Abstract
An 8 weeks trial was performed to test the effects of light spectra [full-spectrum, violet (405 nm), blue (470 nm), cyan (500 nm), green (525 nm), yellow (570 nm), and red (625 nm)] on growth performance, molting, antioxidant capacity, stress response and expression of molting, and apoptosis-related genes in Scylla paramamosain. Results showed that spectrum had a significant effect on S. paramamosain physiology. Compared to blue light, crabs exposed to violet light had a significantly lower survival rate (79.5 ± 3.6% vs. 94.9 ± 3.6%), weight gain (49.2 ± 5.4 vs. 67.6 ± 6.7), molt frequency (4.2 ± 0.2 vs. 4.5 ± 0.1), and extended intermolt intervals between instar 1 and 2 stages (C1–C2) (6.3 ± 0.3 vs. 5.0 ± 0.1 days). Expression of the molt-inhibiting hormone (mih) gene was upregulated in crabs reared under violet light. According to the regression analysis, maximum SGR would be at 449.97 nm. Crabs exposed to blue light also had lower melatonin levels than under full-spectrum and lower cortisol levels than violet and yellow groups. Regarding oxidative stress, crabs in full-spectrum had lower H2O2 and MDA contents, however, no significant difference was found in total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) in hepatopancreas from crabs under different spectra. Gene expression of hsp40, hsp70, hsp90 were down-regulated in crabs exposed to the full-spectrum light group. Regarding apoptosis-related genes, bcl-2 gene expression in crabs under cyan and the cox IV and caspase 3 in green were upregulated, suggesting cyan light may inhibit, while green light may promote apoptosis. Taken together, these results suggest that blue or cyan light would promote growth performance, while full-spectrum light could reduce stress response in S. paramamosain.
Highlights
The mud crab (Scylla paramamosain) is a marine decapod crustacean species which plays a significant commercial and ecological role in marine aquaculture
The relationship between light wavelength and specific growth rate (SGR) based on a 4-parameter saturation kinetic models (4-SKM) showed maximum SGR for spectrum of 449.97 nm (R2 = 0.5961) (Figure 3)
carapace length (CL) was significantly influenced by light spectrum, with crabs reared under a blue light showing a higher CL than under violet
Summary
The mud crab (Scylla paramamosain) is a marine decapod crustacean species which plays a significant commercial and ecological role in marine aquaculture. Previous studies on abalone Haliotis discus have shown improved hatching and larvae growth under blue and green light (Gao et al, 2015) contrasting with positive effect of orange and red light reported on growth performance of juvenile H. discus (Gao et al, 2016a). Such contrasting results reported in the literature clearly illustrate the species and stage of development specific effects of spectrum on aquatic animals and most studies so far have been performed in fish
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