Your store-bought Hippocampus barbouri may well be a wild seahorse, in which case it can be very difficult to wean them away from their dependence on live foods and onto a diet of frozen foods instead.
For example, here’s how I described the difference in the feeding habits between wild seahorses and domesticated seahorses in an article in FAMA magazine (Giwojna, Pete. May 2002. "Ocean Rider: A ‘Horse of a Different Color, Part 1." Freshwater and Marine Aquarium):
As you might expect, its many remarkable features and charming habits have long made the seahorse among the most desirable and highly prized of all aquarium specimens. Seahorses breed more readily in captivity than any other marine fish, and sooner or later, virtually every marine aquarist worth his or her salt aspires to keep and raise these exotic animals. Unfortunately, the dietary requirements of wild-caught seahorses are very difficult to meet. Consequently, maintaining them in captivity–let alone breeding and rearing them–is a daunting challenge best reserved for public institutions and the most experienced, advanced hobbyists.
Proper nutrition is the primary problem. In their natural habitat, seahorses feed more or less continuously throughout the daylight hours, consuming great numbers of small crustaceans and other larval organisms that are collectively termed zooplankton. Thus, in the wild, they are free to select prey items from a lipid-rich planktonic soup consisting of countless copepods, mysids, amphipods, ostracods, isopods, shrimps and the larval stages of myriad larger crustaceans. Attempting to duplicate the quality and quantity of the seahorse’s natural diet is a tremendous challenge for the aquarist.
Furnishing wild-caught seahorses with a healthy, balanced diet is thus a painstaking, time-consuming process. It requires collecting live foods in the field, maintaining live food cultures at home, patiently training them to eat nonliving prey and frozen foods, and even conditioning them to accept handfeeding at times. For those fortunate enough to have access to the seashore, field collecting means enduring endless hours of slogging through saltmarshes in search of mosquito larvae and wading knee-deep across tidal flats at low tide to reach tidal pools that might contain amphipods or small shrimps. It means hand-seining seagrass beds for grass shrimps, towing plankton nets, and diving after shoals of live mysids. And it involves long afternoons at the beach toiling tirelessly under the hot sun, shaking malodorous mats of Sargassum and countless clumps of clammy seaweed over your collecting bucket in search of scuds and beach-hoppers. For the inland hobbyist, it means spending your spare time straining stagnant pools for freshwater Gammarus and Daphnia. After a live-food collecting expedition, insect bites, sunburn, and stinging cuts and abrasions on hands and knees are badges of courage proudly displayed by dedicated seahorse keepers everywhere.
Once back home from a collecting trip, it’s time to look after your catch and tend to your live food cultures. For starters, there is the obligatory large grow out tank for brine shrimp as well as separate tanks for raising amphipods and various types of live shrimp (ghost shrimp, grass shrimp, mysids, caprellids). Serious seahorse fanciers have even been known to employ wading pools and outdoor goldfish ponds (minus the goldfish) as their Artemia grow-out tanks. At least one good-sized aquarium is normally devoted to a harem of live-bearing tropicals, usually guppies or–even better–mollies adapted to full-strength saltwater, so the newborn fry they produce so prolifically can be fed to your hungry seahorses. Breeding a single pair of wild-caught seahorses might easily require a half dozen live-food culture tanks plus several refugia, a whole battery of Artemia hatcheries, rows of "greenwater" infusoria bottles, and banks of rotifer cultures in addition to all the live food that can be collected. In short, with its forest of gleaming glassware and glittering apparatus filled with hissing valves, bubbling flasks, and stewing vats filled with mysterious organisms, the fish room of a dedicated seahorse keeper used to resemble nothing so much as an overworked mad scientist’s diabolical laboratory.
Fortunately for the average aquarist, all of that has now changed. A recent breakthrough in marine aquaculture has revolutionized the ornamental fish industry as far as the ever-popular seahorse is concerned. Carol Cozzi-Schmarr and her husband Craig Schmarr, a husband-and-wife team of marine biologists with over 35 years of hands-on professional experience as mariculturists, are doing something the so-called experts had long deemed impossible: successfully raising large numbers of captive-bred seahorses on a commercial basis at Ocean Rider Inc., their state-of-the-art aquaculture facility in Hawaii. Their success at farm-raising tropical seahorses that are pre-conditioned for the captive environment and pre-trained to eat frozen foods means that, for the first time, these fabulous fish are no more difficult to feed and maintain in the aquarium than the average angelfish, and are far easier to breed. For the first time, Carol and Craig have brought the Holy Grail of aquarium fish within easy reach of the average hobbyist. <End quote>
So, Chris, if the seahorse you thought from the pet store is indeed wild-caught, it may be very difficult to train it to accept frozen foods.
I wrote an article that explains how to go about training wild seahorses to eat frozen foods, which may be helpful in your case. It is available online from the Breeder’s Registry at the following URL:
Click here: FAMA Nov 1996. Seahorse Nutrition – Part II: Frozen Foods for Adults
It should give you a pretty good idea of how to proceed, but bear in mind that in several years old; the article was written before the advent of captive bred seahorses and doesn’t apply to farm-raised ponies. Captive bred seahorses are trained to accept frozen Mysis as their staple, everyday diet and should not go on hunger strikes or require live foods at all except as an occasional treat.
As you know, Chris, enriched Mysis is the best frozen food for your seahorses. You might have your best luck if you stick with frozen Mysis relicta from Piscine Energetics, which contains natural order attractants and appetite stimulants to trigger a strong feeding response.
Bonus tip: adding one or two captive-bred-and-raised seahorses that are aggressively eating the frozen Mysis well to the to the tank with your H. barbouri will often do wonders for this sort of problem by encouraging wild-caught seahorses to follow suit.. Many hobbyists find that finicky eaters learn to take frozen mysids much faster and easier when they are provided with teachers to show them the way. The wild horses are often quick to copy their "mentors," learning from their example.
The following link will direct you to some detailed feeding suggestions which discuss proven techniques for thawing and enriching frozen Mysis with Vibrance, as well as a lot of other information that might be helpful. The feeding suggestions are listed in my response to a discussion on the Ocean Rider Club under the subject "Not feeding? Or just pods?" You can read them online at the following URL, so please check them out when you get a chance, Chris:
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:Not feeding…
Best of luck treating your pet-store ponies to eat frozen fare, Chris!