Growth performance, immunological responses, and the expression of antioxidant, tight junction, and immune-related genes in goldfish (Carassius auratus) fed with Lactobacillus fermentum and malic acid

This study evaluated the effects of malic acid (MA) and Lactobacillus fermentum (LF) on growth performance, immunological responses, and the expression of antioxidant, tight junction, and immune-related genes of goldfish (Carassius auratus). For this purpose, a total number of 240 fish (mean weight = 4.99 +/- 0.10 g) were divided into 12 tanks with 20 fish per tank (4 treatments with 3 replicates). The fish were fed with four prepared diets: unsupplemented diet (Control), 1 x 10(8) CFU g(-1) of L. fermentum (LF), 0.25% malic acid (MA), and 1 x 10(8) CFU g(-1) of L. fermentum +0.25% malic acid (LF + MA) for 56 days. The present results showed that the growth performance significantly improved in the fish fed on LF + MA mixture compared to the fish fed on the control diet. Total immunoglobulin, lysozyme activity, and the alternative complement pathway significantly (p < .05) higher in the LF + MA treatment. The relative expression of antioxidant-related genes including manganese superoxide dismutase, superoxide dismutase, and glutathione reductase-like notably (p < .05) enhanced in goldfish treated with both malic acid and L. fermentum mixture. The mRNA levels of tight junction genes, including occludin-like, claudin-3-like, zo-1-like, and immune-related genes of ribosome biogenesis regulatory protein homolog, lysophosphatidic acid receptor 6-like, and transforming growth factor beta, were significantly (p < .05) higher in the LF + MA treatment. In conclusion, the supplementation of both malic acid and L. fermentum (LF + MA) can be used as feed additives to increase growth performance and improve the immunological and antioxidant responses of goldfish.