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Freshwater fish are restricted by their physiology to rivers and lakes, and are generally limited in their capacity to disperse across basins. As a result, there is often a close match between the evolutionary history of river basins and their natural history. Thus, the regional landscape and ecological features, such as temperature, have shaped the evolution and adaptation of local fish assemblages. Climate change is expected to affect fish diversity and increase extinction, especially in low latitudes, and it has been suggested that species that inhabit low latitude species are more susceptible since they live close to their maximum thermal limits and have low capacity for acclimation. To understand the mechanisms of variation in thermal tolerance across a broad‐scale of South American fishes is fundamental to be able to assess the vulnerability of species and habitat to global warming. Herein, we present the first attempt to analyze the vulnerability of South American freshwater fish species, based on the review of upper thermal limits of 106 species from a broad range of latitudinal habitats. Our findings show that upper thermal limits decrease with latitude, while the thermal safety margin (TSM) increase. Furthermore, the latitude has little effects on the acclimation response ratio, and the TSM decreased with rising temperatures. These data suggest that thermal phenotypic acclimation has low potential for mitigating global warming. These results indicate that South American fish species living in tropical areas are more susceptible to global warming since they are already living close to their maximum habitat temperature.

Photoperiod is considered an important synchronizer of biological activities and endocrine pathways, including growth. As ectotherms, fish have many physiological functions controlled by the photoperiod. However, the combined effects of photoperiod and temperature should be clarified, particularly for tropical fish living near their upper thermal limit, as is the case of Amazonian fish. The central aim of this study was to evaluate the combined effect of photoperiod and temperature on growth and physiological aspects of tambaqui (Colossoma macropomum). Juveniles of tambaqui were distributed in 70 L tank, following a factorial design that included three photoperiods (light 0 h: darkness 24 h; light 12 h: darkness 12 h; and light 18 h: darkness 6 h) associated with three temperatures (26, 29, and 32 • C). They were maintained under these conditions for 2 months. Fish reared in the dark at 29 and 32 • C showed better performance compared to fish reared under extended light conditions at all temperatures. Among physiological responses, it has been observed that blood parameters tend to be disturbed with increasing temperature and that extended light conditions at low temperatures caused similar effects on the analyzed fish, suggesting blood hemoconcentration. Fish under extended light conditions showed an increase in glucose, cortisol, cholesterol, and total proteins, indicating additional physiological disturbances. In conclusion, our study shows that, unlike marine and temperate fish, C. macropomum, a fish species endemic to the Amazon, grows better in warmth dark, showing no significant physiological disturbances, similar to observations described for wild animals of this species. Our results support that changes in fish growth occur in response to environmental conditions. Therefore, fish species from freshwater, estuarine, and marine environments, must be specifically analyzed regarding the combination effects of photoperiod and temperature.

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO2 are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO2 changes in combination with parasite infection would interfere with the host’s physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO2 above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na+/K+-ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na+/K+-ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security.

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Resumo:A pesca artesanal é uma importante atividade econômica e de subsistência para as populações tradicionais da região amazônica. O objetivo deste estudo foi caracterizar a pesca do apaiari, Astronotus ocellatus (Agassiz, 1831), e o perfil socioeconômico dos pescadores artesanais da região dos lagos de Pracuúba, Amapá. De maio a agosto de 2011, foram realizadas entrevistas, através de formulários padronizados, com pescadores selecionados por meio do método 'bola de neve', com idade acima de 18 anos. Dos 68 pescadores selecionados, 55 eram do sexo masculino e 13 do feminino. A partir dos resultados, observou-se que os pescadores possuem um amplo conhecimento da atividade na região, incluindo a pesca do apaiari. Tanto a vida social quanto a econômica desta população dependem totalmente da pesca artesanal.Palavras-chave: Pesca artesanal. Socioeconomia. Etnobiologia. Conhecimento tradicional. Abstract:The artisanal fishery is an important economic and subsistence activity among traditional populations in the Amazon Region. Therefore, the aim of this study was to characterize the fishery of apaiari, Astronotus ocellatus (Agassiz, 1831), and to present a socioeconomic profile of artisanal fishermen in the region lakes of Pracuúba, Amapá, Brazil. From May to August 2011 interviews were conducted using standardized forms with fishermen selected by "snowball" method and aged above 18 years old. A total of 68 fishing workers were interviewed, of which 55 were men and 13 women. It was possible to observe that fishing workers have a wide knowledge of fishery in the Region, including apaiari fishery, and that social and economic lives of the Pracuúba population depend totally of the artisanal fishery.

In this study, we review the state of the knowledge regarding the thermal biology of tambaqui (Colossoma macropomum) with emphasis on reproductive, zootechnical, metabolic, physiological and molecular aspects, which may direct paths for new research. We observed an optimal range for performance of the species, since it grows and reproduces well between 25 and 32 C, though does not tolerate temperatures below 23 C. Temperatures above 30 C cause disturbances in the processes of reproduction and development of embryos and larvae of tambaqui. Its metabolism is influenced by the size of the animal, with greater oxygen consumption in smaller animals and at higher temperatures. Haematology is one of the most often investigated fields and shows an elevation of the analysed blood parameters according to elevation in temperature, which, above 35 C, seems to be harmful to animals. However, studies are needed that examine the relationships between temperature and nutritional aspects (protein, lipid and carbohydrate metabolism), the cellular responses, the relationship with other environmental parameters (pH, oxygen, dissolved organic carbon), pollutants, ionic regulation and excretion, aerobic metabolism, growth and reproduction under warm conditions (>32 C; +60 days). There is also the need to determine the thermal limits of the species as a function of different acclimation temperatures.

Ammonia is toxic to fish, and when associated with global warming, it can cause losses in aquaculture. In this study, we investigated the physiological and zootechnical responses of Arapaima gigas to the current scenarios and to RCP8.5, a scenario predicted by the IPCC for the year 2100 which is associated with high concentrations of environmental ammonia (HEA). Forty-eight chipped juvenile A. gigas were distributed in two experimental rooms (current scenario and RCP8.5) in aquariums with and without the addition of ammonia (0.0 mM and 2.44 mM) for a period of 30 days. The HEA, the RCP8.5 scenario, and the association of these factors affects the zootechnical performance, the ionic regulation pattern, and the levels of ammonia, glucose, triglycerides, sodium, and potassium in pirarucu plasma. The branchial activity of H+-ATPase was reduced and AChE activity increased, indicating that the species uses available biological resources to prevent ammonia intoxication. Thus, measures such as monitoring water quality in regard to production, densities, and the feed supplied need to be more rigorous and frequent in daily management in order to avoid the accumulation of ammonia in water, which, in itself, proved harmful and more stressful to the animals subjected to a climate change scenario.