river rat, some of the benefits of pumping water from your pond through the barrels is that you would probably not need to feed the fish as they will eat the food from the pond water, also you will not need filtration or need to worry about water quality issues.

The downside with however you hold the fish will be cold weather. If the barrel water drops much below 37* the fish will likely die. A flow through will help keep the water temps higher. Pump water from a couple feet deep in warm months and from the bottom in winter months.