Climate change affects the parasitism rate and impairs the regulation of genes related to oxidative stress and ionoregulation of Colossoma macropomum.

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.

Temporal exposure to malathion: Biochemical changes in the Amazonian fish tambaqui, Colossoma macropomum.

The main toxicity mechanism of organophosphate insecticides such as malathion is the acetylcholinesterase enzyme inhibition. However, fish responses to organophosphates may vary depending on the activation of different defense mechanisms as well as the length of exposure. As such, the evaluation of acetylcholinesterase activity, in combination with the evaluation of biotransformation and antioxidants enzymes levels, is useful for indicating damage in fish exposed to this insecticide. Moreover, evaluating mitochondrial activity might evidence how the hierarchic responses occur in relation to the length of time that the fish is exposed. Therefore, the aim of our study is to evaluate whether the length of exposure to malathion differentially affects the biochemical responses of tambaqui. Our hypothesis is that the physiological alterations due to exposure are time dependent. Fish were exposed to sublethal concentrations of the insecticide during 6, 12, 24, 36, and 48 h. Contrary to expectations, there was no acetylcholinesterase activity inhibition during the experiment, which indicates an absence of neurotoxicity. Phase II biotransformation mechanism was activated early, especially in the liver. Oxidative damage was evident in the first hours of exposure and was concurrent with the activation of antioxidant enzymes. Mitochondrial bioenergetics were differentially affected by the length of exposure. The data suggest that the tambaqui regulates mitochondrial respiration differently over time, seeking to maintain homeostasis and ATP demand, and ensures the activation of response mechanisms, thus minimizing oxidative damage and avoiding the neurotoxicity of malathion.

Changes in Glutathione S-Transferase Activity and Parental Care Patterns in a Catfish (Pisces, Ariidae) as a Biomarker of Anthropogenic Impact in a Brazilian Harbor.

Catfish have been used as a model system for studying biochemical mechanisms of biotransformation. The main goal of this study was to identify alterations in hepatic glutathione S-transferase (GST) activity and changes in the parental care pattern of a mouth-brooding catfish, Sciades herzbergii, as a biomarker of anthropogenic impact in a port area on the northeastern coast of Brazil. The fish were sampled from a natural reserve (A1 = reference site) and from an industrialized port area (A2 = impacted site). Two analyses were carried out: hepatic GST activity and mouth-brooding behavior of males. Catfish collected from the A1 site displayed all stages of gonadal maturation, and some of the adult males were mouth brooding 12-30 embryos. Not all gonadal maturation stages of the catfish were represented at the A2 site, and no mouth-brooding males were observed. GST activity in the liver of S. herzbergii was significantly higher in fish from the impacted site compared with fish from the reference site. Values for the enzymatic activity increased progressively in fish sampled from the reserve area as they became more reproductively mature (immature ≤ maturing ≤ mature ≤ spent). However, the greatest values for GST activity (2.84 ± 0.31 µmol min-1 mg protein-1) among fish sampled from the impacted area were found in (immature) juveniles. These data suggest that changes in hepatic GST activity and mouth-brooding behavior of S. herzbergii can be used as biomarkers of anthropogenic impact.