My husband and I have been dipnetting on the Kasilof since 2014. This year we noticed more small fish than usual and all but ~5 of the 35 fish we caught had parasites.
The fish in the Kasilof run are smaller than the Kenai fish, so it’s not unusual to hear them called small. This year though, we caught a few that were between 14-16 inches. We let the really small ones go but kept one that was about 16 inches. A few other people around us also let some small ones go. Usually we don’t see that.
The salmon we got pretty much all had parasites. We’ve seen the small coiled anisakid larva and also have seen longer worms that are not coiled. Are those the mature anisakid worms? This year we also saw some worms that were darker red/purple which we haven’t seen before.
We know to cook fish at 153 degrees F for 5 minutes or to freeze at -4 for 7 days to make sure it a safe. In years past we have made caviar from sockeye roe as a treat because the worms weren’t often in the skeins. This year we had a hard time finding skeins without worms. The Cooperative Extension publication on making caviar (published in 2012) says that parasites aren’t often found in the skeins and that people can just pick them out. I spent a lot of time going through two skeins this year to make caviar and probably won't do it again next year.
Jayde Ferguson, Fish Pathologist with the Alaska Department of Fish and Game, writes:
The large darker worms are Philometrid nematodes. The anisakids mature in marine mammals. The longer whitish worms could be the same worms or adults of a related worm, Philonema. They could also potentially be sub-adult tapeworms, it’s difficult to tell from the photograph.
Some parasites have been associated with reduced growth, such as the adult tapeworm Eubothrium (which infects the intestine as an adult). It’s difficult to attribute reduction in fish size to any one factor. Parasitism, other energetic demands, water temperatures, and prey species availability are all important factors that can contribute and there are likely others as well. Pin-pointing any single factor in a wild population is not readily feasible.