| effects of water ph and calcium concentration on ion balance in fish of the rio negro, amazon. | we examined the effects of acute low-ph exposure on ion balance (na+, cl-, k+) in several species of fish captured from the rio negro, a dilute, acidic tributary of the amazon. at ph 5.5 (untreated rio negro water), the four rio negro species tested (piranha preta, serrasalmus rhombeus; piranha branca, serrasalmus cf. holandi; aracu, leporinus fasciatus; and pacu, myleus sp.) were at or near ion balance; upon exposure to ph 3.5, while na+ and cl- loss rates became significant, they were relative ... | 1998 | 9472808 |