Parasite (Trematoda) – Yellow Grub (Clinostomum), White Grub (Posthodiplostomum minimum)
These parasites are small and cause yellow or white cysts (spots) in fish skin, muscle tissues and in most internal organs that resembles coarse salt sprinkles.
All species of fish in Minnesota lakes and rivers are susceptible. Fish that inhabit shallow areas are most affected.
Eggs are released by fish-eating birds into the water. Eggs develop into intermediate stages of the parasite in snails. These free-swimming parasites penetrate the muscles of fish and encyst, taking on the form of the yellow or white grub. Infected fish are consumed by birds where the life cycle starts all over again. Adult worms are seen in fish-eating birds.
Very common throughout Minnesota. Low infectivity does not appear to affect the fish’s health.
Yes, although unsightly, the fillet is safe to eat if it is well cooked. Always cook fish well before consuming.
There are no practical means to control this parasite.
Unused or uneaten portions of fish should be buried or disposed of with household waste. Fish entrails should never be discarded back into the lake.