Video #1 of the critters.

I have a separate tank that I want to use for breeding. Last week, I had my gourami breeding pair in there. But, then, my angelfish laid eggs on my glass cleaner, so I took the gouramis out and put the angelfish eggs in. The temperature is around 27 Celsius. The eggs all turned grey and none hatched.

But now, I see these other critters on all the surfaces.

I think they may be daphnia, water fleas. But I'm not sure, having never seen them before. So I'm looking for verification, or information on what they actually are.

Also, could these critters have caused the failure of the angel eggs hatching?

Do I need to get rid of these before I try to breed the gouramis again, or are they a good source of food for the breeding gouramis and their fry?

Update 1:

It looks like they could also be ostracod, copepod, or amphipod. It would help if I could get a better view of them!

Update 2:

Video #2 of the critters.

I've been dosing the tank with yeast, as per fedding Daphnia. The critters seem to be doing well. They're not getting bigger, but they're active. After adding yeast the water clears up in two to three days. It's still not a certainty, though.

Update 3:

Confirmed, these are copepods of the cyclops variety. I was able to borrow a microscope and take a look. Pictures for the pleasure of the reader: enter image description here enter image description here enter image description here

  • The way you ask sounds like you know what you are doing. So, no offens meant with a possibly silly question: how exactly did you move the eggs?
    – Layna
    Oct 24, 2017 at 10:59
  • The angels laid them on my tank scraper (goo.gl/sVLYk4). So I transferred it to a bowl with tank water, carried it over to the breeding tank, and put it in there. I didn't need to disturb the eggs at all.
    – Richard C
    Oct 24, 2017 at 11:38
  • 2
    @Henders the one concern that I have is that every video I've seen of daphnia, they have a pinkish colour, where the guys in my tank are white. Now I know there are over 6000 species, so that does not rule it out.
    – Richard C
    Oct 24, 2017 at 12:37

1 Answer 1


You have copepods in your tank, the type is cyclops; be aware they often carry parasites like dinoflagellates.

They are a good startup food for fish fry but have lower nutritional value than Daphnia (water fleas).

Here is some additional reading in this Wikipedia article about copepods.

It is not likely they themselves are the reason your fish eggs died, but the dinoflagellates they carry can infect the eggs; I am not saying they have, but it is possible.

Next time you get fish eggs, take all the water you need for your hatching tank from your main tank to be sure the pH and chemistry is the same, and to reduce the risk of unwanted parasites.

  • That looks about right! Thanks! The water from my breeding tank did come exclusively from my main tank. So that must be something that I have in the tank, but the tank cleaners keep it under control. When the water had no cleaners, they were allowed to thrive. FYI, according to what I've read, copepods fall into the broad category referred to as water fleas. I'm reading into the risk posed by dinoflagelates, and how to eradicate them without killing the copepods. I really want to use them for fry food :D
    – Richard C
    Oct 31, 2017 at 8:27
  • I was fortunate to be able to borrow a microscope from a colleague. I got some great shots of these guys! You're exactly right. At 100x magnification, I could see them clearly, and with your information, confirm your identification. Thanks!
    – Richard C
    Nov 1, 2017 at 19:02

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