EFFECTS OF DIFFERENT ILLUMINATION LEVELS ON ZOOPLANKTON ABUNDANCE, FEEDING PERIODICITY, GROWTH AND SURVIVAL OF THE ASIAN SEA BASS, LATES-CALCARIFER (BLOCH), FRY IN ILLUMINATED FLOATING NURSERY CAGES

The effects of different illumination levels on zooplankton abundance and feeding periodicity, growth and survival of hatchery-produced Asia n sea bass, Lates calcarifer, fry in illuminated floating net cages we re determined in a 35-day experiment. Zooplankton abundance (consistin g mainly of copepods at 64-78% of total abundance in all cages) was hi ghest in cages illuminated at 180 lx (mean: 124 individuals l(-1)) and at 300 lx (mean: 405 individuals l(-1)) and peaked at 0400. High prey densities subsequently resulted in increased fish feeding as evidence d by the greatest number of prey (mean: 416-462 individuals fish(-1)) found in their guts between 0400 and 0800. Feeding incidence (range: 8 4-89%) was generally higher among fish held in illuminated cages than those reared in dark cages (67%). Low feeding of fish held in dark cag es eventually led to starvation and mass mortality. The present result s indicate that a light intensity of at least 300 lx attracts the high est number of zooplankton and promotes the best weight specific growth rate (10% day(-1)) and survival (40%) in sea bass juveniles reared in illuminated nursery cages. (C) 1997 Published by Elsevier Science Ltd .