A NEW METHOD FOR FORCE-FEEDING LARVAL FISH

Knowledge of digestive function in fish larvae may provide insight into the problem of poor survival of first feeding larvae, but research approaches to investigate digestion in larvae are limited. To compare the functional development of the digestive system in altricial and precocious larvae, we developed a method for force-feeding radio-labeled nutrients to fish larvae. The method involves micro-injection of diets into the gut of anesthetized and immobilized larvae in a petri dish under a dissecting microscope. Three protocols are described illustrating the application of this method to studies of larval digestive function. To determine the development of acid digestion, pH indicator solution was injected and the gut of the transparent larvae was monitored for color change. To determine nutrient assimilation efficiency, radio-labeled nutrients were injected. After a period of time, counts of the recovery water and the larvae were made using liquid scintillation counting. Finally, to determine sites of nutrient uptake, radio-labeled nutrients were force fed to larvae that were subsequently examined by microscopic autoradiography. The utility of this method is illustrated with observations of protein, polypeptide and free amino acid assimilation in larval walleye (Stizostedion vitreum) and pH changes in larval striped bass (Morone saxatilis).