Growth performance and immune responses of pengba ( Osteobrama belangeri ) during high‐density fingerling rearing in biofloc system

Abstract

High-density fingerling rearing of pengba was conducted for 90 days in biofloc system (BFS) to study the effect of stocking density on growth, feed utilization, water quality, water use efficiency and health of animals. The study was conducted in 12 continuously aerated tanks (50 m3), grouped into four treatments T-1, T-2, T-3 and T-4, which were stocked with pengba fry (1.25 ± 0.05 g, 4.74 ± 0.70 cm) at 50, 60, 70 and 80 m−3, respectively. Supplementary feed (1 mm floating pellet) was fed twice daily, each time for 30 min duration. Molasses and urea were supplemented to maintain suitable C:N ratio at 15:1. No water exchange was given, except monthly compensation of evaporation loss. While water quality and most of the growth attributes in T-1 and T-2 remained similar, T-3 at 70 m−3 density showed better water quality, higher survival and growth than T-4. Body composition remained consistent across treatments despite impaired feed digestion and utilization associated with higher densities. The non-specific immune responses in fingerlings increased from T-1 to T-3, but further density rise showed compromised immune in T-4. Such results suggested 70 m−3 to be an ideal density for production of healthier fingerlings. But T-4 produced 13.5% more fingerlings than T-3, and fingerlings (7.56 ± 0.50 cm; 5.43 ± 0.09 g) were within acceptable size range for grow-out stocking. T-4 also showed the lowest total water use and the highest water implicating 80 fry m−3 to have more applicability. Thus, the study recommends 70–80 m−3 as ideal range for fingerling rearing of pengba in BFS.