Evacuation of pelleted feed and the suitability of titanium(IV)oxide as a feed marker for gut kinetics in Nile tilapia
H. RICHTER, C. LÜCKSTÄDT, U. FOCKEN AND K. BECKERDepartment of Aquaculture Systems and Animal Nutrition, Institute for Animal Production in the Tropics and Subtropics (480b), University of Hohenheim, 70599 Stuttgart,Germany
(Received 5 September 2002,Accepted 30 July 2003)
The present study assessed the suitability of titanium(IV)oxide, TiO2, as a digesta passage marker in Nile tilapia Oreochromis niloticus and studied the shape of the evacuation curve in this species. In three separate trials, fish were given one dose of either 0.5, 0.25 or 0.1% of their body mass (% BME) of feed marked with 1% TiO2 or 0.5% BME of the same feed without marker. The fish were serially slaughtered at intervals after feeding and the stomach contents analysed for dry mass and marker content. The data for individual trials were analysed with the linear, square root, surface area and exponential evacuation models and variable comparisons showed that, although the marker interfered slightly with the evacuation process, true meal size could be predicted more accurately from the marker data. The results of an analysis of the combined data sets suggested that stomach evacuation in this species is dependent more on food particle surface area (surface area model) than on stomach content mass (exponential model) as is generally assumed. On the basis of these results, it was concluded that TiO2 at an inclusion level of 1% is an acceptable marker for quantifying evacuation with a view to predicting food consumption but should be used with caution in digestibility studies.
Key words: feed marker; mathematical modelling; Nile tilapia; stomach evacuation; titanium(IV)oxide.
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