This study evaluated the effects of short-term exposure to sublethal levels of nitrite on oxidative stress parameters and histology of juvenile Brazilian flounder Paralichthys orbignyanus. An assessment of fish recovery was also performed. Fish were exposed to 0.08 (control), 5.72, 10.43, and 15.27 NO-N mg L for 10 days followed by the same recovery time. Gill, liver, and muscle samples were collected after 1, 5, and 10 days of exposure and after recovery for the measurement of antioxidant capacity against peroxyl radicals (ACAP), glutathione-S-transferase (GST) activity, content of non-protein (NPSH) and protein thiols (PSH), and lipid peroxidation levels by thiobarbituric acid-reactive substances (TBARS) content. Nitrite exposure induced alterations which compromised the overall antioxidant system (reduced ACAP and GST activity) and enhanced oxidative damage in lipids and proteins. Increases in GST activity and NPSH and PSH contents were also demonstrated. The recovery period allowed for resumption of basal levels for all (treatment 5.72 NO-N mg L) or some of the evaluated parameters (other treatments). In conclusion, exposure to nitrite concentrations from 5.72 to 15.27 NO-N mg L induced oxidative stress and antioxidant responses in juvenile Brazilian flounder. The 10-day recovery period was sufficient for a complete resumption of basal physiological condition of fish exposed to concentrations of up to 5.72 NO-N mg L.

In this study, the influence of temperature variation on the blood and oxidative stress parameters of pacu Piaractus mesopotamicus juveniles was evaluated. Fish were subjected to gradual changes of temperature, over 5 days, by 24°C until reaching to experimental temperatures 18, 21, 24 (control), 27 and 30°C. There were significant differences (p < .05) in glucose and lactate of blood in both the haematological relationships and oxidative stress parameters. Glucose levels increased at 30°C and decreased at 21°C. Lactate levels were highest at 18°C. While the haematocrit was higher at all altered temperatures, haemoglobin levels decreased at 21°C and increased at 30°C, causing alterations in haematimetric indices. In the liver, glutathione‐S‐transferase (GST) activity was reduced at 18°C while antioxidant capacity against peroxyl radicals (ACAP) was highest at 30°C. Thiobarbituric acid reactive substances (TBARS) increased at 18, 21 and 27°C. In the muscle, ACAP decreased at 27 and 30°C and TBARS increased at 30°C. The results indicate that the species shows sensitivity to temperature variations. Accordingly, we conclude that with short‐term temperature variations >3°C, it is possible to induce higher alterations in the observed parameters in pacu juveniles.

No abstract

This study aimed to evaluate de effect of the exposure to sub-lethal levels of ammonia on blood parameters and flesh quality of juvenile pacu (Piaractus mesopotamicus), including assessment of such parameters post recovery in ammonia-free water. Juveniles (27.1 ± 5.4 g) were exposed to concentrations of ammonia at 0.0 (control); 0.5; and 1.0 mg N-NH3 L-1 for 10 days followed by the same period of recovery in ammonia-free water. On the 10th day post exposure and after a recovery period, samples of blood were taken for glucose, lactate analyses and evaluation of haematocrit. To evaluate lipid peroxidation, proximate composition and sensory analysis, samples of muscle/fillets were also obtained. Exposure to ammonia caused alterations in haematological response and negatively affected sensory analysis of pacu fillet. However, proximate composition was unchanged and lipid peroxidation process was not intensified in muscle. In conclusion, exposure to sublethal levels of ammonia induces secondary stress responses and altered the organoleptic characteristics of pacu flesh. Nevertheless, a recovery period of 10 days was sufficient to allow for a complete restoration of the homeostasis and organoleptic characteristics of the fillet.

Pacu (Piaractus mesopotamicus) lives in tropical and subtropical regions of South America, mainly in the Plata Basin and the Pantanal. Pacu can survive under conditions of low dissolved oxygen (DO), being considered a hypoxia-tolerant fish (Rocha-Santos et al., 2018). In Pantanal ecosystems, pacu migrates to smaller streams, channels and floodplains during the flood season. After the floods recede, many of them remain behind in shallow lakes and basins which can extend for miles, where the amount of DO may vary from hypoxia to normoxia (Cunha Bastos et al., 2007). In addition, the natural habitat encompasses a wide range of temperatures from 12 to 32°C