The effects of aluminium on some aspects of the physiology and gill histopathology of the Nile tilapia, Oreochromis niloticus (L.), in acidic water

Abstract

The aims of this study were to investigate the physiological effects of aluminium in the tilapia, Oreochromis niloticus (L.), in an acidic environment and to evaluate the possible ameliorative effects of external calcium concentrations. Experiments were conducted in a flow-through exposure system employing synthetic water of precisely known composition, thus facilitating the stringent control of the chemical and physical variants in the exposure media. A pH of 5.2 at two calcium concentrations (0.6 and 16.0 mg 1‘) and a number of aluminium concentrations (0-520 pg 1‘) were selected, thus allowing the investigation of the interactive effects of calcium and aluminium in the imanifestations of toxic actions. Both short-term (4 days) and chronic (21 days) exposure schedules were followed. A series of experiments was carried out to investigate aluminium-induced changes in plasma and tissue concentrations of Na"^, K*, Ca** and Mg^^, and plasma glucose and total protein concentrations, and plasma osmolality. Changes in blood haematocrit levels and haemoglobin concentrations were also measured. Concentration-dependent responses were observed in most of the parameters. Plasma sodium, and tissue sodium and potassium concentrations decreased with a concomitant decline in plasma osmolality, while, in general, plasma potassium and calcium concentrations increased. Plasma glucose levels were greatly elevated by acid/aluminium exposure. Both blood haematocrit levels and haemoglobin concentrations were raised, accompanied by a marked swelling of erythrocytes. Qualitatively similar results were observed in both short-term and chronic exposure experiments. However, responses were modified (both qualitatively and quantitatively) with exposure time during chronic exposures. Increased calcium concentrations in die exposure media reduced or abolished acid/aluminium- induced changes in the majority of the parameters and were particularly effective in reducing ion loss from die body. The manifestation and magnitude of a particular response was clearly dependent upon aluminium and calcium concentrations in the exposure media and duration of the exposure.