Yolk utilization by Atlantic salmon (Salmo salar L.) alevins in response to temperature and substrate

Abstract Atlantic salmon alevins were reared from hatching with and without rugose substrate (gravel) at each of five ambient temperatures (4, 6, 8, 10, 12°C). Gross yolk utilization efficiency was higher for alevins reared on substrate at all test temperatures. Alevins reared on substrate showed the greatest gains at the highest temperatures, whereas alevins without substrate showed the opposite trend. The improved yolk utilization efficiencies by alevins on substrate were due primarily to higher embryonic growth rates, with rates of yolk decrease not differing significantly ( P K D ), and use of thermal sums) as to suitability for estimating times for first feeding. It is suggested that any one of these criteria, with occasional ‘calibration’ by measurement of alevin water content, would be a suitable way to obtain consistency for first presenting food. Use of thermal sums requires calibration for particular thermal regimes.