Growth Performance and Haematological Responses of Juvenile Oreochromis niloticus Exposed to Inorganic Fertilizer

Abstract

Agricultural runoff of inorganic fertilisers (NPK 20:10:10) is a growing threat to freshwater aquaculture, yet quantitative data on the sub-lethal effects of the widely used NPK 20:10:10 formulation on Nile tilapia remain scarce. This study determined the 96-h LC₅₀ of NPK 20:10:10 for juvenile Oreochromis niloticus (25.68 mg L⁻¹) and evaluated growth and haematological responses during an 8-week exposure to environmentally relevant sub-lethal concentrations (0.00 (control), 0.43, 0.86, 1.28, 1.71 and 2.14 mg L⁻¹). Increasing NPK 20:10:10 levels significantly elevated pH, total dissolved solids and conductivity while reducing dissolved oxygen. Growth was significantly impaired: mean final weight declined from 3.21 g (control) to 2.38 g at 2.14 mg L⁻¹, and percentage weight gain fell from 39.3 % to 7.2 %. Concurrently, packed cell volume, haemoglobin and erythrocyte count decreased markedly, whereas leucocyte counts rose, indicating progressive anaemia and stress-induced leucocytosis. These concentration-dependent alterations demonstrate that NPK 20:10:10 compromises both somatic growth and haematological integrity of juvenile Nile tilapia at concentrations far below acute lethality. The findings provide critical toxicity thresholds and physiological biomarkers essential for risk assessment and the sustainable management of inorganic fertiliser use near aquaculture systems.