Effect of fasting and re-feeding cycles on growth, glucose level, glycogen level, and digestive enzyme activity of Nile tilapia juveniles (Oreochromis niloticus) for cost-effective aquaculture

The objective of this study was to assess the impact of short-term fasting and subsequent re-feeding cycles on compensatory growth performance, blood glucose levels, and digestive enzyme activity in mono-sex juvenile Nile tilapia (Oreochromis niloticus) over a 60-day period. A total of 150 juvenile Nile tilapia (Avg. wt. 9.34 +/- 0.97 g) were allocated into five treatment groups: a control group (continuously fed) and four fasting groups-T1 (1-day fasting), T2 (3-day fasting), T3 (5-day fasting), and T4 (7-day fasting). Re-feeding occurred for 7 days in each group immediately following the fasting period in a recurring cycle. The average weight gain, specific growth rate, and feed efficiency ratio significantly (p < 0.05) declined starting from the T3 group. Blood glucose levels during fasting significantly decreased starting from the T2 group, but after re-feeding, they returned to levels comparable to the control group. The liver glycogen levels significantly (p <= 0.05) decreased during fasting and completely recovered upon re-feeding, while muscle glycogen levels did not show any significant (p <= 0.05) changes throughout the experimental duration. The activities of the digestive enzymes amylase and lipase significantly (p <= 0.05) decreased during fasting starting from T1 and T2 groups, respectively, but after re-feeding, they returned to the levels seen in the control group. In contrast, the protease enzyme levels during the fasting period initially increased up to the T2 group and subsequently returned to control levels in the T4 group. The findings of this study indicate that only the groups that experienced very short fasting periods, specifically up to the T2 group, attained body weights like the control group upon re-feeding due to compensatory growth. Therefore, this study concluded that implementing up to 3 days of fasting followed by 7 days of re-feeding in multiple cycles can serve as a strategy for minimizing input costs in tilapia farming.