Digestibility in Sarotherodon niloticus fry: Effect of dietary protein level and salinity with further observations on variability in daily digestibility

Dry matter and apparent protein digestibility coefficients were determined in Sarotherodon niloticus fry of mean weight 21 mg maintained on four artificial diets with protein content ranging from 9.6% (Diet 1) to 30.4% (Diet 4) at salinities of 0‰, 5‰ and 10‰. The total digestibility estimates made using faecal material accumulated through the night did not significantly differ (P > 0.05) from those estimates based on faecal material collected during the day time, between feedings. The mean apparent total, protein and energy digestibility of the different groups of fry ranged from 56.7% to 69.1%, 71.7% to 87.1% and 73.6% to 83.9%, respectively. The dry matter digestibility, in all experimental groups of fry, showed a significant decrease when the dietary protein content changed from 9.6% to 30.4%. Salinity had no significant effect on the digestibility of any of the four experimental diets. In S. niloticus maintained on Diets 3 and 4 at salinities of 5‰ and 10‰ the total and protein digestibility showed daily variation. Generally a day or two of high digestibility was followed by a day of low digestibility. The possible utilization of this rhythmicity, whether apparent or real, in aquacultural practices to reduce the feed costs is suggested. © 1984.