Oh har har, very funny :p Despite your feeble attempts at derailing this thread, I'll steer it back on track!
Since I started out with a fish parasite, I'll do another fish pest.
Oh Darwin, what's happened to these fish? Why, they have fallen victims to malevolent lampreys! Lampreys are jawless and relatively "primitive" fish that are much closer related to hagfish than they are to cod and salmon. Some of them are parasitic and use their funnel like mouth full of sharp little teeth to latch onto their prey. Then they bore a hole into their victims with their sharp, jagged tongues and live off their bodily fluids.
Some of the sea lamprey species reportedly get very large and are even rumoured to attack swimmers.
Once a month, they crawl up on beaches and howl at the moon. Or - at least it would be cool if they did. Watch out the next time you go for a swim in the sea, a lake or a river!