A recreational angler was surprised to find worms in the ovaries of a Dusky Flathead; Fisheries Officer Martin Angle contacted me.

Ovaries and worms
Ovaries and worms Image: Martin Angle
© DPI Fisheries

The 48 cm long fish was caught by Rodney Ralston in Wallis Lake, near Forster, New South Wales. The fish appeared to be very healthy despite the thread-like worms that were discovered while the fish was being cleaned. The largest worms were 12 cm in length.

Rodney reported that "the worms appeared to be attached to, and possibly feeding from, the sac wall." Naturally he was curious, as was I. Despite working in 'the fish world' for over 30 years, it was the first time I had heard of a fish with wormy gonads.

I contacted Stephen Keable the Australian Museum's Marine Invertebrates collection manager. Steve in turn contacted Kate Hutson at James Cook University, who advised us that the worms were philometrid nematodes.

Kate told us that these worms don't have common names but if we called them ‘gonad roundworm’, people would know what we are talking about.

Kate further stated that:

"Philometrid nematodes parasitise male and female fish, with infection usually associated with spawning individuals. The testes can undergo extensive atrophy, while heavy infections in the ovaries can lead to necrosis of the oocytes. They can reduce the reproductive potential of the host fish. Not recorded to be dangerous to people... so tuck into those fish cakes made from roe!"

Apparently these worms are frequently found in the gonads of fishes. So now you know, and so do I.