Seahorse and Mandarin Fish

Dear Dean:

I’m very sorry to hear about the problems you’ve been having with your Mandarins, sir. It’s quite common for them to starve to death in the aquarium if they are kept in tanks that are too small, too new, or that otherwise lack a sufficient population of live copepods, amphipods, and other small crustaceans for them to feed on continuously. Here are some tips that explain the conditions the mandarins need in order to thrive in more detail.

I absolutely love the psychedelic coloration and peaceful nature of Mandarin dragonets! There’s no disputing that they are gorgeous little fishes and make ideal tankmates for seahorses in the right type of setup. They are docile, slow-moving, passive fish that are beautifully marked and very deliberate feeders. And they are quite hardy fish providing they can be fed properly. They have a heavy slime coat that seems to make them quite resistant to protozoan parasites such as Cryptocaryon irritans.

But in order to do well, mandarins need a large, well-established aquarium loaded with live rock that’s teeming with copepods and amphipods. As you know, mandarins must have continuous opportunities to graze on suitable live foods or they generally slowly waste away and starve to death. In the right system, they can thrive, and will often learn to take small pieces of frozen Mysis, but they do best in well-established reef systems or aquariums with at least 1 pound of live rock per gallon, a mature sand bed, and a refugium that can continually replenish the pod population in the tank. Those are typically the conditions that are necessary to assure they have adequate suitable live prey.

It’s going to be difficult to provide them with the conditions they need to thrive unless your aquarium is large enough (at least 50 gallons; 100 plus gallons would be preferable), chock-full of live rock, and has been up and running long enough to establish an abundant pod population. The live rock provides the shelter and feeding opportunities that the copepods and amphipods need in order to build up and maintain a breeding population. With several hungry seahorses competing with them for the available pods, it will be challenging for you to provide a Mandarin goby with enough to eat.

Under the circumstances, Dean, I would only consider keeping a Mandarin if you can equip the aquarium with a good refugium as well. As an example of the type of refuge that produces good results for mandarins and seahorses, Charles Delbeek likes to use colonies of glass shrimp and cleaner shrimp that in the refugium for his seahorse tank, where the regular reproduction of these hermaphroditic crustaceans will provide a continuous supply of nutritious nauplii for his ponies:

"There is a method that can be used to offer an occasional supply of live food for your sea horses. By setting up a separate system housing several species of shrimp such as the common cleaner shrimp (Lysmata amboinensis) or peppermint shrimp (lyse model wurdemanni), or Rhynchocinetes uritai or R. durbanensis, you can get a fairly regular supply of live shrimp larvae. These species are best to use since they can live in large groups and spawn on a regular basis. Such a system is commonly called a refugium. A refugium is a small (10-20 gallon) aquarium that contains live sand, live rock and/or macroalgae such as Caulerpa. It is plumbed such that water from your main system is pumped to the refugium and then returns via an overflow to the main tank. For this type of arrangement to work, the refugium must be slightly higher than the main tank. Shrimp are added to the refugium and within a few months they should start spawning and hatching eggs every few weeks. The larvae are then carried back to the main tank by the overflow, where they become a food source for your sea horses. Of course other life will also thrive in the refugium and it is not unusual for copepods, mysis and crab larvae to also be produced on a regular basis. The key to the refugium is to keep predators out of the system so that the smaller micro-crustacean population can thrive. You would need a fairly large and productive refugium to produce enough food to maintain even a pair of sea horses, so at best, a typical refugium can provide a nice source of supplemental live food; the basic daily diet still needs to be provided by you in the form of the frozen foods mentioned above." (Delbeek, November 2001, "Horse Forum," FAMA magazine)

Aside from the one Delbeek favors, refugia are available in a number of different designs. For example, there are easy-to-install external hang-on refugia and in-tank refugia as well as sump-style refugia that are mounted beneath the main. In the case of the latter, the refugium is installed exactly like any other sump. Here are a couple of online sites where you can look up more information on refugia, including articles explaining how to set up and install a refugium of your own:

Click here: Refugium Setups Information – From About Saltwater Aquariums
http://saltaquarium.about.com/od/refugiumsetups/

Click here: Refugiums
http://www.wetwebmedia.com/refugium.htm

It sounds like you have basically the right set up for the Mandarin, since he is in a modified reef tank with live rock and live corals, but I would recommend establishing a refugium for your seahorse tank as described above, Dean. And in the meantime, I would try target feeding the Mandarin with some of the smallest bite-size frozen Mysis. The Mini Mysis from H2O Life or the miniscule Hikari frozen Mysis would be worth a try for this, sir.

Best of luck fattening up your Mandarin Dragonet, Dean!

Respectfully,
Pete Giwojna

Dear Dean:

You did a good job in obtaining some live Mysis for your seahorses and Mandarin. I haven’t met a seahorse yet that could resist live Mysis. But it will be prohibitively expensive to purchase enough live Mysis on a regular basis to keep up with the appetites of your herd of seahorses and the Mandarin Dragonet. They will do just as well with the frozen Mysis and there are many different brands available that should be carried at any well-stocked fish store or pet store.

Or if you prefer, you may find it more economical to culture live Mysis and feed your seahorses and Mandarin from the excess. Mature grass shrimp are too large for a Mandarin Dragonet to eat, but the larvae they produce would be perfect for your Mandarin. Any marine shrimp that will breed and reproduce in the aquarium is worth culturing to provide additional food sources for the Mandarin. Some of the good species to work with, and culture instructions for raising them, are listed below:

MYSIDS (Opossum Shrimp)

Pros (Giwojna, Oct. 1996):
• Excellent food value.
• A favorite natural food that all large seahorses attack greedily.
• Thrives in saltwater: feed and forget — will survive until eaten.
• Can be easily collected at times.
• Cultured Mysis are available.

Cons:
• Challenging to culture for the home hobbyist.
• Inland hobbyists have no opportunity to collect them.

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 (Giwojna, Oct. 1996). Look for a shallow, sandy, weedy area at low tide during the day, and you can often see them swimming in the weeds or settling on the sand. If there is a significant current, they will congregate in slack water areas on the down-current side of objects. Once you have spotted a likely location, return at dusk when they are more active and net them as described above (Bentley, 2002).

A large net with very fine mesh works best for collecting mysids. I suggest a net with a mouth at least a foot square and mesh less than 1 mm square (Bentley, 2002).

Likewise, mysids are sometimes concentrated in large numbers in tidal pools on mudflats and grassflats by the falling tide. The stranded Mysis can easily be netted from these pools at low tide.

Culture Instructions (Bentley, 2002):

Specific gravity: 1.016 for estuarine species;
pH: 7.8-8.3 (reproduction stops if the pH falls lower than 7.4);
Photoperiod: 14 hours of daylight provided by two Gro-lux fluorescent tubes.
Temperature: 77 degrees F (25 degrees C)

The following guidelines are based on Maureen Bentley’s methods for culturing Mysis (Bentley, 2002). The main culture tank should be large, well aerated, and heavily filtered. I suggest undergravel filtration in conjunction with external biological filters. Mysids are extremely sensitive to water quality, and a good protein skimmer is vital for this reason (Bentley, 2002). Natural seawater is much preferable to artificial, and if you are using a synthetic mix, it’s best to allow the artificial saltwater to age at least one month before use (Bentley, 2002).

When stocking the main tank, introduce the shrimp gradually until you’ve reached a density of about 20-40 adults per gallon (Bentley, 2002). Overcrowding leads to fighting and dead broodstock. If you notice lots of mysids jumping out of the water, the tank is very likely overstocked (Bentley, 2002).

Small quantities of mysids can be harvested daily using a small glass tank equipped with an air-operated undergravel filter. Place 15 to 20 large gravid females in the small tank, returning them to the main tank as soon as they have released their young (Bentley, 2002). (Mysis are cannibalistic and the young must be separated from the adults.) The young can then be raised in the small tank for a short period.

Feed them newly hatched Artemia nauplii or rotifers twice daily until they are a few days old (Bentley, 2002). After a few days, begin supplementing their feedings with marine flake food on occasion, especially brine shrimp flake food (Bentley, 2002).

A feeding frenzy will follow the introduction of live food, which can help you determine the right amount to feed. When fed the proper amount, this frenzy should last around 15 minutes, during which all the live food should be eaten (Bentley, 2002). You will know you have fed enough when the normally transparent mysids have orange stomachs after feeding on the baby brine shrimp (Bentley, 2002). If the adults — especially the males – start eating numbers of the younger Mysis, that’s a sure sign of underfeeding (Bentley, 2002).

Comments:

Mysidacea, or Opossum Shrimps, are found worldwide. They 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 or marsupium formed by thoracic plates at the base of their legs (Giwojna, Oct. 1996). The average life span is about 12 months and adult mysids seldom exceed 1 inch in length. At least 460 Mysis species are found around the world (Bentley, 2002), and wherever opossum shrimp occur, they form a large part of the indigenous seahorses’ natural diet. They are snapped up greedily by even the most finicky syngnathids, including the fabulous but delicate Seadragons (Phycodorus and Phyllopteryx sp.). In fact, large seahorses are so fond of these crustaceans that they scarf up frozen Mysids with relish. This is superb food that should form the basis of your seahorses’ diet if you can possibly obtain it–live, fresh, or frozen (Giwojna, Oct. 1996).

RED FEEDER SHRIMP from Hawaii, a.k.a. Volcano shrimp (Halocaridina rubra)

Pros:
• Excellent nutritional value
• Irresistible to all the greater seahorses.
• Feed-and-Forget — lasts forever in saltwater!
• Easy to enrich.
• Simple to gut-load.
• Can be cultured using simple techniques and the most basic setups.

Cons:
• Reproduces slowly; difficult to build up a large population.

Collecting Tips:
None.

Culture Instructions:
Specific gravity: 1.0145-1.0168; pH: 8.0-8.3
Temperature: 68 degrees F – 73 degrees F (20 degrees C – 23 degrees C)

These fabulous little feeder shrimp can be kept indefinitely in a spare 2-10 gallon tank, or even a clean, plastic bucket, that has be filled with clean saltwater and equipped with an airstone for aeration. Neither a heater nor a fancy filtration system is required. They thrive at room temp and reduced salinity (1.015-1.016), and all they require is an airstone (or a simple air-operated foam filter at most) to keep the water oxygenated, with perhaps a little coral rubble as substrate and a clump or two of macroalgae (sea lettuce, Ogo, Caulerpa) to shelter in. They’re easy to feed — they feed primarily on algal mats and bacteria — but they will accept vegetable-based flake foods and pellets such as various Spirulina products. They are filter feeders and can also be fed with yeast or commercially prepared foods for filter-feeding invertebrates. Many people find an easy way to feed them is to place a small piece of algae-encrusted live rock in their holding tank; once they clean it off, simply replace it with a new piece of algae rock. But if you want to culture them, I’d recommend ordering the special food formulated just for them when you order your feeder shrimp from Hawaii. It’s designed to meet all their needs and requirements.

Comments:
These tiny red feeder shrimp (Halocaridina rubra) are native to Hawaii where they inhabit underground lava tubes and are called Opa’e ula. Brackish water pools collect in the cracks, crevices and depressions in the lava below the water table, thus forming the habitat for the shrimp. The brackish water that fills these pools consists of intrusive seawater diluted by freshwater that percolates downward. Because of their lava-tube habit, they are sometimes called Hawaiian Volcano Shrimp.

Native Hawaiians call them Opa’e-ula, and they are unique among the several different species anchialine pond shrimp in being small, social, herbivorous shrimp that feed mainly on algae and bacteria. They are known to feed on insects that drown in the lava tubes. When conditions are favorable, they may feed en mass at the surface in swarms of countless individuals that turn the water red.

Halocaridina rubra look like miniature, bite-size Peppermint Shrimp, and all seahorses save the miniature species go absolutely nuts for them! They are very nutritious and eat almost anything, making it easy to gut-load them for additional enrichment. They are perfect for seahorses in every way.

Unfortunately, it is very difficult to culture these shrimp in any quantity, since they reproduce slowly and the females only carry 12 to 14 eggs (Bill Stockly, pers. com.). They spawn but 4 or 5 times and produce an average of only 5-10 larvae per spawn. The larvae hatch as free-swimming, yolked zoeae after a brooding period of 38 days (Bill Stockly, pers. com.). Larval development is abbreviated with four zoeal stages and one megalopial stage occurring before they reach the first juvenile stage (Bill Stockly, pers. com.).. Duration of the larval stages in the aquarium is 24 to 27 days at 22 to 23 degrees C (Bill Stockly, pers. com.).

However, they can be purchased in quantity (up to 500 shrimp) at very reasonable prices from Hawaii, and they are easy to keep alive indefinitely, making them ideal to keep around as an occasional treat for your seahorses. Most of the time they ship very well, but occasionally when the weather is extreme, your live feeder shrimp will be delivered DOA. No problem — simply rinse them well and freeze the freshly killed feeder shrimp in a quantity of clean water. Seahorses eat these shrimp without the slightest hesitation, even when frozen. Thaw them as needed.

POST LARVAE SHRIMP (PLS): Ecuadorian White Shrimp (Penaeus vannamei, a.k.a. Litopenaeus vannamei)

Pros:
• Feed-and-forget — thrive until eaten in full-strength saltwater.
• High Health — guaranteed disease-free feeder shrimp for our ponies!
• Natural, highly nutritious food seahorses are accustomed to eating in the wild.
• Easy to feed and maintain.
• Long lasting — remain in the bite-sized larval stage for months.

Cons:
• Only available if purchased in huge quantities.
• PLS are notorious cannibals– will fatten up on each other if not well fed.

Collection Tips:
None.

Culture Instructions:
Post Larvae Shrimp are not suitable for batch cultures and self-sustaining cultures are not possible, but home hobbyists can easily maintain them. A 10 to 15-gallon tank is sufficient for up to 1,000 larval shrimp (Cheryl Colburn, pers. com.). The culture tank can be either an aquarium or any other inert container of sufficient volume. For example, rubbermaid containers work well as long as they are equipped with adequate filtration.

Feeding PLS is a breeze. They will eat just about anything. They’ll take flake food and frozen foods and are especially fond of frozen Mysis relicta, which makes a superb staple diet for them (Cheryl Colburn, pers. com.). Whatever you feed them as their everyday diet, however, be sure to fortify the PLS with a good enrichment product. Enriching PLS with formulas that are rich in HUFA and long-chain fatty acids will assure that the larvae have maximum nutritional value when they are fed to your seahorses (Cheryl Colburn, pers. com.).

PLS will be 4-7 mm in length when you receive them, and at standard aquarium temps of 24 C (74-75 F) they will remain small enough to be eaten by large seahorses for at least 1-2 months (Cheryl Colburn, pers. com.). PLS are thus useful as fry food when they first arrive and are suitable for feeding small ponies for the next 3-4 weeks at 74 F.

Their growth rate is dependent on water temperature. If you can chill their tank, and maintain 60-70 F, they will grow at an extremely slow rate and remain in the larval stage for several months.

Cheryl Colburn is one hobbyist who has worked extensively with PLS and she reports they are almost indestructible in the aquarium. If fact, she has never lost one of her larvae for any other reason than predation by another PLS.

Comments:
If you can obtain them, PLS are the ideal live food for seahorses. They are the larvae of Ecuadorian White Shrimp (Penaeus vannamei), which are cultured in enormous numbers on shrimp farms for human consumption (Cheryl Colburn, pers. com.). Since they are destined to become people food, White Shrimp are raised at High-Health aquaculture facilities and are certified to free of specific pathogens and parasites. You couldn’t ask for a healthier, more nutritious food for your seahorses and all Hippocampines devour them greedily. They can be raised in hobby tanks to provide perfect fodder for any seahorses from fry to young ponies to mature adults, so they are suitable for every aquarist’s needs. Any of the larval shrimp that are able to hide out and evade capture long enough to mature, will eventually breed and provide nutritious nauplii for all your reef inhabitants (Cheryl Colburn, pers. com.).

The only problem is that PLS farmers deal in volume and a shipment of 40,000 larvae is their minimum order (Cheryl Colburn, pers. com.). They are accustomed to dealing with aquaculture facilities that order in the millions. So individual hobbyists are out of luck, but collectively, hobbyists have a perfect opportunity to pool their resources together and provide their seahorses with an unsurpassed live food source quite inexpensively (Cheryl Colburn, pers. com.). Split an order for 40,000 PLS between 40 different hobbyists, and each participant can provide his ponies with the perfect natural food very affordably. This is a great project for marine aquarium societies and the seahorse hobbyist community, in general. Popular groups such as the Ocean Rider Club, Ultimate Seahorse, <http://www.seahorse.org/&gt; and <http://www.syngnathid.org/&gt; could make the necessary arrangements easily and efficiently and provide a wonderful service for members who are interested, as advocated by Cheryl Colburn.

GHOST SHRIMP or GLASS SHRIMP

Pros (Giwojna, Oct. 1996):
• A highly nutritious, natural food for large seahorses.
• Available from pet shops or aquarium stores as well as through the mail.
• Very easy to gut-load and enrich with various supplements
• Good tolerance for saltwater: brackish ghosts last surprisingly long, and even freshwater ghost shrimp survive long enough to be a very useful food.

Cons (Giwojna, Oct. 1996):
• Suitable only for the largest specimens.
• Often too expensive to use more than occasionally.

Collecting Tips:
Ghost Shrimp are seasonally abundant along the Gulf Coast of the US in salt marshes, rivers that empty into the sea, tidal creeks and brackish bays (Ricketts, Robert T. 2003). Brackish Ghosts can be collected easily at low tide by vigorously shaking clumps of floating seaweed into a bucket of seawater, or by dragging a small seine or large aquarium net through tidal creeks or the grass flats just offshore (Giwojna, Oct. 1996). Similar techniques will often produce freshwater Ghost Shrimp from fresh streams or waterways, including grassy canals and ditches (Giwojna, Oct. 1996). Harvest only specimens that are small enough for your seahorses to swallow whole.

Aquarium specimens are available year round. Fish stores carry Ghost Shrimp both as feeders and as oddball pets for freshwater hobbyists (Giwojna, Oct. 1996).

Culture Instructions:
Ghosts do not thrive in soft water, so for best results keep them in slightly hard to alkaline water (Ricketts, Robert T. 2003). Like all crustaceans, these see-through shrimp shed their exoskeletons in order to grow. They may have difficulty molting and become stuck halfway through the process of extricating themselves from their old exoskeletons, particularly in soft water that is deficient in calcium (Ricketts, Robert T. 2003). For this reason, I recommend gradually converting your holding tank for Ghost shrimp to brackish conditions, using a high-quality marine salt mix to slowly raise the salinity (Ricketts, Robert T. 2003).

There are at least two distinct types of Ghost Shrimp (very likely more), which are very difficult to distinguish by casual examination (Ricketts, Robert T. 2003). One category of Ghost appears to be a true freshwater species. The freshwater Ghosts do not tolerate full-strength saltwater for any length of time but withstand brackish conditions without difficulty (Ricketts, Robert T. 2003). The other category of Ghost Shrimp is a brackish species that can be converted to full-strength saltwater, but which also tolerates freshwater for extended periods (Ricketts, Robert T. 2003).

One possible way to determine which type of Ghost Shrimp you have is to examine females that are "in berry" (carrying eggs attached to their swimmerets). The saltwater or brackish Ghosts carry huge numbers of extremely tiny eggs (Ricketts, Robert T. 2003). So small are these that individual eggs cannot be seen with the naked eye. The eggs of freshwater Ghosts are said to be much bigger so that separate eggs are visible (Ricketts, Robert T. 2003).

The freshwater Ghosts breed more readily in the aquarium, and the larval shrimp are somewhat easier to raise (Ricketts, Robert T. 2003), but home culture of Ghost Shrimp is not really practical regardless of which variety you obtain.

Feed Ghosts small amounts of dry food once daily. The fine, leftover particles that accumulate on the bottoms of nearly empty flake food containers are great for feeding Ghosts, or crumble fresh flakes between your fingers to create particles of that same consistency (Ricketts, Robert T. 2003). Soak these fine flakes in a good enrichment formula and then feed them to the shrimp about 30 minutes before feeding the Ghosts to your seahorses (Ricketts, Robert T. 2003). This will gut-load the shrimp and fortify them for maximum nutritional value. (You will actually be able to see the enriched flakes accumulate in the hindgut through the shrimp’s transparent body.)

A 10-15 tank will hold quantities of ghost shrimp, and smaller numbers will do fine in a 5-gallon bucket equipped with an airstone or air-driven foam filter (Ricketts, Robert T. 2003). Sponge filters will suffice; change water once a week to maintain water quality (Ricketts, Robert T. 2003).

Comments:
These shrimp are all but transparent, which explains why they are universally called ghost shrimp or glass shrimp. Their exoskeletons are perfectly clear, the underlying muscles nearly transparent, thus clearly revealing their internal organs and GI tract (Ricketts, Robert T. 2003). A loss of transparency is a sign of severe stress and poor health; upon death, Ghosts typically turn an opaque white like their namesakes (Ricketts, Robert T. 2003). Ghost shrimp are acrobatic swimmers, which propel themselves backward with amazing speed by flexing their tails beneath them.

Fully-grown Ghosts can reach two inches in length, but the best feeder shrimp for the greater seahorses are 1/10 to 1/4 that size, so select your specimens accordingly (Ricketts, Robert T. 2003). Hobbyists estimate that 100 eating-size Ghost shrimp is roughly a one-week supply for two large seahorses. With the high unit cost per shrimp, it’s easy to see than keeping your herd on a staple diet of store-bought ghosts is a very expensive proposition!

CAPRELLID AMPHIPODS (Caprella acutifrons)

Pros:
• Relished by all the greater seahorses.
• Excellent nutritional value.
• Feed-and-forget: survive indefinitely in saltwater until eaten.

Cons:
• Difficult to obtain.
• Preferred habitat is branching, fernlike hydroid colonies.
• Cannot be cultured in quantities.

Collection Tips:
Large numbers of Caprellid skeleton shrimp colonize fouling growths and organisms such as sponges, tunicates, and especially large colonial hydroids such as Obelia (Rudloe, 1971). At some times of year, these sessile organisms will be alive with swarms of skeleton shrimp. The best way to collect them is thus to look for such fouling growths on man-made objects (docks, wharves, jetties, breakwaters, buoys, etc.) and harvest the sessile animals complete with all the Caprellids inhabiting them (Rudloe, 1977). (The skeleton shrimp attach themselves tightly to such growths with grasping hooks and they will cling tightly to the hydroid colony and come along for the ride when you carefully place it in your collecting bucket.)

Culture Instructions:
They cannot really be cultured in any numbers, but you might try placing a heavily colonized clump of hydroids or two in a refugium and hope for the best.

Comments:
Skeleton shrimp are amphipods like Gammarus, but the Caprellids are very different in habits and appearance from Gammarids (The Caprellid, 2004). Whereas Gammarus are flat-bodied and seek shelter beneath vegetation and coral rubble, Caprella amphipods are thin and wiry (i.e., skeletal) and display themselves openly (The Caprellid, 2004). They have a long, slender thorax and almost no abdomen (The Caprellid, 2004). The spindly brown skeleton shrimp (Caprella acutifrons) are in constant slow motion, bending, stretching, somersaulting, and flexing languidly as they forage throughout the large hydroid colony they inhabit, gleaning diatoms from the stems and polyps and snatching up zooplankton (Rudloe, 1971). Thanks to their transparent bodies one can easily see the food particles streaming down their gut (The Caprellid, 2004). They owe their agility and acrobatic antics to the incredible flexibility of their slender, wire-like bodies and the fact that they have terminal hooks at their tail end and large grasping claws (gnathopods) like a praying mantis at the other end (Rudloe, 1971). Like a mantis, they often assume a prayerful attitude, slowly and reverently bobbing, then bowing their heads piously while clasping their "hands" together at their chests (Rudloe, 1971). They have two pairs of antennae and can turn their heads from side to side. Solemnly, they sway side to side, nodding and bowing down with great dignity.

Periodically they will interrupt their penitent meditation to begin actively foraging, and then they move altogether differently, with a unique method of locomotion that seems totally out of place in such clumsy looking creatures. Displaying surprising agility, they bend forward into a loop in order to get a good grip with their front claws. Then they swing their entire body over their heads, tail first, until their terminal hooks can grab a new hold, allowing them to release their grip with their claws and repeat the entire procedure (Rudloe, 1971). They are accomplished acrobats, advancing themselves end-over-end in a series of cartwheels and somersaults in this unorthodox manner. With the nimbleness and flexibility of a contortionist, skeleton shrimp can actually swing from limb to limb in this fashion (Rudloe, 1971), and it’s a comical sight to see them moving through the stems and branches and polyps of a bushy hydroid like a troop of drunken spider monkeys!

Thousands upon thousands of these tiny shrimp many inhabit a large clump of hydroids, and at first glance the entire hydroid colony appears to be writhing and crawling and pulsing with an eerie, unnatural life of its own (Rudloe, 1977). It is the tantalizing movement of these multitudes that apparently makes skeleton shrimp so irresistible to many fishes, and Jack Rudloe has often described how tossing a hydroid colony swarming with Caprellids into a seahorse tank will trigger a feeding frenzy worthy of a school of bloodthirsty sharks:

"Fish love to eat caprellid amphipods. Often we would tear off a clump of hydroids, toss it in the aquarium, and see even the most finicky reluctant feeders go wild and gobble up the tiny crustaceans as fast as they could pick them out of the hydroids. Sea horses especially love to eat them" ((Rudloe 1977, p100).

GRASS SHRIMP/RIVER SHRIMP

Pros (Giwojna, Oct. 1996):
• A highly nutritious, natural food for large seahorses.
• 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 (Giwojna, Oct. 1996):
• 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 floating seaweed into a bucket of seawater, or by dragging a small seine or large aquarium net through tidal creeks or the grass flats just offshore (Giwojna, Oct. 1996). Similar techniques will often produce freshwater grass shrimp and river shrimp from freshwater streams or waterways (Giwojna, Oct. 1996). Remember, keep only shrimp that are small enough for your seahorses 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 (Giwojna, Oct. 1996). River shrimp are simply the freshwater equivalent of marine grass shrimp.

All in all, these crustaceans are ideal foods for the bigger breeds of seahorses. Just be sure to select shrimp of suitable size for your seahorses (Giwojna, Oct. 1996).

Seahorses are so fond of these shrimp that they often attack specimens that are far too big to swallow. They will attempt to break the back of the shrimp by snapping repeatedly at the carapace. If they are successful in severing the abdomen from the cephalothorax, the seahorses will then slurp up the tail section and head half of the shrimp separately. Or should their victim be so large it cannot even be swallowed in sections, they will snick out mouthfuls of the soft tissue exposed inside the abdomen or thorax. At times, several seahorses will gang up on one big shrimp this way, like a pack of lions teaming up to bring down a water buffalo that’s too big for any one of them to tackle alone. Under the right circumstances, a sort of slow-motion feeding frenzy may then ensue, with the seahorses playing tug-of-war over the pieces of their prize.

Grass shrimp that are too large to be overcome by such tactics may survive to become long-term residents of the seahorse tank, coexisting with their reluctant tankmates in a sort of uneasy truce. Such die-hard shrimp provide a useful service as scavengers from then on.

We tend to think of our seahorses as gentle, nonaggressive creatures that wouldn’t harm a fly, but in reality they are surprisingly fierce predators in their own right. To small crustaceans, seahorses are the tigers of the grassblade jungle, striking without warning from ambush and devouring anything of the right size that moves.

Those are some of the shrimp species and crustaceans that make useful foods for seahorses and Mandarin dragonets, Dean. If you can raise any of them in useful quantities, the larval shrimp help to fatten up your Mandarin until you can get a thriving population of copepods and amphipods established in your aquarium.

Best wishes with all your fishes, sir!

Happy Trails!
Pete Giwojna