Ammonia-N efflux rate and nutritional state of juvenile pink shrimp, Penaeus paulensis (Perez-Farfante), in relation to food type

The effects of squid flesh, two pelleted diets containing 41% and 53% protein, and starvation on the ammonia-N efflux rate and the biochemical composition of pink shrimp, Penaeus paulensis (Perez-Farfante), were investigated. A transient increase in the ammonia-N efflux rates of shrimp subjected to starvation was observed. Ammonia-N efflux rates of shrimp fed the diet with 41% protein were lower than in those fed the diet with 53% protein or squid flesh. Ammonia-N efflux rates were inversely related to body weight, except during starvation, which affected mainly small individuals. Increased ammonia-N excretion rates increased immediately after the ingestion of high-protein diets. Such rates were also found to be higher during light periods (cf. dark periods), possibly reflecting differences in activity levels. Dietary-related alterations in the blood, muscle and midgut gland constituents were also detected. In general terms, starvation tended to reduce the levels of such constituents, whilst pelleted diets promoted increases in lipid and carbohydrate concentrations.