Fasting and refeeding in Piaractus mesopotamicus reared in a recirculating aquaculture system: physiological, metabolic, and morphological responses

This study evaluated the physiological, metabolic, and lipid responses of Piaractus mesopotamicus subjected to 15-day fasting and 15-day refeeding cycles in a recirculating aquaculture system. The experiment lasted 61 days. Two hundred fish (45.00 ± 8.36 g; 15.01 ± 1.29 cm) were assigned to two feeding strategies with five replicates: 15-day fasting and 15-day refeeding cycles (CR) and continuous feeding (SR). Fish were fed at 3% of their biomass twice daily. Sampling was performed at multiple time points, and ten fish per treatment were collected for hematological and biochemical analyses, as well as morphological (hepatosomatic index – HSI; intestinal quotient - IQ), histological (liver and intestinal histometry), body composition, fatty acid profile, and digestive enzyme activity. Total cholesterol was higher, and glucose was lower in the CR group. Amylase activity decreased in the CR group, while protease activity was unchanged. HSI and IQ values were reduced in the CR group at specific time points. Histometry revealed transient changes in liver and intestinal parameters in the CR group, with recovery by day 61. Crude protein content was higher in the CR group at days 46 and 61, whereas total lipid content was generally higher in the SR group. The CR group showed increased levels of α-linolenic and arachidonic acids and reduced levels of docosahexaenoic acid. These results indicate that 15-day fasting and 15-day refeeding cycles promote physiological and metabolic adjustments in pacu, with evidence of recovery after refeeding. However, implications for aquaculture management should be interpreted with caution.