No abstract

Tilapia Oraochromis 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 stressors, e.g. aluminium ions and handling stress, were avoided. No mortality or decreased food consumption was observed during the exposure period. No significant changes were observed between the control and acid exposed groups for the energy rich compounds and related parameters, i.e. Lhe adenylate energy charge, the pool of tota! adenine nucleotides, and the IMP load of white muscle and liver, indicating maintenance of homeostasis. Moreover, there were no significant differences between control groups and acidified groups at 3, 17 and 37 days for plasma sodium, chloride, cortisol and glucose, implying that ionic balance was maintained and that there was no activation of the pituitaryinterrenal 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. (Ç) 1997 The Fisheries Society of the British Isles