Early development of milkfish: Effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos, more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20 parts per thousand had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50 parts per thousand. Larvae hatched in 35 and 50 parts per thousand had equal amounts of yolk but those from 35 parts per thousand were larger. Oxygen consumption rates increased during development (from 0.06 +/- 0.01 mu 1 O-2 egg(-1) h(-1) by blastulae to 0.37 +/- 0.01 mu 1 O-2 egg(-1) h(-1) by prehatch embryos and 0.43 +/- 0.03 mu 1 O-2 larva h(-1) by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35 parts per thousand consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35 parts per thousand is probably the most suitable salinity for incubation and larval rearing of milkfish. (C) 1996 The Fisheries Society of the British Isles