Adrian,
I googled for closeup images of the Camallanus worm and although I didn't find any, I reckon these will never reach 5cm in my killies... the poor fish will probably be dead by then, with worm sticking out from both the anus and mouth!
If what you saw looked like the following pic, it's one I couldn't figure out either but I know that the brine solution from my BBS hatchery will kill them.

The C. worm normally don't crawl on gravel but sticking out from where the sun don't shine (refer to earlier pics). I can't remember the incubation period of the C. worm's eggs but it won't hurt if you did a search either. Good luck.
I'm back & keeping 'em fingers wet,
Ronnie Lee
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