Mytilicola intestinalis

Mytilicola intestinalis is a parasitic copepod belonging to the order Cyclopoida and the family Mytilicolidae. Often referred to in aquaculture as the "red worm," it is a significant pest that infects bivalve mollusks, particularly mussels. While not a plant pest in the traditional agricultural sense, it is a primary concern for the health and economic viability of shellfish aquaculture industries globally.

This parasite primarily targets commercial bivalves such as the common mussel (Mytilus edulis) and the Mediterranean mussel (Mytilus galloprovincialis). It is widely distributed across European and Mediterranean coastal waters. Because it lives internally, its presence can go unnoticed until significant impacts on the stock's health and market quality become apparent.

The life cycle begins with planktonic larval stages that inhabit the water column. These larvae enter the mantle cavity of the mollusk host through its filtration system. Once inside, the copepodites migrate to the host’s intestine, where they anchor themselves to the epithelial lining. Here, they mature into adults, feeding on the food particles that the mussel has captured, essentially stealing nutrition from the host.

The damage caused by Mytilicola intestinalis is multifaceted. By living in the digestive tract, the parasite damages the gut lining, leading to inflammation and reduced digestive efficiency. This systemic drain on the host results in several negative impacts:

• Significant reduction in the condition index (meat quality).
• Reduced growth rates and lower yield for producers.
• Increased susceptibility to secondary diseases and environmental stress.
• Potential mortality in cases of heavy infestation density.

Managing this pest requires a proactive approach centered on farm management. Reducing stocking densities is essential to prevent rapid transmission between individual mussels. Furthermore, stringent biosecurity measures, such as monitoring the health of seed mussels before translocation to new areas, are critical to preventing the spread of the parasite. Regular sampling and histological examination of stock are the primary tools used to determine the level of infection and guide management decisions.