Effects of three light intensities on the survival, growth performance and biochemical composition of two size giant clams Tridacna crocea in the Southern China Sea.

Giant clams are able to grow in oligotrophic tropical marine environments with the aid of photosynthates from its symbiotic zooxanthellae. Therefore, light intensity affects the survival and growth of giant clams, and is one of the most important environmental factors in giant clam cultures. In this study, two size classes of Tridacna crocea (small: ~50 mm shell length, large: ~85 mm shell length) were cultured at three light intensities (5000, 10,000, and 15,000 lx) for 16 weeks, to evaluate the effects of light intensity on the survival, growth performance and biochemical composition of different size clams. T. crocea under 15,000 lx light intensity showed a significantly higher survival rate and relative growth rate (RGR) (P <.0001). The RGR in the small group was significantly higher than the large group under 10,000 and 15,000 lx light intensity (P <.0001), while higher RGR was observed in the large group under 5000 lx light intensity (P =.0009). The content of eight amino acids in the mantle was significantly affected by light intensity (P <.05), while only one amino acid (glycine) was found in the adductor muscle (P =.0005). Similarly, there were significant differences in ten mantle amino acids between small and large size groups (P <.05), while three amino acids were found in the adductor muscle (P <.05). C22:6n3 (DHA) was the major polyunsaturated fatty acid (PUFA) in T. crocea. In the adductor muscle, the C22:6n3 profile significantly increased with increasing light intensity and clam size (P <.0001), while no significant differences of C22:6n3 profiles were found among different light intensities in the mantle (P =.3345). Our results demonstrate that a light intensity of 15,000 lx is suitable for T. crocea (45–90 mm in shell length) rearing, and that large size T. crocea has higher tolerance to weak light intensity than small individuals. • The optimal light intensity of T. crocea (shell length 45–90 mm) was 15,000 lx. • The survival and growth of T. crocea were affected by both light intensity and clam size. • The amino acid contents in the mantle were affected by both light intensity and clam size. • The fatty acid profiles of T. crocea were strongly affected by both light intensity and clam size. [ABSTRACT FROM AUTHOR]