CARDIOVASCULAR, VENTILATORY AND HEMATOLOGICAL RESPONSES OF BROWN TROUT (SALMO-TRUTTA L), TO THE COMBINED EFFECTS OF ACIDITY AND ALUMINUM INHUMIC WATER AT WINTER TEMPERATURES

Two year old brown trout (Salmo trutta L.) were exposed for 7 days to pH 4.7 alone and with aluminium at concentrations of 0.28 and 0.45 mg l-1, respectively, in the water of River Rutajoki, Central Finland. Th e labile aluminium accounted for less than 30% of the total added amou nt in the humic water. During the exposures the fish were monitored by a non-contact bioelectronic monitoring system which records heart and ventilation rates of the fish. Terminal blood samples were obtained t o evaluate the degree of stress. No mortality occurred during any of t he exposures. Acid stress alone and with aluminium caused an immediate acute response in heart and ventilation rates, which remained higher in combination with aluminium. Based on both the haematological and bi omonitoring data, the fish were experiencing only slight ionoregulator y stress, but more severe hyperglycaemia in combination with respirato ry stress. Aluminium had no or only minor additional effects on ionore gulation at the end of the exposures.