No abstract

The present study was conducted for 240 days to evaluate the effects of stocking density based on growth attributes, digestive enzymes, muscular composition, biochemical and physiological responses of Labeo rohita fingerlings in tropical inland open water cages. L. rohita (30.35 ± 1.08 g) were randomly distributed into three treatments, namely low stocking density, LSD (10 m−3), medium stocking density, MSD (20 m−3) and high stocking density, HSD (30 m−3) in triplicates. Fish were fed twice daily with CIFRI CAGEGROW® floating feed (crude protein-28%, crude fat-4%). Fish growth and feed efficiency were higher (p < 0.05) in LSD, however, MSD registered a higher yield. Amylase and protease activity reduced whereas lipase activity increased with increasing stocking density. Muscle crude protein and crude fat formed an inverse correlation. The fillet quality deteriorated at higher stocking densities based on Muscle pH, drip loss and frozen leakage rate. The stress biomarkers level (glucose, cortisol, superoxide dismutase and catalase) increased in serum under crowding conditions. Glutamate oxaloacetate transaminase and glutamate pyruvate transaminase in serum were significantly increased in HSD. Serum protein levels decreased with the increase in stocking densities. Body ionic imbalance (Na+, Cl− and K+) was observed under crowding stress. Based on growth attributes and multiple biomarker responses, L. rohita @ 10 m−3 was found to be the optimum density for inland open water cage culture.

Evaluation of efficiency of poultry byproduct meal (PBM) as alternative protein source by replacing fish meal (FM) in the diets of GIFT strain of tilapia (Oreochromis niloticus) was carried out in cages installed in Poondi Reservoir, Tamil Nadu, South India. Six isonitrogenous (30% protein) and isolipidic (7% lipid) diets were formulated using graded levels of PBM protein to replace FM protein. Each diet was fed to two replicate groups of GIFT tilapia with mean initial weight of 20.38±0.0678 g, for 60 days in cages. The best growth performances in terms of mean weight gain (116.72 g), best food conversion ratio (FCR, 1.14) and maximum hepatosomatic index (HIS, 2.47) values were observed in GIFT tilapia fed PBM diet with 40% fish meal replacement. However, no significant (p>0.05) differences were observed in the whole body proximate composition of fish fed control and treatment diets. It was concluded that, poultry byproduct meal can replace 40% fish meal protein in the diets of GIFT tilapia cultured in reservoir cages without compromising growth, FCR and whole body proximate composition. The study suggests that poultry byproduct meal could effectively replace fish meal without affecting growth and feed conversion of the fish. The findings thus may pave a productive way for reducing environmental pressure of disposal of slaughter house waste.

Graphical abstract

Biofloc technology aims to maximize fish farming productivity by effectively breaking down ammonia and nitrite, promoting healthy flocculation, and enhancing the growth and immunity of cultured animals. However, a major limitation in this field is the suitable starter microbial culture and narrow number of fish species that have been tested with the biofloc system. Here, we investigated various microbial inoculum containing beneficial microbes with probiotics, immunostimulatory and flocs development and bioremediation properties would lead to the development of ideal biofloc development. Three treatment groups with different microbial combinations, viz., group 1 [Bacillus subtilis (AN1) + Pseudomonas putida (PB3) + Saccharomyces cerevisiae (ATCC-2601)], group 2 [B. subtilis (AN2) + P. fluorescens (PC3) + S. cerevisiae (ATCC-2601)] and group 3 [B. subtilis (AN3) + P. aeruginosa (PA2) + S. cerevisiae (ATCC-2601)] were used and compared with the positive control (pond water without microbial inoculums) and negative control (clear water: without microbial inoculums and carbon sources) on biofloc development and its characteristic features to improve the water quality and growth of fish. We demonstrated that microbial inoculums, especially group 2, significantly improve the water quality and microbiota of flocs and gut of the test animal, Heteropneustes fossilis. The study further demonstrates that biofloc system supplemented with microbial inoculums positively regulates gut histomorphology and growth performance, as evidenced by improved villous morphology, amylase, protease and lipase activity, weight gain, FCR, T3, T4 and IGF1 levels. The inoculums induced an antioxidative response marked by significantly higher values of catalase (CAT) and superoxide dismutase (SOD) activity. Furthermore, the supplementation of microbial inoculums enhances both specific and non-specific immune responses and significantly elevated levels of immune genes (transferrin, interleukin-1β and C3), and IgM was recorded. This study provides a proof-of-concept approach for assessing microbial inoculums on fish species that can be further utilized to develop biofloc technology for use in sustainable aquaculture.