Effect of feeding different types of β-glucans derived from two marine diatoms (Chaetoceros muelleri and Thalassiosira weissflogii) on growth performance and immunity of banana shrimp (Penaeus merguiensis)

Abstract

β-glucans are produced by many organisms and could be used as supplementary feed to enhance immunity and growth in some aquatic animals. This study aimed to compare the effectiveness of β-glucans derived from two marine diatoms (Chaetoceros muelleri and Thalassiosira weissflogii) as growth promoters and immunity enhancers in banana shrimp (Penaeus merguiensis). Shrimp were divided into 3 groups: the control group was fed without β-glucan; the second and the third group were fed with 2 g kg^-1 of β-glucan derived from C. muelleri and T. weissflogii, respectively. Shrimp were fed over a 30-day period to determine growth performance (final weight, weight gain, average daily gain (ADG), and feed conversion ratio (FCR)) at day 15 and day 30, respectively. The immune parameters determined were total hemocyte count (THC), phenoloxidase activity (PO) and immune gene expression. Survival rates were measured after 14 days of the feeding trial and Vibrio parahaemolyticus infection (6, 24, 48 h post infection). There was no significant difference (P > 0.05) for growth stimulation of shrimps between the two types of β-glucans (C. muelleri or T. weissflogii). Notably, shrimps fed with β-glucans had a higher final weight, weight gain, and ADG (P < 0.05) than shrimps fed with the control diet, while FCR of shrimps fed with both β-glucans was lower when compared to the control diet. Immune parameters, THC, PO, and gene expression of anti-lipopolysaccharide factor (ALF) and crustin were significantly higher (P < 0.05) in shrimps fed with β-glucans, especially with β-glucans from C. muelleri than the control group both before and after V. parahaemolyticus infection. Expression of penaeidin 3 and peroxiredoxin genes was significantly higher in shrimps fed with β-glucans after bacterial infection. Histopathology of hepatopancreas revealed an increase in blasenzellen hepatopancreatic epithelial cells (B cells) after 14 days of feeding which remained higher following infection with V. parahaemolyticus. The survival rate of shrimps fed with the diet containing β-glucan derived from either C. muelleri (82.2%) or T. weissflogii (77.8%) after V. parahaemolyticus infection was significantly higher than for the control group (51.1%) (P < 0.05). In conclusion, we propose that feeding banana shrimps with β-glucans derived from marine diatoms either C. muelleri or T. weissflogii at a 2 g kg^-1 diet can significantly improve their growth performance and immunity.

Keywords: Chaetoceros muelleri; Immune gene expression; Marine diatoms; Penaeus merguiensis; Thalassiosira weissflogii; V. parahaemolyticus; β-glucan.