Effects of light intensity on growth, survival, metabolism and related enzyme activities of Sepia pharaonis.

Abstract

An experiment with single-factor design was conducted to investigate the effects of light intensity on growth and survival of cuttlefish (Sepia pharaonis). The specific growth rate, survival rate, oxygen consumption rate, ammonia excretion rate, lactic acid content in muscle, respiratory metabolic enzymes (including hexokinase, pyruvate kinase, and lactate dehydrogenase), supero-xide dismutase, and malondialdehyde in liver were measured in five constant light intensity treatments (10, 30, 50, 70, 90 μmol·m-2·s-1). The main results were as follows: The specific growth rate and survival rate remained steady initially and then decreased gradually with the increases of light intensity. There was no significant difference between groups 10 and 30 μmol·m-2·s-1, but they were significantly higher than those of the other groups. Exposed to light intensities of 10 and 30 μmol·m-2·s-1, the specific growth rates were (8.43±0.22)%·d-1 and (8.47±0.17)%·d-1, and the survival rates were (79.2±5.9)% and (80.0±4.9)%, respectively. Oxygen consumption rates and ammonia excretion rates increased first slowly and then sharply, and reached the maximum value when light intensity was 90 μmol·m-2·s-1, which was significantly higher than those of the other groups. Lactic acid content in muscle firstly decreased and then increased, with the minimum value at 30 μmol·m-2·s-1. The acid content of 10 μmol·m-2·s-1 was significantly lower than those of the other groups except 30 and 50 μmol·m-2·s-1. With the increases of light intensity, the activities of HK and PK in gills remained steady initially and then decreased gradually, and reached the highest level when exposed to 10 and 30 μmol·m-2·s-1, which were significantly higher than those of the other groups. LDH activity in muscle had the lowest level at the light intensity of 10 and 30 μmol·m-2·s-1, which was significantly lower than those of the other groups. SOD activity in liver firstly increased and then decreased, and reached the highest level ((104.93±4.17) U·mg-1 pro) when exposed to 70 μmol·m-2·s-1, which was significantly higher than those of the other groups. MDA content in liver first remained steady and then increased gradually, and reached the highest level ((5.06±0.35) nmol·mg-1 pro) when exposed to 90 μmol·m-2·s-1, which was significantly higher than those of the other groups. In conclusion, the optimum light intensities for growth, survival and metabolism of S. pharaonis were 10 and 30 μmol·m-2·s-1, beyond which S. pharaonis would be under stress. Therefore, sunproof measures should be taken to keep weak light condition in culture practice.