Toxic stress indices in Oreochromis niloticus (Linnaeus, 1758) challenged with aqueous solution of NPK 15-15-15 in culture media

In fish, like other organisms, the imbalance between the production of reactive oxygen species (ROS) and antioxidant defence system can cause destructive effects on lipids, proteins, and Deoxyribonucleic acid (DNA). A bioassay was conducted on toxic stress indices of Oreochromis niloticus using aqueous solutions of NPK 15-15-15 fertilizer corresponding to the application rate of 120kg/ha/2weeks on a 1ha pond of 0.8m depth. This was serially diluted to yield 0.0mg/l and 15mg/l in control and treated groups respectively. Each treatment was replicated three times. Twenty (20) Day After Hatching (DAH) post yolk sac larvae of Nile tilapia with initial mean length and weight (2.25 cm and 0.44g) respectively were used as test organism. A total number of six (6) rearing troughs with a dimension of 1m×1m×0.5m were used for the study. Post-yolk sac larvae of O. niloticus were raised in the fertilizer solutions for a period of six months (March to August, 2024) at a stocking density of 100 larvae/rearing trough. The levels of ROS, superoxide dismutase (SOD), and total protein (TP) of O. niloticus were determined at the initial stage, 96hrs (March), June and August following standard procedure. Temperature, dissolved oxygen, pH, total hardness, nitrate and phosphate were monitored accordingly. Results showed significant differences (p<0.05) in the levels of TP, SOD and ROS at initial stage, 96hrs (March), June and August between thecontrol fish and those challenged with NPK 15-15-15 fertilizer. Also, the inclusion of fertilizer to the culture media, significantly affected (p<0.05) all the physico-chemical variables of water except temperature. Fish have been the models for aquatic environmental toxicity tests. These findings therefore signal a potentially more pervasive ecosystem damage from fertilizer use, affecting productivity of inland water bodies.