Temperature changes

[blacksmith37]

I just made a mistake that surprised me ( after many years in the hobby,). I took about 20 giant danios out of a pond and put them in a 45g that contained several other fish. The pond is 71, the tank is 79 F; I floated them about 1/2 hour. All the new danios died overnight. The temperature is the only difference i can think of. I have moved fish between tanks with up to 5F difference with no floating. Maybe danios are extra sensitive ?

[Dr Who]

All 20 in one bag? What size bag? Oxygen used?

[blacksmith37]

A gallon milk bottle 3/4 full. no O2. I also put about thirty danios in a 40g (no other fish), and I don't see any floaters. Temp was about 72.

[Brentpitt]

I read somewhere a long time ago that usually moving fish to a tank with warmer temp was not harmful. The fact that you floated them first should have negated that difference anyway. (Although I don't know if a milk bottle would adjust temp the same way a bag would, but still . . . ) How big were the danios? Twenty large danios would use up the oxygen pretty fast, maybe faster than the air would exchange at the surface of the bottle. So how were the fish acting just before and just after you added them to the tank? If they weren't already 'half dead' I would think that they would recover from the oxygen issue after they were placed in the tank. How is the water movement in the 45? A few times I've had issues with inadequate water movement - resulting in poor oxygenation, but when I added aeration or something else to move more water, the fish perked up.

By the way, I love giant danios. I have some that serve as dither fish for African cichlids. When I have them outside in the summer, the grow fast - reproduce fast, and look really good when they catch the sunlight just right.

[blacksmith37]

These were "mill run", 3/4 to 2.5 inch , there were already a couple 3" danios in the tank. I have given my son some, he has about 25 in a 150? African tank , they get along fine. I would say I have good water movement (Emperor 3XX, HOB ).