Metabolic Responses to Cyclic Fasting in Juvenile Turbot (Scophthalmus maximus)

Feed accounts for the majority of aquaculture production costs, making strategies that reduce feed input without compromising growth economically attractive. This 72-day study evaluated the effects of cyclic fasting regimens on growth, body composition, and liver transcriptome in juvenile turbot (initial body weight 5.54 g). Fish were assigned to a control group (CON) (continuously fed) and three cyclic fasting groups: fasting for 1 day followed by refeeding for 3 days (FT1RF3), fasting for 2 days followed by refeeding for 6 days (FT2RF6), and fasting for 3 days followed by refeeding for 9 days (FT3RF9). The FT1RF3 regimen showed potential for inducing compensatory growth, with final body weight comparable to that of the CON and a numerically lower feed conversion ratio. Minimal differences in protein, amino acid, and fatty acid compositions were observed across groups. FT1RF3 was associated with broad metabolic suppression, enhanced fatty acid utilization, heightened innate immune preparedness, and promotion of cellular renewal. In contrast, FT2RF6 and FT3RF9 resulted in systemic lipid accumulation and numerically lower final body weights, with the metabolic strategy appearing to shift toward survival-oriented energy storage at the expense of somatic growth. Overall, juvenile turbot exhibited period-dependent responses to fasting: FT1RF3 showed potential for inducing compensatory growth through metabolic adaptation, whereas fasting for 2-3 days suggested a tendency toward metabolic dysfunction and growth suppression. These findings provide a scientific basis for applying cyclic fasting regimens in aquaculture, with fasting durations tailored to fish developmental stages.