Amazon fish maintain oxygen uptake through a variety of strategies considered evolutionary and adaptive responses to the low water oxygen saturation, commonly found in Amazon waters. Oscar (Astronotus ocellatus) is among the most hypoxia-tolerant fish in Amazon, considering its intriguing anaerobic capacity and ability to depress oxidative metabolism. Previous studies in hypoxia-tolerant and non-tolerant fish have shown that hypoxia-inducible factor-1α (HIF-1α) gene expression is positively regulated during low oxygen exposure, affecting vascular endothelial growth factor (VEGF) transcription and fish development or tolerance in different manners. However, whether similar isoforms exists in tolerant Amazon fish and whether they are affected similarly to others physiological responses to improve hypoxia tolerance remain unknown. Here we evaluate the hepatic HIF-1α and VEGF mRNA levels after 3 h of acute hypoxia exposure (0.5 mgO2/l) and 3 h of post-hypoxia recovery. Additionally, hematological parameters and oxidative enzyme activities of citrate synthase (CS) and malate dehydrogenase (MDH) were analyzed in muscle and liver tissues. Overall, three sets of responses were detected: (1) as expected, hematocrit, hemoglobin concentration, red blood cells, and blood glucose increased, improving oxygen carrying capacity and glycolysis potential; (2) oxidative enzymes from liver decreased, corroborating the tendency to a widespread metabolic suppression; and (3) HIF-1α and VEGF increased mRNA levels in liver, revealing their role in the oxygen homeostasis through, respectively, activation of target genes and vascularization. This is the first study to investigate a hypoxia-related transcription factor in a representative Amazon hypoxia-tolerant fish and suggests that HIF-1α and VEGF mRNA regulation have an important role in enhancing hypoxia tolerance in extreme tolerant species.

Growth and hematological responses of tambaqui fed different amounts of cassava (Manihot esculenta) ABSTRACTTambaqui,Colossoma macropomum is a fish of primary importance in Brazilian aquaculture and in the Amazon region in particular. The aim of this work is to analyze the combined effects of physical training and levels of dietary cassava (Manihot esculenta) on the hematological parameters, food intake, conversion efficiency, growth ratio and swimming performance of this fish. A diet for tambaqui consisting of 30% cassava caused decreases in weight gain and specific growth rate compared with the control group. Diets containing 15% or 45% cassava did not affect these indices and did not cause hematological changes in tambaqui juveniles, indicating that some amount of cassava can be used as an alternative energy source for this important aquaculture species.Keywords: teleosts, growth, feed evaluation, stress, blood RESUMO

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The effects of temperature and carbon dioxide (CO 2 ) changes on different haematological parameters and enzymes activities such as on LDH (Lactate de Hydrogenase), MDH (Malate de Hydrogenase) & GST (Glutathione-STransferase) were studied in the liver and skeletal muscles of Tambaqui fish (Collosoma macropomum, Cuvier, 1818) in the Laboratory of Ecophysiology and Molecular Evolution (LEEM) of the National Institute for Amazonian Research (INPA). The experimental procedures involved the exposure of fish to temperature rise from 28Cº to 32Cº and an increased in CO 2 concentration up to 10 times higher than the current levels for 24, 48, 72 and 96 hours. The levels of LDH, GST and MDH in both the tissues of Tambaqui (Muscles & Liver) showed a significant decreased at different along the different exposure periods. The levels of plasma glucose in blood decreased and the values of Hb, Ht, RBC, VCM, and HCM & CHCM showed increased after the exposure.