Royal Netherlands Institute for Sea Research

Rare parasite on thicklip mullet

On Friday morning 12th June, Dennis Mosk and Maureen Sikkema found a thicklip mullet in the NIOZ fyke with a large parasite attached to it’s anal fin. They regularly find parasites on fish from the NIOZ fyke, but this type of parasite is not so common.

Dennis Mosk and Maureen Sikkema emptying the nets.

A rare one

Between March and October, the NIOZ fyke is checked upon every day. Caught fish are identified and measured at NIOZ. Parasites are regularly found on fish but this was a rare one. We found a parasitic isopod, a large female with a length of 25mm. Probably this is the species Nerocila orbignyi,  an external parasite of fish which attaches itself with the recurved dactyls at the ends of its prehensile legs. But species from the Nerocila genus are very similar in appearance and difficult to identify. The parasite is preserved for further analysis.

Another remarkable parasite

A few weeks before we found another remarkable parasite on a sprat that was caught in the NIOZ fyke. This time it was a parasitic copepod called Lernaeenicus sprattae. These parasites are commonly found on the eyes of sprat, but in this case the parasite burrowed into the spine of the sprat. This species of parasite is only found on sprat. Sprat is a small marine fish in the herring family.