Back in mid-December I collected a couple of small intertidal fishes and brought them back to the lab for observation and identification. Then the female laid a batch of eggs, which I’ve been watching ever since. Today the eggs are 15 days old. They are developing pretty quickly, I think, at ambient seawater temperatures of 12-13.5°C. Some of the changes can be seen with the naked eye, while others are visible only with some magnification.
Here’s a timeline of development for the first couple of weeks in the earliest life of bald sculpins.
Day 4: The egg mass is clean and the eggs are clear and pink. The very young embryo can be faintly seen as a paler pink strip lying on top of the darker pink yolk, which fills most of the internal volume of the egg. There are also some oil droplets associated with but not part of the yolk.
It wasn’t until this day that I was convinced the eggs were alive. Until then they looked like undifferentiated pink blobs with not a lot going on.
Day 7: Today they had eyes! And they were swimming around inside their eggs!
Day 10: Today the eyes look more like fish eyes and are taking on a silvery sheen. Black pigment spots are forming along the dorsal surface of the embryos, and the yolk is noticeably smaller. The eggs are starting to look dirty to the naked eye, due to the darkening eyes and pigment spots.
Today was the first day I could see their heartbeats! It was surprisingly difficult to capture the beating hearts with the camera.
Day 15: Some of the eggs have died, becoming opaque and hard. A few have broken open and are empty. The overall color of the egg mass is paler, as the larvae are consuming their yolks. The black pigment spots are becoming more prominent and seem to be concentrated on the top of the head.
They look like baby fish now! They’re still flipping around inside their eggs and I think may be responding to light. They don’t seem to like it when I shine the light on them.
I’ve put together a short video of the eggs at various stages of development so far.
Let me know what you think!