YOLK UTILIZATION BY ATLANTIC SALMON (SALMO-SALAR L) ALEVINS IN RESPONSE TO TEMPERATURE AND SUBSTRATE

Atlantic salmon alevins were reared from hatching with and without rug ose substrate (gravel) at each of five ambient temperatures (4, 6, 8, 10, 12 degrees C). Gross yolk utilization efficiency was higher for al evins reared on substrate at all test temperatures. Alevins reared on substrate showed the greatest gains at the highest temperatures, where as alevins without substrate showed the opposite trend. The improved y olk utilization efficiencies by alevins on substrate were due primaril y to higher embryonic growth rates, with rates of yolk decrease not di ffering significantly (P<0.05) between treatments at any test temperat ure. Alevin water content increased linearly with time under all exper imental conditions until a value of 82% was attained, and may be used to determine time to first feed. Water content was compared with other criteria (behavioral, maximum alevin wet weight, a development index (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, wi th occasional 'calibration' by measurement of alevin water content, wo uld be a suitable way to obtain consistency for first presenting food. Use of thermal sums requires calibration for particular thermal regim es.