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Knowing
Nemo
by Pradeep P.J, Srijaya T.C, Mithun S, Anuar H, Anil
Chatterji (Institute of Tropical Aquaculture)
Shahreza Md. S (Faculty of Agrotechnology and Food Science)
and Benno Periera (St. Alberts college, Cochin, India.)
W
hen asked to picture what
would be the most dazzling,
ravishing beauties of the
marine world, many would today have
‘Nemo’ as part of that picture. These are
the brightly coloured electric-orangeand-white clown fishes which are often
seen, hovering, displaying quirky antics
while playing in a mass of loose fleshy
anemone. It is the anemone that gives
them their name ‘clown’.
Clown fish are native to the wide ranges
of the tropical waters of the Indian and
Pacific oceans and distributed over the
Great Barrier Reef and the Red Sea. The
swimming pattern of this charming
beauty is an eye catching sight, bobbing
their body up and down in an amazing
way. Unlike other fishes, it’s waddling
reminds us of a happy dog coming
near its loving master. Their symbiotic
relationship with its host anemone – the
anemone’s stinging tentacles is lethal to
other fishes - is an awesome wonder of
nature. Disney and Pixar created movie
magic when they released the animation
movie ‘Finding Nemo’, which made the
clown fish so popular and easily-andinstantly recognisable all over the world
among both adults and children.
‘Finding Nemo’, Disney and Pixar
Beauty Queen of the Corals
If we were to have a debate on which fish
species would have the characteristics
that would make them the most
glamorous, interesting, tender and
colourful, it is likely that today the most
common answer would be the gorgeous
clown fish. Part of their beauty lies in
their contrasting colours.
Clown fish belong to the damsel fish
family pomacentridae. The anemone fish
is one of the important sub-groups of
damsel fishes which forms the sub family
Amphiprioninae. There are about 28
species of anemone fishes in two genera:
Amphiprion (27 species) and Premnas
(1 species), Premnas biaculeatus being
the largest at 6.5 inches (17 cm). The
main reason for including this species
in another genus is the presence of a
spine on the gill cover below the eye
and a narrower white band in the body.
Anemone fish family members falls
into the six groups called “complexes”.
For example A. percula and A. ocellaris
under the percula complex. The tomato
complex includes A. ephippium, A.
frenatus, A. mcCullochi, A. melanopus
and A. rubrocinctus. The skunk
complex consists of A. akallopisos, A.
leucokranos, A. nigripes, A. perideration,
A. sandaracinos, and A. thiellei. The
clarkii complex includes A. akindynos,
A. allardi, A. bicinctus, A. clarkia,
A. chagosensis, A. chrysogaster, A.
chrysopterus, A. fuscocaudatus, A.
latifasciatus, A. omanensis and A.
tricinctus. The saddleback complex
consists of A. latezonatus, A. polymnus,
and A. sebae. However, P. biaculeatuis is
a single member in the maroon complex.
Symbiotic Relationship
Clown fishes are found in singles, pairs
or often as a small group hovering
around their host anemone and seeking
protection in the anemone’s venomous
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tentacles when threatened by danger. It
has been an interesting question for the
scientist how this bright coloured fish
are able to survive in the midst of these
venomous tentacles when other fish are
not able to. The immunity enjoyed by
clown fishes has only recently become
properly understood and a scientist
named Schlichter in 1968 had come
up with the finding that clown fishes
develop a special immune system, which
is a mucus layer protecting them against
the stinging cells of their host anemones.
The clown fish develops its immunity
by slowly covering itself with a layer
of mucus from the anemone itself. It is
interesting in fact to watch how a young
“unprotected” clown fish dashes its body
through the tentacles of an anemone to
pick some of the mucus. The stinging
cells of anemone are triggered mainly by
the chemical signalling from the proteinbased mucus covering most of the fishes.
As the anemone is self-equipped to avoid
stinging itself by recognizing its own
mucus, the clown fish is masked by the
coating of the same mucus assuming that
the fish is part of itself. Their venomous
cells do not react to other non-living
items in their surroundings, as these do
not have the right chemical make-up to
be identified as food.
In return, the clown fish feed on
undigested matter (in captive conditions,
this reduces the ammonification of the
water), and the faecal matter from the
clown fish provides nutrition to the
sea anemone. In addition, although it
has not been observed in the wild, in
home aquariums it has been observed
that clown fishes take excess food to an
anemone and feed them. In captivity, the
bobbing and swimming pattern of clown
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fishes result in greater water circulation
around the sea anemone. Although small
in size anemone-fishes are ferocious in
defending their territory by offering
protection to their host with bites and
ramming motions. This way they drive
away anemone-eating-crabs and fish such
as butterfly fish and unwanted parasites
from their host.
The Sea Anemones as Protectors
Sea anemones, the true protector of
anemone fishes like the clown fish,
remind us of jelly fishes upside down.
The anemones are stuck on the bottom
of the sea bed and they use their noxious
tentacles to snap their food items and
reel them in. the anemone tentacles are
also covered with millions of stinging
cells called cnidocytes and get triggered
when prey comes in contact with them,
and in fact these cells fires tiny harpoonlike structures into the prey. The most
spectacular activity of the anemone
fishes we observe is the scene where the
clown fish dive right inside the stinging
poisonous tentacles of anemones, where
as in the case of other marine life they
would be paralyzed when they do this
and come into contact with the tentacles,
thus becoming prey of the anemones. For
the clown fish, however, this is truly a
symbiotic relationship where the clown
fish are immune to the poisonous stings,
which is one among the most interesting
and mutually beneficial associations
known to man and Mother Nature.
However not all anemones are hosts,
and only 10 species support them. All
these anemones are of tropical and
zooxanthellate species. Each species
of clown fish is specialized to live in a
particular species of anemone. At times,
when in captivity, the clown fish can be
persuaded to accept a species of anemone
which they won’t accept in normal
circumstances. Clown fish are more
in need of anemones, since in nature
these fishes are rarely seen without
being associated with an anemone for
protection and shelter. If not for the
anemone, most of the clown fish would
be serving as a meal for predators.
Different species of clown fishes may
interact differently with the same species
of sea anemone. Mostly these ‘Nemo’
fishes use chemical cues to recognize
specific host anemones. Almost all
species of clown fishes have varied types
of chemical cues in terms of its activity,
amino acid contents, structure and
function. This may be one of the reasons
for these symbiotic species’ specific
integrity.
Males First
In clown fishes, sexes are not genetically
fixed but rather they have the ability
to transform their sex. It is a unique
adaptation in all clown fish species
that they are born as males, but only
the strongest and most aggressive
individuals develop into females. This
could be arising from the possibility
that there is selective pressure for the
female to be larger so as to produce more
eggs. A few males may indeed set up
their territory in a host anemone with a
dominant pair, but only the dominant
one sexually matures. In case the top
ranked male suddenly dies or changes
into a female, within a few hours the next
highest ranked male becomes sexually
functional. Even though there will be
changes in the hierarchy, the top ranked
male is submissive to the larger female
and interestingly each fish is exactly
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20% smaller than the one above it. The
males will be able to overcome this
hurdle in the social hierarchy only when
the female dies or somehow removed
from the group. They will then become
a fully functioning female within a few
days, and all other males move up a
step in the hierarchical rank. The sexual
development of juvenile clown fish is
thus regulated by aggression.
This type of arrangement is a form of
hermaphroditism called protandry. The
word means “male first”, since the young
fish cannot become functionally female
directly, but only by becoming males
first.
Unlike the wild fish, captive production
of clown fishes has its own hurdles.
However, the University of Maryland,
along with scientists from Roger
Williams University, is trying to perfect
the techniques for raising clown fish
in captivity. Indeed, several countries
including India, USA and Australia
have already standardized the breeding
techniques of several species of clown
fish. Yet we cannot meet the increased
demand as less number of hatcheries
are involved in its production and also
the breeding technique has not been
completely disseminated to the Aqua
culturists.
Clownfish Breeding
A clown fish pair may live
together in an anemone for
years and over the course of
that long time will spawn
frequently. Lunar phases
strongly influence the
spawning activity of anemone
fishes. Newly hatched larvae
are attracted to moonlight
and they will be drawn
towards the surface there by
facilitating their subsequent
dispersal by waves and
currents. Male fishes initiate
the spawning by nipping the
host anemones slightly in
their tentacles, forcing them
to contract a little and clear the intended
spawning area. It may be usually
adjacent to a section of coral rock. Then
both the partners will start cleaning the
specified place with their mouth. In the
meantime the animals stimulate each
other with quivers and belly touches.
Finally the eggs are laid and depending
on the species it may range from 300 to
2000 in number. The male fertilizes them
immediately.
Clown fishes have demersal eggs which
are large and each is at the end of a short
stalk. After laying their eggs, the duty
of the female brood is fulfilled and she
will again devote herself to feeding them
and defending them. The males usually
fan the eggs and remove the damaged or
unfertilized eggs. Hatching mostly occurs
at night or dusk, and the newly hatched
ones are swept away by the current to the
planktonic raft, and become a part of the
planktonic community. However, even
in the act of dispersal many are caught by
the filter feeders and larger zooplanktons.
They tend to have a short planktonic
larval stage. Those larvae’s that survive
until their planktonic life in the open
waters return to the bottom seeking
shelter among the heavily structured
terrain. Once these larvae attain their
proper colour they settle up on suitable
anemones.
of the same kind and many are a pest to
other sorts of fishes. Some clowns can
harm by biting the fins of other similar
sized or smaller fishes.
The great rapport and solidarity between
clown and anemone has always been
an interesting topic for scientists.
There are many researches ongoing
behind this elegant beauty, in many
countries, especially Australia, U.S.A,
Japan, Singapore, India, Thailand
and Philippines. In Malaysia, many
researches have been conducted and are
also continuing on clown fish, whereby
Dr. Abul Munaffi and Mr. Liew with
his team from University Malaysia
Terengganu have successfully
raised Ocellaris clown in
captivity. Some of their
related topics of research
include behaviour, sexual
interchange, sex markers,
etc. A number of new
findings about this little
star have given some better
understanding of their life.
Nemo’s Nose
Clown Fishes in Home Aquariums
Clown Fishes in Home
Aquariums
The elaborate and marvellous mutualism
between clown fishes and anemones
prompt many aquarium hobbyists to
have a desire to keep these animals
together in the tanks. Whether it is the
bright striking contrasting colours or
the symbiosm between the fish and an
anemone, the clown fishes are enjoyed by
fish watchers and hobbyist alike. Since
the beginning of the saltwater hobby,
clown fishes have been undeniably one
of the most favourite marine species.
This dazzling beauty has received the
most attention for the longest time,
because of the ease in handling and
the tranquil life of the fish. They are
among the hardiest marine creatures and
can be recommended for beginners in
marine keeping. However, on the other
hand, anemones are among the most
difficult and demanding animals to be
kept in captivity. In fact, anemones are
fundamentally unsuited to aquariums,
since in home aquariums the clowns do
not have any enemies and can survive
well without the help of anemones.
Unfortunately, the biggest downside
found in clown fishes in captivity is their
aggressiveness. Most species of clowns
cannot tolerate other clowns, especially
Clownfish larvae have very
sensitive noses and can
detect tiny concentrations of
smelly molecules. A team of
Australian marine biologists
from James Cook University
found that an ample number of young
clown fish choose to stay close to home.
It was an interesting question how a
clown fish manages to get back home in
the vast ocean. Recently, scientists have
come up with an answer. Clown fish find
their home back by remembering the
smell of their birth place. This chemical
imprinting occurs in the very early stage
of life, as an embryo inside the egg,
which is then fixed firmly for the rest of
the life of the clown fish. The chemistry
behind this fact is that anemones secrete
out strong olfactory compounds, which
acts as a perfume for these fishes to trace
back, the path to their home.
As with many other reef fish larvae,
clown fish babies also swim to the
surface as soon as they emerge out of
the egg case. In the open ocean, they
swim freely, drifting along with water
currents and feeding on the planktons.
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After, two weeks, when it comes time
for them to settle down on a suitable
host, this memory of smell becomes their
passport towards safety to find suitable
host anemones. Surprisingly, larvae also
use the capability of olfactory sensation
to recognise the scent of their parents to
avoid inbreeding.
Like most other crustaceans and shell
fishes along with reef corals, clown fishes
are also severely affected by the impact
of global warming, which causes a terrific
imbalance in the marine ecosystem.
Acidification severely affects clown fish
babies. In more acidic waters clown
fish larvae lose the ability to sense vital
odours, probably due to the damage
University of Liege in Belgium
caused to their olfactory systems. A
recent study found that an increased
level of carbon dioxide can make clown
fish completely discombobulated. They
were unable to find a suitable home and
avoid predators, since many of their
sensations have been lost, especially the
sense of smell. This also stops them from
distinguishing the scent of their parents,
and are thus unable to repel the scents
from some vegetated plants which they
dislike. It was a surprise in terms of how
this acidification altered the olfactory
senses of clown fish. Interestingly
there were no possible anatomical and
morphological changes in clown fish,
which still remains a mystery. However,
one of the serious concerns for us over
the future will be whether a clownfish
and other marine organisms can evolve
to cope with the increased acidity. Since
the acidification is happening at a pace
which is more rapid compared to the
greatest ability of evolution to cope with,
the capacity of the organisms to evolve
could be limited.
Researchers from Australia surveyed
waters around Papua New Guinea for
clown fish populations. Interestingly,
there was a huge difference in the
number of clown fishes between where
there were islands and where there were
no islands. They found that the clown
fishes and its partner sea anemones are
concentrated only on the shallow waters
where coral reefs are surrounded with
vegetated islands but not on the islands
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with only coral reefs. The study showed
that clown fishes have preference for
certain kinds of leaves from the island.
They also tested this phenomenon in
captivity-raised clown fish where they
had never lived on the reefs or the open
sea. Surprisingly, they were also strongly
attracted to the scents of leaves and
anemones, suggesting these preferences
are innate. It points out clearly that
even the reef preservation won’t help to
protect the clown fish.
Talking Nemo
Research led by Eric Parmentier of the
University of Liege in Belgium and
Michael Fine, a biologist at Virginia
Commonwealth University found that
the clown fishes employ various sounds
tp communicate. The team used a
combination of sound recordings with
high-speed video and x-rays to observe
how the fish moved when making the
sounds. They have sorted out the voices
of ‘chirps’ and ‘pops’ during territorial or
courtship displays in their real ecology.
This was accompanied by a series of
rigorous movements, including elevation
of the head and also lowering of the
bottom jaws. The host clown fish will
attack the intruder fish, if the intruder
has not listened to his warning calls.
This is a new finding that a fish species
was found to use its jaws to produce
communication sounds. The sounds were
produced due to the collisions of the jaw
teeth, transferring energy to the jaws that
are presumably the sound radiator.
Even though a lot of research has been
done on this marine beauty, there are
still many mysteries to be found and
many un-researched areas. So many
interesting questions arise, for example:
whether it is possible to cross breed
different species of anemone fishes so
that characters of both species can be
combined to get a new hybrid variety
with even more colourful and varied than
the parents. Clown fish host are known
for their bio-medical properties, as they
have revolutionized the biomedical
research with their fluorescent proteins
enabling the imaging of processes
within living cells and tissues. Other
than clown fish, some damsel fishes
and a few other organisms can also
survive with anemones, but are they
using the same mechanism as clown
fish for protection from stinging cells?
Molecular techniques in clown fishes
can be applied for biomedical research
including screening pharmacological and
therapeutic substances. The possibility
of sea ranching activities for clown fishes
to save them from becoming extinct
should also be explored. It will be quiet
interesting to know how a captive breed
clown fish behaves in the wild, how it
settles and how they make their own
territories and their selection pattern
of sea anemones. There are quiet wide
variety of possibilities for future research
and experimentation on this lovely pet
and also its partner anemones.
Facing Extinction
The main goal of the Disney and Pixar
released hit movie, Finding Nemo
(2003) was to spread the message that
the ornamental fishes should be left in
the wild, but its effect on clown fish in
the Wild and in the Aquarium Trade
made them the most traded tropical fish,
together with the blue-green damselfish.
The message ironically actually back fired
and all over the world kids have become
fascinated with the idea of having their
very own “Nemo”, which ultimately
resulted in high demand for clown fish.
Unfortunately, the movie has led to the
over harvesting of clown fish, resulting in
a drastic decrease in the population size.
There has been a tremendous fall in the
number of clown fishes in certain areas
around the world in the five years since
the hit movie “Finding Nemo” first came
out.
The demand for this real life exotic
fish could result in the fish becoming an
endangered species soon because of its
high demand as a pet. The ornamental
fish industry has grown tremendously
in the last two decades, so that so many
business people are actively involved
in this trade even without having any
technical knowledge. At least 95 percent
of the saltwater fish bought and sold
in the aquarium hobby come from the
wild. However this wild collection can
seriously affect the social structure of
clown fishes which has a unique feature
that is hermaphroditism. This can lead
to the devastation of this species in
the wild as only one functioning pair
occurs in a group. Attempts should
be extensively done to propagate this
beautiful fish in captivity in order to meet
the demands of hobbyists. The ability to
have an adequate supply through captive
breeding and the production of brood
stock in captive condition will greatly
reduce the dependency of obtaining the
fish from the wild. Such an achievement
would certainly save their population in
the wild.
In the great depth of the ocean, the most
splendid and stable of environments,
from where almost all forms of life have
branched out, we realise that there has
now been a great disturbance from
human activities including the little
movie-star “Nemo”. However, there
is nothing so wonderful than to have a
spectacular miniature ocean in our home,
and also to have our small celebrity to
populate that miniature world.