A Simple Method for Estimating the Food Consumption of Fish Populations from Growth Data and Food Conversion Experiments}

Experimental data on the gross food conversion efficiency of fishes (KI growth increment/food ingested) are usually reduced to a model of the form K I = aWb ; it is shown that the model K I = 1 (WIW_)~ has a number of advantages over the traditional model. The new model can be used to compute the food consumption per unit biomass of an age-structured fish population, by relying on the first derivative of the von Bertalanffy growth formula (VBGF) to express growth increments, and the identity of W~ in the VBGF and in the model expressing KI as a function of weight. Computed examples, using published growth and mortality parameters, and the results of food conversion experiments were used to obtain consumption estimates in a carnivorous grouper (Epi'MPMI1Ul !J'I'ttatus) and an herbivorous angelfish (HolacantkU8 berm:uMlI8is). Results were shown to be most sensitive to the parameter (I. Various applications of this simple model are discussed, particularly as a method to estimate key inputs in J. J. Polovina's ECOPATH model. A multiple-regression extension of the basic model is presented which accounts for the impact of factors other than body weight on values of K I and (I. This method is illustrated with an analysis of data on dab (Lil/la7lda limanda).