Unsightly bass parasites cause no harm to humans

Unsightly fish parasites reported in bass almost statewide are not harmful to humans, according to the S.C. Department of Natural Resources, and little evidence exists that the parasites cause significant harm to fish.

An increasing number of anglers are reporting strange "sores" or "maggot-like worms" in the mouths or on the gills of some of the striped bass they have caught. What they are likely seeing, according to the S.C. Department of Natural Resources, is a parasitic copepod of the genus Achtheres. These are one of several external parasites that attach to the oral cavity of a number of both fresh and saltwater fish species. In a severe infestation of Achtheres it may appear as if numerous maggot like worms are attached to the inside of the fish’s mouth and gills; hence the common term "gill maggots."

Anglers should be aware that while these organisms are unsightly, they have not been linked to any fish mortalities in South Carolina. There is little evidence that Achtheres causes significant harm to an otherwise healthy fish. In cases of severe infestations, a secondary bacterial or fungal infection may result, which could further stress or compromise the health of the fish. Similar "outbreaks" that have occurred in other states have generally subsided after a period of time without any measurable impact to the fish population. Also, the parasites are not harmful to humans, and fish infected with the parasite remain safe for human consumption as they are destroyed by cooking and are not found in the flesh of the fish.

The life cycle of Achtheres requires several stages to complete. The adult female copepod attaches itself to the mouth and gill structures of the fish by means of an anchoring structure known as a bulla. Here it feeds on the soft tissues and blood of the host fish. In time the female produces two sacs containing eggs. Upon hatching as free-swimming nauplii, this stage soon molts into copepodids and are now infectious to other fish. These young copepods seek out and attach themselves to a new host and further develop into a life stage known as a chalimus. As adults, the male copepod moves freely on the host fish, while the female attaches permanently, where it begins its egg producing cycle again.

The first reports of Achtheres in South Carolina occurred several years ago in striped bass caught in the lower Saluda and Congaree Rivers. Since that time, the parasite has been confirmed in striped bass from Lake Murray and Santee as well as in spotted bass in Lake Keowee. It is also been found on largemouth bass in several other Southeastern states. It is likely that Achtheres will be documented in other lakes and rivers and possibly other fish species in South Carolina in the future.

DNR protects and manages South Carolina’s natural resources by making wise and balanced decisions for the benefit of the state’s natural resources and its people.