Breeding SeahorsesAuthor: José María Cid Ruiz
The fishes of the genus Hippocampus, commonly known as seahorses, are reported to frequently reproduce in captivity. Most of the literature is also optimistic about the viability of seahorse fry. However, my experiences with maintaining and reproducing several species of Hippocampus demonstrates that a labor-intensive effort is required to obtain a new generation of adult seahorses, and even then the final outcome is uncertain.
Since seahorses only reproduce in optimal conditions, some notes about their general husbandry requirements are important. The approximately 35 species of seahorses come in a wide range of sizes, from a mere 3 cm (a little over 1 inch) for H. zosterae to 30 cm (about 1 foot) for H. abdominalis. A good general rule is that the height of the aquarium should be at least double the length of the species being kept to allow swimming room, since all species swim vertically in the water column. Even taller is better to accommodate the ascending mating dance that is vital for successful reproduction.
Although seahorses are not quick swimmers, they are vigorous and active when healthy, and therefore the aquarium should be reasonably spacious. As a general rule, I have kept groups of three to six individuals of H. kuda and H. reidi in aquariums of 150 to 250 liters (40 to 65 gallons). I have also occasionally kept H. hippocampus and H. ingens.
The aquarium requires open areas where the seahorses can swim freely, but it must also provide structure that the seahorses can hold onto with their prehensile tails. It is desirable to provide an area with a swift current (in their natural environment I have found seahorses in areas with considerable current), but the current should only be present in one area because these animals are not strong swimmers. In addition, if it permeates the whole aquarium the mated pairs will be unable to transfer their eggs.
Temperatures lower than 26.5°C (80°F) and/or insufficient illumination, in my experience, drastically reduces their feeding instinct. I have also read that a photoperiod of less than 12 hours inhibits reproduction. I have found that photoperiods between 12 and 14 hours are useful for getting seahorses to spawn.
Seahorses need to be kept in very clean water, which requires excellent filtration and frequent partial water changes. In order for them to breed, ammonia and nitrite need to be kept at 0 mg/l and nitrates should not be higher than 10 to 15 mg/l. In general the water chemistry parameters should be stable and kept at values like those of a reef tank.
The mouth at the end of their long, tubular snout gives seahorses the ability to capture prey through suction. They are basically ambush predators, waiting and watching with a 360-degree field of vision thanks to their independently moving eyes until a prey item comes within range. In the aquarium the fish will more readily leave their perches and hunt down prey. Hippocampus species have a rudimentary digestive system with a simple, small stomach that has very little storage capacity. Their digestive tube is simple and short, so the seahorse has very little time to absorb nutrients before the food is eliminated. Therefore seahorses need to constantly search for and ingest food.
Seahorses are often very selective in what foods they will accept, with different species of small crustaceans—Artemia, Mysis, Gammarus, Talitrus, and others—forming the base of their diet.
Seahorses prefer living food, but alternating live and frozen food helps keep them on their diet. A varied diet is essential, and in medium to large species it should include very small whole fish. Captive-bred seahorses are much easier to feed than wild-caught ones, as they are trained from birth to take nonliving foods.
In nature seahorses feed continuously. Feeding them at least twice a day, but preferably three times a day, is the minimum required to keep seahorses in aquaria. Undernourished pairs rarely reproduce and, when they do, there are often severe defects in the fry because the eggs and embryos do not receive the necessary nutrients.
It is especially important to note that if seahorses go too many days without feeding, they start absorbing their own tissues. Death is inevitable once they start consuming the tissues in their digestive system even if they are properly fed after that.
Although there are reports of successful seahorse reproduction in community tanks, these are the exception. It is often difficult for seahorses simply to survive when they have competition for food. Use a dedicated species tank large enough to house two to three pairs together.
A healthy seahorse is one that is active, constantly moving its eyes, breathing calmly, and regularly ingesting food. These fish are relatively resistant to disease, though they will occasionally suffer from protozoans like Amyloodinium and Cryptocaryon, fungal infections, and crustacean parasites like Argulus. Breeding males often suffer from gas bubbles in their brood pouches. This is typically encountered after the male delivers a brood, and it is very difficult to treat. Treatment usually consists of dilation of the pouch opening and massage to expel the gas, and then a course of antibiotics. Obviously such action should be taken only under the supervision of a veterinarian or other fish health professional.
Healthy and well-nourished individuals grow quickly. Life expectancy appears to be about 3½ years. Captive-bred individuals (whose exact age can be known) occasionally show signs of senescence after the age of 3.
When kept under good conditions, seahorses easily form pairs that in captivity at least appear very stable. I have observed pregnant males in the wild (H. hippocampus in the Mediterranean Sea, H. reidi in the Caribbean Sea, and H. guttulatus in the Atlantic Ocean), and they were always alone.
Courtship occurs in open areas usually first thing in the morning either when there is faint sunlight or shortly after the aquarium lights turn on. Usually the male approaches the female and his color turns more intense, especially the black borders on his fins.
Once he is parallel to the female, the male strongly vibrates. If the female is ready to spawn, she also vibrates and stays next to the male. They may entwine tails, and the male occasionally rubs his brood pouch against her ventral area.
The male’s pouch swells, and the orifice at the top of the pouch opens. His movements appear aimed at drawing the female’s attention to the pouch. She inserts her ovipositor into the pouch and transfers the eggs, which takes about five seconds. As soon as the eggs are transferred, they are fertilized and the brood pouch seals shut.
The individuals separate after the spawning. The male sometimes attaches himself firmly to a perch with his tail and proceeds to make a characteristic rocking movement of his ventral area, which, according to my interpretation, is so the eggs are homogeneously distributed in the bag. Brood size (from 25 to 220) depends on species and on the size and maturity of the individuals.
My observations based on an unconventional group of three males and one female reveal that all three males show a swollen pouch, though only one of them has spawned with the only female in the group. All of the males also show courtship behavior, and I believe the inflation of their bags is to show that they are ready to spawn. Therefore every male with a swollen bag is not necessarily pregnant. This also may explain why the time estimates for embryological development is so variable.
In the male’s pouch, tissues dense with blood vessels wrap around each egg. This acts like a placenta, providing gas exchange, osmoregulation, and nutrients to the eggs. In my aquariums, development has taken between 14 and 18 days, with 16 days being the most common. While courting males can be difficult to differentiate from pregnant ones, near the end of the pregnancy the difference is unmistakable. The behavior of a male about to deliver is also much more reserved.
I never isolate pregnant males and I have not observed fry predation. Fry are born individually or in small groups, expelled by their father’s labor-like muscle spasms. They are usually born in the semi-light just at dawn. Often a few will be born at sunset the day before the whole brood is delivered the next morning. Fry are exact miniature copies of the adults and are between 6.80 and 8.00 mm.
Fry are positively phototropic—they go directly to the light at the surface, where they swallow air through their mouth to fill up their swim bladder, which then seals up. In the wild the fry disperse immediately after reaching the surface, but in the aquarium individuals frequently get tangled at the surface and form a large mass of struggling fish.
It is important to separate the fry by groups to break up the masses before the individuals expend lots of useless energy trying to swim. I place groups of 30 to 40 fry in 10-liter (2½-gallon) aquaria. Always keep the fry submerged! In my experience, fry that have been kept out of water for even a few seconds acquire too much air and float helplessly at the surface, where they die from starvation.
The small aquariums must always have very clean water. Excess food should be siphoned off the bottom one to two times per day and daily water changes should be conducted. Small filters that do not create a lot of water movement must be used because excess water movement prevents the fry from eating. I keep the lights on 24 hours a day during the first few weeks so the fry can eat around the clock.
Newborn Hippocampus do not feed during the first hours after being born, though they are very active in the middle and toward the surface of the water column. About 18 to 20 hours after hatching the fry will start seeking food. I have tried two different feeding regimens, both based on the fact that at first Artemia nauplii fed to the fry must be less than three hours from hatching. During the first week young seahorses are unable to digest the shells (which harden in three to fours hours after hatching) of Artemia nauplii. Microsopic evaluation indicates that if the fry eat these older nauplii, they become impacted and die.
With either regimen, suitable prey items must be constantly available in sufficient quantities that the feeble fry can eat enough. Starvation claims a large number of fry the first week.
The fry are fed just-hatched Artemia three times a day. When the fry are satiated, the uneaten shrimp must be siphoned out. This regimen requires a lot of time and discipline, and there is very little margin of error. The uneaten shrimp remain small enough for the fry to eat, but once they are past three hours old eating them will kill the young fish.
This regimen is further complicated by the fact that hatching time for Artemia cystsvaries from 18 hours to 28 hours, depending on to geographic origin of the cysts, temperature, and salinity.
The other option is to feed seahorses rotifers until they are five days old. The rotifers should be raised in a culture of unicellular algae in concentrations of 200,000 to 300,000 cells per milliliter. The concentration of rotifers in the seahorse fry tanks should be kept about 10 to 15 rotifers per milliliter (15,000 per liter).
Success is low with either regimen—about 10 percent for the first and 18 percent for the second. The surviving fry grew faster with the first regimen, however, growing 2.5 to 3.5 mm the first week, compared to 1.5 to 2.0 mm for the second regimen. The fry show more interest in the shrimp nauplii than in the rotifers, but in either case there is a learning curve during the first few days, with the fry improving their predation skills over time.
After the first week the fry are able to handle baby brine shrimp up to a day old, and the fry are much hardier. They now measure about 10 mm long. After this time I enrich the Artemia unsaturated fatty acids using a salmon-based oil. At the end of the second week I rotate frozen Cyclops with the Artemia and move the seahorses to a larger aquarium of 20 to 30 liters (5 to 8 gallons) that has moderate filtration with intakes that are covered by a plankton net. The daily cleaning and water changing regimen must be strictly maintained throughout. I also add calcium and magnesium every two weeks along with strontium, iodine, and a multi-vitamin.
At the end of the third week I add small live copepods to their diet. By the end of the fourth week I reduce the photoperiod, providing six to eight hours of darkness.
After six or seven weeks, when the young seahorses show more interest in consuming copepods, the diet should change again. I continue feeding Artemia for a few days a week and I continue with the copepods, but I substitute frozen Daphnia for Cyclops.
I have obtained best results when my Stenopus hispidus have spawned at the same time. Stenopus hispidus larvae that are between one and five days old seem to attract the most interest from the seahorses. I have also had similar results with Palaemon elegans and the European green crab Carcinus maenas.
At this time I also move the seahorses to a 60- to 80-liter (15- to 20-gallon) tank. I continue the same cleaning regimen.
Once the seahorses are capable of capturing adult Artemia (which have been fed well with either phytoplankton or spirulina powder), it is time to start switching them over to frozen Artemia and Mysis shrimp. In general, Mysis is more nutritious and they enjoy it better. It is also a good time to introduce small young fish into the diet of medium to large species.
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