TILAPIA ARE ABLE TO WITHSTAND LONG-TERM EXPOSURE TO LOW ENVIRONMENTALPH, JUDGED BY THEIR ENERGY STATUS, IONIC BALANCE AND PLASMA-CORTISOL

Tilapia Oreochromis mossambicus were exposed to water at pH 4.0 for 37 days. The water was acidified slowly over 6 h enabling the animals to acclimate and preventing damage of the gill epithelium. Additional st ressors, e.g. aluminium ions and handling stress, were avoided. No mor tality or decreased food consumption was observed during the exposure period. No significant changes were observed between the control and a cid exposed groups for the energy rich compounds and related parameter s, i.e. the adenylate energy charge, the pool of total adenine nucleot ides, and the IMP load of white muscle and liver, indicating maintenan ce of homeostasis. Moreover, there were no significant differences bet ween control groups and acidified groups at 3, 17 and 37 days for plas ma sodium, chloride, cortisol and glucose, implying that ionic balance was maintained and that there was no activation of the pituitary-inte rrenal axis. It is concluded that Tilapia can acclimate to water at pH 4.0 when the acidification rate is slow and additional stressors are avoided. (C) 1997 The Fisheries Society of the British Isles.