Biofloc technology (BFT) has been developed recently as a promising technology to enhance animal production especially, shrimp species. BFT rely on using an economic carbon source to promote the development of heterotrophic bacteria which can enhance water quality, animal growth, reduce stress and prevent diseases. Studies on the molecular effects of biofloc (BF) addition on shrimp physiology, growth, immunity and reduce stress are limited; a field known as nutrigenomics. In our study, we attempted to study the differential changes of expression of different immune and antioxidant genes upon direct utilization of sugarcane bagasse pulp by L. vannamei larvae reared for 45 days under two different densities (400 and 700). Our data have shown that after 45 days of rearing, antioxidant gene sod and gpx were highly expressed (50 and 6 fold change respectively) in the high-density control group (700) as compared to the low-density control group (400) which indicate that high level of reactive oxygen species was generated in the high-density control group. Besides, the high-density control group showed a lower expression level of immune gene bgp, proph and lys (0.4, 0.5 and 0.8 respectively) in comparison to the low-density control group. On the other hand, BF treated high-density group showed lower levels of antioxidant genes sod and gpx (0.9 and 1.1 respectively) and higher levels of immune genes bgp, proph and lys (3.5, 5 and 1.2 respectively) in comparison to the BF treated low-density group. Furthermore, normalizing gene expression values of BF treated groups in relation to control non-treated groups have shown that BF treatment had higher immune gene expression of lys, proph and bgp under low density treatment (2, 2 and 2-fold change respectively) and high-density treatment (2, 20 and 4 fold change respectively). Not only improving immunity and reducing stress in the high-density group but also, growth of shrimp was also enhanced after BF treatment in terms of growth performance, survivability and feed utilization.
To sum up, this study has shown that direct addition of sugarcane bagasse pulp as a direct feed to L. vannamei for 45 days was associated with enhancing shrimp growth performance, survivability and reducing stress in accordance to underline molecular changes in expression of antioxidant and immune genes and we, therefore, strongly recommend the use of sugarcane bagasse pulp as an economic and feasible source of carbon in L. vannamei intensive rearing.
Acknowledgements: The research was performed within the "Development and Research Application of bioFloc Technology for increasing shrimp production in Egypt (EGY-DRAFT)" project, which is financially supported, by the Science & Technology Development Fund (STDF), Ministry of Scientific Research, Egypt. (Agreement No. 25305, Reintegration Grants). The authors are grateful for all the support.