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Nutrition Part II: Frozen Foods for Adults

by Pete Giwojna
from the November 1996 issue of Freshwater and Marine Aquarium magazine (FAMA)

In the last issue of FAMA ("Sea Horse Nutrition, Part I: Live Foods for Adults"), we discussed how to help newly-acquired sea horses make the transition to life in captivity by providing them with live foods that closely resemble their natural diet. As soon as they have adjusted to their new surroundings and are feeding well, however, it is important to begin weaning them away from a staple diet of live foods by training them to accept frozen substitutes instead.

This will allow the hobbyist to use a much greater range of readily available foods, making it much easier to provide these finicky fishes with a balanced, nutritional diet. Aside from greatly expanding your sea horse's diet, frozen foods are invaluable for stretching your live food cultures when they are depleted, and they can be a real life saver in an emergency. Should a seashore collecting trip for live foods prove to be unproductive, or if your cultures should fail, frozen foods can keep your sea horses alive until better fodder can again be obtained. In short, your sea horse's chances of long-term survival improve immeasurably once it learns to eat nonliving prey.

The best way to acclimate Hippocampines to nonliving foods is to offer them one of their favorite live foods after it has been freshly killed. If you have been feeding your sea horses with live Mysids or grass shrimp, then freshly-killed or frozen specimens of these same crustaceans will be ideal for this training process. If they are fond of Gammarus, try tempting them with newly dead side-swimmers6. Likewise, if your sea horses prefer newborn guppies or mollies, they can often be gradually converted to a diet of freshly-dead fry without difficulty4. Once they are accustomed to eating such nonliving items, it is then fairly easy to train them to accept commercially-prepared frozen foods as well.

The first step in this process is to thaw the frozen food carefully--all in one piece--so that it remains intact and retains its natural, lifelike appearance. Once it has been thawed out properly, the tasty tidbit must be rinsed gently and swirled through the water so that it appears to swimming normally and moving in a realistic manner. The idea is to deceive the sharp-eyed sea horses into thinking the frozen food is actually very much alive.

Movement is the key to this deception. (Sea Horses are very reluctant to eat nonmoving prey regardless of how lifelike it appears.) Using heavy aeration to create a rapid turnover of water is a good way to impart the necessary movement to frozen morsels during your training sessions. The aquarist can achieve this by generating short periods of fierce aeration to create powerful but short-lived currents that will waft the frozen items through the water1. (The easiest way to produce these bursts of heavy aeration is to momentarily increase the air flow to your airstones or the bubbler stems of your undergravel filters. If you have power heads on your u.g.'s, switching them on full blast for 5-10 seconds and then turning them back down will also produce the extra circulation required to swirl the frozen food about as if were swimming under its own power.)

Hungry sea horses will then often be tricked into snatching the tempting tidbits as they drift past. To the sea horse, the movement makes it appear as if its "prey" is about to escape, triggering an automatic feeding response. Any uneaten food will settle to the bottom, whereupon it can be "reanimated" by renewed bursts of aeration that will lift it off the substrate again and send it swirling through another circuit of the aquarium1. This process can be repeated as often as required.

Most sea horses can readily be persuaded to take frozen food when it is offered in this way, but you may have to resort to a more gradual weaning process involving live brine shrimp (Artemia salina) if your sea horse happens to be an especially finicky feeder. Adult Artemia are available at most pet stores that carry marine fishes, and brine shrimp are one food that nearly all large sea horses attack with relish. Therefore, in really stubborn cases, I suggest giving daily feedings of live adult Artemia mixed with a small amount of frozen brine shrimp, using short bursts of vigorous aeration to keep it all moving, as described above. The first feedings should be nearly 100% live brine shrimp, but the proportion of frozen to live food should be gradually increased over a period of days or weeks until your sea horses are finally eating 100% frozen brine shrimp2.

The frozen Artemia used for this weaning process must be thawed out with great care. It is vital that whole, individual brine shrimp separate from the frozen mass as it melts. Any attempt to rinse off the frozen clump or break it into smaller pieces will only macerate the soft-bodied shrimp, transforming the Artemia into a shapeless, unrecognizable mess that no self-respecting sea horse would consider edible. The best way to prevent this is to buy a good brand of frozen brine shrimp and place an entire cube directly into the aquarium to melt. As it slowly thaws, it should release intact shrimp in nearly perfect condition. If you are having trouble finding high-quality frozen brine shrimp that works well for this, try using a good brand of freeze-dried brine shrimp instead. San Francisco Bay freeze-dried brine shrimp, for example, will reconstitute to whole shrimp when fed. The thawed or freeze-dried brine shrimp should then be virtually indistinguishable from the living Artemia, and with a little luck your sea horses will soon be gobbling up the frozen food right along with the live.

As soon as one of the sea horses in a tank begins to eat frozen foods, others will usually follow6. The feeding behavior of the first sea horse seems to stimulate the others, and it doesn't take long for one or more of his tankmates to learn from his example. Sea Horses are always hungry, and once they have been shown that the frozen items are good to eat, the rest of the latecomers soon join in, eager to get their share of the goodies. From that point on, your feeding problems as a sea horse keeper will be greatly reduced.

Nevertheless, there are a few inherent problems with nonliving foods the aquarist must keep in mind while this training proceeds. First of all, they pose a greater danger of fouling the water than live foods do, since any uneaten morsels will rapidly begin to decay. The aquarist must therefore be especially diligent in cleaning up all the leftovers after each training session.

Secondly, frozen foods are only feasible for adult sea horses of the larger species. The reduced size of the food required by small sea horses (less than 3-4 inches or about 10 cm in length) makes it very difficult to thaw, prepare, and handle bite-sized portions without destroying the food in the process. Detecting and cleaning up any uneaten food just becomes too hard when the size of the morsels decreases beyond a certain point.

Thirdly, it is no secret that sea horses can be picky eaters at times, particularly when it comes to frozen goodies. They have definite likes and dislikes, and frequently refuse to eat anything but what their heart is set on at the moment. Worst of all, they tend to change their preferences unpredictably and with dismaying regularity--sometimes going through periods where their personal favorites seem to change almost daily1. (Ever take a kid to a fancy restaurant offering all manner of culinary delights, only to have the little monster hold out for his familiar favorite--hamburgers? Well, sea horses are a lot like spoiled kids when it comes to their eating habits. I have a kid brother who went through a stretch where he would eat nothing but ravioli for lunch. After a few weeks, he suddenly switched to peanut butter-and-jelly sandwiches with a layer of potato chips in between, and he would never touch ravioli again. After that it was a certain brand of hot dogs, and then he went through his "pancakes-with-maple-syrup" phase. Sea Horses are the same way. When it comes to putting on the old feed bag, I guess they're just spoiled brats at heart. It's pointless to try to make 'em eat something they no longer like. Anyone who has ever tried to make a stubborn child eat his veggies can tell you that.)

The best way to overcome this difficulty is to experiment with a wide variety of freshly-killed foods and frozen fare until you find something your sea horses like, and then concentrate on their current favorites during your training sessions. Proven favorites that are often acceptable to sea horses in freshly-killed or frozen form are grass shrimp, Mysids, Gammarus, gamma shrimp, prawns, krill, and zooplankton.

In general, hard-shelled crustaceans are preferable to soft-bodied crustaceans for training purposes, since they withstand the freezing-thawing process in better condition, retaining their natural form and lifelike appearance longer. Some hobbyists even report good success with freeze-dried foods, so freeze-dried krill, shrimp, and plankton may also be worth a try--if you can find a high-quality product that reconstitutes well.

A more serious problem is that frozen foods alone cannot provide a balanced diet for sea horses. Frozen foods retain less nutritional value than live foods, and in the long run, a diet consisting solely of frozen fodder will result in malnutrition and illness6. To overcome this difficulty, I recommend placing a portion of frozen food in a small plastic cup and soaking it in a good liquid vitamin complex or a special concentrate such as Selcon while it thaws. Fortifying frozen or freeze-dried food this way can help prevent nutritional deficiencies--providing your sea horses don't object to the taste of these additives.

But the biggest drawback to frozen food is the simple, inescapable fact that it's not alive. No matter how varied the menu, how carefully the frozen cuisine is prepared, or how enticingly it's served, sea horses will eventually lose interest in a diet that consists exclusively of frozen fodder. Sooner or latter they will begin to eat it half-heartedly, their appetite will suffer, and they may even go on a hunger strike.

Live foods are the answer to this problem. When sea horses tire of the same old, boring frozen food and refuse to eat their "veggies," living prey is what they crave: Mysids, grass shrimp, or adult Artemia--the type of food isn't really as important as the fact that it's alive and kicking. Nothing stimulates a sea horse's feeding instinct like the frantic movements and evasive maneuvers of real, live, "catch-me-if-you-can" prey items. Live foods are guaranteed to perk up an ailing appetite and excite the interest of the most jaded "galloping gourmets." When it comes to a hunger strike, commercially prepared appetite stimulants can help, but living prey is the only sure cure for the “Bird Eye blue.”

Consequently, your ultimate goal should be to provide your sea horses with a wide range of fortified frozen foods as their basic diet, supplemented by an assortment of live foods as often as possible. Live foods such as Gammarus amphipods and the fry of live-bearing tropical fishes will add more variety to their regular diet of frozen fodder, and assure that your prized pets keep eating. I recommend providing live foods two or three times a week at the very least--more often, if you really want to keep your sea horses fat and happy.

In fact, if you can manage it, daily supplements of live foods would be even better. Ideally, this would allow the aquarist to provide his sea horses with a good portion of live foods such as adult brine shrimp, mysids, or marine Gammarus before he leaves for work in the morning. These are ''feed-and-forget'' foods which will survive in the aquarium until eaten, allowing the sea horses to dine on them at their leisure throughout the day. Then, when he gets home, the hobbyist can feed them one or two servings of their favorite frozen foods before the aquarium lights go out.

With patience and hard work, the techniques described in this article will enable you to train your sea horses to accept frozen foods. And once they are accustomed to eating nonliving prey, you will be ready for the sea horse fancier's ultimate adventure--feeding hungry Hippocampines by hand! There is no greater thrill than having these enchanting animals eating right from your fingers, and the next installment in our discussion of sea horse nutrition will be devoted to the many important advantages and health benefits of handfeeding, and the behavior modification techniques that make it possible.

Author's Note: Prospective sea horse keepers must always remember that furnishing these fascinating fish with a healthy, balanced diet is a painstaking, time-consuming process. It requires collecting live foods in the field, maintaining live food cultures at home, and conditioning them to eat nonliving prey and frozen foods, as described in this segment. Anyone who is unwilling or unable to follow the feeding procedures outlined in these articles should stick to less demanding fishes more suitable for beginners.

Because of these difficult feeding requirements, you will find it much easier to meet the needs of your sea horses if you limit yourself to a single specimen or a mated pair. And when selecting a specimen, always try to obtain a fully mature adult of the species you desire. Adults are generally easier to feed than juveniles, and in the interests of conservation, young sea horses should be left in the ocean until they have had a chance to reach adulthood and reproduce. Fewer immature specimens would be removed from the wild if hobbyists everywhere refused to buy subadults, and as Dr. Amanda Vincent has pointed out7, sea horse populations around the world would surely benefit as a result.

REFERENCES

(1) Corser, Peter. Sea Horse Study Group. 14 Knaves Hill. Linslade, Leighton Buzzard. BEDS, LU7 7UD, U.K. (Personal communication).

(2) Giwojna, Pete. 1990. A Step-By-Step Book About Sea Horses. T.F.H. Publications, Inc.: Neptune City, New Jersey.

(3) Hoff, Frank F. and Snell, Terry W. 1987. Plankton Culture Manual. Florida Aqua Farms: Dade County, Florida.

(4) Schmidt, Thierry. 1995. About sea horses. Seascope (Summer 1995) 12: 2.

(5) Vincent, A.C.J. 1990. Reproductive Ecology of Sea Horses. Ph.D. Thesis, University of Cambridge: 15, 61.

(6) Vincent, Amanda, Ph.D.. 1995. Sea Horse keeping: feeding adults, mating, rearing the young, mariculture. The Breeder's Registry . Volume 3, Number 2: 1-5.

(7) Vincent, Amanda, Ph.D.. 1995. Update on sea horses. SeaScope (Summer '95) 12: 4.

CAPTIONS AND LEGENDS

(13), (14), & (15): Fattened-Up on Frozen Fodder. Large sea horses like this trio of hefty adults are the best candidates when it comes to training these finicky feeders to accept frozen substitutes in place of living prey. As explained on page 5 of Sea Horse Nutrition Part II: Frozen Foods for Adults, ''...frozen foods are only feasible for adult sea horses of the larger species. The reduced size of the food required by small sea horses (less than 3-4 inches or about 10 cm in length) makes it very difficult to thaw, prepare, and handle bite-sized portions without destroying the food in the process. Detecting and cleaning up any uneaten food just becomes too hard when the size of the morsels decreases beyond a certain point.''

(16) Impeccable Table Manners. As shown here, these aquatic equines are equipped with toothless jaws at the end of a narrow, tubular snout, so even the hungriest sea horses are delicate feeders that never bite off more than they can chew. In fact, the most common mistake aquarists make with frozen foods is offering morsels that are just too large for their sea horses to handle. This often happens inadvertently when several frozen brine shrimp stick together in a clump during the thawing process, but many aquarists deliberately select jumbo grass shrimp, Mysids or krill for their training sessions, thinking they are picking out fat, juicy, frozen treats that their sea horses will find irresistible. In actuality, they're doomed to failure since sea horses automatically reject outsized prey that's too large to be swallowed whole. (That's why large sea horses are especially well suited for converting to frozen fodder--they can accept a bigger range of potential food items.)

(17) & (18): Sharp-Eyed Sentries. Hungry sea horses scrutinize their immediate surroundings very carefully, as this pair is doing, searching for isopods, amphipods, and other minute crustaceans that cling to the seagrass and gorgonians or slowly drift past their post. They instantly zero in on any likely prey items nearby, lock in on an individual target, and track their intended victim intently until it comes within striking distance. Persuading these sharp-eyed gourmets to accept frozen substitutes in place of their usual prey is therefore no easy task, for they must first be convinced that the frozen food is actually very much alive.

There are two keys to successfully pulling off this deception: the substitute must appear lifelike and it must display tantalizing movements. As explained on page 3 of Sea Horse Nutrition Part II: Frozen Foods for Adults, ''...the first step in this process is to thaw the frozen food carefully--all in one piece--so that it remains intact and retains its natural, lifelike appearance. Once it has been thawed out properly, the tasty tidbit must be rinsed gently and swirled through the water so that it appears to swimming normally and moving in a realistic manner.''

(*19) & (20): School's in Session: Sea Horses often teach each other that frozen foods are good to eat, so when one of them learns to eat nonliving foods, its tankmates soon follow. Feeding on frozen fodder is highly contagious, and once the first sea horse learns to accept nonliving prey, an epidemic of learning often breaks out among its tankmates and spreads quickly through the community until the whole herd is infected with the urge to feast of frozen foods. As explained on pages 4-5 of Sea Horse Nutrition Part II: Frozen Foods for Adults, ''...the feeding behavior of the first sea horse seems to stimulate the others, and it doesn't take long for one or more of his tankmates to learn from his example. Sea Horses are always hungry, and once they have been shown that the frozen items are good to eat, the rest of the latecomers soon join in, eager to get their share of the goodies. From that point on, your feeding problems as a sea horse keeper will be greatly reduced.''

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