Richard J. Gonzalez

Diverse Strategies for Ion Regulation in Fish Collected from the Ion‐Poor, Acidic Rio Negro

We measured unidirectional ion fluxes of fish collected directly from the Rio Negro, an extremely dilute, acidic blackwater tributary of the Amazon. Kinetic analysis of Na+ uptake revealed that most species had fairly similar Jmax values, ranging from 1,150 to 1,750 nmol g−1 h−1, while Km values varied to a greater extent. Three species had Km values <33 μmol L−1, while the rest had Km \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Protection by Natural Blackwater against Disturbances in Ion Fluxes Caused by Low pH Exposure in Freshwater Stingrays Endemic to the Rio Negro

\mathrm{values}\,\geq 110

Responses of an Amazonian Teleost, the Tambaqui (Colossoma macropomum), to Low pH in Extremely Soft Water

\end{document} μmol L−1. Because of the extremely low Na+ concentration of Rio Negro water, the differences in Km values yield very different rates of Na+ uptake. However, regardless of the rate of Na+ uptake, measurements of Na+ efflux show that Na+ balance was maintained at very low Na+ levels (<50 μmol L−1) by most species. Unlike other species with high Km values, the catfish Corydoras julii maintained high rates of Na+ uptake in dilute waters by having a Jmax value at least 100% higher than the other species. Corydoras julii also demonstrated the ability to modulate kinetic parameters in response to changes in water chemistry. After 2 wk in 2 mmol L−1 NaCl, Jmax fell >50%, and Km dropped about 70%. The unusual acclimatory drop in Km may represent a mechanism to ensure high rates of Na+ uptake on return to dilute water. As well as being tolerant of extremely dilute waters, Rio Negro fish generally were fairly tolerant of low pH. Still, there were significant differences in sensitivity to pH among the species on the basis of degree of stimulation of Na+ efflux at low pH. There were also differences in sensitivity to low pH of Na+ uptake, and two species maintained significant rates of uptake even at pH 3.5. When fish were exposed to low pH in Rio Negro water instead of deionized water (with the same concentrations of major ions), the effects of low pH were reduced. This suggests that high concentrations of dissolved organic molecules in the water, which give it its dark tea color, may interact with the branchial epithelium in some protective manner.

Interspecific differences in gill morphology of freshwater fish in relation to tolerance of low-pH environments

SUMMARY Environmental hypercapnia induces a respiratory acidosis that is usually compensated within 24-96 h in freshwater fish. Water ionic composition has a large influence on both the rate and degree of pH recovery during hypercapnia. Waters of the Amazon are characteristically dilute in ions, which may have consequences for acid-base regulation during environmental hypercapnia in endemic fishes. The armoured catfish Liposarcus pardalis, from the Amazon, was exposed to a water PCO2 of 7, 14 or 42 mmHg in soft water (in μmol l-1: Na+, 15, Cl-, 16, K+, 9, Ca2+, 9, Mg2+, 2). Blood pH fell within 2 h from a normocapnic value of 7.90±0.03 to 7.56±0.04, 7.34±0.05 and 6.99±0.02, respectively. Only minor extracellular pH (pHe) recovery was observed in the subsequent 24-96 h. Despite the pronounced extracellular acidosis, intracellular pH (pHi) of the heart, liver and white muscle was tightly regulated within 6 h (the earliest time at which these parameters were measured) via a rapid accumulation of intracellular HCO3-. While most fish regulate pHi during exposure to environmental hypercapnia, the time course for this is usually similar to that for pHe regulation. The degree of extracellular acidosis tolerated by L. pardalis, and the ability to regulate pHi in the face of an extracellular acidosis, are the greatest reported to date in a teleost fish. The preferential regulation of pHi in the face of a largely uncompensated extracellular acidosis in L. pardalis is rare among vertebrates, and it is not known whether this is associated with the ability to air-breathe and tolerate aerial exposure, or living in water dilute in counter ions, or with other environmental or evolutionary selective pressures. The ubiquity of this strategy among Amazonian fishes and the mechanisms employed by L. pardalis are clearly worthy of further study.

A pharmacological examination of Na+ and Cl- transport in two species of freshwater fish.

Stenohaline freshwater stingrays (Potamotrygon spp.) are endemic to the very dilute (Na+, Cl−, \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Unusual physiology of scale-less carp, Gymnocypris przewalskii, in Lake Qinghai: a high altitude alkaline saline lake

\mathrm{Ca}\,^{2+}\leq 30