Join a fish or aquarium club in your area and you can sell your fish to some of the other members and at the fish club auctions. Many clubs have 2-3 auctions per year where you can take your extra fish and make enough money to buy their food and maybe pay for some or all of the electricity used to keep the tanks going. That is what I do.
I live near Cleveland, OH and there are 6-7 clubs within an hour and a half of my house. Each one has 2-3 auctions a year. I buy most of my new fish at these and the prices are quite reasonable. It is about the same as paying wholesale price for the fish.
I spawn and sell bushynose plecos, hi-fin cory catfish, many different species of cichlids, shrimp and some livebearers.
Do not try to breed and sell common fish like tetras, danios, barbs and things you see all the time in the pet shops, the oddball and seldom seen fish are the ones people want.
Very few people can make a profit from the fishkeeping hobby. You would need many, many tanks (some for breeding, some for grow-out, some for display). A friend of mine has over 100 tanks in her basement and makes a little money, but not much. She ships all over the US, sells at auctions and gives talks at the various clubs on breeding and fish room set-ups.
If you have some fish that are out of the ordinary, you might try putting them on one of the fish auction sites online (like aquabid.com). Check them out and see what kind of prices different fish are selling for and then decide what fish you want to start breeding.
Good luck, it is a great hobby. Mine has almost paid for itself over the last few years. Feel free to email me if you have more questions you think I might be able to answer.
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