Microplastics have a more profound impact than elevated temperatures on the predatory performance, digestion and energy metabolism of an Amazonian cichlid.

Mechanisms of toxic action of copper and copper nanoparticles in two Amazon fish species: Dwarf cichlid (Apistogramma agassizii) and cardinal tetra (Paracheirodon axelrodi).

Transcriptome and physiology analysis identify key metabolic changes in the liver of the large yellow croaker (Larimichthys crocea) in response to acute hypoxia

Equatorial fishes, and the critically important fisheries based on them, are thought to be at-risk from climate warming because the fishes have evolved in a relatively aseasonal environment and possess narrow thermal tolerance windows that are close to upper thermal limits. We assessed survival, growth, aerobic performance and critical thermal maxima (CTmax) following acute and 21 d exposures to temperatures up to 4°C higher than current maxima for six species of freshwater fishes indigenous to tropical countries and of importance for human consumption. All six species showed 1.3–1.7°C increases in CTmax with a 4°C rise in acclimation temperature, values which match up well with fishes from other climatic regions, and five species had survival >87% at all temperatures over the treatment period. Specific growth rates varied among and within each species in response to temperature treatments. For all species, the response of resting metabolic rate (RMR) was consistently more dynamic than for maximum metabolic rate, but in general both acute temperature exposure and thermal acclimation had only modest effects on aerobic scope (AS). However, RMR increased after warm acclimation in 5 of 6 species, suggesting incomplete metabolic compensation. Taken in total, our results show that each species had some ability to perform at temperatures up to 4°C above current maxima, yet also displayed certain areas of concern for their long-term welfare. We therefore suggest caution against the overly broad generalization that all tropical freshwater fish species will face severe challenges from warming temperatures in the coming decades and that future vulnerability assessments should integrate multiple performance metrics as opposed to relying on a single response metric. Given the societal significance of inland fisheries in many parts of the tropics, our results clearly demonstrate the need for more species-specific studies of adaptive capacity to climate change-related challenges.

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Predicted impacts of climate warming on aerobic performance and upper thermal tolerance of six tropical freshwater fishes spanning three continents.

We examined whether oxidative damage and antioxidant responses are more likely to occur during hypoxia or re-oxygenation in hypoxia-tolerant fish, and whether there is an influence of the rate of re-oxygenation. An hypoxia/re-oxygenation experiment using wild-caught Cyphocharax abramoides (Rio Negro, Brazil), was designed to answer these questions. Lipid peroxidation (MDA), a measure of oxidative damage, and antioxidant activities (superoxide dismutase (SOD), glutathione peroxidase (GPx), antioxidant capacity against peroxyl radicals (ACAP)), were measured in brain, gill and liver tissues after normoxia, 3-h hypoxia (2.7 kPa), and 3-h hypoxia followed by 1-h or 3-h re-oxygenation, implemented either immediately or slowly (3.0 kPa·h −1 ). Critical oxygen tension of routine oxygen consumption rate (Pcrit) (4.1 kPa) and the P O2 at loss of equilibrium (LOE) (1.7 kPa) were determined to set the experimental hypoxia exposure. The Regulation Index, a measure of oxyregulation with declining P O2 , was 0.32. Oxidative damage occurred during hypoxia: no additional damage was observed during re-oxygenation. Tissues responded differentially. GPx and MDA rose in the brain and gills, and SOD (and likely GPx) in the liver during hypoxia. Antioxidants increased further at LOE. Rate of oxygen increase during re-oxygenation did not affect antioxidant responses. In brain and gills, GPx and MDA decreased or recovered after 1-h re-oxygenation. In liver, SOD remained high and GPx increased. In summary, C. abramoides incurred oxidative damage during hypoxic exposure with no additional damage inflicted during re-oxygenation: the rate of re-oxygenation was inconsequential. Literature data support conclusion of greater damage during hypoxia than during re-oxygenation in hypoxia-tolerant fish.

Does hypoxia or different rates of re-oxygenation after hypoxia induce an oxidative stress response in Cyphocharax abramoides (Kner 1858), a Characid fish of the Rio Negro?

Temperature is the main factor affecting the distribution of the sympatric Amazon fishes Paracheirodon axelrodi and Paracheirodon simulans. Both species are associated with flooded areas of the Negro river basin; P. axelrodi inhabits waters that do not exceed 30°C, and P. simulans lives at temperatures that can surpass 35°C. The present work aimed to describe the biochemical and physiological adjustments to temperature in those species. We determined the thermal tolerance polygon of species acclimated to four temperatures using critical thermal methodology. We also determined the chronic temperature effects by acclimating the two species at 20, 25, 30, and 35°C and measured the critical oxygen tension (PO2crit) for both species. Additionally, we evaluated the metabolic rate and the enzymes of energy metabolic pathways (CS, MDH, and LDH). Our results showed a larger thermal tolerance polygon, a higher energetic metabolic rate, and higher enzyme levels for P. simulans acclimated to 20 and 35°C compared to P. axelrodi. Paracheirodon simulans also presented a higher hypoxia tolerance, indirectly determined as the PO2cri. Thus, we conclude that the higher metabolic capacity of P. simulans gives this species a better chance to survive at acutely higher temperatures in nature, although it is more vulnerable to chronic exposure.

Metabolic rate and thermal tolerance in two congeneric Amazon fishes: Paracheirodon axelrodi Schultz, 1956 and Paracheirodon simulans Géry, 1963 (Characidae)

The aquatic habitats of the Amazon basin present dramatic variation of oxygen level, and, to survive such changes, many aquatic animals developed biochemical and physiological adaptations. The advanced teleost Astronotus crassipinnis (Perciformes) is a fish tolerant to hypoxia and known to endure such naturally variable environments. Hypoxia-Inducible factor-1α (hif-1α) is among the most important and studied genes related to hypoxia-tolerance, maintaining regular cellular function and controlling anaerobic metabolism. In the present work, we studied hif-1α expression and related it to changes in metabolic pathways of Astronotus crassipinnis exposed to 1, 3 and 5 h of hypoxia, followed by 3 h of recovery. The results show that A. crassipinnis depresses aerobic metabolic under hypoxia, with a decrease in glycolysis and oxidative enzyme activities, and increases its anaerobic metabolism with an increase in LDH activity coupled with a decrease in oxygen consumption, which indicates an increase in anaerobic capacity. In addition, the animal differentially regulates hif-1α gene in each tissue studied, with a positive relationship to its metabolic profile, suggesting that hif-1α might be one of the most important induction factors that regulate hypoxia tolerance in this species.

Oxygen-dependent distinct expression of hif-1α gene in aerobic and anaerobic tissues of the Amazon Oscar, Astronotus crassipinnis.

The control of abiotic parameters is fundamental for fish survival, growth and reproduction. These factors have a direct effect on sperm quality. Thus, this study evaluated the effect of different temperatures (29, 31, 33, and 35°C), pHs (4 and 8), and hypoxia (1 mgO2 L-1) on sperm motility of Colossoma macropomum (tambaqui). The results indicated a longer duration of sperm motility at 29°C (50.1 ± 2.70 s) that progressively decreased when exposed to 35°C (31.2 ± 1.31 s) and hypoxia at pH 4 (27.4 ± 1.42 s) and pH 8 (30.44 ± 1.66 s; p < 0.05), respectively. Sperm oxygen consumption increased in hypoxia at both pH (pH 4 = 61.22; pH 8 = 54.74 pmol s-1). There was an increase in the activity of glutathione-S-transferase (GST) and superoxide dismutase (SOD), as well as in lipid peroxidation levels (LPO) and DNA damage in sperm exposed to higher temperatures and hypoxia. The pH 4 and pH 8 under normoxia did not affect the quality of C. macropomum sperm. These results suggest that water warming and acidification, consequences of climate changes, significantly affect the reproduction of C. macropomum, reducing the quality of spermatozoids during fertilization.

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High Temperature, pH, and Hypoxia Cause Oxidative Stress and Impair the Spermatic Performance of the Amazon Fish Colossoma macropomum.

Roundup® (RD) is a glyphosate-based herbicide used to control weeds in agriculture, and fishponds. In the Amazon, hypoxia is a natural phenomenon in flooded areas. Beyond the challenge of hypoxia, fish need to cope with the use of pesticides as RD that increases in the aquatic environment through the leaching of agricultural areas, and in aquaculture fish tanks. Thus, there is a need to better understand the combined effects of hypoxia and RD contamination for aquatic biota. The aim of this study was to investigate the effects of Roundup® (RD) and subsequent acute hypoxia in the gene expression, genotoxicity, histological and physiological responses of Colossoma macropomum. Fish were individually exposed to four different treatments during 96 h: normoxia (N), hypoxia (H), RD plus normoxia (NRD), and RD plus hypoxia (HRD) (RD concentration represents 75% of LC50 - nominal concentration 15 mg L−1 to C. macropomum). HRD fishes presented down-regulation of hif-1α gene and ras oncogene, while NRD fish presented overexpression of ras; no difference occurred in hif-1α gene expression in both normoxia treatments. The glutathione-S-transferase and catalase activities increased in HRD fish liver compared to NRD. Otherwise, there was no difference in lipoperoxidation (LPO) between all treatments. Genetic Damage Index, measured throughout comet assay in erythrocytes of all treatments, presented similar values, excepted by fish exposed to NRD. As regard as hypoxic exposure, hypoxic fish presented significantly lower values, compared to HRD fishes. An increase in liver histological injuries occurred in H and HRD fish groups. In conclusion, we may affirm that C. macropomum is sensitive concerning RD contamination and that this sensitivity increases when combined with hypoxia.

Gene expression, genotoxicity, and physiological responses in an Amazonian fish, Colossoma macropomum (CUVIER 1818), exposed to Roundup® and subsequent acute hypoxia.

Derek Felipe de Campos

Papers

Metabolic rate and thermal tolerance in two congeneric Amazon fishes: Paracheirodon axelrodi Schultz, 1956 and Paracheirodon simulans Géry, 1963 (Characidae)

Oxygen-dependent distinct expression of hif-1α gene in aerobic and anaerobic tissues of the Amazon Oscar, Astronotus crassipinnis.

High Temperature, pH, and Hypoxia Cause Oxidative Stress and Impair the Spermatic Performance of the Amazon Fish Colossoma macropomum.

Gene expression, genotoxicity, and physiological responses in an Amazonian fish, Colossoma macropomum (CUVIER 1818), exposed to Roundup® and subsequent acute hypoxia.