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Acclimation to humic substances prevents whole body sodium loss and stimulates branchial calcium uptake capacity in cardinal tetras Paracheirodon axelrodi (Schultz) subjected to extremely low pH

2007; Wiley; Volume: 70; Issue: 4 Linguagem: Inglês

10.1111/j.1095-8649.2007.01358.x

1095-8649

A. Y. O. Matsuo, Adalberto Luís Val,

Environmental Toxicology and Ecotoxicology

Kinetics of sodium (Na + ) and calcium (Ca 2+ ) uptake were studied in cardinal tetras Paracheirodon axelrodi acclimated to humic substances (HS, 35 mg C l −1 ) and low pH (pH 3·72), parallel to analysis of whole body Na + and Ca 2+ content. This species had a high uptake capacity ( J max ) for both Na + and Ca 2+ in soft, ion‐poor water. The affinity constant ( K m ) did not vary significantly among treatments for either Na + or Ca 2+ . J max Na + increased 30% in fish acclimated to HS for 5 weeks. Acclimation to low pH had no effect on J max Na + but this treatment was associated with a 32% decrease on whole body Na + content, suggesting that fish were unable to compensate for the increased Na + loss induced by extreme acidity. Exposure of fish to HS + low pH, the treatment most closely approximating to the conditions experienced by the species in its native environment, resulted in an increase in whole body Na + by 31% relative to acclimation to low pH alone. J max Ca 2+ in cardinal tetras was high relative to that documented in other freshwater species acclimated to soft water ( J max = 30 nmol g −1 h −1 ). Prolonged exposure of fish to pH 3·72 inhibited J max Ca 2+ by 53%, although whole body Ca 2+ content remained unchanged relative to control. Acclimation of fish to HS + low pH resulted in an increase of J max Ca 2+ by 166% relative to low pH alone. Collectively, these results suggest that HS protect cardinal tetras acclimated to soft, acidic waters by preventing excessive Na + loss (as indicated by whole body Na + content) and by stimulating Ca 2+ uptake (as indicated by increased J max Ca 2+ ) to ensure proper homeostasis.