COMMON MARINE PARASITES

Isopods

There are many types of isopod, and not all are parasitic. Wood lice or pill bugs, which you might find under rotting wood in the garden, are a kind of isopod. Parasitic isopods range in size from 1 to 5 centimetres, with females generally far larger than males. Like many parasites, they’re very specific about the host species they'll infect, as well as whereabouts on the body they'll attach. There are several types of parasitic isopods: scale-attaching, flesh-burrowing, mouth-living and gill-attaching – I will admit, they’re all pretty gruesome sounding, but fascinating nonetheless. Although they rarely kill the host, they can cause localised lesions, reduced growth and behavioural changes.

One of the best known and macabre of the isopods is the cymathoid tonguebiter. When small, the parasite crawls into the fish’s mouth through the gills and attaches to the tongue. Over time it devours the tongue and takes its place in the mouth. The fish can even use the new tongue-shaped parasite to grip and swallow prey. It is actually the female that we can see; her partner is located further down the fish’s throat.

LEFT PAGE ABOVE Certain copepods attach themselves to the outside of fishes. They often have a pair of egg sacs, which extend from the animal LEFT PAGE BELOW Like many of the parasites depicted here, this isopod hasn’t previously been recorded by...