Re:collecting wild copepods and amphipods

Pete Giwojna

Dear Scott:

Outstanding! Thank you very much for sharing your ‘pod collecting techniques with us and especially your ingenious method of separating the amphipods from the plant matter and debris. It sounds like it works like a charm and not only is it an ideal method of separating the ‘pods from the gunk and inedible debris, it also segregates the liveliest of the amphipods from the weak and injured specimens that make less desirable food items.

I’m not sure how well the amphipods would survive in freshwater, however, Scott, so be careful if you’re thinking of using a freshwater bath to disinfect them as an added precaution. Adult brine shrimp (Artemia spp.) can go from hypersaline water to freshwater with no ill effects whatsoever, so they can be disinfected in freshwater without any difficulty, but most crustaceans are not nearly so euryhaline. Try performing a test with your particular amphipods to see if they can tolerate the freshwater before you try cleansing a whole batch of them using a freshwater bath. You don’t want the frisky amphipods to be stunned or incapacitated by the freshwater, because it is their herky-jerky movements that make them so irresistible to seahorses. Besides, your innovative techniques for separating out the ‘pods from the trash is so effective that they shouldn’t really require any further cleansing.

You are fortunate to live near the seashore where you can find a ready supply of choice live foods for your seahorses right on your doorstep, sir. That is something that I would encourage all seahorse keepers in your situation to take full advantage of, Scott. The following excerpt from my new book is what I normally advise hobbyists regarding collecting and culturing amphipods and copepods for their ponies:

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Pros (Giwojna, Oct. 1996):
· Highly nutritious, hard-bodied crustaceans.
· Favorite food of many larger seahorse 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 increasingly available as fish food.
· Starter cultures are widely available through the mail.

Cons (Giwojna, Oct. 1996):
· 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 tide (Giwojna, Oct. 1996). Also know as scuds or beach-hoppers, scads of the land-dwelling form of these amphipods (Talitrus saltator) can often easily be collected from the mats of seaweed washed up on shore at the tide line. Simply gather up clumps of the freshly deposited seaweed and shake it vigorously over your collecting bucket to dislodge the amphipods.

Freshwater Gammarids–Gammarus fasciatus can be collected from vegetation and leaf litter on the bottoms of ponds and slow-moving streams (Giwojna, Oct. 1996).

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 (Giwojna, Oct. 1996). Encourage a lush growth of green algae and restock periodically.

Under the right conditions, these small, shrimplike crustaceans mate and reproduce readily in captivity. Provide them with a lush green mat of Ulva macroalgae as natural habitat, and they will soon take up residence and establish a breeding colony of amphipods (Indo-Pacific Sea Farms, 2003). Provide them with low light levels, good aeration, and a pinch of flake food twice a week and you’ll soon have a growing population of Gammarus to dole out to your seahorses (Indo-Pacific Sea Farms, 2003).

Freshwater Gammarus can be cultured in a plastic wading pool or similar spacious receptacle equipped with an airstone (Giwojna, Oct. 1996). 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 growth (Giwojna, Oct. 1996).

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 (Giwojna, Oct. 1996). Commonly known as side-swimmers, these hard-shelled amphipods have a herky-jerky, sidestroke swimming style that most large sea horses find irresistible (Giwojna, Oct. 1996). 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 Hippocampines will actively pursue and search out. Some sea horses will even accept freshly killed or dead Gammarus (Giwojna, Oct. 1996). An ideal food: substantial enough to be your sea horses’ staple diet, if you can obtain it in sufficient quantity!

When mating, the male amphipod carries the smaller female grasped between its legs, a breeding method known as amplexus (Biology of Amphipods, 1996). Thus, when you see pairs swimming together while locked in amplexus, it’s a sure sign your amphipod colony is growing. The female subsequently releases the fertilized eggs into a ventral brood chamber where the unattached eggs are held by extra branches of her walking legs and incubated during development (Biology of Amphipods, 1996).

Unlike crab and shrimp larvae, baby amphipods are not released as zoea that develop into adults after several stages of metamorphosis (Biology of Amphipods, 1996). Instead, the young look like miniature versions of their parents when released, and some species even show parental care of their young after they leave the brood chamber (Biology of Amphipods, 1996).

Different types of amphipods move differently, depending on the arrangement of their legs. Most species can walk upright, scuttling along by using most of their thoracic legs, but this is a slow, rather cumbersome method of locomotion (Biology of Amphipods, 1996). Practicing their sidestroke and swimming along using three pairs of pleopods is much faster (Biology of Amphipods, 1996). But the true specialty of amphipods is the tail-flip, a rapid escape response where the abdomen flicks the animal away after the uropods are dug into the substrate (Biology of Amphipods, 1996). Terrestrial amphipods (scuds, sand fleas, beach hoppers, etc.) are especially adept at this startling maneuver. It is this variety of frantic movements and escape maneuvers that triggers the seahorse’s feeding response and makes amphipods so irresistible to Hippocampus. Seahorses love to hunt them!

As we’ll see below, Caprellids cannot use any of the amphipod’s usual methods of locomotion. They are restricted to slow-motion somersaults and painstakingly stepping along like an inchworm.

CAPRELLID AMPHIPODS (Caprella acutifrons)

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

· 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.

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).


· Naturally high levels of essentially fatty acids.
· Natural food that forms a large portion of the seahorses’ diet in the wild.
· Elicits a strong feeding response.
· Perfect first food for seahorse fry.
· Feed-and-forget: marine species survive until eaten and will colonize live rock, filters and refugia.
· Starter cultures readily available.
· Easily collected by hobbyists with access to the seashore.

· Complex life cycle complicates home culture.
· Many species too small to interest adult seahorses.
· Some species are parasitic — can be difficult to tell the good guys from the bad boys.

Collecting Tips:
Free-swimming copepods can easily be collected by anyone who lives within a reasonable distance of the ocean (in parts of the sea, larval calanoid copepods comprise the bulk of the zooplankton). Simply tow a plankton net (an elongated conical net made of fine material) slowly behind a boat in an area well away from possible sources of pollution, stopping periodically to empty its contents into a collecting container. (A mesh size of 250-500 microns will collect ‘pods that are about the right eating size for medium seahorses.) Cover the collecting bucket with a damp towel to keep it cool during the heat of the day and provide aeration to make sure the plankters stay alive until you get home.

Culture Instructions:
Suitable for batch culture with greenwater (phytoplankton). See the rearing chapter for complete directions for culturing copepod nauplii.

Providing copepod nauplii as the first food for pelagic seahorse fry results in faster growth and often dramatically increases survivorship.

Copepods are an extremely diverse group of Crustacea with more than 10,000 known species with different lifestyles filling a great variety of environmental niches, both marine and freshwater (Dürbaum and Künnemann, 2000). There are three major groups of free-living copepods that are useful in aquaculture (Dürbaum and Künnemann, 2000): the Calanoida (primarily free-swimming planktonic animals), the Cyclopoida (either planktonic or demersal), and the Harpacticoida (entirely benthic).

Copepods undergo a remarkably complex life cycle. After hatching from the egg, they pass through six distinct nauplius stages, undergo a metamorphosis that completely transforms their body shape, and then go through six additional copepodid stages, culminating with the mature adult (Dürbaum and Künnemann, 2000). The first nauplius stages have only 3 pairs of appendages, which are used for locomotion and feeding (Dürbaum and Künnemann, 2000). The 6th and final naupliar stage molts into the first of the copepodid stages, and important development marked by major morphological changes (Dürbaum and Künnemann, 2000). The emerging copepodid larvae resemble the adults in large part. With the increasing number of body segments in the copepodid, more of their appendages become fully functional (Dürbaum and Künnemann, 2000). After the fifth copepodid molt adulthood is reached and the mature copepods are able to reproduce. There are two different sexes and reproduction is sexual (Dürbaum and Künnemann, 2000).

Growth is very rapid, with most species going from the embryo to mature adult in 10-12 days at 25-degrees C. The free-swimming nauplii are attracted to light, becoming less phototropic as they mature, until the adults begin to settle and attach to the substrate. As adults they swim less, remaining attached to substrates for anywhere from a few seconds to a few minutes at a time.
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Best of luck with your seahorses, Scott! Thanks again for sharing your collecting tips with the group!

Pete Giwojna

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