Hypoxia tolerance of Amazon fish

The Amazonian cichlid is highly tolerant to hypoxia, and is known to reduce its metabolic rate by reducing the activity of energetically expensive metabolic processes when oxygen is lacking in its environment. Our objectives were to determine how protein metabolism is regulated in during hypoxia. Fish were exposed to a stepwise decrease in air saturation (100%, 20%, 10% and 5%) for 2 h at each level, and sampled throughout the experiment. A flooding dose technique using a stable isotope allowed us to observe an overall decrease in protein synthesis during hypoxia in liver, muscle, gill and heart. We estimate that this decrease in rates of protein synthesis accounts for a 20 to 36% decrease in metabolic rate, which would enable oscars to maintain stable levels of ATP and prolong survival. It was also determined for the first time in fish that a decrease in protein synthesis during hypoxia is likely controlled by signaling molecules (4EBP1 and eIF2-α), and not simply due to a lack of ATP. We could not detect any effects of hypoxia on protein degradation as the levels of NH excretion, indicators of the ubiquitin proteasome pathway, and enzymatic activities of lysosomal and non-lysosomal proteolytic enzymes were maintained throughout the experiment.

Section: Discussionmentioning

confidence: 99%

Section: Protein Synthesismentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Protein synthesis is lowered by 4EBP1 and eIF2-α signaling while protein degradation may be maintained in fasting, hypoxic Amazonian cichlid, Astronotus ocellatus

Cassidy

Driedzic

Campos

et al. 2017

“…In addition to ASR and air breathing, hypoxia-adapted Amazonian fishes tend to possess characteristics across the multiple steps of the O 2 cascade that enhance O 2 extraction and delivery. These include high ventilation rates, large gill surface areas (Saint-Paul, 1984), and high blood-O 2 carrying capacities through increased red blood cell count, [Hb] and Hb-O 2 binding affinities (Saint-Paul, 1984;Val and Almeida-Val, 1995;Muusze et al, 1998;Val et al, 1998;Affonso et al, 2002). Beyond sustaining aerobic metabolism, hypoxia-exposed Amazonian fishes also strongly activate anaerobic metabolism (e.g.…”

Section: Heterogeneous Hypoxic Environments In the Amazonmentioning

confidence: 99%

Can variation among hypoxic environments explain why different fish species use different hypoxic survival strategies?

Mandic

Regan

2018

In aquatic environments, hypoxia is a multi-dimensional stressor that can vary in O 2 level (partial pressure of O 2 in water, Pw O2), rate of induction and duration. Natural hypoxic environments can therefore be very different from one another. For the many fish species that have evolved to cope with these different hypoxic environments, survival requires adjusting energy supply and demand pathways to maintain energy balance. The literature describes innumerable ways that fishes combine aerobic metabolism, anaerobic metabolism and metabolic rate depression (MRD) to accomplish this, but it is unknown whether the evolutionary paths leading to these different strategies are determined primarily by species' phylogenetic histories, genetic constraint or their native hypoxic environments. We explored this idea by devising a four-quadrant matrix that bins different aquatic hypoxic environments according to their duration and Pw O2 characteristics. We then systematically mined the literature for well-studied species native to environments within each quadrant, and, for each of 10 case studies, described the species' total hypoxic response (THR), defined as its hypoxia-induced combination of sustained aerobic metabolism, enhanced anaerobic metabolism and MRD, encompassing also the mechanisms underlying these metabolic modes. Our analysis revealed that fishes use a wide range of THRs, but that distantly related species from environments within the same matrix quadrant have converged on similar THRs. For example, environments of moderately hypoxic Pw O2 favoured predominantly aerobic THRs, whereas environments of severely hypoxic Pw O2 favoured MRD. Capacity for aerial emergence as well as predation pressure (aquatic and aerial) also contributed to these responses, in addition to other biotic and abiotic factors. Generally, it appears that the particular type of hypoxia experienced by a fish plays a major role in shaping its particular THR.

“…Acclimation to normoxia has been used in other studies of hypoxia-tolerant fishes prior to exposure to acute, graded or chronic hypoxia (e.g. Muusze et al, 1998;Chipari-Gomez et al, 2005;Almeida-Val et al, 2011); such conditioning should minimize inter-individual variation in plastic traits and allow us to then evaluate plastic responses to controlled chronic and acute hypoxia exposure. One treatment group then underwent an 8 week acclimation to chronic hypoxia, while the other group stayed under chronic normoxia for an additional 8 week period.…”

Section: Introductionmentioning

confidence: 99%

Effects of hypoxia on swimming and sensing in a weakly electric fish

Ackerly

Krahe

Sanford

et al. 2018

Low dissolved oxygen (hypoxia) can severely limit fish performance, especially aerobically expensive behaviours including swimming and acquisition of sensory information. Fishes can reduce oxygen requirements by altering these behaviours under hypoxia, but the underlying mechanisms can be difficult to quantify. We used a weakly electric fish as a model system to explore potential effects of hypoxia on swim performance and sensory information acquisition, which enabled us to non-invasively record electric signalling activity used for active acquisition of sensory information during swimming. To quantify potential effects of hypoxia, we measured critical swim speed () and concurrent electric signalling activity under high- and low-dissolved oxygen concentrations in a hypoxia-tolerant African mormyrid fish, Fish were maintained under normoxia for 6 months prior to experimental treatments, and then acclimated for 8 weeks to normoxia or hypoxia and tested under both conditions (acute: 4 h exposure). Acute hypoxia exposure resulted in a significant reduction in both and electric signalling activity in fish not acclimated to hypoxia. However, individuals acclimated to chronic hypoxia were characterized by a higher under both hypoxia and normoxia than fish acclimated to normoxia. Following a 6 month re-introduction to normoxia, hypoxia-acclimated individuals still showed increased performance under acute hypoxic test conditions, but not under normoxia. Our results highlight the detrimental effects of hypoxia on aerobic swim performance and sensory information acquisition, and the ability of fish to heighten aerobic performance through acclimation processes that can still influence performance even months after initial exposure.