Tessellated Darter Problem

I recently collected a large group of small tessellated darters from the Brandywine river in Delaware. I now have them in an aquarium, and several have died in the past week (though most appear healthy). Before death, they breath quickly, and die with the mouth open. The ammonia and pH levels on my tester read safe, so my only guess is temperature...the tank has been around 82-84 this week from all the heat. In anyone's experience with tessellated, is this too high a temperature? Thanks.

Yeah, sustained temperatures in the 80s F will likely induce respiratory stress and failure. Ones I caught on Cape Cod years ago in August were in a pond with 76 F water, and I'd be surprised if their thermal tolerance was much higher.

With high temperature comes low dissolved oxygen. I was able to keep sculpin alive at 85F for a weeks time when my AC kicked it last year mainly because of the low fish population, lots of plants, and good water agitation. Also, check your nitrate levels to make sure they are low.

With high temperature comes low dissolved oxygen. I was able to keep sculpin alive at 85F for a weeks time when my AC kicked it last year mainly because of the low fish population, lots of plants, and good water agitation. Also, check your nitrate levels to make sure they are low.

I second that. Keep the surface water agitated and good aeration. This will maimise your oxygen levels. It's 81 in my tank right now and my assortment of darters are happier than pumpkins. Also some plants give off more oxygen than others such as anarchis. My tank is heavily planted. I would bet my oxygen level is close to saturation for the temperature it is at.

You also have to consider the time of year. Catching large numbers of a fish that is relatively heat intolerant in the hot weather will stress them out big time and kill them pretty easily. I won't collect anything until the weather gets cooler because I don't think I can keep enough fish alive to be worth it. It sucks because I have a tank that is way understocked right now and I want to get some fish for it but I have to wait.

If you can't wait until cooler weather, take less at a time so as not to crowd the bucket and add a lot of salt and novaqua or stress coat or something like that. Move them fast, and SLOWLY acclimate them to the new tank temperatures before putting them in.