Abstract
Simple SummaryThe 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.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.
Highlights
In recent decades, recirculating systems have been developed in the course of sustainable aquaculture, involving an appropriate approach to control aquaculture wastewater [1]
The juveniles of Nile tilapia reared on biofloc conditions (BFT) using glycerol, molasses, and starch as carbon sources at both LSD and HSD presented a significant increase in red blood cell count (RBCs), hemoglobin (Hb), and packed blood volume (PCV) values
We suggested that increased expression of immune response genes (TLR7 and interleukin 8 (IL-8)) occurs simultaneously in normal health condition related to the spleen as an immune response organ, this is in agreement with Qian, et al [65] who approved that the TLR7 was constitutively expressed in immune-related tissues especially in spleen, gills, and head kidney
Summary
In recent decades, recirculating systems have been developed in the course of sustainable aquaculture, involving an appropriate approach to control aquaculture wastewater [1] In this system, 10% of the total volume of water is replaced daily, but due to the high operating and maintenance costs, adoption of the recirculating system among farmers, especially in developing countries, is low [2]. The biofloc system, called biofloc technology (BFT), has recently attracted great attention as a cost-effective, sustainable, and environmentally friendly (as the water exchange rate and artificial feeding ratio are reduced) way that improves water quality as well as produces microbial protein for aquatic species [3,4]. BFT results in enhanced growth performance, immune response, antioxidative status, and resistance to aquaculture stressors [9]
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