siblings.

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