Effects of Different Light Colors on Growth, Feeding, Distribution and Metabolism of Lateolabrax maculatus

Abstract

Lateolabrax maculatus belongs to the order Perciformes and is distributed in the coastal waters and estuaries of China, Japan, and the Korean Peninsula. Its muscle protein contains many high-quality amino acids necessary for the human body, which have extremely high edible value. Lateolabrax maculatus has the advantages rapid growth under wide temperature and salt ranges and is suitable for various culture modes, such as cages, ponds, and factories. It is an economically important marine fish occurring in China. Light is a key environmental factor that affects the behavior and physiological and biochemical indices of fish, and optimizing the growth environment of fish by controlling different light color conditions can markedly improve aquaculture efficiency. However, it is not completely clear what kind of light color L. maculatus adapts to, and the influence of different light colors on its growth, feeding, distribution, and metabolism. To explore these effects, blue, green, yellow, and indoor natural lights were used to clarify the relationship between light color and L. maculatus growth, determining the optimal light color for its culture, and providing a theoretical basis for the optimization of artificial culture technology and environmental regulation.Four light color groups—blue, green, yellow, and natural light—were used. Two circular light strips were fixed around the bottom of each experimental pool to provide light sources. The distance between the light strips was 15 cm, and the light intensity was measured 5 cm above the water center. The light intensity was ~300 lx, and the light period was 12 h light: 12 h dark. During the experiment, the compound feed was given twice daily at 08:00 and 18:00, and the single feeding amount was 1.5%–2 % of the total weight of the sea bass in the pond. After feeding for 1 h, residual bait and feces were removed. Video monitoring equipment (Hikvision camera, Smart265) was placed above the experimental pool, and the time from the first experimental fish to the end of feeding was recorded. Feeding time was measured every five days. The distribution of L. maculatus in the experimental pond was recorded 30 min before and after feeding. The number of nodes per minute was recorded, and 60 images were captured for each process. All images of L. maculatus were manually marked according to the division area—black dots represented the location—and compared with the video to ensure the location accuracy. The fish were cultured for 45 days.The results showed that the weight growth and specific growth rates of juvenile L. maculatus under blue light were (45.70±2.20) and (0.90±0.08) (%/d), respectively and were significantly higher than those under yellow and natural lights. The feed coefficient of L. maculatus under blue light was the lowest. The relative expression levels of insulin growth factor (igf-1 and igf-2) and growth hormone receptor 1 (ghr-1) genes in the liver of L. maculatus under blue light were higher than those under natural light. The phototaxis distribution of the fish differed for different light colors, with positive and negative phototaxis for blue yellow light, respectively. Metabolomic analysis showed that the fish under blue light were significantly upregulated by metabolites such as L-isoleucine and lysophosphatidylethanolamine (LPE, 18:2/0:0). This affected nine pathways—including amino acid and glycerol phospholipid metabolism—thereby affecting amino acid and phospholipid synthesis. Under green light, fumaric acid, L-tyrosine, and other metabolites were significantly downregulated. This affected five pathways—including phenylalanine metabolism and oxidative phosphorylation—and protein synthesis and hormone secretion in sea bass. No significant enrichment was observed under yellow light.In conclusion, the relative expression levels of igf-1, igf-2 and ghr-1 in L. maculatus could be improved by blue light illumination, and L-isoleucine and LPE (18:2/0:0) contents could be significantly increased under blue light. This affects amino acid and glycerophospholipid metabolism, and other metabolic pathways, thus increasing the speed of substance synthesis in L. maculatus and significantly improving its growth. Combined with the fact that the distribution behavior of L. maculatus in culture ponds tends toward blue light, this shows that L. maculatus is suitable for culturing under blue light. These results provide a theoretical basis for the selection of light color and the formulation of a culture strategy for L. maculatus.

Keywords

• lateolabrax maculatus
• light color
• growth
• behavior
• metabolome