Effects of light intensity on phototaxis, growth, antioxidant and stress of juvenile gibel carp (Carassius auratus gibelio)

To explore the effect of light intensity on phototaxis, growth performance and physiological condition of juvenile gibel carp, a short-term ethological experiment and a long-term cultivation experiment were carried out Light intensity generated by white light emitting diodes (LEDs) was graded during the whole experiment. In the ethological experiment, juvenile gibel carp (5.00 +/- 0.02 g) were exposed to light intensities of 0, 0.03, 0.09, 0.24, 0.56 and 1.06 mu mol.m(-2).s(-1) in a 6-cell behavior study facility. Gibel carp exhibited negative phototaxis in the short-term ethological experiment. In the long-term cultivation experiment, juvenile gibel carp (5.20 +/- 0.05g) were cultured under seven illumination levels (0, 0.03, 0.24, 1.08, 4.7, 9.46, 19.36 mu mol.m(-2).s(-1) in bottom water at a 0.5-m water depth) in an indoor recirculation water system for 70 days. The fish were fed to satiation three times daily (8:30, 14:30 and 18:30). The photoperiod was 12 L:12D (8:00-20:00). The results showed that the best growth of juvenile gibel carp were observed at 0.03-1.08 mu mol.m(-2).s(-1). The hepatopancreas oxidative stress of juvenile gibel carp were induced in a dark environment (0 mu mol.m(-2).s(-1)); plasma cortisol, glucose and lactic acid increased significantly when the light intensity increased to 9.46 mu mol.m(-2).s(-1). Based on the quadratic regression analysis of specific growth rate, the optimal light intensity for juvenile gibel carp was 0.39 mu mol.m(-2).s(-1).