The Charm of Seahorses

Few fish are as instantly recognisable or so surrounded by myth and legend as seahorses. Back in the 15th century, they were even believed to have hooves and hair which dropped off when they died. A dead seahorse was considered to be a lucky charm with miraculous healing powers.

Lifestyle

Most seahorses (Hippocampus species) measure between 20-25cm (4-6in) long when adult, although some species can grow to 30cm (1ft) in length. The small dorsal fin along their back enables them to swim vertically through the water. It can oscillate 35 times every second when the seahorse is swimming fast and, if damaged, this fin can regenerate very quickly.

The coloration of seahorses varies greatly, from shades of grey and brown through to red and yellow. Some species are even able to change colour so as to blend in with their background, rather like chameleons. There are about 35 different types of seahorse around the world, some of them to be found in British waters. Seahorses even occur in colder waters further north, in the sea off Norway and a few have adapted to live successfully in a freshwater environment.

All seahorses prefer shallow waters however, where there are dense patches of seaweed, coral or aquatic plants which provide cover and anchorage points for them. The seahorses which are usually kept and bred in aquarium surroundings originate from tropical areas.  Watching a small group of them swimming gracefully in an aquarium can give countless hours of pleasure, but they are demanding creatures to look after, and not just in terms of their housing requirements.

An aquarium set-up

In the first instance, a marine set-up will be needed and this will be quite a costly undertaking. An all-glass or acrylic tank is essential for this purpose as salt water will corrode metal.  Technology can help though, with specially prepared sea salts being available to mix with tap water and produce a suitable salt water substitute. The specific gravity (SG) reading should lie between 1.021-1.024, with the water being alkaline, in a pH band of 8.1-8.3.
Other essential equipment includes a heater-stat, to keep the water at about 24°C (75°F), a gentle filtration system such as an undergravel filter and a plastic hood with a light. Avoid using a power filter in their aquarium because seahorses are not strong swimmers and much of their food will be rapidly be drawn into a filter of this type, out of their reach.  

Decor in the aquarium should include corals or similar items which the seahorses can hold on to using their tails. Since they are slow-moving and inoffensive, seahorses need to be kept apart from most other fish. Many enthusiasts house them in groups on their own, sometimes in a tank alongside invertebrates which will not interfere with them.

Seahorses feed on tiny sea creatures which they suck into their mouths, sometimes from more than 2.5cm (1in) away. This is rather like eating through a straw. Their food needs to  be small so that it can be swallowed easily. One of the difficulties in keeping seahorses successfully is being able to supply them with adequate quantities.

Minute brine shrimps feature prominently in their diets. Supplies of brine shrimps are purchased in the form of eggs, which are then hatched in salt water. Although brine shrimp eggs can simply be tipped into the aquarium alongside the seahorses, it is better to rear the young shrimps in separate quarters. This avoids unnecessary pollution of the water in the seahorses’ tank. The brine shrimps can then be sieved out an offered to the seahorses as needed.  These fish tend to feed constantly, and so should be offered food at regular intervals through the day.

Breeding

One of the great fascinations of seahorses is their peculiar breeding habits. The male starts the courtship process by holding on to a branch next to a female, quivering his body to attract her attention. When they mate, the male wraps his body around her. The female then lays about 200 eggs on average, although it can be up to 1,500 or so. She transfers these after mating using a special egg tube in her body, depositing them in a pouch at the front of the male’s body.

This pouch located on the abdomen provides an easy way to tell the sexes apart. The male then takes care of these eggs by himself and the young should hatch out anywhere from two to five weeks later. At this stage the young seahorses are living miniatures of their parents, but considerably smaller, measuring only about 1.25in (0.5in) long. They wriggle out of the hole in the male’s pouch as they hatch from the eggs, and immediately start to fend for themselves. But they remain near him for the first few days after hatching.

Once a pair of seahorses is established in aquarium surroundings, females may lay quite regularly but rearing the young once they hatch is frequently a problem. Successful breeders, notably in the United States, can often rear several hundred babies over a period of several months from just a single pair of adults.

There needs to be a very good supply of brine shrimps in the aquarium for the young seahorses, and the water must also be well-aerated to provide them with adequate oxygen. Under good conditions, the youngsters can grow to a size of 6.25cm (2.5in) in just two months after hatching, but they must be given adequate space as they become bigger.

Sadly, like many fish, seahorses are not long-lived. Their maximum lifespan is about three years, so when purchasing stock, it is a good idea to choose smaller, younger individuals if possible, with rounded bellies as this is a sign that they will have been eating well.

Although the costs of setting up an aquarium for these fish is high, there is no doubt they are a source of real fascination. As more is being learnt about these peculiar creatures, so research into their care and breeding is now proceeding apace, partly because of the huge number of seahorses being caught for the Chinese medicinal trade, which may threaten their survival in some areas.