Unless a retailer can obtain good quality fish from you when they want them you will not be in the same class as a wholesaler that can supply them what they want when they want it. If you breed a type of fish once you will not get a good price because you are a bigger risk than a wholesaler that has to carry stock to be able to supply what retailers want. You can sell privately and get more and when the shops find out they will not buy from you. Welcome to the real world. As importing costs go up---and I am sure they will, locally bred fish should become more atractive to the shops but you will need to obtain a reputation to get top dollar. You basically have to provide better fish at a better price when they want them to take the market from their present wholesaler---not easy from your back yard.