Digestive Gland as a Feed Index for Juveniles of Queen Conch Strombus gigas Reared with Formulated Food

The queen conch Strombus gigas is a marine resource of ecological and economical importance in all the Caribbean countries. A severe depletion of most populations due to over-fishing is forcing the establishment of regulatory measures and closure of fishing areas in most Caribbean countries. Aquaculture programs are developing in Mexico as well as in the USA and some other countries. However, one of the bottlenecks for Queen Conch culture is the lack of well adapted formulated food for optimal growth in high density rearing. Nutrient requirements for conch, as well protein and energy level as micronutrient are unknown. The digestive gland tissues of conchs fed with nine formulated feeds from 19.3 to 38.1% of proteins and 2.6–8.2% of lipids were studied by histological techniques versus the digestive gland from conchs fed with natural algal diet. Digestive gland was fixed in alcoholic Bouin solution and sections stained with a trichrome method including Alcian blue. This histochemical method permitted a detection of proteoglycan molecules. In wild juveniles fed on a natural algal diet, the larger columnar cells contain large proteoglycan granules that occupy most of the volume of the cells. In the digestive gland of conchs fed with various artificial diets, the granular content of the digestive cells is very scarce when compared with conchs fed on natural algal diet. Therefore, the Alcian blue staining may discriminate the nutritional status much better than a simple growth index and help to adjust better the feed formulation and the frequency of feeding to the real need of the juveniles according to their age and size.