Dietary sodium propionate enhanced the growth performance, immune-related genes expression, and resistance against Ichthyophthirius multifiliis in goldfish (Carassius auratus)

Abstract

Sodium propionate (SP) is a short-chain fatty acid that has long been used to improve the growth, physiological and immunological properties of aquatic animals. The aim of the current study was to assess the effect of SP intake on growth, immune-related genes, and resistance against Ichthyophthirius multifiliis in goldfish (Carassius auratus). The juvenile goldfish (initial weight = 8.61 ± 0.01 g) fed on diets supplemented with different levels of 0, 1.2, 2.5, and 5 g/kg diet) of SP for 50 days. At the end of the experiment, the treated fish were exposed to theronts stage of I. multifiliis at 5000 theronts per fish. Results showed that higher final weight, red blood cells (RBC), and white blood cells were seen in fish fed 5 g SP/kg than other treatments (P < 0.05), while no significant differences were seen in Na+ and Cl−1 electrolytes levels. With an increase in the level of SP in the diet, a significant up-regulation was observed in the expression of g-type lysozyme (gLys), interleukin-1β (IL-1ß), inducible nitric oxide synthase (iNOS), and tumor necrosis factor ɑ2 (TNF-ɑ2) genes (P < 0.05). Total numbers of parasite trophonts were also significantly decreased in fish treated with SP (P < 0.05). In addition, values of RBC and Cl−1 increased in the treated fish compared to control one, and lower glucose level was obtained in the treatment groups post-challenge with the parasite infection. These data revealed a positive effect of dietary SP on growth, immune response, and pro-inflammatory related genes and increased disease resistance towards I. multifiliis challenge in goldfish.