In the Seahorses exhibit, visitors learn about how seahorses swim, how
they eat, and why they have the tail of a monkey, a head like a horse, and a
mouth like an aardvark. And, visitors will find out exactly why it’s the
father seahorses – not the moms – that give birth to the babies.
The seahorses on display include the Longsnout Seahorse, Lined Seahorse and
Potbelly Seahorse. Exhibit highlights include three towering cylindrical
tanks so that visitors can get a 360 degree view of the seahorses.
Photo by Paul Riley
“Seahorse” is a general name for a group of about 34 species of these
beautiful little fish, ranging in size from 1/8 of an inch to seven inches
in length. They are found in temperate and tropical oceans worldwide, but
only near the coasts. If anyone has been to the beach anywhere from
Maine to Florida, they have been near seahorses, but probably never saw
them, since they hide so well.
All seahorses belong to the genus Hippocampus, from the Greek words for
horse (hippos) and sea monster (campus). They are all members of the family
Syngnathidae, from the Greek syn, meaning together or fused, and gnathus,
meaning jaws. Other fish in the family Syngnathidae include pipefishes,
pipehorses, and sea dragons.
Stars throughout history, seahorses are represented in artwork from
ancient Rome and Greece, often in the guise of their namesakes, the equine
horse. But seahorses bear little real resemblance to equines. Seahorses are
true fish. They have gills to breathe underwater, fins to propel themselves,
and skin adapted to an aquatic environment. Their heads are at right angles
to the body and their fully prehensile tails wrap around sea grass stems,
corals, sticks, or any other suitable natural or artificial object.
Instead of the scales found on most fish, seahorses have a thin layer of
skin stretched over a series of bony plates visible as rings around the
trunk. These rings are useful in identifying species, as are the cheek
spines and coronet (a crown-like group of spines on the top of the head).
While these plates are not a true exoskeleton like crabs have, they do make
the seahorse’s body very strong and resistant to being eaten by anything
that cannot swallow them whole. These traits, along with a pouch for the
young and eyes that swivel independently of each other, lend to the unique
nature of these fish.
Seahorses are masters of camouflage, changing color and growing skin
filaments to blend in with their surroundings. Short-term color changes may
also occur during courtship displays and daily greetings. Male and female
seahorses can be told apart by the presence of a brood pouch on the male.
Seahorses have no stomach or teeth. They suck in prey through a tubular
snout and pass it through an inefficient digestive system. Like other fish,
they breathe through gills, extracting oxygen from the water that passes
over them. Unlike other fish, however, the gills are small and compacted,
almost “grape-like” in structure. Seahorses swim using the propulsive force
of a quickly oscillating dorsal fin, and use the pectoral fins on either
side of the body for steering and stability. They are more adapted to
maneuverability than speed, and therefore rely primarily on camouflage to
avoid detection from predators.
Seahorses lay eggs rather than giving live birth. Although, strangely
enough, the female will transfer the eggs to a special brood pouch on the
male and the male will carry the eggs until they hatch. The male then
“gives birth” to the young. This reproductive method confused
scientists for years. This unusual mode of reproduction is the most extreme
form of male parental care yet discovered, although it arises from a general
bias towards paternal care among fishes.
Sexual maturity in males is usually determined by the presence of the
brood pouch. Male seahorses are able to become pregnant any time during the
breeding season, which varies with species, and is most likely dependant on
temperature of the water. Most species of seahorses are monogamous, forming
pair bonds that last the entire breeding season (and perhaps even last over
several breeding seasons), although some species may not be pair-bonded.
Pair bonds are reinforced by daily greetings in which the female and male
change color and promenade and pirouette together. This dance lasts several
minutes, and then they separate for the rest of the day. The greetings occur
throughout the male pregnancy, and are even thought to ensure that the male
and female are ready to re-mate at the same time. Once the male has given
birth and it is time to re-mate, sometimes only hours later, this greeting
is extended into a courtship that, for one species, lasts up to nine hours.
The female deposits her eggs into the male’s brood pouch, where he
fertilizes them and they become embedded in the pouch wall. The pouch acts
like the womb of a female mammal, providing nutrients and oxygen to the
developing embryos while removing waste products.
Pregnancy lasts between two and four weeks, and at the end of gestation,
the male goes into labor (usually at night), pumping and thrusting for hours
to release his brood. Young are miniature adult seahorses, independent from
birth, and receive no further parental care. Newborns of most species
measure 7-12 mm. The number of young released averages about 100-200 for
most species, but can be a low as five for the smaller species, or as high
Seahorses are also not strong swimmers, unlike the horse, which is known
for its running ability. They are such poor swimmers that during times of
high current they can be found clinging fast to any plant or object to keep
from being washed away. Seahorses are predators, eating small shrimp,
invertebrates, and fish. They hunt by ambush using the same camouflage
that makes them blend into their habitat. Because of their diet of
small animals, seahorses have a short digestive tract (without a stomach!),
which again, is unlike terrestrial horses that have a very long digestive
system to process the grass and hay they eat.
Natural life spans for seahorses are virtually unknown. Most estimates
come from laboratory or aquarium observations. Known life spans for seahorse
species range from about one year in the smaller species to an average of
three to five years for the larger species.
Seahorse behavior and ecology make them very vulnerable to
over-exploitation. In the 2003 World Conservation Union (IUCN) Red list of
Threatened Species, 9 of the over 30 seahorse species are listed as
Vulnerable, with one listed as Endangered. Twenty three others are listed as
Data Deficient, demonstrating the lack of knowledge of seahorse biology, and
the urgent need for more research. The Red List also indicates the need for
the development of conservation programs. Seahorses are exploited for use as
traditional medicines, aquarium fishes, curios (souvenirs), and tonic foods.
Traditional Chinese medicine is the largest direct market for seahorses, but
they are also used in other traditional medicines. Preserved seahorse
specimens are incorporated into jewelry, key chains, paper weights, and
other crafts. They are also threatened by the destruction of their coral
reef, mangrove, sea grass, and estuarine habitats through human activities.
Many seahorses are caught accidentally in fishing nets, particularly in
trawl nets intended to catch shrimps.