Abstract
Since bioenergetics models for 0+ fish have seldom been validated by field consumption estimates, field‐based and indirectly estimated daily food rations were compared in larval perch Perca fluviatilis and zander Stizostedion lucioperca. Field‐based estimates were calculated with linear and exponential evacuation rates based on gut fullness data during a 24‐h cycle, with hourly field samplings instead of the normally recommended 3‐h intervals. Indirect calculations used bioenergetics modelling with variable activity multipliers ( A ). Field‐based estimates of daily rations ranged between 0·21 and 0·27 g g −1 day −1 in perch (mean L T 13·1 mm) and 0·31–0·40 g g −1 day −1 in zander (mean L T 10·6 mm). The higher values were calculated by using the exponential model. Daily rations calculated by bioenergetics modelling with A = 1 were only slightly higher than direct estimates in both species. However, if A values >1 were used, calculated daily rations were substantially higher than direct estimates. Estimates of daily ration based only on every third value ranged between 41 and 72% compared with 1‐h intervals, mainly because of lower estimates of evacuation rate.