Killifish Egg Harvesting

Caring for killifish eggs is one of the more tedious tasks involved with these fishes. There are a number of tricks and several rather diverse methods of incubation. We will share methods we use in taking care of eggs. Only Mop Spawned harvesting and water incubation are discussed on this page.

If you are new to killifish you might be wondering just what you are going to be looking for. When you are dealing with mop spawning killies, the eggs are pretty obvious. But, if you have never had the opportunity to see one, you will be wondering. We took this photo of some Fp. gardneri eggs in a nylon mop. The red worm things at the top of the photo are some "blackworms" that have been caught up in the in mop. They don't hurt the eggs...but they are rather gross. To light colored orbs are the eggs. Grindal worms are great for young Killifish!

Proper egg care starts with the harvesting of the eggs.
Wash your hands! Don't use soap, but put a little more effort into the process than simply rinsing. Start with clean containers, clean water and if you chose to use any tools, they should be cleaned also.

We use a anti-fungicide (Acriflavin) in the water we use to store eggs in. We prepare the water before we start collecting eggs. We use an eyedropper and after we take some of the Acriflavin up into the eyedropper and squirt it all back into the container, we rinse the eyedropper into a quart of clean water and it is that water (which should be tinted a faint yellow if you use Acriflavin) which we use to store the eggs. We put about an inch of the water into small plastic cocktail cups in preparation of the eggs hunt.

We remove the mop from the breeding box and check to make sure that the pair is in the water and not in the mop. Sometimes one or both of the fish will stay in the mop as we take the mop from the water...it is important to keep the fish in the water, especially for this next step...we then squeeze the mop...now you get it...we don't want to squeeze the mop with the fish in it (the fish hate it).

While the mop is damp (we don't let it dry out) we look for eggs. With some pairs, seeing the eggs is very easy. Other pairs challenge you to find their eggs. Some fish lay primarily in the top portion, some the bottom. Some lay in groups of eggs, some scatter them all through the mop. You will have to find which "style" your fish choose and focus your efforts on that part of the mop.

The first time you work with a particular pair and especially a new species, you might want to take note of where the fish tend to lay. It will make your subsequent harvests move a lot more quickly. The first time or two, we generally check each strand of the mop. We get a better feeling of what we are dealing with. After a time or two we can be a little more casual about the search.

So what do you do once you find an egg? We use cocktail cups to water incubate those eggs that call for it along with a cover system that is used for sauces from fast food places. The lids snap on and are not air tight but they do cut down on the evaporation. The cups we use are only 5 ounces each. We keep them on large plastic trays similar to the ones in cafeteria lines. We can put 20 of the 5 oz. cups on each tray and stack the trays 5 high.

When you find an egg, gently remove it from the yarn with your fingers. Eggs which are very fresh may pop between your fingers. If the first couple of eggs you attempt to lift from the mop pop, put the mop back into the water and wait a couple of hours and re-check the mop. Apparently the eggs are rather soft for the first couple of hours after they are laid. When you have the eggs between your finger, put the eggs in the cup of water and kinda roll it off into the water.

When you are done harvesting the eggs...label the cup. You will forget what is in it if you don't...I know you think you won't...trust me on this issue. You will find it helpful to put the name of the fish and the date of the harvest on the cup...not the lid. The lid may be set next to another lid and...well it gets hectic and confusing sometimes. When you label the cup, use a water-proof marker.

If you put too many eggs into a cup you may find (like we did) that the tendency to fungus increases. When one egg funguses, there are usually more to follow and when the eggs are crammed into a cup, the likelihood of spreading fungus increases. For most species we put no more than 25 eggs in a cups. With some of the Rivulus species, we put 15 because the eggs are larger and when they go bad, they go bad...big. We also found that covering the cups is not a bad idea, but covering them air tight and putting too many eggs into the cups is extremely risky and is generally a bad thing to do. . Vinegar Eels are a super first food for Killifish!

On the second day we check the cup for funguses, infertile or dead eggs (white ones and furry ones) and we remove those with an eye dropper. On the third day the water is changed. We use treated water for the water change. Some people chose to use clean water for all water changes.

Changing the water becomes an easy process with just a little practice. We gently swirl the eggs in the cup and set the cup down for a minute or two. The good eggs drift to the center and the bad eggs, which are generally lighter than the healthy eggs continue to swirl around...decant the water and the bad eggs into a second container. The second container is to give some protection just in case a good egg is decanted by mistake. When the water is decanted, pour about an inch of the Acriflavin tinted water into the cup. Check for fungused eggs daily and remove them as they are found.

At the end of a week, change the water again. This time, instead of using treated water, use clean water without fungicide. Any benefit of using a fungicide is probably exhausted in the first week and the chances of hardening the shell of the egg may be an issue to be concerned about.

Check the eggs daily and keep the cups filled with water. The eggs don't do too well if you let the cups dry out. If you have covered the cups like we are suggesting, you will not have too many problems trying to hatch crispy eggs.

Remember that the eggs are living organisms. They should be kept at the proper temperature and out of bright lights. You don't have to keep them dark and they don't have to be 80 degrees...room temperature and out of direct light usually works. If you don't know the ideal temperature for incubation a particular species...try 75 degrees and see what happens.

The length of time it takes to hatch varies between the various killifish. Some may take only a week or so...others take several weeks. Temperature has a lot to do with the time it takes. We consider 2 weeks to be about average and use that as a target when working with a new fish.

Once a cup is found to have newly hatched fry in it, we remove the lid and leave it off for the rest of the use of the cup. The fry are removed soon afterwards but the removed lid is a signal of which cups need to be harvested. We have several cups of the same species/location hatching at the same time, so we frequently sort the cups and harvest all of the same species at the same time, combining them into shoe boxes as we go.

What about the newly harvested fry

If you are having trouble hatching a batch of eggs or if it seems to be taking too long...email us and we will walk you though the process and talk it out with you.
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