Nutrition Part I: Live Foods for Adult Seahorses

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

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Proper nutrition is the key to keeping sea horses healthy and breeding them in captivity. In their natural habitat, sea horses feed 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 this natural diet is the sea horse keeper’s greatest challenge.

This series of articles will explain exactly how this daunting task can be accomplished. It will provide step-by-step instructions for providing sea horses with a balanced, nutritional diet by collecting live foods in the field, maintaining live food cultures at home, and gradually conditioning them to accept a variety of frozen foods. Since new acquisitions require living prey when first introduced to the aquarium to help them adjust to captivity, as well as regular supplements of live foods thereafter, we will begin our investigation of sea horse nutrition with a discussion of the best live foods for adults (specimens larger than 3-4 inches or about 10 cm).

BRINE SHRIMP (Artemia salina)

Pros:

• Adult Artemia widely available in pet shops and aquarium stores.
• Easily raised from eggs or cysts to provide nauplii of all sizes and stages of development.
• Excellent tolerance for saltwater: feed and forget–survives until eaten.
• Relished by sea horses of all kinds.

Cons:

• · Poor food value–good source of protein, but lacking in other essential nutrients.
• Must be fortified or enriched to increase nutritional content.
• Cannot be used as staple diet.

Collecting Tips:

• None

Culture Instructions:

• Specific gravity: 1.020-1.026; pH: 8.0-9.0;
• Temperature: 77 degrees F (25 degrees C)

An easy way to raise small quantities of brine shrimp is to set up a 10-20 gallon tank in a location where it receives natural sunlight to promote the growth of green algae, and provide gentle aeration using a length of airline tubing as a bubbler (avoid fine bubbles and the use of airstones). Sprinkle 1/2 teaspoon of eggs on the surface of the water. The nauplii will hatch 24-36 hour later, and the day after they emerge, they can be fed sparingly with Selcon Concentrate (*see discussion of food additives below) at the rate of 0.5 ml per 5 gallons8. Adjust the amount so a slight haze barely clouds the water for a few hours each day. Do not feed again until the water is crystal clear, and avoid overfeeding at all costs. Maintain constant aeration to keep the food in suspension, and feed very small amounts fairly often–never a large quantity at any given time. The first generation of brine shrimp will reach maturity after 2-3 weeks, and the culture will then be self-sustaining1. Add more eggs as needed to supplement natural reproduction and bolster the population of brine shrimp. Top off the tank with freshwater regularly to make up for evaporation, and replace about 25% of the culture water on a monthly basis.

It’s a good idea to set up 2 or more culture tanks for adult Artemia at the same time so you can harvest a little from each culture and prevent the population of shrimp in any one tank from being depleted to the extent it can no longer sustain itself 11 .

Rearing Artemia this way makes it easy to select nauplii at just the proper stage of development and size for your sea horses.

Comments:

Brine shrimp are no doubt the most widely-used live foods for sea horses. They are convenient, always available, easy to hatch and raise, and adults can be bought by the pint or quart at many fish stores.

However, commercially raised brine shrimp have one big drawback. By the time they are purchased and released in the aquarium, they usually have not eaten for several days, and starved brine shrimp are nutritionally barren8. It is therefore imperative that brine shrimp be fortified before they are fed to your sea horses.

Fortunately, brine shrimp are filter feeders and will take in whatever is suspended in the water with them. This can be yeast cells; unicellular algae; rotifers; micronized rice bran, whey, wheat flour, or egg yolk; dried Spirulina algae; water-soluble vitamin and mineral formulations designed for marine fish; or whatever else the aquarist cares to add to their culture water1.

I recommend using one of the concentrated food additives such as *Selcon, which have recently been developed specifically for mariculturists. Selcon is rich in highly unsaturated fatty acids (HUFA), stabilized Vitamin C, and cyanocobalmin(B-12), and is thus a superb food for culturing brine shrimp. Store-bought adult Artemia can also be fortified by adding Selcon at the rate of 1.0 ml per 6-ounce portion of brine shrimp, and then allowing at least 12 hours for the shrimp to ingest it1.

The survival rate of marine fish fry improves dramatically when they are fed lipid-enriched brine shrimp nauplii 13, and the importance of fortifying Artemia in this manner cannot be overemphasized. In fact, the Steinhart Aquarium in San Francisco has successfully raised Hippocampus erectus from birth to maturity on a diet consisting solely of brine shrimp3. For best results, however, brine shrimp should be considered only a dietary supplement, with of the bulk of your sea horses’ diet consisting of hard-bodied crustaceans such as Mysids or Gammarus.

GAMMARIDS

Pros:

• Highly-nutritious, hard-bodied crustaceans.
• Favorite food of many larger sea horse species.
• Good tolerance for saltwater (marine Gammarus survive indefinitely and even freshwater Gammarus will last until eaten if your sea horses are fond of them).
• Live Gammarus are available in some areas (Kordon markets them pre-packaged in small poly bags called “Gourmet Sachets”).
• Starter cultures are available through the mail (Florida Aqua Farms; Daleco “Master Breeder” Products).

Cons:

• Slow reproductive rate makes it difficult to raise them in large quantities.
• Slight risk of introducing disease with Gammarus collected in the wild.

Collecting Tips:

Marine Gammarids – Gammarus locusta, a marine amphipod, can often be found in large numbers at the seashore by overturning rocks and coral rubble at low tide2.

Freshwater Gammarids–Gammarus fasciatus can be collected from vegetation and leaf litter on the bottoms of ponds and slow-moving streams.

Culture Instructions:

Marine Gammarus will maintain a self-sustaining colony if established in a standard saltwater aquarium with coral gravel and rubble and left undisturbed while their population grows. Encourage a lush growth of green algae and restock periodically. Freshwater Gammarus can be cultured in a plastic wading pool or similar spacious receptacle equipped with an airstone. Feed sparingly with chopped raw spinach, Spirulina, or a pinch of dry fish food. Include plenty of algae-covered rocks and driftwood for shelter, and position where strong direct sunlight will produce heavy algal growth2.

Comments:

To feed these 1/4″-5/16″ crustaceans to your fish, siphon water from around the rocks, shells, and gravel in the culture tank and strain it through a net to separate the Gammarus from the debris. Commonly known as side-swimmers, these hard-shelled amphipods have a herky-jerky, side-stroke swimming style that most large sea horses find irresistible. Their seemingly frantic movements and tendency to dart out from hiding suddenly seldom fail to trigger a sea horse’s feeding response, and this is one food hungry Hippocampids will actively pursue and search out. Some sea horses will even accept freshly killed or dead Gammarus11. An ideal food: substantial enough to be your sea horses’ staple diet, if you can obtain it in sufficient quantity!

GRASS SHRIMP/RIVER SHRIMP

Pros:

• A highly-nutritious, natural food for large sea horses.
• Available from bait shops or aquarium stores in some areas.
• Can be collected locally by many aquarists.
• Good tolerance for saltwater: marine grass shrimp are a “feed-and-forget” food, and freshwater grass and river shrimp last surprisingly long as well.

Cons:

• Suitable only for the largest specimens.
• Cannot be cultured in home aquaria.
• Marine grass shrimp are unavailable to inland aquarists.

Collecting Tips:

Grass shrimp can be collected easily at low tide by vigorously shaking clumps of seaweed into a bucket of seawater, or by dragging a small seine or large aquarium net through tidal creeks or the grass flats just offshore2. Similar techniques will often produce freshwater grass shrimp and river shrimp from freshwater streams or waterways. Remember, keep only shrimp that are small enough for your sea horses to swallow whole.

Comments:

“Grass shrimp” is an all-purpose term loosely applied to several species of small marine shrimp as well as the young of a variety of larger shrimp. River shrimp are simply the freshwater equivalent of marine grass shrimp.

All in all, these crustaceans are ideal foods for Hippocampus kuda, H. ingens, H. abdominalis, big specimens of H. erectus or reidi, and other large sea horses. Just be sure to select shrimp of suitable size for your sea horses.

MYSIDS

Pros:

• Excellent food value.
• A favorite food which large sea horses attack greedily.
• Thrives in saltwater: feed and forget – will survive until eaten.

Cons:

• Live Mysids are generally unavailable in the U.S.

Collecting Tips:

Mysis shrimp follow a daily rhythm in their movements, regularly forming dense shoals over sandy bottoms or amidst seaweeds10, and they can sometimes be collected in vast numbers while shoaling by seining or dragging a large aquarium net through mats of vegetation.

Culture Instructions:

Jack Rudloe has developed a simple technique for raising small quantities of certain Mysids and other mudflat organisms7 in a bare marine aquarium equipped with only a standard undergravel filter: First he cuts up a clean nylon stocking and fits it over the u.g. so it covers all the slots in the filter plate. Then he covers the u.g. filter plates with about 3″ (7.5 cm) of freshly-collected mud spaded up from the end of a mudflat at low tide or collected from the bottom of a bay with a bucket dredge. The undergravel filters quickly clear the water, and–in the absence of predators–Mysids, copepods, and numerous other small crustaceans will soon proliferate, nourished by the rich organic mud.

Comments:

Mysids are small shrimplike crustaceans with a heavy carapace covering their thorax. They are commonly called opossum shrimp because the females carrying their developing young in a bulging pouch formed by thoracic plates at the base of their legs. Numerous Mysis species are found around the world, and wherever opossum shrimp occur, they form a large part of the indigenous sea horses’ natural diet.

Although they are seldom seen in the U.S., where the ubiquitous brine shrimp dominate the market, live Mysids are sometimes available in London pet shops5, and sea horse keepers in the U.K. and Australia report great success with these crustaceans11. In fact, the experts at Underwater World in Western Australia maintain the fabulous but delicate Seadragons (Phycodorus and Phyllopteryx sp.) on an exclusive diet of Mysis shrimp6 collected by SCUBA divers–the only food they have ever observed the finicky ‘dragons to eat! Underwater World is conducting a breeding program for Sea Horses and Seadragons, and has successfully raised the Western Australia Sea Horse (Hippocampus angustus) through successive generations on a diet of Mysids supplemented by copepods and brine shrimp6. In fact, large sea horses are often so fond of these crustaceans that they readily accept frozen Mysids. A superb food that should form the basis of your sea horses’ diet if you can possibly obtain it–live, fresh, or frozen.

LIVEBEARER FRY

(Newborn Gambusia, Guppies, Mollies, Platys, Swordtails, etc.)

Pros:

• Excellent food value: high in protein, lipids, and other essential nutrients–a complete package of vitamins and minerals.
• Available in all pet shops and aquarium stores.
• Easy to breed and maintain at home.

Cons:

• Poor tolerance for saltwater (except for mollies adapted to brackish conditions).
• Not acceptable to all sea horses–refused by many specimens.
• Slow rate of reproduction limits usefulness.

Collecting Tips:

• None

Culture Instructions:

Set up breeding groups (trios or harems consisting of several mature females for every male) in a standard aquarium for tropical fish. Feed and maintain exactly as if keeping them as pets. Mollies require a vegetable-based diet and do best with a little non-iodized salt or sea salt added to their water (about 1/4 teaspoon per gallon). Isolate obviously pregnant females in breeding traps to prevent cannibalism of the fry.

Comments:

Offer your sea horses only a few fry at a time, since the delicate newborns won’t last long in saltwater. The fry should be used immediately after they are born, since they grow rapidly and may be too large to eat a few days after birth (remember sea horses must swallow them whole). Newborn guppies and Gambusia are smallest and the easiest for sea horses to handle. Molly fry are bigger, but they can be gradually acclimated to brackish or even full-strength saltwater, allowing them to survive indefinitely in your sea horse tank2.

In my experience, the biggest problem with newborn fishes is that many sea horses simply refuse to eat them. The fry tend to hug the surface, where sea horses are unaccustomed to feeding, and some Hippocampids are put off by their size. However, some large sea horses attack them voraciously, and the San Antonio Aquarium in Texas has successfully maintained sea horses on an exclusive diet of newborn mollies 3. From France, Thierry Schmidt reports good success raising Hippocampus kuda, supplementing their diet with newborn guppies as the juveniles grow9.

DAPHNIA

Pros:

• Can be collected from ponds in warm weather.

Cons:

• Large sea horses tend to ignore them.
• Poor tolerance for saltwater leads to danger of fouling the aquarium.

Collecting Tips:

Use a fine net to gather them when their population peaks in the summer months and they form reddish-brown “clouds” in shallow ponds, ditches, temporary pools, or slow-moving streams and backwaters.

Culture Instructions:

Set up a 5-10 gallon aquarium with boiled water and adjust the temperature to 68-70 degrees F (20-30 degrees C). Provide continuous aeration and maintain moderately hard, alkaline conditions, adding a handful of calcareous gravel if necessary. Feed sparingly with dry baker’s yeast, manure extracts, or Selcon just as instructed for raising brine shrimp to maturity. Sterilize your equipment and start a new batch culture every month or so. Try to keep two or more cultures going at once, since Daphnia cultures tend to “crash” with little warning1.

Comments:

Daphnia are highly-sensitive to changes in ionic concentration, and thus quickly become immobile and finally die when exposed to seawater due to the sudden increase in salts such as sodium, calcium, and magnesium4. Worse yet, only the smallest sea horses show any interest in “water fleas,” making them worthless for feeding adults or juveniles of the larger species. If your sea horses are bigger than about 3 inches (7-8 cm), then don’t waste your time with Daphnia–you’ll be much better off concentrating on raising other live foods such as Gammarus, adult Artemia or livebearer fry instead.

LIVE WORMS

(Tubifex, Bloodworms/Chironomid larvae, Blackworms, Glassworms, etc.)

Pros:

• Widely available from pet shops and aquarium stores.

Cons:

• High risk of fouling the aquarium due to poor tolerance for saltwater.
• Danger of introducing parasites or disease organisms with these worms.
• Elongated shape makes it difficult for sea horses to swallow worms.Comments:

Avoid these live foods. As a rule, sea horses won’t eat them, so they’re not worth the trouble and expense as far as sea horses are concerned.

Regardless of what type of live foods you will be feeding them, it is important to remember that sea horses do much better when given several small feedings each day rather than one big meal. They are accustomed to feeding virtually nonstop throughout the daylight hours, and in order to really thrive in the aquarium, they should have an adequate supply of food available at all times.

If possible, the best compromise for most aquarists is to provide three offerings of “feed-and-forget” live foods as follows: the first feeding as soon as the full tank lights go on, a second feeding at mid-day, and a final feeding a couple of hours before lights out11.

However, it there will be no one at home to provide a mid-day feeding,

two meals a day can still suffice. Just be sure to give your sea horses a very generous serving of ”feed-and-forget” live foods (i.e., adult Artemia, Mysids, marine Gammarus, or marine grass shrimp), which will survive until eaten, before you leave for work in order to tide them over until you return. As soon as you get home, give your sea horses a second portion of live food.

Above all, be sure to make provisions for feeding your sea horses before you buy them. Sea Horses must NEVER be purchased on impulse! It is vital that you line up your live food sources or establish your own live food cultures before you bring your sea horses home. And keep in mind that it will be much easier to keep up with the bottomless appetites of these seagoing gluttons if you keep them singly or in pairs.

With patience and hard work, most sea horses can be trained to accept nonliving prey once they have adjusted to aquarium life. The sea horse fancier should begin weaning his prized pets onto a staple diet of frozen foods as soon as possible, and the next installment in this series on sea horse nutrition will describe exactly how this can be done.

Author’s Note: By now it should be clear that sea horses are generally not suitable specimens for beginners or casual aquarists. Furnishing them with a balanced, nutritious diet is a painstaking process that requires collecting live foods and maintaining live food cultures, at least initially, so stop to consider whether you are really up to the task before you commit yourself to providing a varied menu for a tankful of these gluttonous gourmets. Anyone who is unwilling or unable to follow the feeding procedures outlined in this article should stick to less demanding fishes that are more suitable for the novice.

And when selecting a specimen, always try to obtain a fully mature adult of the species you desire. In the interests of conservation, juvenile sea horses should be left in the ocean until they have had a chance to reach adulthood and reproduce. As Dr. Amanda Vincent points out12, if hobbyists refuse to buy subadults, marine collectors will have less incentive to remove immature specimens from their natural habitat, and sea horse populations around the world will benefit as a result.

REFERENCES

(1) Daleco Aquarists Supply Manual. 1995. Daleco “Master Breeder” Products: Tonawanda, New York.

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

(3) Herald, E.S. and Rakowicz. 1951. Stable requirements for raising sea horses. Aquarium Journal 22: 234-242.

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

(5) Keeley, D. 1980. Raising baby sea horses. Practical Fishkeeping. September 1980: 33.

(6) Mackay, Bruce (Curator). 1991. Underwater World. P.O. Box 424, Hillarys; Perth, Western Australia 6025 (Personal communication).

(7) Rudloe, Jack. 1971. The Erotic Ocean: a handbook for beachcombers and marine naturalists. Fitzhenry & Whiteside Limited: Toronto, Canada.

(8) Selcon Concentrate User’s Guide. 1990. American Marine, Inc.: Ridgefield, Connecticut.

(9) Schmidt, Thierry. 1995. About sea horses. SeaScope (Winter 1995) 12: 2.

(10) Talbot, Frank. 1984. Reader’s Digest Book of the Great Barrier Reef. Reader’s Digest Services Pty Limited: Sydney, NSW.

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

(12) Vincent, Amanda, PhD. 1995. Update on sea horses. SeaScope (Summer ’95) 12: 4.

(13) Young, Forrest. 1991. Dynasty Marine Associates. 10603 7th Avenue, Gulf; Marathon, Florida 33050. (Personal communication).

CAPTIONS AND LEGENDS

(*1) & (*2): Home, Sweet Home. Just as marine algae, sponges, sea whips and gorgonians make sea horses feel at home in the aquarium, new acquisitions also require living prey similar to their natural diet to help them adjust to life in captivity. In the wild, they feed continuously on a rich harvest of tiny crustaceans and larval organisms that inhabit the seagrass beds or drift past in the plankton, and duplicating the quality and quantity of this diet is the sea horse keeper’s greatest challenge. This means providing a variety of live foods such as Gammarus amphipods, Mysids, grass shrimp, adult Artemia and livebearer fry (guppies, mollies, platys, gambusia, etc.) on a daily basis. (*Possible Cover Photos.)

(3) & (4): Sniper of the Seagrass Jungle. Whenever I see a hungry sea horse patiently stalking its prey, like this Hippocampus erectus, I am always reminded of a Japanese sniper in a WWII John Wayne movie. With a lush growth of leaves and foliage draped over his helmet and extra shrubbery strapped to his back, the cunning jungle fighter literally melts into the shadowy undergrowth. From his strategically selected vantage point, the sharp-eyed sentry waits for his unsuspecting victims to come to him, picking off hapless GIs one by one as they pass his secret hideout.

That’s a pretty fair description of a hungry Hippocampid on the lookout for its supper. Masters of camouflage, sea horses are the snipers of the grassblade jungle into which they blend so well, and their preferred hunting technique is the ambush. Concealed absolutely motionless amidst a clump of Caulerpa or a patch of gorgonians, only a flicker of its busy, watchful eyes ever betrays its presence. Patiently lying in wait for its next meal, one of its independent eyes scans upward while the other scrolls downward so as not to miss any potential prey passing nearby. As shown here, nothing in the immediate vicinity escapes the scathing scrutiny of a stealthy sea horse intent on filling its belly.

(*5), (6) & (7): Portrait of a Bushwhacker at Work: This is the typical feeding posture of a hungry sea horse, frozen in mid-strike the instant before snapping up its prey. When some unwary victim does blunder within range of one of these seagrass snipers, the sea horse tracks it intently, stalking its prey in ultra-slow motion. With its tail securely anchored in place, it stretches its body in the direction of its chosen quarry ever so s-l-o-w-l-y, making itself seem like a harmless frond of algae or a natural extension of the coral. But when this painstaking pursuit finally brings it within striking distance, it’s all over in a hurry:

Drawing a bead on its ”dinner” exactly as if its hollow snout were the barrel of a high-powered rifle, the sea horse gives a sudden jerk of its head, accompanied by a distinctly audible ”click,” and its hapless victim disappears as if by magic, sucked up faster than the eye can follow. (*Possible Cover Photo.)

(8), (*9) & (*10): Slurp-Gun Snout. Anyone who has ever collected fishes with a slurp gun knows exactly how a feeding sea horse accomplishes this vanishing act. The toothless jaws at the end of its snout operate with a rapid springlike action, and the spasmodic jerk of the sea horse’s head as it snatches its prey represents the cocking and firing of this spring-loaded mechanism. Thus, when a sea horses points the barrel of its snout at its intended victim, lining up the target in its sights, and pulls the trigger, well-developed muscles raise its gill covers sharply , creating a strong inrush like an expanding bellows, and the powerful suction pulls in its prey irresistibly along with a little water. The sea horse’s mouse-trap jaws spring open and snap shut again, and it literally inhales its victim in the blink of the eye. One moment the prey is there, and the next it’s gone.

Since sea horses swallow their prey whole and cannot chew their food, it’s important for the aquarist to pay close attention to the bore or ”caliber” of his sea horse’s snout when offering live foods such as Gammarus, Mysids, grass shrimp, or livebearer fry. There’s no way a sea horse can cram 12-gauge goodies down a .22-caliber snout, so be sure to select appropriately-sized prey items for your galloping gourmets. (*Possible Cover Photos.)

(11) & (12): Hungry Sea Horse on the Prowl. Feeding sea horses are fascinating to watch, and the attentive aquarist can learn a lot about his pets from watching them eat. For instance, if they’re really hungry, sea horses will take off in hot pursuit when some mouth-watering morsel wanders by just beyond reach. No longer content to wait for their supper to come to them, they’ll launch themselves on a ”high-speed” chase at a blistering pace that’s just about capable of overtaking a lumbering brine shrimp or weary water flea. Once they’ve closed to within about one-quarter inch of their target–often prodded along by their tails to gain a final burst of added propulsion–that distinctive ”snick!” will announce the sudden demise of their quarry.

And when no prey is evident, sea horses will sometimes set off on hunting expeditions in a effort to scare up a meal on their own. A sea horse on safari will patrol the perimeter of its aquarium, carefully searching every nook and cranny as it skims along just above the bottom. (This behavior is often displayed when sea horses are hunting Gammarus, since the side-swimmers hug the bottom and seek shelter under every scrape of cover they can find. These isopods are a favorite food of sea horses, which will often resort to amazing acrobatics in an attempt to winnow them out of their hiding places.) Suffice it to say, when you see your sea horses conducting these search-and-destroy missions, it’s time to feed them!