Low pH and calcium effects on net Na+ and K+ fluxes in two catfish species from the Amazon River (Corydoras: Callichthyidae)

Abstract

The present study analyzes Na + and K + disturbances caused by low pH in two catfish species from the Amazon River. Corydoras adolfoi inhabits ion-poor, black-stained, low pH (3.5-4.0) waters, while C. schwartzi is native to ion-rich waters at circumneutral pH. Fish were exposed to pH 3.5 Ca 2+ -free, and Ca 2+ -enriched (~500 µmol/l) water to determine the protective effects of calcium. Net Na + and K + fluxes were measured in the water collected from the fish experimental chambers. C. adolfoi was unable to control the Na + efflux at low pH, exhibiting Na + loss up to -594 ± 84 nmol g -1 h -1 during the first hour. After 3 and 6 h, net Na + flux increased by 7-and 23-fold, respectively. In C. schwartzi, at pH 3.5, the initial high Na + loss (-1,063 ± 73 nmol g -1 h -1 ) was gradually attenuated. A K + loss occurred in both species, but remained relatively constant throughout exposure. High [Ca 2+ ] affected ion losses in both species. C. adolfoi had 70% loss attenuation, indicating incapacity to control Na + efflux. In C. schwartzi, elevated [Ca 2+ ] completely prevented the Na + losses caused by exposure to low pH. Rather different patterns were seen for K + fluxes, with C. adolfoi showing no K + disruption when exposed to low pH/high [Ca 2+ ]. Thus, C. adolfoi loses Na + during acid exposure, but has the ability to control K + loss, while C. schwartzi controls diffusive Na + loss but exhibits a slightly higher K + loss. Ion balance was influenced by [Ca 2+ ] at low pH in C. schwartzi but not in C. adolfoi.

Tolerance response of tambaqui Colossoma macropomum (Cuvier) to water pH

“…Three main water types occur in the Amazon: white (muddy) water (pH 6.2–7.2), black water (pH 3.8–4.9) and clear water (pH 4.5–7.8). Seasonal and daily variations in water pH levels are an important environmental factor affecting ion homeostasis in fish of the Amazon (Matsuo & Val 2002). Extreme water pH represents a challenge for many fish species and can limit their growth (Aride, Roubach & Val 2004), which is relevant to local producers.…”

Physiological and morphological correlates of extreme acid tolerance in larvae of the acidophilic amphibianLitoria cooloolensis

“…A similar protective effect of elevated [Ca 2+ ] e has been demonstrated for larval Rana pipens where Na + efflux rates were suppressed almost completely (87%) following acute exposure to high Ca 2+ , low pH water (Freda and Dunson, 1984). Likewise, studies of acid tolerant fish have shown that in most cases, the presence of elevated [Ca 2+ ] e levels reduces Na + efflux rates in waters of low pH, resulting in substantially reduced mortality rates (Glynn et al, 1992; Gonzalez and Dunson, 1989a; Gonzalez et al, 1998; Matsuo and Val, 2002; McWilliams, 1983; see also review by Walker et al, 1988), suggesting that tolerance of low pH environments is at least somewhat calcium-dependent. However, an understanding of the mechanistic basis by which [Ca 2+ ] e allows acid-tolerant species overcome the physical challenges imposed by low pH environs is lacking.…”

Osmoregulation in freshwaters: Gene expression in the gills of a Neotropical cichlid in contrasting pH and ionic environments

“…In addition, the DOC found in Negro habitats may have unique chelating properties utilized by native fishes to minimize ion loss [78,79], and attempts to recreate this with other DOC sources (including Sigma humic acid) have produced mixed results [26,80,81]. The latter observation may partially explain why several Negro fishes tested in native water have shown lower dependency on external Ca 2+ to charge paracellular junctions [82,83].…”