That’s a problem that crops up all too often with wild-caught seahorses, particularly the beautiful Brazilian seahorses (Hippocampus reidi), which can be picky eaters under the best of circumstances. Captive-bred Brazilians are much better adapted for life in the aquarium than their wild conspecifics. This is perhaps best reflected in their eating habits. Wild-caught (WC) H. reidi are notoriously finicky eaters. Very often, they disdain frozen foods and outright refuse adult brine shrimp (Artemia) and guppy fry, which are the only live foods most hobbyists can readily provide. Consequently, many proud owners of wild-caught Brazilians go to a great deal of trouble and expense to provide them with live ghost shrimp, grass shrimp and Gammarus on a daily basis (Giwojna, Jun. 2002). Captive-bred H. reidi, of course, usually accept frozen Mysis as their staple diet quite readily, a tremendous boon for long-suffering supporters of this much-sought after species (Giwojna, Jun. 2002).
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 for the home hobbyist.
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.
So I can sympathize with your plight completely — I’ve been there and done that myself many times in the past. Nowadays, I always opt for domesticated seahorses that are pre-conditioned for the captive environment and pre-trained to eat frozen foods as their staple, everyday diet — it makes things so much easier for us seahorse keepers!
I think you’re right — your H. reidi must be grazing on the copepods and amphipods in your system. But it’s a good idea to keep supplementing her diet with ghost shrimp and homegrown Mysis and volcano shrimp on a regular basis lest the pod population in the tank becomes too depleted.
Best of luck with all your seahorses, loveless!