An adult male Blue Gularis Killifish.

I have been talking about killifish in my last few blogposts—I am in absolute awe of them. The way they reproduce is just amazing. In this installment, I am going to show you another very interesting phenomenon—the process of eclosion.

When I got some eggs of Blue Gularis (Fundulopanchax sjoestedti) in peat, I simply put the peat in a cup and filled the cup with water. In an hour or so when the peat settled on the bottom, I could see free swimming fry. That made me wonder, how does this happen? How fast does it happen?

To answer these questions, I decided to take closer observations. I took some eggs from the peat, placed them in a petri dish, wet them, and made video of the whole process. 

Eggs that I took out of peat. Eggs have some kind of a sticky material on them that makes them stick to anything that they come in contact with. In aquaria it can be mop or peat.

An “eyed up” egg. Eyeing up of the eggs means that the embryo has developed (or is developing) inside the egg and the eye of the embryo is visible.

After soaking the eggs for 5-10 minutes, you can see movement inside the eggs. You can clearly see the fry moving inside as if they are trying to find the best spot to come out from. In the next 5 minutes they start breaking the egg shell and you can see tails or heads emerging from the eggs.

After 10-15 minutes of soaking the eggs in water, process of eclosion is visible. You can see tails and heads coming out of the eggs

I repeated this documentation process a couple of times. It was my observation that around 80% of the time it was the tail that came out first. Only a few times a fry came out the headfirst.

Within a few more minutes the entire fry was out of the egg’s shell:

After coming out, it takes another 2-3 minutes for them to get their act together. When they come out, they bump into other eggs as if they can’t see properly. They also swim strange as if they don’t have sense of direction. In a few minutes they learn all of it and in the next 10 minutes they even start picking on micro worms.

Here is the video that I made. The video shows the progression in ascending order. Wetting the eggs, movement inside the egg, eclosion and then finally free swimming fry.

I hope you all enjoy these observations as much as I enjoyed making them.

-Sumer.