Emulsifier is beneficial for declining dietary lipid requirement of aquatic crustaceans by accelerating the absorption, transport and deposition of lipids: A case study in mud crab (Scylla paramamosain)

Abstract

To investigate the potential of emulsifiers in reducing dietary lipid requirements of juvenile Scylla paramamosain and the associated physiological and biochemical responses, three isonitrogenous experimental diets (45 % crude protein content) with 10 % lipid content (FO, fish oil as the main lipid source), 5 % lipid content (LF) and 5 % lipid content with the addition of 0.2 % emulsifier (LF+EMU) were formulated. A total of 30 juveniles mud crabs (30.56 ± 0.56 g) per treatment was cultured for 12 weeks in single crab cells. Compared to LF, the LF+EMU group had higher weight gain and specific growth rate. Crabs in the LF+EMU group had significantly lower lipid contents in muscle and hepatopancreas, along with reduced lipase activity, resorptive and blister-like cell quantity in hepatopancreas than those in FO group, while these values were higher than that in crabs from LF group. Emulsifier supplementation into LF diet elevated the activity of superoxide dismutase, glutathione peroxidase and catalase, while exhibiting a significantly decrease in malondialdehyde content in hepatopancreas. Furthermore, the addition of an emulsifier into LF diet did not only upregulate genes associated with lipid anabolism like sterol regulatory element binding protein 1, glucose-6-phosphate dehydrogenase, delta-9 fatty acyl desaturase and fatty acid synthase, but also upregulate genes related to lipid catabolism such as acyl-CoA oxidase 3, carnitine palmitoyl transferase Ⅰ, and transport such as fatty acid-binding protein 1 and 3, fatty acid transport protein 4, scavenger receptor b, low-density lipoprotein receptor and low-density lipoprotein receptor-related protein 2. The analysis of intestinal microbiota revealed that crabs fed with LF+EMU and FO had significantly higher Simpson, Shannon, Ace, and Chao 1 than those fed with LF diet. In the LF+EMU treatment, the abundances of Fusobacteria and Bacteroidetes phyla, along with the genera Photobacterium and Hypnobacterium, were significantly elevated compared to LF treatment, the abundances of Candidatus_Hepatoplasma genera presented an opposite trend. Therefore, emulsifier supplementation in low-fat diet could regulate intestinal microbiota, accelerate secretion and activities of digestive enzymes, facilitate the upregulation of genes associated with lipid metabolism, and thus improve the absorption, transport, deposition of lipid and growth performance and indicate the potential in diminishing dietary lipid requirement of S. paramamosain.