Shiners and creek chubs will kill themselves is a container with square corners. I keep them alive in 5 gallon buckets filled about 1/2 full of pond water with an aerator and a 2 liter ice bottle. Rarely do we loose any.

I have a 6x6 fish pen in my pond and put my left overs there for another day of fishing. Luckily, I have a spring fed pond and the fish pen is located right over the spring. I did find the need for an aerator in the pond during the Aug Sept hot dry times. Other than that, they survive year round.