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

Abstract

The effects of different illumination levels on Zooplankton abundance and feeding periodicity, growth and survival of hatchery-produced Asian sea bass, Lates calcarifer, fry in illuminated floating net cages were determined in a 35-day experiment. Zooplankton abundance (consisting mainly of copepods at 64–78% of total abundance in all cages) was highest 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 evidenced by the greatest number of prey (mean: 416–462 individuals fish⁻¹) found in their guts between 0400 and 0800. Feeding incidence (range: 84–89%) was generally higher among fish held in illuminated cages than those reared in dark cages (67%). Low feeding of fish held in dark cages eventually led to starvation and mass mortality. The present results indicate that a light intensity of at least 300 lx attracts the highest 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.