Dietary betaine supplementation promotes growth, n-3 LC-PUFA content and innate immunity in Macrobrachium rosenbergii

Macrobrachium rosenbergii, the giant freshwater prawn, is an important aquaculture species in China and other Southeast Asian countries. Here, we report the positive effect of dietary betaine supplementation on growth performance and the innate immune system in M. rosenbergii. Four diets were formulated containing graded levels of betaine, and a 10-week feeding trial was conducted. Prawns fed a diet containing 0.5% betaine (B-0.5) showed significantly higher growth performance, while feed efficiency was not significantly influenced compared with the control group. Moreover, the survival rate under bacterial challenge in the B-0.5 group was significantly higher than in the control group infected. Betaine supplementation also significantly reduced crude lipid content and significantly increased crude protein content in the B-0.5 and B-1 groups. Similarly, the contents of total (essential) amino acids and many flavorful amino acids such as Aspartic, Serine, Alanine and Glycine in the muscle were also significantly higher than in the control group. Most interestingly, the contents of n-3 PUFA and n-3 LC-PUFA in all betaine supplementation groups were significantly higher than in the control group. In addition, significantly higher activities were detected in the B-0.5 group than in the control group for hepatopancreas digestive enzymes Pepsin, Trypsin and Lipase, and serum enzymes including CAT, SOD, and TNF-alpha. We also checked the expression levels of five immune-related genes and found that Relish, TLR-1, and TLR-2 were all significantly down regulated in all supplementation groups, while HSP70 was significantly upregulated only in the B-0.5 group. Taken together, our results demonstrated that a moderate amount of dietary betaine supplementation not only promotes growth but also benefits the innate immune system of M. rosenbergii.