Abstract
Variations in dissolved oxygen levels are common in the Amazonian aquatic environments and the aquatic organisms that inhabit these environments developed a variety of adaptive responses to deal with such conditions. Some Amazonian fish species are tolerant to low oxygen levels and the cichlid Astronotus ocellatus is one of the most hypoxia-tolerant species. Herein, we aimed to unveil the biochemical and molecular responses that A. ocellatus presents when submitted to hypoxia. Hypoxia indicators were measured, such as plasma glucose, plasma lactate, hepatic glycogen and relative transcript levels of prolyl hydroxylase 2 (phd2) and hypoxia-inducible factor-1α (hif-1α) in juveniles of approximately 50 g exposed to 1, 3, and 5 hours of hypoxia (0.7 mg O2.L-1), followed by 3 hours of recovery in normoxia (6 mg O2.L-1). Fish exposed to hypoxia reduced liver glycogen levels within 3 hours of hypoxia, when comparing with 1 hour, and increased plasma glucose and lactate. Under the same condition, phd2 transcripts levels increased in gills, but decreased in liver. In contrast, hypoxia did not affect relative gene expression of hif-1α in both tissues. Based on the transcription pattern of phd2, these results showed that liver and gills of A. ocellatus have different molecular strategies to cope with environmental hypoxia.
Highlights
The annual and regular variation of water level of the Amazon basin rivers described by Junk et al (1989) as the “flood pulse” is the main driving force responsible for the productivity, existence and interaction between the biota and the river-floodplain system
With three hour of hypoxia, glycogen content decreased in liver of A. ocellatus (Figure 1A)
The hepatic glycogenolysis caused by hypoxia increases the levels of plasma glucose in order to supply energy to the body in anaerobic conditions through anaerobic glycolysis (Scarabello et al, 1992; Schulte et al, 1992; Chippari-Gomes et al, 2005)
Summary
The annual and regular variation of water level of the Amazon basin rivers described by Junk et al (1989) as the “flood pulse” is the main driving force responsible for the productivity, existence and interaction between the biota and the river-floodplain system. The Amazonian fishes present biochemical, physiological and behavioral adaptations to deal with hypoxic environments (Val et al, 1998). These adaptive responses can be related to reduced energy demand, improved oxygen uptake, or avoidance of hypoxic areas (Val, 1995; Muusze et al, 1998; Almeida-Val et al, 1999; Sloman et al, 2006). Compared to other Amazonian fishes, Astronotus ocellatus ( known as Oscar fish) is a highly hypoxia tolerant Cichlidae species (Muusze et al, 1998; Sloman et al, 2006).
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