I killed 20 or more sticklebacks from similar lack of knowledge, fished them out of a running stream with my net. Brought them home and made a garden 'location' for them in a small plastic ice cream box. Next morning they were all floating and I was devastated to have caused their death. I did not know about oxygenating water, or that maybe 1 stickleback might have survived in that tub, but not 20.