The activity of alevins of Atlantic salmon and rainbow trout, incubated on different substrates
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Atlantic salmon (Salmo salar) and rainbow trout (S. gairdneri) eggs were incubated in plexi-glass aquariums. After hatching, alevins were kept in darkness, two groups of each species without substrate, two groups in gravel and two groups in Astroturf artificial substrate. Every sixth day after hatching until the end of emergence, their activity was monitored with a video recording system in a five minutes period of darkness, followed by five minutes exposure to light. The use of ordinary 60 watts bulb lights and infrared light, made it possible to measure their swimming distances within a definite coordinate system in the aquariums, both in darkness and under illumination. Alevins of both species showed a higher activity when incubated without substrate than those within the two substrates. The differences in activity were, however, least developed between the groups of rainbow trout. Activity, caused by lack of ventra lateral support among the flat screen reared Atlantic salmon alevins, was most conspicuous between days 8 and 23. Illumination caused increasing activity until days 28 and 40 of rainbow trout and Atlantic salmon, respectively. The presentation of food stimulated the alevins to increase their activity.