Effects of temperature on zootechnical performance, metabolic, hematological and oxidative stress parameters in pacu Piaractus mesopotamicus
Pacu (Piaractus mesopotamicus) is a native species from South America, which presents great potential for aquaculture, being currently the second most cultivated native species in Brazil. However, its creation can be limited by the wide thermal variation of the region where it inhabits: tropical and subtropical. Thus, the present thesis aimed to determine the effects of temperature variation in the short and long term, evaluating blood, oxidative stress, and growth performance parameters. Two experiments were performed (E1 and E2), in which the fish were exposed to four temperature variations (E1 - from 24 °C to 18, 21, 27 and 30 °C) for a period of 5 days and at five different temperatures (E2 -18, 21, 24, 27 and 30 °C) for 45 days. At E1, at the end of the experimental period, blood, liver and muscle samples from nine fish were collected per treatment. Glucose levels increased and decreased as the temperature ranged from 24 to 30 and 21 °C, respectively. Lactate levels were higher when the temperature ranged from 24 to 18 °C. Hematocrit increased at all temperature variations and hemoglobin levels decreased and increased when the temperature ranged from 24 to 21 °C and 30 °C, respectively. In the liver, glutathione-S-transferase (GST) activity was reduced when the temperature ranged from 24 to 18 °C, while total antioxidant capacity (ACAP) increased when the temperature ranged from 24 to 30 °C. The concentration of thiobarbituric acid reactive substances (TBARS) in the liver increased when the temperature ranged from 24 to 18, 21 and 27 °C. The concentration of non-protein thiol groups (NP-SH) in the liver decreased when the temperature ranged from 24 to 18, 27 and 30 °C, while the concentration of protein-thiol groups (P-SH) decreased and increased when the temperature ranged from 24 to 21; and 27 and 30 °C, respectively. In muscle, ACAP decreased when the temperature ranged from 24 to 27 and 30 ° C, and TBARS increased when the temperature ranged from 24 to 30 °C. The concentration of NP-SH in muscle did not change, whereas the concentration of protein thiols increased when the temperature ranged from 24 to 18 °C. At E2, at the end of the experimental period (45 days), biometric analyses were performed and blood, liver and muscle samples from nine fish were collected per treatment. With the biometric analysis, was observed that the growth increased proportionally with the temperature. Food intake and feed conversion rate increased, while protein efficiency decreased with increasing temperature. In the proximal fillet composition, the ethereal extract increased and the humidity decreased with temperature. In addition, the protein content was lower at 18 and 30 °C. Growth and feed intake showed a positive correlation (R2 = 0.95), while food consumption and protein efficiency showed a negative correlation (R2 = 0.89). The robust fit curve between the protein efficiency ratio and the protein content in fillet was best at 21 °C. With the hematological analysis, was observed that the levels of glucose, hematocrit and hemoglobin were higher at 27 and 30 °C. Lactate levels were higher at extreme temperatures of 18 and 30 °C. Pacus raised at 18, 21 and 27 °C showed lower ACAP in liver and muscle. GST activity in the liver was lower in fish raised at 18 ° C, while in the muscle there were no differences. Based on the linear regression method, the content of P-SH and NP-SH in the liver had a positive relationship with water temperature: P-SH (R2 = 0.90) and NP-SH (R2 = 0.90). However, in the muscle, the thiol groups presented lower and higher concentration in the fish grown at 27 and 30 ° C and 18 ° C (P-SH), and 21 ° C (NP-SH), respectively.. The content of TBARS, in muscle and liver, was related to water temperature. Based on the polynomial regression method, the temperature at which the lipoperoxidation levels are lower is 24.09 and 22.16 ° C for muscle and liver, respectively. The results obtained in the exposure of variation in the temperature of the water in the short term indicate that temperature variations above 3 oC can induce major changes in hematological parameters and cause oxidative damages in pacu juveniles. Regarding the prolonged exposure to different temperatures, it was observed that, although the alterations in the hematological parameters allow the creation of pacu at 21 to 27 ° C, however, in order to preserve the muscle, organ of greater commercial importance, the best temperature is 24. 09 °C, where the lipid peroxidation is lower. Although pacu juveniles show a positive growth relationship with temperature, the best protein efficiency in relation to food consumption is between 21 and 27 ° C, reflecting a better meat quality. Thus, we conclude that variations in water temperature above 3 °C are detrimental to pacu and the best breeding temperature is between 24 and 27 °C.