Fertilized or unfertilized?

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Aquarium Advice Regular
Oct 4, 2023
For once I have a post that is not related to any fish dying ... :cool:

Please see the attached picture, showing portions of my spawning mop with some forktail rainbowfish eggs attached. Is the egg near the top (more opaque) unfertilized (cf to the transparent ones near the bottom)? If so, should I remove it before it develops a fungus?
would probably help if I posted the actual picture ... :whistle:


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If the eggs are clear, they are viable. If they turn all white, they are dead. You should see a yolk inside the clear eggs and that spot will grow but before it gets so big that the embryo fills the entire shell, you should see eyes so you know the embryo is growing. You shouldn't need to pick off the dead ones but if you are seeing fungus on the dead eggs, I would remove them with either a pair of tweezers or siphon the fungused egg(s) with some airline tubing.
If you plan on raising these fry, I'd take the time now to learn about creating infusoria cultures and hatching out brine shrimp eggs. (y)
Egg update

Good morning from the hatchery! :brows:

I removed many solid white eggs from the breeding box (the large majority) and noticed this morning that a couple of the remaining eggs (see picture) seem to have some black in them ... is this a good sign? Are they likely viable?

Also, following up on the infusoria, I found a few recipes online. Is there any particular one that is relatively straightforward (and doesn't require sunlight ... it's dead of winter here) that has worked for you in the past?

Alternatively, I have some high qualify flake food that I can basically grind into dust if that might also work.



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Yes, the clear with black in them are viable. ( I believe I saw the eyes in one of the eggs. :) ) Get yourself a good magnifying glass so you can see inside the eggs. ( I get mine from places like The Dollar Store or Harbor freight if you have them up your way.) They are cheap but they have that small section which is high magnification so you can see in almost as good as using a microscope. (y)

To answer your question about light and infusoria, NOPE, it needs the light. I have used incandescent lights in the past but since they are almost extinct now, you'd need to use a bulb emitting a range of sunlight rays if you have no natural sunlight to work with through a window.

I spoke with a friend up in St John who bred many species of rainbowfish and he remembers the gurtrude going straight to newly hatched brine shrimp so you may not need the infusoria after all. He got the eggs from a company near Montreal called Aquarium Direct. Here's their brine shrimp eggs page: https://aquariumdirect.ca/en/search?controller=search&s=brine+shrimp+eggs
These shrimps apparently are smaller in size than the usual San Francisco Bay or Great Salt Lake brands eggs. One thing when using newly hatched brine shrimp, they are their most nutritious for the first 6 hours +/- after they have hatched so you want to time their hatching with your feeding schedule. In my hatcheries, since I fed 3 times a day, I had 3 different batches of eggs hatching at 3 different times so that they were as newly hatched as possible at feeding times. You'll want to hatch a small sample of eggs to see how long it takes to get them to hatch so you can time it for your schedule. No need to pre-make them.
Now, just to confuse you a little more. ;) you have another option and that is to use the decapsulated brine shrimp eggs. These will not hatch and fish fry are supposed to feed on them. I say "supposed to" because some fry need to see the movement of the food to stimulate the feeding reflex. I have tried using the decaps with mixed success which is why I stay with hatching them out. :whistle:
So there you have your options. (y)
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