Fish Gill Isopods

Type: Chesapeake
Region: Various
Location: Potomac and Choptank Rivers and in Middle, Gunpowder and Tred Avon Rivers.

We’ve been recording anomalies found on fishes in our surveys and thought we’d share some information about one of the more common parasites found on several Chesapeake game fish. The fish gill isopod (Lironeca ovalis) is a small (up to 1 inch) crustacean that uses hooked feet to attach to a host fish underneath the gill flap. The fish gill isopod can be found on medium-sized (smaller than harvestable) white perch, striped bass, and bluefish. They can also attach to menhaden, silver perch, spot, and weakfish. These parasites do not feed off of their host fish but simply use them for a free ride. They rarely kill the fish but do tend to weigh them down and slow their growth. So if you’re about to throw a fish back with a fish gill isopod, consider pulling the crustacean out so the fish has a chance to grow even bigger for next time it may be caught!

Although the parasites tend to be more abundant in the saltier systems, we have recorded them in tributaries of the Potomac and Choptank rivers and in Middle, Gunpowder and Tred Avon rivers.

Tags: fish gill isopod, white perch, striped bass, bluefish, menhaden, silver perch, spot, weakfish