ACIAR Project FIS/97/73 - Library - Network of Aquaculture Centres ...

un. Consequently, larval survival was poor. By day 6 post-hatching there was closeto 100% mortality. Larvae were attracted to the water surface and a large number ofmortalities between days 4 and 6 were due to larvae becoming caught at the watersurface. On day 3, a small number of larvae were transferred into two 75ml pots withhigh densities of either copepod nauplii or rotifers. After two hours one larva hadingested rotifers and all larvae had ingested copepod nauplii. More thoroughassessment of prey preference of this species will be undertaken this season withemphasis on eliminating mortalities due to water surface tension.At Gondol, research has primarily concentrated on the problem of early larvalmortality due to death by surface tension. Cromileptes altivelis larvae at 0–5 daysafter hatching are relatively weak swimmers and move slowly. They are easilytrapped at the water surface by surface tension. When larvae receive a stress like thetrapping, they secrete sticky mucus that will accelerate the trapping of other larvae.Finally, a significant number of larvae die in a short time.The addition of oil to the water surface of larval rearing tanks improved the survivalrate of C. altivelis larvae. The survival rate of larvae in tanks without oil wassignificantly lower (P