The development, verification and validation of a bioenergetics growth model for the European minnow,Phoxinus phoxinus, are described. Sensitivity analysis showed that the growth predicted by the model was sensitive to parameters used in the estimates of the energy and dry matter content of the fish and metabolic rate. The model gave good predictions of the form of the growth‐temperature relationship, but failed to predict the growth‐ration relationship well. Validation of the model against experimental data showed that the model underestimated growth at lower rations and overestimated growth at higher rations. Only at low ration levels did the model predict growth rates equivalent to those recorded for a natural population of minnows. Analyses of an empirical regression equation for growth rate, as well as the bioenergetics model, highlighted four areas for future research: (1) the energy content of fish in relation to environmental factors; (2) the feeding metabolism of fish in relation to environmental factors; (3) the regulatory mechanism of long‐term growth; (4) the effect of gonadal maturation on long‐term growth. The identification of these problems illustrates the advantage of a partially explanatory model, the bioenergetics model, over a descriptive empirica