While not a breeder, I'd like to perhaps make a few comments on this thread from the retailer's perspective.
First off - simply an echo of the common consensus that A. ocellaris is our bread and butter. I sell very close to twice as many Ocellaris as all other clownfish varieties combined, and I tend average somewhere between eight and a dozen species, roughly twenty to twenty five SKU's of clownfish in total, in stock at any given time. We do purchase some wild clownfish - primarily full-adult mated pairs, though we also purchase a fair number of wild "onyx" Percula clowns.
Of the non-Ocellaris species, Perculas are far and away the best-selling for us. Clarkii, Bicinctus, and Polymnus are next, with the single-band species and maroons bringing up the rear. Small Tomato and Rubrocinctus sell fairly well, but only when small enough to still retain their extremely bright red-orange colour.
We've seen maroons take a very sharp decline in popularity over the past two years. They sell fairly well when they're large - four inches plus - to customers with predatory fish-only aquariums, but they sit in our tanks aside from that.
Moving on from clownfish, there are three other major groups of fish I'd love to see more of: Jawfish, Cardinalfish, and Gobies.
Of the jawfish, we're able to fill roughly half our demand for Dusky (Opistognathus whitehurstii) and about a fifth of our demand for Yellow-head/Pearly jawfish with locally captive-bred fish. Occasionally we'll have a breeder bring in a couple of Bali Tiger (undescribed as far as I know, sorry for the lack of a proper name), but those are the only two species out of the half-dozen or so varieties we try to stock that I can get any quantity of captive-raised. Yellowhead/Pearly jawfish are the species that are needed in quantity. Not Ocellaris quantity, no, but I sell roughly one yellowhead jawfish for every four ocellaris clowns - on par with A. percula, and far more than any of the other clowns. They've been steadily getting more and more expensive of late, too - average wholesale for me is now US$8-12 a fish, up from US$5-6 just a couple of years ago. If you can figure out how to make $10-15 a fish profitable, they'll be a mainstream seller. Opistognathus rosenblatti isn't going to be mainstrem, but wholesale has been creeping up from the US$38-40 they were a few years ago...$52-60 is about average for that species now, and that seems like it could be worth some investigation to my non-breeder mind.
Of the cardinals, S. nematoptera is pretty readily available cultured and isn't as popular as it used to be anyway. The huge demand for P. kauderni isn't going anywhere - we have several local breeders working with them and purchase them from ORA whenever they have them available...and we still can't meet demand for them. They're just not worth importing these days (of the final six batches of wild Kaudern's we brought in, over 80% died within the first three days), so we're stuck with whatever we can find captive-bred. Apogon leptocanthus is becoming quite popular - we don't have a captive source for it yet. There are at least half a dozen different cardinalfish species that come in under the trade names of "dwarf" or "Japanese" cardinalfish that seem to be several things - ideal ultra-peaceful reef fish, wildly popular, and next to impossible to identify. There's certainly potential there.
With the flourishing popularity of nano-reef tanks, I think the gobies might perhaps be among the most interesting prospects for captive-breeding. There are so many unique little fish that are going to be lost to the trade as CITIES and other import/export restrictions grow. Too many of the dwarf, nano, and shrimp gobies we bring in sell before we can even attach a scientific name to their tag. Local enthusiast breeders are probably the only hope of keeping some of these fish in the trade, long-term.
But, this thread is about marketablitity...and there are some species that are clearly marketable. The obvious one is Gobisoma oceanops, the every-day cleaner goby, though all the species in the oceanops-complex are certainly popular. The smaller shrimp gobies - Amblyeleotris randalli, A. fasciata, A. guttata, A. wheeleri, and Stonogobiops nematodes are the most popular for us. The Yellow Watchman Goby isn't as popular as it used to be, but it's a good staple goby. Amblygobius hectori and rainfordi are both quite popular. Some of the sleeper/sand-sifting gobies sell in massive quantities, and I've never seen/heard of anyone even making an atttempt at raising them. Valenciennea puellaris, strigata, and wardii are the most popular three, with the first outselling the other two at least six to one.
If there's one commercially-raised group of fish I've never fully understood, it's the dottybacks. Some sell in okay numbers, but they're just not that popular a group of fish. If you've got them, I'll certainly buy them...but I'm going to be calling you about more Ocellaris, more Perculas...not orchid dottybacks. And absolutely no hybrids. I certainly have to make decisions that make the ethics-centre twitch all the time, but as
MWP has stated a few times, why waste the time and facilities when there are other
species that you could be breeding?
Speaking as a retailer, I'm not going to buy them.