Effects of days-fasting and refeeding on growth, biochemical and histometric liver parameters in pacu Piaractus mesopotamicus

Abstract This study evaluated the effects of days-fasting followed by days-refeeding on growth, biochemical, and hepatic parameters in pacu (Piaractus mesopotamicus). One hundred and twenty juveniles P. mesopotamicus with initial average weight and length of 47.7 ± 9.2 g and 13.4 ± 0.9 cm were randomly distributed into six experimental units (20 fish per unit) and subjected to treatments: 30 days-fasting followed by 50 days-refeeding, and control group, fed continuously throughout the period. During the fasting period, samples were collected at 10, 20, and 30 days, while during the refeeding period at 15 and 50 days. Animals in the control group were sampled at the same periods. Weight (g), relative condition factor (Kn), and hepatosomatic index (biometric parameters) were measured. Liver assessments were performed. Additionally, glucose, plasma biochemical parameters levels were measured. After 30 days of fasting, hepatocyte density (73.8 ± 1.09%), liver glycogen (14.9 ± 0.87%) and hepatocyte nuclear volume (27.3 ± 0.30 µm3) were lower compared to the control group (82.0 ± 0.67%, 19.4 ± 0.74% and 43.40 ± 0.48 µm3 respectively). The relative condition factor remained unchanged. Cholesterol values, blood vessels, and sinusoidal density increased significantly during fasting. After refeeding, parameters were restored to the control level. On the 50th day of refeeding, the hepatosomatic index was significantly higher than the control group. The results showed that fasting associated with refeeding did not affect fish growth. The period over 50 days of refeeding may influence the pacu's compensation compared to daily-fed animals. The effects of fasting and its relationship with the pacu's physiological response through nutritional status become useful in contributing to feeding practices in P. mesopotamicus fish farming.