Ion fluxes in silver catfish (Rhamdia quelen) juveniles exposed to different dissolved oxygen levels

Abstract

Low dissolved oxygen levels in the water (hypoxia) can be provoked by oxygen consumption by fish and other organisms, organic matter decomposition, phytoplankton blooms, and temperature increase. The objective of the present study was to investigate Na + , Cl -, K + , and ammonia fluxes in silver catfish (Rhamdia quelen) exposed to different dissolved oxygen levels. Juveniles (9 ± 1g) maintained at 6.0 mg.L -1 dissolved oxygen were transferred to four 40 L aquaria with different dissolved oxygen levels (in mg.L -1 ): 6.0, 4.5, 3.5, and 2.5. In another series of experiments, juveniles were acclimated at 6.0 or 2.5 mg.L -1 dissolved oxygen levels, and then placed in two 40 L aquaria with 6.0 mg.L -1 dissolved oxygen. For both series of experiments, 1, 24, 48 or 120 h after transference juveniles were placed in individual chambers of 200 mL (with the same dissolved oxygen levels of their respective aquaria) for 3 h. Water samples were collected for analysis of Na + , Cl -, K + , and ammonia levels. The obtained results allow concluding that exposure to 2.5 mg.L -¹ dissolved oxygen levels promotes loss of ions and lower ammonia excretion in silver catfish juveniles, but these losses are rapidly stabilized for Na + and Cl -. Exposure to less hypoxic levels also changes ion fluxes and ammonia excretion, but there is no clear relationship between both parameters in this species. Therefore, silver catfish osmoregulation seems to be affected when this species is transferred from normoxic to hypoxic waters and vice-versa.Baixos níveis de oxigênio dissolvido na água (hipóxia) podem ser causados pelo consumo de oxygênio por peixes e outros organismos, decomposição de matéria orgânica, "blooms" de fitoplâncton e aumento de temperatura. O objetivo do presente estudo foi analisar os fluxos de Na + , Cl -, K + e amônia em jundiás (Rhamdia quelen) expostos a diferentes níveis de oxigênio dissolvido. Juvenis (9 ± 1g) mantidos em 6,0 mg.L -1 oxigênio dissolvido foram transferidos para quatro aquários de 40 L com diferentes níveis de oxigênio dissolvido (em mg.L -1 ): 6,0; 4,5; 3,5 e 2,5. Em outra série de experimentos, juvenis foram aclimatados a 6,0 ou 2,5 mg.L -1 oxigênio dissolvido e então colocados em dois aquários de 40 L com 6,0 mg.L -1 oxigênio dissolvido. Para ambas séries de experimentos, 1, 24, 48 ou 120 h depois da transferência os juvenis foram colocados em câmaras individuais de 200 mL (com os mesmos níveis de oxigênio dissolvido dos seus respectivos aquários) por 3 h. Amostras de água foram coletadas para análise dos níveis de Na + , Cl -, K + e amônia. Os resultados obtidos permitem concluir que a exposição a 2,5 mg.L -1 oxigênio dissolvido promove uma perda de íons nos juvenis de jundiá, mas estas perdas são estabilizadas rapidamente no caso de Na + e Cl -. A exposição a níveis não tão hipóxicos também altera os fluxos iônicos, mas não há nenhuma relação clara entre ambos parâmetros. Portanto, a osmorregulação do jundiá parece ser afetada quando exemplares são transferidos de águas normóxicas to hipóxicas e vice-ve...

Dissolved oxygen and ammonia levels in water that affect plasma ionic content and gallbladder bile in silver catfish

“…Low DO levels (3.5mg L -1 ) for 6-24h increased plasma Na + , K + and Cl -levels in the silver catfish irrespective to NH 3 levels in the water (Table 2). In disagreement with the present results, ROSSO et al (2006) demonstrated that exposure to 2.5-3.5mg L -1 DO levels for 1h increased Na + and Cl -loss in silver catfish. However, these ion losses in hypoxia observed by ROSSO et al (2006) were similar to control values 24h later, but intermediate measurements were not performed.…”

“…In disagreement with the present results, ROSSO et al (2006) demonstrated that exposure to 2.5-3.5mg L -1 DO levels for 1h increased Na + and Cl -loss in silver catfish. However, these ion losses in hypoxia observed by ROSSO et al (2006) were similar to control values 24h later, but intermediate measurements were not performed. Consequently, a recovery of ion losses in Ciência Rural, v.39, n.6, set, 2009. this species could appear between 1h and 24h, thus justifying the results of the present study.…”

“…Hypoxic conditions reduced plasma osmolarity in traíra (Hoplias malabaricus) (SAKURAGUI et al, 2003), changed net ion fluxes in silver catfish, Rhamdia quelen (ROSSO et al, 2006), but had no effect on plasma Na + levels in European sea bass (Dicentrarchus labrax) exposed to four different DO levels (CECCHINI & CAPUTO, 2003 Argentina, and is the native freshwater species most raised in southern Brazil (BALDISSEROTTO, in press). It is a suitable species for fish culture because it has a good growth rate and is able to use numerous kinds of nutrient sources (LAZZARI et al, 2006;MELO et al, 2006).…”

Dietary salt and water pH effects on growth and Na+ fluxes of silver catfish juveniles

“…Fish were weighed at the end of the flux experiment. Previous experiments of Rosso et al (2006) demonstrated that net ion fluxes of juveniles maintained for 24 hours in chambers were not significantly different from the fluxes of those which measurements started around 10 min. after placing them in the chambers.…”

Calcium fluxes in Hoplosternum littorale (tamoatá) exposed to different types of Amazonian waters

“…Stress increases gill blood flow and paracellular permeability, resulting in ion loss (Cech et al, 1996). Recovery is variable depending on the intensity of stress and species (Gonzalez & McDonald, 1994;Baldisserotto & Val, 2002;Rosso et al, 2006). In the present experiment apparently stress was reduced after 2 h, since net Ca 2+ fluxes in tamoatás in black water and well water became net influxes, and values were similar to those determined by Wilson et al (1999) for the same species and Brycon erythropterum (= Brycon cephalus) exposed to well water at pH 6.0.…”