Abstract:Paralichthys olivaceus is an economically important target species in marine aquaculture because of its large size, rapid growth rate, excellent meat quality, rich nutritional value, and short-distance migratory habits. Industrial farming models have been widely used owing to their high degree of intensification and environmental controllability. Artificial lighting is commonly used in factory farming to meet the farming requirements. Compared to the traditional artificial lighting of straight-tube fluorescent lamps or compact fluorescent lamps, LED lamps have the advantages of energy saving and environmental protection, long service life, low heat generation, and high photoelectric conversion efficiency. Additionally, LEDs can accurately regulate the spectrum and intensity of light according to demand, which has been rapidly promoted in factory farming. Different light-colored environments have a certain degree of inhibitory or promotional effects on the growth, physiological and biochemical processes, and stress responses of aquatic organisms. The study aimed to provide theoretical support for the selection of light colors for juvenile P. olivaceus in factory farming. In this study, a total of 450 individuals with good body condition and uniform body size were selected, with a mean body mass of (309.66±32.73) g and an initial total length of (28.67±2.66) cm. Five LED spectral parameters were set, which were red (λ 625–630 nm), yellow (λ 570–575 nm), blue (λ 450–455 nm), and green (λ 525–530 nm), and full spectrum (λ 380–780 nm) as the control group. Water temperature was controlled at (18.0±1.0 ℃), photoperiod was 12L:12D. The light intensity was set at (250±20) mW/m2 . The effects of five different light colors on the growth, enzyme activity, hormone levels, and gene expression of juvenile P. olivaceus were studied. The enzyme activities included two antioxidant enzymes, SOD and CAT, and two digestive enzymes, amylase and fibrillase; whereas, the hormones included growth hormone and cortisol, and the genes were mainly SOD and CAT. The results showed that the weight gain and specific growth rates of juvenile P. olivaceus in the blue and green light groups were significantly higher than those in the other groups (P < 0.05). The growth hormone content of juvenile P. olivaceus in the blue light group was the highest at (20.74±1.52) ng/mL, which was significantly higher than that of other groups (P<0.05). The growth hormone content of juvenile P. olivaceus in the red light group was the lowest at (10.68±0.61) ng/mL, which was significantly lower than that of other groups (P<0.05), while the cortisol content was the highest at (1 487.44±54.42) pg/mL, which was significantly higher than that of other groups (P<0.05). The gastric amylase activity of juvenile P. olivaceus in the green light group was significantly higher than those in the red light and control groups (P<0.05). The gastric cellulase activity of juvenile P. olivaceus in the red light group was significantly lower than that in the control group (P<0.05). The intestinal cellulase activity of juvenile P. olivaceus in the red light group was significantly lower than that in the other groups (P<0.05). CAT activity in the serum of juvenile P. olivaceus in the red light group was significantly lower than that in the other groups (P<0.05), and liver CAT activity was significantly lower than that of the control group (P<0.05). The differences in the liver SOD activity of juvenile P. olivaceus in each light-colored group were not significant (P>0.05). The relative expression of liver SOD gene of juvenile P. olivaceus in the red light group was significantly lower than that in the yellow light group (P<0.05), but the difference with other groups was not significant; the relative expression of CAT genes in the liver of juvenile P. olivaceus in the red light group was the lowest and significantly lower than that in the other groups (P<0.05), the relative expression of liver CAT gene of juvenile P. olivaceus in the yellow light group was the highest, and significantly higher than that in the other groups (P<0.05), and the relative expression of CAT gene of juvenile P. olivaceus in the blue light group, green light group and control group was not significant different. These results show that blue and green light cultures significantly affected the growth of juvenile P. olivaceus, whereas red light continuously stressed juvenile P. olivaceus weakening their antioxidant and digestive capacities. Furthermore, these results provide a theoretical basis for improving the indoor factory aquaculture efficacy of juvenile P. olivaceus and promoting green healthy factory aquaculture of juvenile P. olivaceus.
