I have a few things to consider speaking from personal experience breeding fish as well as being a store owner.
I have bred lots of different fish over the years and have seen many other aquarist breed lots of neat stuff as well. I have found it to be fun and very rewarding successfully breeding and raising the fry. I have also found it to be very time consuming and costly and even frustrating with some (Like shrimp and clown fish) I at one time had big dreams of supporting my hobby or even making money off breeding and selling fish but then reality hit me. Many years ago I had a pretty large scale operation breeding some of the higher end African cichlids and was very successful at it. The problem was finding buyers and maintaining their value. I sold my fish to local and semi local shops & hobbiests and took them to the GCAS auctions to sell. What I learned is that even rare, valuable fish can become worthless real quick if you flood the market with them. In other words, after you sell them to everyone who wants them, you can't give them away. If I had hooked myself up with a good wholesaler (I know that there is / was a local wholesaler at that time - notice I said good) perhaps I could have done better but typically, wholesalers want to buy large quantities at a time, not just a dozen or two at a time and pay very little for them. After I started paying closer attention to what I was spending to maintain all these fish, it was pretty clear that I was not profiting much off it (if at all) It was lots of fun and really cool but it was time consuming and cost, not made money.
From a store owners perspective, I am not interested in paying top dollar for something common that everyone else (both shops and hobbyists) has or can easily get. For example, branching hammer corals, I got lots of them, they are healthy and beautiful but are just about worthless because so many people here locally have done so well with them that they give them away to each other. If someone breeds something else and distributes it to everyone in the club and local shops, it will be worthless really fast too.
If I were to get back into breeding or fragging / growing something to sell, I think that I would do something relatively unique and that can ship easily and inexpensively. Ebay and similar opened up a huge market of potential buyers to sell to once the local demand is filled. Keep in mind the ease of shipping though, persons buying your product expect it to show up un damaged. Hammer corals or xenia for example, although very hardy, they don't ship well, they damage easily.
Speaking from experience, a lot of for thought needs to be put into your process if it is your intention to make money off breeding, growing out & selling live stock for profit. It may cost a lot more that you might think and if your getting into breeding clowns, raising / growing out the fry is extremely time consuming, you can't take a brake from it for a day or two, your fry and food cultures will die.
Doing it for fun is very rewarding and certainly give a person bragging rights but doing it for profit is an entirely different game.