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

Abstract

Our goal was to compare the internal physiological responses to acid challenge in an acidophilic tropical teleost endemic to dilute low-pH waters with those in nonacidophilic temperate species such as salmonids, which have been the subjects of most previous investigations. The Amazonian tambaqui (Colossoma macropomum), which migrates between circumneutral water and dilute acidic "blackwater" of the Rio Negro, was exposed to a graded low-pH and recovery regime in representative soft water (Na+ = 15, Cl- = 16, Ca2+ = 20 mumol L-1). Fish were fitted with arterial catheters for repetitive blood sampling. Water pH was altered from 6.5 (control) to 5.0, 4.0, 3.0, and back to 6.5 (recovery) on successive days. Some deaths occurred at pH 3.0. Throughout the regime, there were no disturbances of blood gases (O2 and CO2 tensions and contents) or lactate levels, and only very minor changes in acid-base status of plasma and red cells. However, erythrocytic guanylate and adenylate levels increased at pH's less than or equal to 5.0. Down to pH 4.0, plasma glucose, cortisol, and total ammonia levels remained constant, but all increased at pH 3.0, denoting a stress response. Plasma Na+ and Cl- levels declined and plasma protein concentration increased at pH 3.0, indicative of ionoregulatory and fluid volume disturbance, and neither recovered upon return to pH 6.5. Cortisol and ammonia elevations also persisted. Transepithelial potential changed progressively from highly negative values (inside) at pH 6.5 to highly positive values at pH 3.0; these alterations were fully reversible. Experimental elevations in water calcium levels drove the transepithelial potential positive at circumneutral pH, attenuated or prevented changes in transepithelial potential at low pH, and reduced Na+ and Cl- loss rates to the water during acute low-pH challenges. In general, tambaqui exhibited responses to low pH that were qualitatively similar but quantitatively more resistant than those previously documented in salmonids.

Avaliação dos efeitos da adição de sal e da densidade no transporte de tambaqui

“…Houve aumento de NH 3 do tempo 0 para 90 minutos, permanecendo com valores iguais a este no tempo 180 minutos (Tabela 1). As águas ácidas, além de serem as mais comuns em estações de piscicultura da Região Amazônica, são uma característica marcante de muitos corpos de água dessa região (Wood et al, 1998). O caráter ácido da água utilizada no experimento fez com que apenas 0,08% da amônia total (NH 3 +NH 4 ) estivesse em seu estado tóxico (NH 3 ).…”

“…Nos dois experimentos, a alteração da glicose só ocorreu após o transporte, retornando para níveis normais na amostragem de 24PT, ou seja, o tambaqui recuperou rapidamente sua condição glicêmica normal. Esta rápida recuperação glicêmica em situações estressantes já é conhecida nessa espécie (Wood et al, 1998). Resultado semelhante foi obtido por Robertson et al (1987) com red drum (Sciaenops ocellatus).…”

Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia

“…Teleosts living in these waters exhibit exceptional acid tolerance, and studies on ion fluxes of some Amazonian species deal with the effect of low water pH and low calcium levels (Gonzalez et al, 1997;Wood et al, 1998). As far as we know, few studies have analyzed the effects of hypoxia on ion fluxes in Amazonian teleosts.…”

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

“…In contrast, ionoregulatory control in C. schwartzi is clearly Ca 2+ dependent, as shown for the tambaqui (C. macropomum), a blackwater-whitewater migratory species (12,18,20,21). This indicates that C. schwartzi has a high branchial affinity for Ca 2+ , particularly at the paracellular tight junctions, thus presenting diffusive ion losses.…”