THE EFFECT OF PH AND CONDUCTIVITY ON THE ELECTRIC BEHAVIOR OF APTERONOTUS ALBIFRONS (FAMILY APTERONOTIDAE) IN A POLLUTION MONITORING-SYSTEM

The Electric Organ Discharge (EOD) frequency and waveform of the neotr opical fish, Apteronotus albifrons (Gymnotiformes) are used to monitor water quality. This study evaluates the effects of two environmental variables, pH and water conductivity on the fish's electric behaviour. Variation in pH is shown to have no effect on the EOD waveform. On th e other hand, the EOD frequency decreases significantly under acidic c onditions (down to FH 3.6) and increases as the pH rises (to 10.6). A closer examination shows that the most satisfactory mathematical model for describing the pH frequency variation is a three degree polynomia l. For narrow pH intervals, EOD frequency and pH are shown to be linea rly related with significant increases in the discharge rate taking pl ace on the two pH intervals: 5 to 7.6 (Student t-test value greater th an or equal to 23.47; degree of freedom = 48; probability < 0.001) and 9.2 to 10.5 (Student t-test value greater than or equal to 6.186; deg ree of freedom = 48; probability < 0.001). It is also possible to show that the EOD frequency varies between 6.1 and 10.8 Hz per unit acid t o neutral pH (mean: 8.5 Hz; SD: 1.6) and between 2.4 and 10.2 Hz per u nit alkaline pH (mean: 6.1 Hz; SD: 2.6). With reference to the influen ce of water conductivity, the analysis of the results with different i onic charges (in the range of 54 to 484 mu S cm(-1)) revealed no effec t neither on the EOD frequency nor its waveform. Visual observations d id reveal an effect on the signal amplitude although the biomonitor wa s not designed to analyse this. Different hypotheses are advanced to e xplain the observed results in the light of which the appropriate in s itu use of the electric fish to biomonitor the water quality is consid ered.