Mitigation of pathogens and marine biotoxins contamination in shellfish

Abstract

The EU FP7 funded project “Bio-engineered micro Encapsulation of Active agents Delivered to Shellfish (BEADS)” is focused on mitigating the impact of marine biotoxins (ASP/DSP), microbial contamination (bacteria/norovirus) and the parasitic protozoan Bonamia ostreae on shellfish aquaculture. Purpose: to develop probiotic diets and a microencapsulated delivery system in the digestive tract of shellfish to improve depuration. Feeding experiments were performed to identify the optimum size of alginate microcapsules, testing three different sizes and colours containing nondegradable fluorescent dye microbeads. Oysters and mussels were placed in tanks containing filtered seawater. Three sizes of microcapsules were mixed and shellfish were fed for 3 hours. Shellfish were removed during the feeding period at 0.5, 1, 2 and 3 hours and dissected. Any capsules remaining in the water and in the digestive organs of shellfish were extracted and measured using a fluoroskan analyzer. A higher concentration of the smaller capsules was found in the digestive gland, indicating that the smaller capsules were preferentially ingested. The ingestion increased during the three-hour period. Fluorescent beads of different colours embedded in alginate capsules were observed bound to the mucus string. Mussels were more efficient than oysters in incorporating alginate beads that were observed by light microscopy as intact in the digestive gland of mussels and oysters during feeding period. Broken alginate beads were found in faeces. During passage through the intestine, active agents embedded by alginate capsules are released into the digestive gland providing a useful tool to transport active agents.