Different biochemical strategies of two Neotropical fish to cope with the impairment of nitrogen excretion during air exposure

Abstract

The exposure of fish to air is normally expected to interfere with the nitrogen excretion process. Hoplias malabaricus and Hoplerythrinus unitaeniatus, two teleost species, display distinct behaviors in response to decreases in natural reservoir water levels, although they may employ similar biochemical strategies. To investigate this point, plasma levels of ammonia, urea, uric acid, and the two urea cycle enzymes, ornithine carbamoyl transferase (OCT) and arginase (ARG), as well as glutamine synthetase (GS) were determined for both species after exposure to air. Plasma ammonia increased gradually during exposure to air, but only H. malabaricus showed increased concentrations of urea. Plasma uric acid remained very low in both fish. Enzymatic activities (mean ± SD, µmol min -1 g protein -1 ) of H. malabaricus showed significant increases (P<0.05, N = 6) in OCT from 0.84 ± 0.05 to 1.42 ± 0.03, in ARG from 8.07 ± 0.47 to 9.97 ± 0.53 and in GS from 1.15 ± 0.03 to 2.39 ± 0.04. The OCT and ARG enzymes remained constant in H. unitaeniatus (N = 6), but GS increased from 1.49 ± 0.02 to 2.06 ± 0.03. Although these species are very closely related and share the same environment, their biochemical strategies in response to exposure to air or to increased plasma ammonia are different.

Trophic cascade effects of Hoplias malabaricus (Characiformes, Erythrinidae) in subtropical lakes food webs: a mesocosm approach

“…malabaricus is a voracious piscivore feeding on numerous fish species and even birds (Ringuelet et al, 1967) and small mammals (Teixeira-de Mello unpublished data), which may enhance its carrying capacity. It exhibits parental care of hatchings (Ringuelet et al, 1967) and tolerates very turbid and hypoxic conditions (Rantin & Johansen, 1984;Polez et al, 2003), which are common features of eutrophic systems. These characteristics, considered as the key factors for its successful colonization of almost all water ecosystems in the region, may also be useful in the biomanipulation of eutrophic ecosystems.…”

Hypoxia-induced differential apoptosis in the central nervous system of the sturgeon (Acipenser shrenckii)

“…Clearly, both exposure methods cause stress, and this is associated with increases in blood cortisol, catecholamines, ammonia, and lactate levels (Arends et al, 1999;Maxime et al, 1995;Polez et al, 2003). We measured the blood cortisol levels, as described by Lankford et al (2003), from each of two air-and hypoxic water exposed sturgeons immediately, 6, and 30 h after the hypoxic insults.…”

Primeiro registro e aspectos ecológicos de Hoplerythrinus unitaeniatus (Agassiz, 1829) (Characiformes, Erythrinidae) como espécie introduzida na Bacia do Rio dos Sinos, RS, Brasil

“…O gênero Hoplerythrinus possui como principal característica a capacidade de sobreviver a longos períodos de hipóxia pela habilidade de absorver oxigênio atmosférico (Polez et al 2003, Jucá-Chagas 2004, Oliveira et al 2004. A respiração aérea facultativa é resultante da grande vascularização e esponjosidade da bexiga natatória, conferindo-lhe a possibilidade de fazer incursões terrestres entre corpos de águas adjacentes (Val & Almeida-Val 1995, Graham 1997, Jucá-Chagas 2004.…”

“…Segundo Sato et al (2003) a média de ovócitos para a espécie encontra-se na faixa de 1.064 a 1.370 ovócitos.g -1 gerando ovos do tipo adesivo, comum para espécies não-migradoras e com cuidado parental como o jeju. Encontrado em ambientes lênticos apresenta facilidade de adaptação às mudanças ambientais, físicas e químicas da água (Nelson 1984, Polez et al 2003.…”