Investigations on feeding rates, feeding frequency and compensatory growth of gilthead sea bream, Sparus aurata (L.)

Abstract

Three growth trials were performed on S. aurata, which is of importance to the aquaculture industry in the Mediterranean region. In the first investigation, a feeding trial was conducted to investigate the influence of feeding rates on the growth performance. Five feeding rates were employed, 0.5, 1.0, 1.35, 1.7 and 2.0% body weight (BW) /day. The fish increased in body weight, with time for all feeding regimes. At the end of the trial, the feeding rate of 1.7%BW/day gave the best growth performance in terms of SGR, but this growth was not significantly higher (p < 0.05) than that observed with 1.0%BW/day. The feeding regime of 1.0%BW/day gave the best performance and improved feed utilisation overall with regard to food conversion ratio (FCR), feeding efficiency (FE), protein efficiency ratio (PER), apparent net protein utilisation (ANPU) and apparent net lipid utilisation (ANLU). This should be seen both in the light of economical as well as environmental implications. No important differences were observed in the carcass and fillet composition or condition factor (K). Histological studies showed an increased lipid deposition in the liver with increased feeding rates. In the second experiment, a feeding trial was carried out to investigate the influence of feeding frequency on growth performance and food utilisation. Five feeding regimes were employed, once/day (morning), once/day (afternoon), twice/day, 3 times/day and 4 times/day. The best growth performance with improved food utilisation was obtained in feeding frequencies once a day (in the morning) and 4 times a day. SGR, FCR, FE, PER and ANPU were significantly similar (p < 0.05) for both these feeding regimes. From the point of view of food utilisation, feeding once a day in the morning may be considered the optimum feeding frequency. No important differences were noted in the carcass and fillet composition or the condition factor and hepatosomatic index. Histological studies showed an increased of lipid deposition in the liver with increased growth performance. In the third study compensatory growth was investigated. A feeding trial was carried out to investigate the possibility of using the phenomenon of compensatory growth to improve growth and food utilisation. Five feeding cycles were employed: daily feeding, one week of starvation followed by one week feeding (1:1), two weeks of starvation followed by two weeks of feeding (2:2), three weeks of starvation followed by three weeks of feeding (3:3) and six weeks of starvation followed by six weeks of feeding (6:6). By the end of the trial, fish subjected to a feeding cycle of 3 weeks starvation followed by 3 weeks satiation feeding produced comparable results in terms of growth performance to fish that were fed daily. These showed improved food utilisation in terms of FCR, FE, PER, ANPU and ANLU compared to those on the other treatments. Carcass and fillet analysis of protein, lipid, moisture and ash showed some differences with the most notable being the relatively higher moisture levels in both carcass and fillet, as well as the relatively lower crude lipid levels in both carcass and fillet. Histological studies showed that lipid deposition in the liver of fish fed on 3:3 and on the basis of daily satiation was higher than in the rest of the fish. The studies provide evidence of the adaptation of the fish to starvation followed by what may be termed compensatory growth, once feeding was resumed.