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Quantification of Fish Feed Intake with the Model MAXIMS: Evidence for Severe Underestimation of Daily Ration

H. Richter, C. Lückstädt, C. Schlechtriem, U. Focken & K. Becker

One of the principal fish feeding models used in recent years is the MAXIMS model based on the Elliott-Persson model, which calculates daily ration of fish showing diel feeding periodicity with continuous feed intake in the feeding period. The model has often been used on filter feeders such as Nile tilapia, Oreochromis niloticus L. and milkfish, Chanos chanos Forsskål but recent investigations have suggested that this model tends to underestimate consumption. In order to verify the model under conditions where total food intake is certain, two experiments were conducted with these species and the model prediction compared with the known ration.

Milkfish (mean wt: 15.4g) were kept in a 3000l concrete tank at constant salinity and temperature, acclimatised for six weeks, starved for 36 hours prior to the experiment and given suppplemental feed at 3.3% body mass equivalent (% BME, dry:wet basis) in five equal doses at hourly intervals. Starting one hour before feeding, three fish were sacrificed every hour for 13 hours and stomach contents weighed. Nile tilapia (mean wt: 182g) were stocked in 36 solid-bottom cages in a fishpond and given 1.9% BME in a single ration. Subsamples of 12 fish were collected every two hours for 18 hours, starting four hours before feeding. Different cages were used for each subsample to avoid disturbing the fish. No unconsumed food was found after the experiment in either case. Both data sets were analysed with the SAS 6.11 version of MAXIMS; the data for individual fish was used in preference over subsample averages.

Daily rations of 1.76 and 0.87% BME for milkfish and tilapia respectively were predicted by the model, both considerably below the true value. Previous studies have suggested that the stomach is evacuated at a faster rate in the case of multiple meals or continuous feeding. A re-analysis with the evacuation rate doubled in the feeding phase gave ration estimates of 2.76 and 1.05% BME for the two species respectively; additionally the estimate for start of the feeding period became more realistic in the case of milkfish. These results demonstrate a strong need for the assumptions of the MAXIMS model to be verified and possibly modified.