Fertilization sources fallout: Unveiling the impacts on growth, metal accumulation, and physiological responses in Nile Tilapia, Oreochromis niloticus

This study investigates the impact of various fertilization sources on the growth performance, digestive enzyme activity, heavy metal accumulation, hemato-biochemical parameters, antioxidant responses, and immunity in Nile tilapia (Oreochromis niloticus). A total of 15 outdoor earthen ponds, each with a 200 m3 volume, were utilized. Fifteen thousand Nile tilapia fingerlings, initially averaging 39.81 +/- 0.22 g, were distributed at a density of 5 fish/m3 across 3 replicates. The experimental treatments included: a control group with no fertilizer, biofloc system-derived fish sludge (BFT-Sludge), conventional system-derived fish sludge (Fish-Sludge), and their combinations with sugar beet factory pulp (SBP) in a 3:1 ratio (BFT-S + SBP and Fish-S + SBP). Over a 75-day period, the ponds were monitored for water quality, heavy metal concentrations, growth parameters, and fish health indicators. The results demonstrated that the combination of BFT-S + SBP significantly (P < 0.05) enhanced water quality, with higher oxygen levels, reduced ammonia, and lower heavy metal concentrations compared to other treatments. Growth parameters such as final body weight, weight gain, and specific growth rate were markedly (P < 0.05) improved in the BFT-S + SBP and Fish-S + SBP groups, with the latter showing the highest performance. Additionally, the BFT-S + SBP treatment led to significant (P < 0.05) reductions in heavy metal accumulation in fish tissues, particularly in the liver, gills, and muscle, enhancing the overall safety and quality of the fish. The study also found elevated digestive enzyme activities (e.g., protease, amylase, lipase), improved hematological profiles (e.g., red blood cells, hemoglobin, hematocrit, white blood cells, lymphocyte, monocyte, neutrophil), and enhanced antioxidant defenses (e.g., superoxide dismutase, catalase) in fish subjected to the BFT-S + SBP treatment compared to other treatments including control. In conclusion, the combination of BFT-S + SBP is an effective sustainable fertilization strategy in aquaculture, significantly enhancing water quality, reducing heavy metal accumulation, and promoting growth, digestive enzyme activity, and overall health in Nile tilapia (O. niloticus). Further research is warranted to focus on the molecular mechanisms behind these responses, which will help validate this sustainable strategy.