Effects of Vitamin C on Growth and Non-Specific Immune Response of Labeo gonius Fry in Density-Dependent Biofloc Rearing

Biofloc technology offers a viable choice for the rearing of fish seed by offering a safe and protected habitat for young fish. Nevertheless, it is crucial to establish a standardised stocking density and implement effective ameliorative steps in order to successfully utilise this technology. In this study, a 90-day investigation was conducted to assess the effect of stocking density and dietary vitamin C (Vit C) levels on the growth and immunity of Labeo gonius fry (1.03 ± 0.01 g) reared in a biofloc system. Three stocking density groups (5, 10 and 15 fish per 50 L) were established, and each experimental group was supplemented with three levels of Vit C (0, 500 and 1000 mg kg⁻¹). The highest survival rate was observed in the lowest density group (five fish per 50 L) fed with 1000 mg kg⁻¹ Vit C. A better feed conversion ratio and significantly higher protein efficiency ratio were found in the moderate stocking density group (10 fish per 50 L) fed with 500 mg kg⁻¹ Vit C. Total leukocyte count (TLC), haemoglobin, and packed cell volume improved in Vit C-fed groups. The total erythrocyte count (TEC) increased in groups fed Vit C and stocked at lower densities (5 and 10 fish per 50 L). Total serum protein (TPP) content increased when Vit C was added at a rate of 500 mg kg⁻¹. Serum glucose and cortisol levels were significantly reduced in Vit C-supplemented groups. Supplementation of Vit C at 500 mg kg⁻¹ resulted in a significantly lower value of malondialdehyde (MDA). Thus, the findings confirm that the incorporation of Vit C in the basal diet promotes the growth and health status of L. gonius fry reared in the biofloc system at high-density rearing.