i usually catch a bunch o baby blugill and sunnies about 1/4-1/2 " put them in a 5 gal bucket. keep them in my room over night next to my 29 gal. the in the morning i put them in it, the tank stays at 75 deg. F. naturally but has a heater so it does not drop below 72 deg. , just in case. i let the bluegill and sunnies grow to about 2" to the point where i can see exactly what is what , and the colors start to develop. i pick about 3-4 of them i want, then either let the rest go were i got them or go catfishin. when they get about 5" they go in with my oscar in the 75 gal. Ive done this about 5 times, only the first 2 were in a ten gal, then put into the 29. that was b-4 i got my 75....
p.s. to make them feel even more comfortable, float plastic plants at the top. they like to hide in thses more than in rocksa and rooted plants, or burried plastics. i would also recomend plastic plants 'cause the BG like to "garden". theye tear up everything IMO.