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The Knysna seahorse - a curious, legendary
African fish
Jackie Lockyear
 Seahorses are thought to have evolved at least 40 million years ago and have
survived from ancient times with only very small changes in body structure or
organ function. They are unusual fish that have captured the imagination of
artists, writers and poets, being found in the mythology, legends, folklore and
superstitions of almost every country in the world. In fact some people still
believe that these endearing creatures exist only in fables and children's
stories. The fact is however, that these creatures are just as real as the
threats that they face in our world today.
Given their unusual appearance and extraordinary biology, it is not
surprising that Asians have credited seahorses with magical powers. Seahorse are
therefore exploited as traditional medicines. This use has led to concerns that
the natural seahorse stocks are being depleted at a rapid and unsustainable
rate.
Why is the Knysna seahorse considered the most endangered seahorse in the
world?
The Knysna seahorse is not exploited for traditional medicines. However,
according to the IUCN's red data book, they are listed as the most endangered
seahorse in the world. The reason for this is primarily due to their
exceptionally limited distribution range as they are endemic to a few southern
Cape estuaries. A recent survey of these estuaries, conducted by the Seahorse
Research Group as part of the Green Trust funded "Knysna Seahorse
Project" confirmed that the Knysna seahorse is only found in three southern
Cape estuaries: The Knysna, Swartvlei and Keurbooms estuaries. This means that
if these estuaries are not correctly managed and conserved, South Africa's only
seahorse species may be wiped out for good. Conservationist now say that it is
important that funding become available to continue the monitoring of these
populations.
Why is the seahorse a fish?
Seahorses are unique in appearance, resembling an amalgamation of body parts
taken from numerous animals: a horse-like head, a monkey-like prehensile tail,
chameleon-like eyes and insect-like body armor. Despite its atypical appearance,
the seahorse is indeed a fish, equipped with a backbone, (unusual grape-like)
gills, swim bladder and fins. The scales of the seahorse have over time fused to
form the locust-like exoskeleton.
How do they move with such small fins?
Seahorses are slow moving animals, better suited to maneuverability than
speed. They have small fins, with the dorsal fin providing propulsion while the
pectoral fins are used for stability and steering. The function of the small
anal fin is unknown but is probably used during the birth process of the male.
With the use of these fins the seahorse glides vertically through the water from
one attachment to the next. On rare occasions the animal can be seen swimming
horizontally with its neck extended forward when chasing a prey item or swimming
away from danger. In general, seahorses spend most of their time attached to
seaweed, seagrass or corals using their prehensile tails which acts as an anchor
to prevent the animal from being swept away in currents.
The seahorse on the hunt for food
The seahorse is an ambush predator, it uses it's tail to anchor itself around
the base of the seagrass and will lie in wait of prey. The seahorse is hidden
well by its ability to change colour in order to blend into its surroundings.
When a prey item swims, crawls or slithers past the waiting (and hungry)
seahorse's snout, the seahorse will suck the unsuspecting prey in through it's
tubular mouth. The sucking mechanism is in fact so strong that a click can be
heard when the food is ingested. Seahorses have no stomachs or teeth and are
therefore unable to store large meals or chew their food. They therefore need to
eat small crustaceans such as shrimp at very regular intervals. Their eating
style results in very particular food requirements which would challenge the
most dedicated aquarium hobbyist. Seahorses will only eat live food, thus food
needs to be caught daily for them. If not given the correct nutrition the
seahorse will develop tuberculosis. In the absence of live food they will in
fact starve slowly to death. They would indeed rather die than lower themselves
to eat fish flakes.
It is important to note that the Knysna seahorse is protected by law and it
is illegal to remove or keep this fish in aquaria.
The pregnant male?
 Seahorses are the only fish species where the male experiences a true
pregnancy. The pregnancy is considered true, as fertilization is internal and
the eggs are held in a pouch consisting of tissues, which contain a capillary
network which provides oxygen and placental fluid to the embryos. The pregnancy
of the Knysna seahorse lasts up to two or three weeks. The male will then give
birth to between 5 and 200 young from one pregnancy and during the male's
pregnancy the female will be busy producing more eggs. This means that just a
few hours after the male giving birth, the female will once again pass her now
ripe eggs into the male's pouch. The male will therefore be pregnant throughout
the entire breeding season which is usually during the summer months when the
water temperature reaches about 20°C.
Flirting seahorses?
The seahorses mate monogamously for the entire breeding season. Every day the
pair will come together in a ritualistic flirtatious dance to reinforce their
connection. While the male is pregnant he will move very little, which for a
seahorse means not more than a few centimeters. The male will eat food that
happens to be in the area while the female will roam about in search of food.
Regardless of this separation however, the female will always come back to the
male to perform their daily ritual of entwining their tails and spiraling to the
surface. This ritual helps keep the pair synchronized reproductively. If a mate
is removed or dies, it will take weeks to find a new mate, that is, if it is
able to at all! This is because seahorses live in isolated groups and move very
little. It is thus extremely difficult to find another seahorse in the same part
of the reproductive cycle. Due to the fact that it is the male that becomes
pregnant it was previously believed that it would be the females that competed
for the male partners. This however is simply not the case. Like in most
species, it is the male that competes with other males to attract and defend his
female seahorse. So, it would appear that the male actually wants to be
pregnant. The seahorse male is sounding more and more like every woman's perfect
mate!
A happy end for the Knysna seahorse?
Strangely enough even though the Knysna seahorse is so unique and endangered,
up until two years ago, other than a few short research trips, no work had been
done on the Knysna seahorse. This is a major problem when trying to protect the
species. For the past two years the Seahorse Research Group (Rhodes University)
have completed work on quantifying the seahorse populations and habitats. This
data has helped greatly in increasing awareness and protection of the Knysna
seahorse but only further study will be able to assess the stability of the
species. The status of the seahorse populations will give an indication of the
health of the lagoon acting as a early warning system for any serious problems
in the lagoon. This is of particular importance to the oyster industry and other
groups that require the resources of a healthy estuary. It may then be a very
important exercise to conduct an economic analysis of the financial benefits
from the Knysna seahorse and potential costs of its extinction. But as always,
research requires funding!
One can only hope that while other endangered species draw such large
attention the Knysna seahorse may find a little spotlight in which to swim.
This project is funded by the Green Trust, made possible by Nedbank Green 
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