Optimum light conditions for egg incubation and larval rearing of brown-marbled grouper, epinephelus fuscoguttatus

Abstract

Light conditions are important for aquatic living things, as they affect the growth and development. Although studies regarding light conditions for egg incubation and larval rearing of teleost fish have been done, there are only a few studies regarding light wavelengths and light intensities. Brown-marbled grouper, Epinephelus fuscoguttatus is an important fish species for aquaculture in Southeast Asia. This study was conducted to examine the optimum light wavelength and intensity for egg incubation and larval rearing of brown-marbled grouper using light emitting diode (LED) lamps. Experiments were conducted using 40 L aquaria (in dark shelves) and 0.5 tonne tanks. Fertilized eggs were incubated in the experimental aquaria and tanks under white light (broad spectrum with double peaks 452 and 557 nm) as control, blue (peak, 458 nm), green (528 nm), yellow (593 nm) and red (636 nm). The intensities for each wavelength were setup at 0.53, 2.7 and 13.3 µmoles/m²/s. The light conditions were set up as 0600 on and 1800 off. The density of Nannochloropsis sp. in each experimental aquarium and tank was maintained at 1 million cells/ml. The water salinity and the temperature were maintained at 29 – 30 ppt and 27.5 – 28.5 °C respectively. The number of hatching larvae in each aquarium and tank was counted to examine the egg hatching rates. The larval rearing experiments were carried out following the egg incubation experiments. Larvae were sampled at the end of the experiment to examine the survival and growth rates. Cortisol analysis was done to examine the relationship of stress level of brown-marbled grouper larvae with their growth under different light conditions. Results showed that hatching rate under green light was significantly higher than white and yellow (p < 0.05). The results of survival and growth rates of brown-marbled grouper larvae showed higher tendency under green light wavelength with the light intensity of 2.7 µmoles/m²/s. The cortisol analysis results showed that larvae reared under green 2.7 µmoles/m²/s had the highest cortisol level compared to the other light conditions (192 pg/g). Therefore, it can be determined that the green 2.7 µmoles/m²/s is the optimum light wavelength and light intensity for egg incubation and larval rearing of brown-marbled grouper