Dinner Time, Parasite Time

My sweetheart, socialized in the Philippines loves fish. She loves it grilled, steamed or deep-fried. Especially deep fried. With rice.

I also love fish. I love them as people. I grew up keeping South American freshwater fishes in tanks, and spent countless hours observing them. The teenage fishkeeping really paved my path to becoming a biologist. These days, I enjoy few things as much as watching fish behave in their natural habitats, underwater, in the ocean.

I’m not a big fish eater. I’m not fundamentalist about that, and if there is absolutely no other source of protein, I’ll eat it. But I don’t like the taste very much, and I do think that it’s particularly good for you. Many parts of the country where we live are pretty overfished, so someone else can have the fish meant for me to eat, thank you.

So, one dinner time last week said sweetheart brought home some sardines from the fish market (where the fish are usually not on ice … another reason I’m not too keen on eating them). When opening up the gills of one of the fish, we saw this:

It turned out these were fish parasites, isopods of the family Cymothoidae (thanks to Prof. Paul Sikkel for the ID!). They suck blood out of the gills of the fish, which is a good blood-sucking spot, since the gills are rich in blood vessels. Of the ~20 fish which came over for dinner, 4 had parasites on them. The parasites covered about half a gill. That must have caused serious problems for the affected fish!

Curiously, the parasites had fairly big compound eyes. They live in the dark – below the fish’s gill cover, where there is little light. Do they use vision to get to the fish in first place? It seems so. There is a very old paper on the topic. The eyes are also very pretty blue.

Best Fishes,

Klaus

The paper I mentioned:

Beddard, F. E. (1888). XIX.—On the Minute Structure of the Eye in certain Cymothoidæ. Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 33(2), 443-452.