The aim of this study was to gain insight into how Nile tilapia (Oreochromis niloticus) regulate feed and energy intake in response to diets low and high in starch and cellulose. It was hypothesized that high-starch diets would reduce feed intake due to the effect of high blood glucose level, and that stomach volume may limit feed intake of fish fed diets low in energy. Four experimental diets, low starch-no cellulose inclusion, high starch-no cellulose inclusion, low starch-with cellulose inclusion, and high starch-with cellulose inclusion, were formulated. The high-starch diets and diets with cellulose inclusion were 17.5% more energy-diluted than the low-starch diets and diets without cellulose inclusion, respectively. Two weight classes of male Nile tilapia were studied in two separate experiments: Exp I (50 g fish) and Exp II (375 g fish). Fish were fed to apparent satiation for six weeks. In 50 g fish, feed and digestible energy intake of fish fed diets with cellulose inclusion increased and decreased by 8.3% and 5.5%, respectively, compared to fish fed diets without cellulose inclusion. This suggests the role of stomach volume in restricting feed consumption. Fish fed high-starch diets achieved only 0.5% more feed intake and 13.9% less digestible energy intake than fish fed low-starch diets. The lower increase in feed intake and higher decrease in digestible energy intake of fish fed high-starch diets than of fish fed diets with cellulose inclusion suggests that high blood glucose suppresses feed intake in Nile tilapia. An alternative explanation for the differences in feed and digestible energy intake of fish fed different diets was based on the fact that heat production was not influenced by starch nor cellulose inclusion levels. Thus, under satiation feeding, oxygen uptake capacity may determine feed and digestible energy intake in fish rather than blood glucose or stomach volume. In 375 g fish, feed intake, digestible energy intake and energy partitioning did not differ among the experimental diets. This was due to the high variation in the observed variables of the replicates within experimental groups, being related to large differences in group behavior between replicates. By behavioral observation, aggression levels were scored per tank. Diets did not affect the observed behavior. Inclusion of aggressive behavior parameters as co-variables into the analysis significantly explained part of the variation in maximal feed intake and energy partition. This demonstrates that group feed intake in big tilapia (>375 g) can strongly be determined by the group behavior (i.e., aggression levels).
|Title of host publication||Abstracts of the XIIIth International Symposium on Fish Nutrition and Feeding: Fish and Crustacean Nutrition: Present Knowledge and Future Perspectives, 1 - 5 June, 2008, Florianopolis, Brazil.|
|Publication status||Published - 2008|
|Event||XIIIth International Symposium on Fish Nutrition and Feeding: Fish and Crustacean Nutrition: Present Knowledge and Future Perspectives - |
Duration: 1 Jun 2008 → 5 Jun 2008
|Conference||XIIIth International Symposium on Fish Nutrition and Feeding: Fish and Crustacean Nutrition: Present Knowledge and Future Perspectives|
|Period||1/06/08 → 5/06/08|