Ecological adaptations of Amazonian fishes acquired during evolution under environmental variations in dissolved oxygen: A review of responses to hypoxia in fishes, featuring the hypoxia‐tolerantAstronotusspp.

Abstract

The Amazon Basin presents a dynamic regime of dissolved oxygen (DO) oscillations, which varies among habitats within the basin, including spatially, daily, and seasonally. Fish species inhabiting these environments have developed many physiological adaptations to deal with the frequent and periodic events of low (hypoxia), or no (anoxia) DO in the water. Cichlid fishes, especially the genus Astronotus (A. ocellatus and A. crassipinnis), are hypoxic‐tolerant species that can survive in very low DO levels for long periods, while adults often inhabit places where DO is close to zero. The present review will focus on some metabolic adjustments that Amazonian fish use in response to hypoxic conditions, which include many strategies from behavioral, morphological, physiological, and biochemical strategies. These strategies include ASR (aerial surface respiration), lip expansion, branchial tissue remodeling, increases in glycolytic metabolism with the increase of blood glucose levels, and increases in anaerobic metabolism with increases of plasma lactate levels. Other groups over evolutionary time developed obligate aerial respiration with changes in pharyngeal and swim bladder vascularization as well as the development of a true lung. However, most species are water‐breathing species, such as A. ocellatus and A. crassipinnis, which are detailed in this study because they are used as hypoxia‐tolerant model fish. Herein, we draw together the literature data of the physiological mechanisms by which these species decrease aerobic metabolism and increase anaerobic metabolism to survive hypoxia. This is the first attempt to synthesize the physiological mechanisms of the hypoxia‐tolerant Astronotus species.

The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia

“…Species greatly differ in their ability to survive in hypoxic conditions; aquatic organisms are no exception. A vast literature exists on hypoxia response in fish; in particular we have learned a great deal about adaptation to hypoxia from studies of hypoxia tolerant species (Braz‐Mota & Almeida‐Val, 2021; Mandic et al, 2018; Sloman et al, 2008; Somo et al, 2020; Zhou et al, 2020) and from comparison of transcriptional responses between hypoxia‐tolerant species and their more hypoxia‐sensitive relatives (Heinrichs‐Caldas & De Almeida‐Val, 2021; Lau et al, 2019; Mandic et al, 2014). Coherently with the data from terrestrial vertebrates reviewed above, studies reported decreased oxygen consumption, metabolic depression and, transcriptionally, upregulation of glycolysis and amino acid degradation pathways, oxidative‐stress‐related enzymes and pathways, such as mitogen‐activated protein kinase (MAPK) signaling pathway, and apoptotis‐related genes, among others.…”

Effect of stocking density in plastic boxes without oxygenation on the transport of pirarucu,Arapaima gigas (Schinz, 1822)

“…In this study, pirarucus showed oscillations in lactate parameters at times AT and 48 h, and at time 48 h we observed a sudden drop in plasma lactate at a density of 195 g L À1 . In the literature, it is reported that Amazonian fish perform metabolic adjustments because of stressful situations, one of which is the increase in anaerobic metabolism with increased levels of plasma lactate (Braz-Mota & Almeida-Val, 2021). Exposure to stress results in increased lactate levels and altered oscillation, which is to be expected because the stress response results in the activation of mechanisms involved in nutrient supply over the time a stressor is present (Hernández-Pérez et al, 2019).…”

Capítulo 23: Impactos de la deforestación y el cambio climático sobre la biodiversidad, los procesos ecológicos y la adaptación ambiental

“…However, the current challenging conditions of particular water bodies, such as low pH, high temperature, and low dissolved oxygen, could be worsened by the ongoing climate changes. As many fish species already live near their physiological limits, environmental impacts on those water characteristics would impact the local aquatic biota (Braz-Mota and Almeida-Val 2021) This chapter will discuss the observed and predicted impacts of climate change in the Amazonian terrestrial and aquatic ecosystems. We will focus on the impacts on biodiversity, ecosystem services, carbon cycling, fisheries, and biomass burning emissions.…”