Zebrafish Cruelty

So I just did the most horriblest thing to my little baby zebrafish, ever.

We're working with embryos that are 24, 48 and 72 hours post-fertilisation. On Monday, I paired a male and female fish but of course kept them separated by a clear screen to build up the sexual tension. On Tuesday, I removed the screen and they made lots of babies which I collected and incubated. Yesterday, I took some of them, used pronase to digest the chorion, fixed them in PFA and then put them at -20C in MeOH.

That was all fine.

It was today that was horrible. This morning, it was time for the 48hpf. As only some of them still had a chorion, I had to use tweezers to physically tear it apart as using pronase on all of them would kill the ones without a chorion. As soon as you release them from the chorion, they spaz and swim like crazy. Even when I took them out of the incubator, some of them were already trying to swim for freedom! Anyway, I then used a pipette to choose 30 of the best looking ones. That wasn't easy at all. They instinctively try to swim away from the pipette, as if they already knew what was coming...

So I had 30 reasonably calm fish in my eppendorf tube. I then added the paraformaldehyde, and seriously, they wriggled like crazy. It was like a fishy death camp. After about 10s, the wriggling ceased and they were again just flaccid fish embryos that I'd been working with for the last few weeks.

I think it was the wriggling that got to me. Even yesterday's 24hpf embryos were fine - they weren't quite developed enough to wriggle for freedom. I guess they were totally innocent and helpless. Tomorrow's 72hpfs should be interesting. They must hate me so much!