Potential nephrotoxicity in African mud catfish (Clarias gariepinus) following exposure to compost derived humic acid

Influence of compost-derived Humic Acid (HA) on nephrotoxicity in juvenile African mud catfish (Clarias gariepinus) was evaluated in static water culture. Fish samples were exposed to different HA concentrations (0, 100, 250, 500 and 1000 mg L(-1)) for 45 days at 5 samples per aquarium. Renal function was assessed spectrophotometrically via levels of serum albumin, measured using bromocresol green, creatinine by Jaffe method and urea by Nesslerization method. Results revealed that the mean value of albumin or urea in the exposed group (1), at each HA concentration, was lower than the value found in the control group (II). Creatinine was relatively higher in I relative to II. Significant (p < 0.05) variations for I and II were obtained at 250 to 1000 mgHA L(-1) for the three biomarkers. Relative to increasing HA concentration, decreasing albumin (0.84 to 0.43 g dL(-1): r = -0.114; p > 0.10), urea (5.21 to 1.95 mg dL(-1); r = -0.586; p > 0.10) and increasing creatinine (0.20 to 1.53 mg dL(-1): r = +0.704; p > 0.10) were recorded; r is correlation coefficient. Changes in urea were not predictive of nephrotic syndrome but alterations in albumin and creatinine revealed induced nephrotoxicity, especially at elevated HA concentrations (above 100 mg L(-1)). Overall, the effect of humic acid was dose-dependent. Further studies at various humic acid concentrations, especially below 100 mg L(-1), are required to establish the actual nephrotoxic dose.