Re:fry: how to keep them?

#2389
Pete Giwojna
Guest

Dear Nigel:

Zulu fry will do best on newly-hatched brine shrimp (Artemia nauplii). Live baby brine shrimp (bbs) will produce the best results, since the newborns are unlikely to accept frozen baby brine shrimp at first and the uneaten frozen shrimp will quickly degrade water quality. Newly-hatched brine shrimp don’t have mouthparts and therefore cannot be enriched, so Vibrance isn’t needed. The newly hatched brine shrimp are nutritious on their own because they still have the bulk of their yolk supply.

Zulu fry are relatively large and well formed and these big, benthic babies might do well in an in-tank refugium, as described in greater detail below.

The newborns need to be fed frequently but should be all right from 8 a.m. to 4 p.m. as long as you give them one good meal in the morning. I would give them a feeding of newly-hatched brine shrimp before you leave for work, a second feeding after you get home, and another feeding a few hours before lights out. Given your schedule, a feeding regimen like that might be your best bet.

Cured ”seahorse trees” make good hitching posts for the fry, as do artificial aquarium decorations such as small seafans and soft plastic plants with fine, branching leaves (Giwojna, Jan. 1997). Strips, sections, and cylinders of plastic window screen or the plastic mesh sold in craft stores for needlepoint projects also work well. Short lengths of polypropylene rope (the kind sold at hardware stores and marine outlets for boating purposes) are another good option for hitching posts in the nursery. They come in many different colors, can be cut to any desired length, and are buoyant so if one end is anchored and the other end is unraveled, they will wave gently in the current like natural plants. (Avoid nylon rope, however — it bleeds in saltwater and will leech color and who knows what else into your tank!) If necessary, the holdfasts can be secured to the bare glass with silicone aquarium cement or suction cups designed for use in marine aquaria, or secured to a piece of coral rubble to anchor them in place.

If you can obtain the fine-bladed or feathery varieties, live Caulerpa will help maintain good water quality by removing excess nitrates, as well as providing natural hitching posts that help benthic seahorse fry feel right at home (Giwojna, Jan. 1997). These marine plants grow from woody holdfasts and don’t need to be anchored in a sand or gravel substrate, so they’ll do fine in a bare-bottomed nursery (Giwojna, Jan. 1997). However, live Caulerpa is more difficult to keep clean and sanitary, and for this reason, many breeders prefer artificial hitching posts for their nurseries such as those described above (Mai 2004b).

In addition, hydroids and miniature jellyfish (the free-swimming hydromedusae stage of the hydroids) are often present on live marine plants, and they can easily be accidentally introduced to the aquarium along with the Caulerpa. Ordinarily, this is not a problem for the greater seahorses, but hydrozoans can wreak havoc when they become established in a nursery tank. Not only will they compete with the fry for food, their stings can be lethal to the babies or leave them susceptible to secondary infections (Vincent, 1995c), and hydroids are sometimes responsible for mass mortalities in nurseries.

A brief quarantine period for Caulerpa and other marine plants, during which they can be treated with fenbendazole granules for several days, is therefore strongly advised. Fenbendazole is an inexpensive deworming agent used for hoses and other large animals, and treating the quarantine tank with 1/8 teaspoon per 10 gallons is guaranteed to eradicate hydroids before they can gain a foothold in your nursery tank (Liisa Coit, pers. com.).

Here are some excerpts from a species summary on H. capensis from my new book (Complete Guide to the Greater Seahorses in the Aquarium, TFH Publications, unpublished). They discuss the aquarium requirements for Zulu-lulus or Cape seahorses (Hippocampus capensis) and include additional information on rearing newborn fry and juveniles::

Hippocampus capensis (Temperate, Benthic)

Common name: Cape seahorse, Knysna seahorse, Knysna-seeperdje (South Africa), South African seahorse, Zulu-lulu (US), and Zulus (US).

Scientific name: Hippocampus capensis Boulenger, 1900
Synonyms: none

Maximum size: 11.2 cm total length

Climate: temperate: 33° S – 34° S

Breeding Habits:
Breeding Season: summer months (September to April) when water temperatures rise above 68°F (20°C).
Gestation Period: 14-21 days, dependent on diet and temperature.
Brood Size: 25-200
Size at Birth: 8-16 mm
Onset of sexual maturity: as early as 10-12 weeks.
Pelagic/Demersal (benthic): benthic; newborns orient to the substrate and seek out hitching posts immediately after birth.

Ease of Rearing:
Very easy! The newborns drop like rocks, the large, well-developed, benthic babies can take Artemia nauplii as their first food, and the young grow rapidly. Mortality is low with very few surface huggers or buoyancy problems. Cape seahorse fry are eminently suitable for the easy rearing method and this species is a good choice for hobbyists who are primarily interested in breeding and rearing seahorses.

Natural Habitat:
Hippocampus capensis is strictly an estuarine seahorse. It is native to South Africa where it is found only in a few select bays and estuaries along the southern coast and nowhere else. Its natural habitat includes the Knysna, Swartvlei, Keurbooms, and Klein Brak estuaries (Lockyear 1999). It is a bottom-dwelling seahorse that lives among submerged vegetation in river mouths and bays ranging from 0-20 meters (Bull and Mitchell, 2002, p27). As a result of its estuarine habit, this species can adapt to fluctuating conditions and tolerates salinities from 1 – 59 ppt (Whitfield 1995).

Natural History:
These amazing animals are found in bays and river mouths in association with submerged aquatic plants, such as eelgrass (Zosterae capensis) and macroalgae (Codium sp.) (Bull and Mitchell, 2002, p27). Cape seahorses are very much bottom dwellers and seldom venture up into the water column. They feed exclusively on zooplankton as fry and juveniles, but adult capensis feed primarily on small, benthic crustaceans (Whitfield 1995). Interesting, Neil Garrick-Maidment reports they are accustomed to eating nonmotile foods in their natural habitat (Garrick-Maidment, pers. comm.). Although these highly adaptable seahorses tolerate a wide-range of salinities, collection data suggests H. capensis occur most abundantly where the salinity approximates normal seawater (34 ppt) (Toeffie 1998).

The breeding season in the wild is dictated primarily by the temperature, and is thus restricted to the summer months when water temperatures reach around 62°F (20°C) (Bull and Mitchell, 2002, p27). H. capensis appears to mate monogamously in the wild (Grange & Cretchley 1995). Gravid males carry their developing young in their brood pouch for 14-45 days, depending on water temperature, and typically deliver between 30 and 120 young (Whitfield 1995). The fry grow rapidly, becoming sexually mature at a standard length of about 2.5 inches (6.5 cm) and begin producing offspring of their own within their first year (Bull and Mitchell, 2002, p27).

Preferred Parameters:
Carol Cozzi-Schmarr recommends the following parameters for keeping High Health H. capensis farm-raised in Kona, Hawaii:
Temperature = range 68°F to 77°F (20° C-25° C), optimum 72-75°F (22-23° C).
Specific Gravity = range 1.018 – 1.026, optimum 1.023.
pH = 7.8-8.2
Ammonia = 0
Nitrite = 0
Nitrate = 0-10 ppm
Suggested Stocking Density: 1 pair per 5 gallons (20 liters).

Aquarium Requirements:
The following recommendations are based on Brian Zimmerman and Heather Hall’s extremely successful rearing program for Hippocampus capensis at the London Zoo (Bull and Mitchell, 2002, p29). They describe the system used for displaying adult Knysna seahorses at the Zoo:

Population: 60-70 adult individuals
Volume: 350 gallons (1338 liters)
Height: 31.5 inches (80 cm)
Circulation: closed
Water: natural seawater
Filtration: plenum with live sand bed supplemented with an Eheim power filter containing mechanical filtration and carbon.
Substrate: coral sand with "live" sand.
Holdfasts: Caulerpa prolifera, netting, live rock.
Light: 2 HQI metal halide, 150 watts each, 10,000 Kelvin.
Photoperiod: 11 hours light
Temperature range: 73-79°F (23-26°C)
Nitrite (NO2): 0
Nitrate (NO3): <20ppm
Ammonia (NH4): 0
pH: 8.2
Specific gravity: 1.022-1.025

The display tank at the London Zoo has proven to be a stable system, which only requires about a 20% water change every other week. A cleanup crew consisting of small hermit crabs, black sea cucumbers, brittle stars and even bristle worms is very helpful for scavenging uneaten food (Bull and Mitchell, 2002, p29). A healthy growth of Caulerpa, which the Zoo harvests regularly, helps remove phosphates and nitrates.

The rearing and holding tanks for juvenile H. capensis at the Zoo are designed differently than their main exhibit, as described below (Bull and Mitchell, 2002, p29):

Juvenile/Fry Rearing Tanks:

Population: average is 20 juveniles.
Volume: 14.5 gallons (55 liters)
Height: 12 inches (30 cm)
Circulation: closed
Water: natural seawater
Filtration: Double Algarde air driven sponge filter
Substrate: thin layer of coral sand
Holdfasts: artificial seagrass and live rock.
Light: fluorescent room lights (no light directly above tanks)
Photoperiod: 11 hours light
Temperature range: F 73-79 (23-26 C)
Nitrite (NO2): 0
Nitrate (NO3): <50ppm
Ammonia (NH4): 0
pH: 8.2
Specific gravity: 1.022-1.025

The rearing tanks at the London Zoo are set up like basic SHOWLR systems. The rearing tanks each consist of a shallow coral sand substrate (1-cm deep), a piece of live rock (about 10x8x8 cm), ten short artificial plants (4 inches or 10.5 cm tall), and a long artificial plant (12 inches or 30 cm tall) arranged to simulate a seagrass bed (Bull and Mitchell, 2002, p29). These items are positioned to create a complex environment with varied microhabitats in order to maximize the seahorses’ welfare, in accordance with a study (Tops 1999) which demonstrated that creating complex surroundings encouraged more "natural" behavior in Hippocampus capensis.

Each of the rearing tanks at the Zoo is filled with 12.5 gallons (47 liters) of natural seawater, a double sponge filter, and an extra airline to increase airflow, primarily to aid food circulation (Bull and Mitchell, 2002, p29).

The bottoms of the rearing tanks are siphoned clean of debris and uneaten food daily. A partial water change is accomplished during the siphoning, which amounts to about 2-5% of the water in each tank being replaced every day (Bull and Mitchell, 2002, p29).

Heather Hall notes that hydroids or polyps often build up in the rearing and holding tanks at the London Zoo. When the hydroid colonies reach a high density, the entire tank is broken down, cleaned, and soaked in freshwater overnight, and reestablished anew (Bull and Mitchell, 2002, p29). Occasionally outbreaks of Aptasia rock anemones at the Zoo are dealt with via biological control by introducing Berghia sp. nudibranchs, which are natural Aptasia predators (Bull and Mitchell, 2002, p29). The Zoo maintains a colony of these sea slugs in reserve for that very purpose. The home hobbyist will find it easier and more practical to control outbreaks of hydroids and Aptasia anemones using fenbendazole, as described in the chapter on rearing.

The sponge filters in the rearing tanks are rinsed with tank water until clean at least every week. In heavily stocked tanks, the sponge filters are cleaned more frequently and each holding tank also has a piece of live rock to provide supplemental biofiltration and extra stability (Bull and Mitchell, 2002, p30).

The London Zoo measures pH, dKH, nitrate (NO3), and dissolved oxygen (O2) every other week (Bull and Mitchell, 2002, p30). The water temperature is monitored three times per day and specific gravity is checked every other day (Bull and Mitchell, 2002, p30). The photoperiod is 10 hours of light, from 8 a.m. to 6 p.m., and 14 hours darkness.

Diet, Nutrition, and Feeding Techniques:
Cape seahorses at the London Zoo are fed three times daily on a combination of thawed Mysis and Artemia, with live adult Artemia enriched with Super Selco mixed in with the frozen foods (Bull and Mitchell, 2002, p30). Multiple airlines are used to provide a very strong airflow, which has the added benefit of helping to keep food in suspension longer and wafting it past the seahorses (Bull and Mitchell, 2002, p30). This eliminates the need for powerheads, which can be risky to use with Hippocampus unless the inputs are screened off and carefully shielded from the seahorses. All frozen foods (Artemia, Mysis) at the Zoo are rinsed very thoroughly in freshwater through a fine net before feeding (Bull and Mitchell, 2002, p30). This helps maintain water quality by reducing the milky "juice" given off by thawed foods.

Discussion:
Also known as the Knysna Seahorse or the Cape Seahorse, Hippocampus capensis is well suited for beginners. For one thing, these ponies are just the right size for the average home aquarium and are natural born gluttons — the easiest seahorses of all to feed. They are smallish-to-medium seahorses, but they have BIG appetites and will eat most anything and everything the giant breeds do. They are aggressive feeders and, in an impressive display of voracity, even small specimens will unhesitatingly tackle large frozen Mysis that may take them two or three snicks to successfully swallow. A hungry Cape seahorse will often have more than half of a large mysid protruding from its snout, making it look like a sword swallower in mid-performance as it gradually works its gargantuan meal down with a series of mighty snicks! It is an amazing sight to watch an undersized capensis choke down several oversized frozen Mysis in quick succession and come hurrying back for more like it was starving with the tail of the last shrimp still sticking out of its mouth! They are capable of remarkable feats of sheer piggery, and everyone marvels at how rotund they are when they get their first good look at well-fed, captive-bred capensis.

Of course, they love frozen Mysis relicta and are accustomed to eating that as their staple diet, but these chow hounds are not at all picky when they put on the ol’ feed bag. These galloping gourmets also eat rotifers, brine shrimp, amphipods, copepods, red feeder shrimp (Halocaridina rubra), Caprellids — you name it and they’ll eat it. All the usual seahorse foods are taken with relish and these seagoing gluttons don’t seem to mind a bit whether they are live, freshly killed or frozen. They normally feed on nonmotile food in the wild (Garrick-Maidment, pers. comm.), so they thrive on frozen food in the aquarium. In short, feeding these fat little fellas is the last thing the hobbyist has to worry about!

Hippocampus capensis are fat, pudgy little ponies with a very distinctive appearance. Short and stout, with that portly profile, stubby snouts, big bulging eyes, and perfectly smooth bodies — I can’t decide whether these captivating characters are more cute or more comical looking! They are very unusual for seahorses in that they have no semblance of a crest or coronet whatsoever.

These thick-bodied little seahorses are the perfect size for the home aquarium. They reach a total length of just over 4 inches, and are shipped to you at the modest size of 2-3 inches. That makes them around three times the size of dwarf seahorses — small enough to feel right at home in the average aquarium, yet large enough to make fine display specimens and to eat frozen mysid shrimp as their staple diet. They have proven to be very hardy and easy to breed, and when you’re ready for the challenge of rearing, you’ll find newborn H. capensis are relatively easy to raise, much like dwarf seahorse fry.

Like most captive-raised seahorses, H. capensis are very social, highly gregarious animals that very much enjoy the company of others of their kind.

This is another species that is reported to monogamous in the wild but which is polygamous in captivity. In the aquarium, they court constantly and breed like bunnies when kept in a group situation, but one male tends to do the bulk of the breeding (Neil Garrick-Maidment, pers. comm.). Trios and foursomes will often court together until a pair emerges. They will pair bond, but such pairings may only last one or two breeding cycles. Any time males and females are kept together under good conditions, you are going to see courtship and mating (Giwojna, Sep. 2003). Just feed them well and provide them with clean water and a tank that’s tall enough to allow for the copulatory rise — a water depth of at least 12 inches, in this case — and these prolific ponies will take it from there (Giwojna, Sep. 2003)!

The gestation period for H. capensis is about 21 days, perhaps a bit shorter if you’re keeping them at temps in the mid-70’s (Giwojna, Sep. 2003). Brood size is about 50 to 200 with the exceptional large brood of around 300 (Garrick-Maidment, pers. comm.). The fry are quite large, usually 8-10 mm in total length (Garrick-Maidment, pers. comm.). They grow very fast and reach sexual maturity as early as 10 to 12 weeks (Giwojna, Sep. 2003; Garrick-Maidment, pers. comm.).

Compared to most other seahorses, rearing these chubby little charmers is a breeze. The newborns seek out hitching posts from day 1, meaning the fry rarely gulp air, floaters and surface huggers are virtually nonexistent, and they are largely immune from the buoyancy problems that so often decimate other seahorse fry (Giwojna, Sep. 2003). H. capensis fry are the most benthic of babies and thrive on newly hatched brine shrimp as their first food (Giwojna, Sep. 2003). Just feed them plenty of baby brine shrimp as soon as possible after the Artemia hatches and they will grow like weeds. They will be ready to be weaned onto frozen Mysis between the age of three to six weeks (Giwojna, Sep. 2003). They make the transition from live food to frozen fodder remarkably easily, without missing a beat (Giwojna, Sep. 2003)!

In fact, Heather Hall found them almost too easy to raise at the London Zoo. In order to keep from being overrun with captive-bred capensis, the Zoo was forced to resort to unusual methods to reduce the reproductive rate of their colony. She describes her experience raising these bountiful breeders as follows: "H. capensis is a relatively prolific species. Brood sizes average about 50 babies… Since survival rate is high with good husbandry and diet, it is easy to become overpopulated with animals. In order to avoid overpopulation we have tried different ways of managing the population in our collection. Separating the sexes was employed in several tanks. Sexes were kept isolated in groups of 20. We found that this led to many problems. The animals exhibited a number of stress signs: disease outbreaks increased and aggression was high between males. Females became swollen with eggs and suspected egg binding occurred. Respiration rates and twitching also increased. Therefore, we decided to separate the sexes of our seahorses no longer. Animals in the display tank are allowed to reproduce as normal, and young are only removed when required. Some young survive in the display tank, feeding on naturally available foods and make it to adulthood. To keep the generations turning over, we can remove up to 20 individuals and raise them in the holding tanks. They can be given special attention there and their growth monitored. This method has worked well for us" (Bull and Mitchell, 2002, p30).

In the end, H. capensis fry were simply left to their own resources in the display tank with their parents, yet some of them routinely survived to adulthood on their own with no special care whatsoever. Now that’s what I call easy to rear!

These are VERY adaptable animals, a necessary trait for estuarine seahorses that customarily inhabit the mouths of rivers and lagoons, where winter gales or the influx of freshwater from flooding and torrential rains can change conditions drastically overnight. Cape seahorses are rugged little rascals as a result — adaptable fishes that can survive wide variations in salinity ranging from water that is barely brackish to water twice as salty as normal seawater (Whitfield 1995). The ability to tolerate such extremes allows H. capensis to withstand changing parameters in the aquarium as well. But, as always, they will do best under stable conditions, and prefer a specific gravity in the low-normal range for a marine aquarium (e.g., 1.022-1.023).

Considering the conditions they are accustomed to in the wild, we shouldn’t be surprised to find that captive-bred H. capensis can adapt to considerable temperature variations as well. For example, the London Zoo found they do well when maintained at 23-27.6ºC (73-82ºF) (Bull and Mitchell, 2002, p29). In my experience, however, the home hobbyist will fair better by keeping these temperate seahorses at somewhat cooler temperatures (68-75ºF or 20-24ºC). Maintain stable temperatures between a range of 70F-75ºF (21-24ºC) and they will do just fine. Just don’t let the water temp creep above 75ºF for any length of time!

When subjected to heat stress, Cape seahorses are susceptible to tail rot (a.k.a. white tail disease). Such problems often begin to appear in the home hobby tank when a summertime heat wave raises aquarium temps above 77F (25C) for an extended period or causes temperature spikes to 80F (27C) or above. For this reason, an air-conditioned fish room or mini aquarium chiller may be necessary for the home hobbyist. The best time to order captive-bred Hippocampus capensis is fall through spring, when they will not be subject to heat stress when making the long trip from Hawaii to your doorstep.

Cape seahorses are bottom huggers by nature. They spend most of their time slipping along the bottom on their bellies, actively searching for food underneath objects or at the base of plants, or perched on low holdfasts while they intently scan the bottom for prey. Only rarely do they visit tall hitching posts or venture up into the water column.

These are remarkably rugged, hardy little seahorses, but their bottom-hugging behavior sometimes leaves H. capensis prone to tail infections. It is important for the capensis keeper to provide his charges with a nonabrasive substrate such as fine-grained sand and to keep the bottom of the aquarium scrupulously clean. Some Cape seahorse owners even go as far as keeping them in bare-bottom tanks, which facilitates cleaning and maintenance. That’s fine for nurseries and rearing tanks but is certainly not necessary for the display tank.

Should tail rot or other bacterial infections arise, H. capensis responds well to treatment for bacterial infections by using antibiotics in the live foods offered (Bull and Mitchell, 2002, p28). Reducing the aquarium temperature to the lower end of their range, as low as 66-68 F (19-20 C) if possible, while providing live adult Artemia or red feeder shrimp (Halocaridina rubra) that have been gut-loaded with the appropriate antibiotic is often an effective treatment regimen for this species.

Bottom Line:
These are fantastic fishes for anyone who can meet their temperature requirements (70F-75F or 21-24C). Hippocampus capensis are equally well suited for beginners as their first seahorse and for advanced marine aquarists as their first serious breeding project. These remarkable rarities are ideal for seahorse keepers with a serious interest in breeding and rearing, for conservation-minded aquarists who like the idea of working with an endangered species, or for anyone who is looking for truly exotic specimens that have never been available to hobbyists before. H. capensis is best suited for species-only tanks of 20-30 gallons or less. For best results, their aquarium should be heavily planted with macroalgae to simulate the seagrass beds that are their natural habitat.

Best of luck with your Zulu-lulus, Nigel! Keep their aquarium a little on the cool side (75°F or lower) and they should do well.

Happy Trails!
Pete Giwojna


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