Status of the digestive gland and feed index in juvenile green abalone Haliotis fulgens fed rehydrated macroalgae

One of the bottlenecks in cultivating juvenile green abalone Haliotis fulgens is the lack of well-adapted natural or formulated food for optimal growth. The goal of this study was to analyse the digestive gland structure of juvenile green abalone fed rehydrated natural feed, Ulva sp. (Chlorophyta), Eisenia arborea, Macrocystis pyrifera, Egregia menziesii (Phaeophyta) and Porphyra perforata (Rhodophyta), using histochemical techniques. Structure of the digestive gland was described, and proteoglycan granules were detected in the digestive cells. The abundance of granules was variable, depending on the feed provided to the abalone, and this was reflected in their growth. Granular content in digestive cells fed Ulva sp. was scarce, leading to low growth rate and high feed conversion ratio (FCR). Digestive cells of juveniles fed E. menziesii led to the best nutritional condition, including many proteoglycans cellular granules, best weight growth rate and a low FCR. Histochemical analysis of the digestive gland, differentiated by a modified Goldner trichrome method that included Alcian blue, was a useful tool for determining the nutritional status of farmed abalone, therefore recommended for assessing adjustments to the natural feed or formulation to meet the nutritional needs of abalone.