Yes, the Domino Clownfish is a new, melanistic form of the false percula clownfish (Amphiprion ocellaris), which I like to call the "Nemo" clownfish. As such, it should do splendidly with large seahorses such as Mustangs and Sunbursts (Hippocampus erectus).
However, like all clownfish, a Domino Clownfish color morph is an aggressive eater that will have a taste for frozen Mysis, so you should be aware that such clownfish will occasionally attempt to dominate the feeding station. Should that prove to be a concern with your Domino Clownfish, Gwen, then you would need to target feed your seahorses in order to make sure that they get their fair share at mealtime, as explained below:
Target feed your seahorses and remove uneaten leftovers promptly.
The individual personalities of seahorses naturally extend to their feeding habits. Some are aggressive feeders that will boldly snatch food from your fingers, while some are shy and secretive, feeding only when they think they’re not being observed. Some like to slurp up Mysis while it’s swirling through the water column, and some will only take Mysis off the bottom of the tank. Some are voracious pigs that greedily scarf up everything in sight, and some are slow, deliberate feeders that painstakingly examine every morsel of Mysis and stare it down forever before they accept or reject it. Some eat like horses and some eat like birds. So how does the seahorse keeper make sure all his charges are getting enough to eat at mealtime? How does the hobbyist keep the aggressive eaters from scarfing up all the mouth-watering Mysis before the slower feeders get their fair share? And how can you keep active fishes and inverts with seahorses without the faster fishes gobbling up all the goodies before the slowpoke seahorses can grab a mouthful?
Target feeding is the answer. Target feeding just means offering a single piece of Mysis to one particular seahorse, and then watching to see whether or not the ‘horse you targeted actually eats the shrimp. Feeding each of your seahorses in turn that way makes it easy to keep track of exactly how much each of your specimens is eating.
There are many different ways to target feed seahorses. Most methods involve using a long utensil of some sort to wave the Mysis temptingly in front of the chosen seahorse; once you’re sure this has attracted his interest, the Mysis is released so it drifts down enticingly right before the seahorse’s snout. Most of the time, the seahorse will snatch it up as it drifts by or snap it up as soon as it hits the bottom.
A great number of utensils work well for target feeding. I’ve seen hobbyists use everything from chopsticks to extra long tweezers and hemostats or forceps to homemade pipettes fashioned from a length of rigid plastic tubing. As for myself, I prefer handfeeding when I target feed a particular seahorse.
But no doubt the all-time favorite implement for target feeding seahorses is the old-fashioned turkey baster. The old-fashioned ones with the glass barrels work best because the seahorses can see the Mysis inside the baster all the way as it moves down the barrel and out the tip. By exerting just the right amount of pressure on the bulb, great precision is possible when target feeding with a turkey baster. By squeezing and releasing the bulb ever so slightly, a skillful target feeder can keep a piece of Mysis dancing at the very tip of the baster indefinitely, and hold the tempting morsel right in front of the seahorse’s mouth as long as necessary. Or if the seahorse rejects the Mysis the first time it drifts by, a baster makes it easy to deftly suck up the shrimp from the bottom so it can be offered to the target again. In the same way, the baster makes it a simple matter to clean any remaining leftovers after a feeding session. (You’ll quickly discover the feeding tube is also indispensable for tapping away pesky fish and invertebrates that threaten to steal the tempting tidbit before an indecisive seahorse can snatch it up. And it’s great for tapping on the cover to ringing the dinner bell and summon the diners for their gourmet feast!)
Other hobbyists prefer a large glass eyedropper or disposable plastic laboratory pipettes for target feeding frozen Mysis to their ponies. Such utensils are considerably smaller and lighter than a cooking baster, making them easier to maneuver and control with one hand. Because of their smaller size, they may appear to be less intimidating to new seahorses when they are first learning your new feeding regimen, and timid seahorses are therefore less likely to be leery of them or to shy away from. In the case of the disposable laboratory pipettes, they can simply be discarded at the end of the day, which simplifies cleaning. As a rule, anything you can do to make the feeding process cleaner and more sanitary will be beneficial to your ponies.
For these reasons, many hobbyists find large eyedroppers made of glass or disposable laboratory pipettes to be ideal for target feeding their seahorses, as shown in the photos below:
In short, target feeding allows the hobbyist to assure that each of his seahorses gets enough to eat without overfeeding or underfeeding the tank. And it makes it possible to keep seahorses in a community tank with more active fishes that would ordinarily out-compete them for food, since the aquarist can personally deliver each mouthful to the seahorses while keeping more aggressive specimens at bay.
The key to keeping active specimens like firefish or compatible clownfish or cleaner shrimp successfully with seahorses is to feed the other fish and inverts with standard, off-the-shelf aquarium foods first, and once they’ve had their fill, then target feed the seahorses.
Okay, Gwen – providing you are willing to hand feed or target feed your seahorses to make sure they get their fair share at mealtime, should it prove necessary, then I would approve of your plan to include a Domino Clownfish as a tank mate for your ponies. It helps that your Domino Clownfish is captive-bred-and-raised, but it’s always best to quarantine new arrivals before you add them to your main tank to make sure that they are completely healthy.
Good luck! Best wishes with all your fishes, Gwen!