Effect of food deprivation on physiological parameters and muscle quality of Nile tilapia ( Oreochromis niloticus )

Food deprivation is a pre-harvest management practice that can alter body composition and muscle quality in cultured fish. This study compared growth performance, physiological indices, histological characteristics, muscle texture, proximate, fatty acid and amino acid content between food-deprived and normally fed Oreochromis niloticus over a 30-day period. Food deprivation significantly reduced specific growth rate (SGR), and liver somatic index (LSI) after 15 days and body weight (BW), weight gain rate (WGR), SGR, viscerosomatic index (VSI) and LSI after 30 days (p < 0.05), whereas condition factor (CF) and visceral fat index (VAI) did not differ significantly between treatments. There were no significant changes in activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and aspartate aminotransferase (AST) after food deprivation. Muscle hardness was significantly greater in food-deprived O. niloticus than in normally fed O. niloticus after 15 days (p < 0.05). Micrographs from food-deprived O. niloticus showed liver cells to be slightly irregular in shape, with some showing signs of dispersion and vacuolization; in addition, the intestine showed substantially more pronounced vacuolation, enlarged intercellular spaces and shortened villi compared with normally fed fish. Muscle crude protein content was significantly higher in food-deprived O. niloticus than in normally fed O. niloticus (p < 0.05); however, this increase may partly reflect a relative concentration effect associated with lipid depletion rather than an increase in absolute protein deposition. Serine and tyrosine concentrations were significantly higher after 15 days of food deprivation than in normally fed fish; the reverse was seen for total lipid content (p < 0.05). After 30 days of food deprivation, muscle n-3 PUFA content was significantly lower, whereas the n-6/n-3 PUFA ratio was significantly higher, than in normally fed fish (p < 0.05). These findings indicate that a 30-day food deprivation period reduced growth performance and altered muscle composition and texture, while producing only limited changes in the physiological indicators examined.