Thanks Tom, but I tried the one I had laying around from back when I bred goats. I used it for castrating my baby bucks. I didn't like it for that because the poor animal walked around all scrunched up for a week. I ended up doing it the old fashioned way, with a scalpel blade. Plus the dogs gathered around for the testicle treat every time. On the fish bags I didn't think that those bands gave a very secure seal.
I used the heat sealer on the breather bag when I shipped a ram last week. The fish arrived alive and well even after being a day late. I think the heat sealer does the best job, I just need to get the better quality one.