Biofloc based nutrient dense culture system for nursery and grow-out farming of Pacific white shrimp Penaeus vannamei Boone, 1931

Abstract

The concept of “biofloc technology” is changing the facet of intensive aquaculture with scope to attain high productivity in a sustainable manner. In biofloc, dense heterotrophic bacterial community is developed through C:N ratio manipulation, where the system becomes bacterial dominated rather than algae dominated and takes care of the wastes generated through in situ bioremediation. Protein is utilised in two ways; as feed for the shrimp and as microbial floc when the heterotrophic microbes convert the nitrogenous wastes into protein. It also promises a healthy rearing system, which is increasingly identified as one possible solution for disease problems especially those striking at early stages. The purpose of this study was to evaluate the effect of biofloc and periphyton technology (BPT) on the growth and immunomodulatory performance of Pacific white shrimp Penaeus vannamei during nursery and grow-out culture. The experimental BPT treatments with three tier substrate system with molasses as carbohydrate (CHO) source were compared with the conventional autotrophic system. The immunomodulation and cumulative percentage mortality upon challenge with pathogenic strain of Vibrio parahaemolyticus were assessed in the reared animals. We have successfully demonstrated the BPT based nursery and growout systems for P. vannamei with the advantage of providing significantly (p<0.05) better growth (27.6% improvement in average body weight, ABW) and feed utilisation (31% improvement in feed conversion ratio, FCR). A production level of 4-4.5 kg m-3 of water was achieved through this BPT system registering a significant improvement over the conventional system (p<0.05). The cumulative percentage mortality following pathogen challenge was significantly lower (p<0.05) in the biofloc grown shrimps compared to that of the control group, thus showing better resistance to pathogenic challenge. Furthermore, the biofloc reared shrimp did exhibit significant improvement in non-specific immune response in terms of serum phenoloxidase activity and total haemocyte counts possibly suggesting potential immunostimulatory role of the biofloc associated heterotrophic bacteria. This eco-based technology as revealed through our studies brings substantial improvement in productivity, minimising water requirement, recycling in situ nutrients and organic matter in turn improving farm biosecurity, augmentation of natural food, improvement of FCR and better health of the cultured shrimp.