Effect of in-situ and ex-situ biofloc on immune response of Genetically Improved Farmed Tilapia

Abstract

The present study is aimed to investigate the effect of biofloc intake on Genetically Improved Farmed Tilapia (GIFT), developed within the system and its influence as feed supplementation on water quality, growth performance, immunological parameters, antioxidant status, immune gene expression, and its resistance to Aeromonas hydrophila infection. GIFT Tilapia juveniles of 5.1 g (±0.05) were stocked at a density of 15/m3 in lined ponds of 300m2 in triplicates for 180 days. The experimental groups consisted of T1-biofloc developed within the culture systems (insitu), T2-biofloc supplementation in fish feed (exsitu) and C- Control without biofloc. Distillery Spent wash was used as a carbon source to maintain the C/N ratio of 10:1 for floc development in T1. Free CO2, pH, BOD, dissolved oxygen, alkalinity, Calcium and Magnesium ions, Nitrate, Nitrite and ammonia were found to be significantly different between the treatments and control throughout the experiment. The immunological (Serum protein, Respiratory burst test (RBT) and Myeloperoxidase) and antioxidant indicators (Glucose, Superoxide dismutase (SOD) and catalase) were found to be significantly higher in T1 at the end of the trial. Increased weight gain, specific growth rate, survival and decreased feed conversion ratio was found in T1 when compared with the other experimental groups. Real time quantitative PCR analysis revealed that there was no folded expression of the immunological genes such as Metallothionein gene, cathepsin L, Toll like receptor 7, Interleukin 1 β and Tumour necrosis factor α in liver and intestine for both control and treatment. However, the upregulated expression of targeted genes except tumour necrosis factor α was found in head kidney of T1. At the end of the study, GIFT Tilapia when infected with Aeromonas hydrophila showed an improved immune response in T1 and T2 with lesser signs of infection than Control. The findings of the present study affirmed the importance of biofloc technology in triggering the immunomodulatory response of GIFT Tilapia with its upregulated immune gene expression and its role as an antimicrobial agent against Aeromonas hydrophila. This study suggests the adoption of in-situ (T1) based biofloc method to obtain better performance of GIFT Tilapia culture.