The ability of Nile tilapia to regulate protein and energy intake evaluated by carbon relative enrichement
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The aim of this study was to assess the ability of Nile tilapia to balance its own diet, when two ingredient mixes were offered, using carbon stable isotopes. In order to accomplish that, 225 Nile tilapia juveniles (average initial weight 5.0 g ± 0.5 g) were distributed in five tanks, each containing a group of 45 fish. One group of fish were fed exclusively with a high protein mix (HPM; δ¹³C = -22.62‰), the second one fed only with a low protein mix (LPM; δ¹³C = 14.34‰). The other groups fad free access to both mixes (free choice system). The fish from all tanks were fed four times a day. Muscle, liver and blood samples were collected at each five days (from 2 fish/tank/collection) for 86 days, except for the fish fed with LPM (fed for a 120 days period). The samples were analysed in a mass spectrometer and proportions of the mixes consumed were estimated through its carbon isotope enrichment (δ¹³C). Energy intake slightly decreased after the 50th day and protein consumption increased after the same period. However, consumption did not present a clear pattern in relation to the individual weight, i. e., protein consumption patterns are mainly related to the age of the individuals and it is not clear if it is also correlated to their weight. Additionaly, this technique allowed the observation of differences regarding consumption among the individuals from the experimental group.