The Effect of Stocking Density and Carbon Sources on the Oxidative Status, and Nonspecific Immunity of Nile tilapia (Oreochromis niloticus) Reared under Biofloc Conditions

Simple Summary

The present study investigated the effect of stocking density and dietary carbon sources on the water quality, oxidative status and immune-related of Nile tilapia (Oreochromis niloticus) reared under biofloc conditions (BFT). Eight groups were established at two levels of stocking densities (140 fish per m³: low stocking density, LSD) and (280 fish per m³: high stocking density, HSD) (5.15 ± 1.12 g) and kept in eight biofloc units containing water without carbon sources (control groups) or with glycerol, molasses, or starch. Overall, this study has reported that immune response gene expression is better in LSD than HSD and improved by carbon addition. More specifically, based on the overall performances of tilapia reared under LSD or HSD, using molasses is recommended as a carbon source to promote the performances and health status of Nile tilapia cultured in a biofloc system.

Abstract

The present study investigated the effect of stocking density and dietary carbon sources on the water quality, oxidative status, and immune-related genes of Nile tilapia (Oreochromis niloticus) reared under biofloc conditions (BFT). Eight groups were established at two levels of stocking densities (140 fish per m³: low stocking density, LSD) and (280 fish per m³: high stocking density, HSD) (5.15 ± 1.12 g) and kept in eight biofloc units containing water without carbon sources (control groups) or with glycerol, molasses, or starch. Red blood cells count, hemoglobin, and hematocrit values were reduced in fish stocked in control groups at LSD and HSD than biofloc groups. Control fish groups reared at both LSD and HSD have the highest significant (p < 0.05) white blood cells number than other fish groups. Meanwhile, fish groups that received glycerol, molasses, and starch maintained in both LSD and HSD presented a higher significant (p < 0.05) monocyte % than in the control group reared at both LSD and HSD. The fish group reared in biofloc conditions (BFT) using starch carbon source and reared at the HSD presented a significantly higher (p < 0.05) increase in total serum protein and albumin levels as well as globulin value than the control fish group reared at both LSD and HSD. The highest glucose and cortisol levels were showed in the control fish group reared at both LSD and HSD. Fish maintained in glycerol-based biofloc at LSD attained the highest (p < 0.05) serum superoxide dismutase (SOD), glutathione reductase (GR), and catalase than other experimental groups. Regarding the nonspecific immune status, significantly increased expression of CC-chemokines, CXC-chemokines, TLR7 and IL-8 genes was found in molasses based biofloc groups. The data of the present study revealed that using molasses promotes health status of Nile tilapia cultured in a biofloc system.

Miswak (Salvadora persica) dietary supplementation improves antioxidant status and nonspecific immunity in Nile tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is the most common aquaculture fish, but is exposed to various pollutants and may be susceptible to infectious diseases due to reduction in their antioxidant status and immune defense. Therefore, researchers have tried to find feed supplements of natural origin to increase the health status of fish and decrease the incidence of drug resistance. The current study was conducted to investigate the effect of dietary supplementation of Miswak (Salvadora persica, SP) on Nile tilapia. Fish were randomly allocated into four experimental groups (30 fish each); the control fish were fed on the basal commercial diet and the SP-treated groups were fed basal diet supplemented with different concentrations 0.5, 1, and 2% for 30 days. The SP supplementations had no significant effects of SP on fish growth performance traits and lipid profiles but augmented the serum protein and globulin levels. The SP significantly improved the hepatic antioxidant status through the significant decrease of malondialdehyde (MDA) and the increases of reduced glutathione (GSH) levels and the activities of total superoxide dismutase (T.SOD), catalase (CAT) and glutathione peroxidase (GPx), especially in the SP 1% group, while glutathione S-transferase (GST) activities were significantly increased due to SP in a dose-dependent manner. The same results were obtained for the mRNA expression of CAT and GPx. Regarding the nonspecific immune status of the fish kidneys, SP, especially SP1, significantly increased interleukin-1 beta (IL-1β) and interferon-gamma (INF-γ). The data of the present study revealed the protective effect of SP on Nile tilapia health status. Therefore, SP can be considered as a promising feed additive for Nile tilapia.