The Seahorse
Introduction:
The seahorse is named after from the shape of the animal, the
position of the head, and its upright position, which bear a striking
resemblance to a horse (the equine animal).
Seahorses are marine fish that inhabit temperate and tropical shallow
waters of the world. The seahorse distribution is very wide; they live
among seagrasses, mangroves, and coral reefs in shallow warm waters,
they occupy a latitude from roughly 45 degrees south to 45 degrees north.
The taxonomy of the seahorse is confused because the seahorse has not been
studied at depth, it is thought that there are at least 20 to 50 species
of sea horses, half of which inhabit the Indo-Australian region. The others
species of sea horses occupy the Atlantic coasts of Europe, Africa and North
America, and there are two species living in the pacific coast of America
It is in the southern Asian regions were the population of seahorses are most
at risk.
Seahorses are known to have "the head of a horse, the tail of a monkey,
the pouch of a kangaroo, the hard outer skeleton of an insect, and their
independently moving eyes of a chameleon" (Larousse, 1975).
It is also known to change color like the chameleon.
*)Characteristics and classification:
1)Classification:
Seahorses form part of the family Syngnathydae. The Order is thought to
be Syngnathyformes, even though, some scientists refer to them as Gasteriformes.
The order Sygnathyformes (or Gasteriformes) contains a group of bony,
soft ray, tube-mounted fishes, with pelvic fins located in the abdomen,
an air bladder without a duct to the gut, and a primitive kidney.
This order contains organisms like, seahorse, pipe fish, stickleback and
less known species like the snipefish, tubesnout, shrimpfish.
The majority of the sea horse species belong to the genus Hippocampus.
There is very little known about these fish and the information tends to be
confusing.
There is believed to be about 20 to 50 species of these fish but there are
150 different scientific names that exist for them.
2)Sizes:
Seahorse sizes vary from 2 inches (5 Cm) long to 2 ft (30 Cm)long,
on average their size is usually 6 inches (15 Cm). The ones that occupy
China and Australian temperate waters of the genus Solenognathus are
the only ones that can reach up to 2 ft. in length.
3)Body structure:
Seahorse is one of the most unusual fishes in appearance that inhabit
the oceans. A seahorse has a large head that ends in an elongated tubular
snout. They also have a movable neck, and a strong "armored" body.
Their tail is long and slender and can reach up to 8 in. and it is
prehensile (it can curve forwards) which allows it to attach itself to
seaweed or other objects in the shallow areas of the oceans. The upper
part of the body is compressed in such a way that the head is joined to
the neck-like part of their body, which makes it resemble the equine horse.
The body and neck are marked with circular and longitudinal ridges with
bony bumps in between the ridges ( they have bony plate rings instead of scales).
The bony plates form rings of about 50 plates each, and encase the body forming
a semirigid skeleton. These plates inhabit dorsal flexion but allow a ventral
and a somehow lateral extension. Seahorses have a single dorsal fin, an anal
fin in some species, and a pair of small pectoral fins. These fish lack
teeth on their snout and a caudal fin.
Gills:
Their gill structure is very different from other fishes. The gill of this
fish group forms a convex mass that is composed of small rounded lobes
which attach themselves to the branchial arches.
4)Swim pattern:
These animals hover instead of swim, they are poor swimmers and not able to
resist currents. With the help of the only dorsal fin in the middle of their
body they use it on an undulatory motion to propel themselves or remain
stationary among plants or coral surrounding them. Their habitat is composed of
seaweed, coral, or beds of eelgrass in statuaries. They swim in a vertical
fashion, with the aid of the dorsal fin that moves on rapid waves and
undulatory movements. Their fin speed can move at a velocities up to 35
oscillations per second, and makes it look like a small propeller.
The pectoral fins oscillate at the same velocity and they use their head
for steering while swimming to turn or move towards the desired location.
Seahorses maintain their vertical position while they are attached to any
support. Their fins can be regenerated easily when damaged. A general work
on fishes states that it takes a seahorse five minutes to cross a bathtub.
These fish are neutrally buoyant and can hover in one spot in the water column.
Seahorses are capable to adjust their orientation by using high-frequency,
low amplitude movements with their pectoral and dorsal fins. Their movements
can be minute but allows them to move forward, backward, up and down. It was
measured that Hippocampus hudsonius could change the wavelength and amplitude
on their beat fin frequency very accurately. The fin of this species could
change the length on the waves from 1.3 to 2.5 on its dorsal fin. Scientists
have found similar fin frequency changes in different seahorse species of
about 11 cm in length. Their swimming rate can reach up to 55 cm/s.
The density of these fish matches that of the water. They use the swim
bladder to aid their buoyancy but only to a certain depth, unless they adjust
the gas intake and out take their density allows them to hover in midwater.
The swim bladder hold enough air to enable the fish to stay at certain depth
without any waste of energy use.
5)Vision:
The seahorse eyes can move independently from one another, which
provides them a binocular vision. This is an advantage for detection of
any type of movement on a large range of vision. Even though these animals
do not swim very fast they are very good camouflashing in between seaweed
and their vision aids them avoid predators by hiding or remaining still
imitating plants drifting in the water.
6)Coloration:
The sea horse is capable of a great variety of coloration changes.
This attribute allows the seahorse to be relatively inconspicuous to the
habitat surrounding it. An Australian species has developed the adaptation
to form dermal flaps that cover its body and tail and makes it resemble the
vegetation (seaweed) in which it lives. The colors vary greatly but mostly
are light to medium brown, with scattered white spots, and usually but not
always have fleshy ornamental strands. The coloration of their fins,
tubercles, spines, flaps, and filaments on their bodies resemble their
surroundings, which aids them in camouflage against predators. This is
their defense mechanism to avoid detection. This adaptation is most developed
on the Australian species of the genus Phyllopteryx, which is one of the most
different types of littoral fishes. In the Bahamas most seahorses are found
in shallow bays with turtle grass covering the substrate, which aids their
camouflage.
7)Feeding habits:
These fish eat minute planktonic crustaceans in the water, like copepods
and even baby fish. These are ingested through their snout by a rapid
intake of water. These animals usually eat critters small enough to enter
their tiny mouth. Seahorses locate their prey by sight and they sucked or
snapped into their mouths from even 1« in. away.
*)Reproduction:
The seahorse is one of the few animals in which the male carries the
young during gestation. Their reversal on the sex roles is a very unusual
on a fish. The male has a kangaroolike pouch on its ventral side, in which
the female lays her eggs, and the male carries them until birth. The eggs
are fertilized on the pouch and usually hatch in some species on approximately
10 days. Breeding starts with the male looking for a mate and starting
courtship (some males have been known to court other male species). When he
pairs up with a female the two of them entwine their tails. The female
inserts her long ovipositor on the male to lay her eggs. In some species
it is known for the female to deposit as much as 200 eggs in the male pouch.
The normal number of eggs that the female places on the male pouch is between
12 to a 100 eggs. The eggs are carried by the male seahorse from 10 to 45 days
depending on the species. At birth seahorses are as big as « in. long, and
they are perfect imitation of the adult seahorses. The first thing they do
at birth is to go up to the surface of the water to gulp some air to fill
their swim bladders. Baby seahorses eat insatiably on small crustaceans and
grow very fast. In aquaculture seahorses have been known to grow from 3/8 in.
at birth to 2« in. in only 2 months.
The male seahorse has a placenta on its pouch. The inside of the pouch
changes before he starts the courtship. The walls become full of blood
and spongy before the female put her eggs and the male fertilizes them.
It is thought that oxygen and carbon dioxide diffuses through the blood
vessel network on the walls of the pouch. Food is provably passed to the
eggs in the same manner that the mammalian placenta, through blood.
The same is thought to happen to the pipefish, a member of the same family.
Each hatch of eggs is deposited on the pouch and the male seahorse goes
through spasms to move the eggs to the bottom of the pouch to make place
for more eggs. When the young have to be born the male bends and
straightens to jerk the baby seahorses out of the pouch. After birth
the malesea horse shows signs of exhaustion. In aquaria many males die
after giving birth but this does not occur on the wild because males look
for the female to fill his pouch. The dwarf seahorse, Hyppocampus zosterae,
breeds nine months out of the year. Their eggs hatch after 10 days and they
mature into adults in two or three months. The baby seahorses often form
small groups by holding each other with their tails.
The seahorse usually lives less than a year when adult. Seahorses have a
complex social life; every morning, the female of the species goes to her
mate and entwines their tail for at least 10-min, while changing color and
strolling among the seabed. In the wild they remain faithful to one partner
throughout their lives.
Classification and characteristics of some important species:
Almost all seahorses belong to the Genus Hippocampus.
-) Hippocampus europaeus (I could not find the name of the person
that named it):
This is a European seahorse that is found abroad the Mediterranean Sea,
along the Portuguese and Spanish Atlantic coasts. It breeds through the
summer months between April and October. Its length reaches up to
16 cm (6« in. long)
-) Hippocampus kuda (same): This is one of the largest seahorses and
it is usually liked and kept on aquariums. It is distributed among the
Indo-Pacific coasts. From the East Coast to the North coast of Australia.
It size can reach up to 30 cm (12 in.)
-) Hippocampus ramulosus (same): This is the more common of the
European seahorses. It is found in the British waters, and mostly on
the coast of Holland, also on the South of the Mediterranean and the
North African coasts. Found over all the Mediterranean and the black seas.
It breeds in the summers from May to August. It has a very long snout
and a very narrow head. It reaches a size of about 16 cm (16¬ in.)
-) Hippocampus zosterae Jordan and Gilbert: This is the smallest of
the species of seahorses. It can reach at maturity a length of 4 cm (1«.)
It populates the waters of Bermuda, Florida, The Gulf of Mexico, the Caribbean,
and even Cuba. It usually breeds from mid-February to late-October.
-) Hippocampus erectus Perry: This is one of the large seahoses it can
reach up to 10 cm. long. They have been recorded to live from Nova Scotia
to Argentina, and the Gulf of Mexico. Also they have been found in the West
of Africa.
-) Hippocampus antiquorum (same): It is common on the Mediterranean
coast and also the Portuguese and French coasts. It is rare in the British
coast but it has been fished there in the 1885's. These are the ones commonly
seen in aquariums all over the world.
*) Characters for classification of the seahorse:
Seahorses are classified from characters that cannot be measured on the
field, some of these measurements are:
A) Dorsal rays 11 to 13 or 16 to 21.
B) Dark pigment on body on form of lines, streaks, or tiny round dots.
C) Trunk rings 24, or 21 or less.
D) Anal fins present or absent.
E) Tail rings 34 or more.
F) Etc.
These are only few of the characters that can be found for the
classification of these fishes.
*)Evolution:
Paleontological data shows that these species order appeared first
in the Miocene Era strata (7,000,000 to 26,000,000 years ago) and became more
abundant in the Tertiary Period strata (2,500,000 to 65,000,000 years ago).
Most of the order occurred mostly in the mid-Eocene Epoch
(38,000,000 to 54, 000,000 years ago) and Oligocene Epoch
(26,000,000 to 38,000,000 years ago). The fossils belonging to these
Epochs were found mostly in the area of Monta Bolca in Verona, Italy.
These fossils constitute mostly pipefishes, there a very small amount of
seahorses fossils found throughout Earth history. There are some fossils
found of extinct species related to the family Syngnathydae, the family
Protosyngnathydae is one of them.
As explained before, the seahorse belongs to the class Osteichthyes,
the skeleton of these early fish was conserved throughout history.
The freeing of the jaw and cheeks bones helped these fish to adapt to a
great variety of feeding mechanisms, one of those is the tube-mouth or
snout of the seahorses, which enables them to suck water to eat plankton.
One adaptation that is very interesting in the seahorses is the position
and composition of their scales. This has been thought to come as an
adaptation from the interlocking of the ganoit scales on members of the
subclass Actinopterygii. It is thought that this subclass first developed
on the Euramerican continent when Gondwana land separated during the late
Devonian.
The development of a suspensorium during the late Paleozoic and gave
the infraclass Neoterygian its beginnings. The jawbones became more firmly
attached and gave the upper jaw its freedom. This freedom gave the
possibility for the development of the snout on the seahorse. The dorsal
and anal fins evolved in this period of time as well, and gave the ability
to hover to the seahorse. The evolution of the tail might have come from
the ancestors of the Teleostan division. The presence of certain bones on
the tail that evolved in this period of time might have given the seahorse
its ability to move the fins at such high frequency.
The presence of a large number of otholiths gave us the certainty that
the majority of the modern groups of fishes, subdivided later in families,
emerged in the early Cenozoic Era.
*)Conservation:
One of the reasons that I decided to do a research paper on these
fish is because of their unusual sexual life and their interesting life style.
What I did not know was that there is very little known about them.
A British marine biologist, Amanda Vincent, is the only scientists to have
studied seahorses successfully on the wild. What she discovered is alarming
The Philippines, Taiwan, and Hong Kong are involved in a massive trade
in value and volume of seahorses. 20 million seahorses are traded each year
for medicine purposes, aquarium pets, and curios
(dried seahorses for key rings, earrings, and brooches). The biggest
demand of seahorses is for traditional Chinese medicinal, more than 50%
of seahorses population has been lost worldwide in the past five years.
Chinese believe that sea horses can treat asthma, heart diseases, many other
type of disorders, and also that they are aphrodisiac. It is Dr. Vincent
belief that there are at least 36 countries involved on this trade, from
Australia to Ecuador. If we keep on exploiting the sea horse populations
the community will collapse in a manner of years. The most expensive seahorse
is the large bleached seahorse; they are worth more than their weight in silver.
Dr. Vincent discovered this trade and teamed up with the Zoological
Society of London to raise some funds for the conservation of the seahorse.
She has developed the first seahorse conservation project on the Philippines.
She has also persuaded fishermen not to fish the male seahorses and leave the
pregnant males alone. Villagers of the Handdumon, on their own, patrol the
non-fishing reserve that Dr. Vincent built. A team of local biologist of the
Vietnam, is attempting to improve the captive breeding programs to develop a
method that would help the development of sea horse aquaculture. A video
that was broadcast on July of 1997 helped raised the public awareness for the
conservation of these fish. The video talked about Dr. Amanda Vincent and her
work on the seahorses, it was very interesting because it showed the animals
on the wild and it explained their reproductive life style and some very
interesting characteristics about them. It is important for us to study more
in depth the seahorses, in order for us to help do something about them and
keep the population from declining even more. A good management plan needs
to have a detailed information about the animal and the environment in which
it lives.
No part of this paper can be reproduced without the consent of the author,
Alicia Beltran as it was given to me. To contact her, send an e-mail to :
abmlenn@hotmail.com
© Francisco Beltran, 1997