Fish parasite?

[kgr320]

My fish have been down for the count for the past week, my betta especially. He started with a low appetite and listlessness, but now only moves once or twice a day, stays at the bottom of the tank with labored breathing and no appetite. I saw him flashing once but now he seems just too tired. At first I thought it might've been bacterial infection, which he's been prone to having but then I spotted these little things crawling around the glass and swimming through the water column. They're extremely small, just under one millimeter long to less than half that, white or colourless, wriggling free swimmers or climbers, they sort of looked like really tiny shrimp. I saw one swimming out from between the bettas gills and have noticed up to a hundred of them, hanging about the rest of the tank. Attached is a picture of one, which I caught in a little test tube and examined under my microscope at X120 magnification with a pink-red stain and gum medium. They're extremely active swimmers, and are all over the place. They kind of look like silverfish larvae, are they a parasite?

 

[mfdrookie516]

Looks like a copepod to me. They're harmless crustaceans, most fish will eat them too. Some saltwater fish live primarily off copepods.

 

[kgr320]

Do they pose any threat to fish in large numbers? I haven't introduced any new water or fish to the aquarium so I don't understand how there can suddenly be hundreds of them.

 

[HN1]

I agree with MFD that it looks to be a FW copepod, probably a species of cyclops. They should be harmless and a good source of hunted food for small fish.

Fresh Water Copepod Crustaceans: Introduction with photomicrographs of copepods (Cyclops, etc.).

 

[BigJim]

+1 for MFD and HN1. Looks harmless to me.

What are your water parameters?