Aggression behaviour of Amphiprion bicinctus (the Red Sea Anemone fish) against anemone predators and its reaction on enemy schemes
Miriam Reininger - Magistra der Naturwissenschaften - January 2006 - Leopold-Franzens-University Innsbruck
In 1868 the symbiotic relationship between anemones and anemone fish was
described for the first time. Since then scientists investigated many different
fields concerning the symbiosis, the social organization of anemone fish, sexual
stunts and the immunity to the nematocysts of the host anemones. In the last
more than 170 years of investigation, research has led to a lot of contradictory
results. This thesis deals with the aggression behaviour of Amphiprion bicinctus (the Red Sea Anemone fish) against predators and its reaction on enemy
A. bicinctus belongs to the Pomacentridae (Reef Perch) and is endemic in the
investigated area where it is at the same time the only species of anemone fish
found. Their natural distribution range includes the Red Sea and the Gulf of
Aden. Anemone fish are unique among Reef Perch because they live in lifelong
partnerships. Their small territory is probably the reason for this faithfulness.
The host anemone is in the centre of the territory in which the fish reproduce,
hide and search for food. All the species of anemone fish are obligate symbiosis-partners of sea
anemones. One benefit of the symbiosis to the fish is obvious: its major source
of protection is its anemone, which forms the core of its territory. The symbiosis
is commonly regarded as facultative for anemones. However, anemone fish
also provide protection against predatory fish to their hosts.
Innumerable theories about how the anemone/fish-partnership works have been
elaborated. Behaviour and biochemistry, probably both, play roles to varying
degrees. In fish that live with many types of host behaviour is likely to be more
important to adaptation, whereas for host-specific fish biochemistry is probably
the more significant factor.
Facultatively symbiotic Pomacentridae of the genus Dascyllus may occupy
hosts instead of or along with true anemone fish. In some host anemones
shrimps and crabs live together with anemone fish. Juvenile Labridae (Wrasse),
Bleniidae (Blenny), Anthiidae (Fairy basslet) and Apogonidae (Cardinal fish)
sometimes seek refuge near the tentacles of the anemone. They are not
considered as true anemone fish, because the symbiotic relation is facultatively.
A. bicinctus lives in relatively large social units, often consisting of an adult pair
and a series of juvenile sub-adults. Size-related dominance hierarchy exists in
anemone fish. The larger female controls the production of other females by
aggressive dominance. Like in other species of marine fish with closed social
systems a subdominant individual can be induced to change sex by removal of
the dominant one. This phenomenon has been described as socially controlled
sex reversal. Sex change is relatively commonplace among fish, a remarkable
adaptation that helps prevent any lull in reproduction, but it typically involves a
female-to-male switch. The unusual male-to-female reversal in anemone fish is
known as protandrous hermaphroditism.
My field studies took place from July to September 2005 at the Red Sea
Environmental Centre in Dahab, in the Gulf of Aqaba. In total I did 80 dives with
more than 83 hours of underwater-observations. In the first half of my stay I
registered the exact sites of the anemone/fish-partnerships and the parameters
of the surrounding area to (e. g. depth, fish and anemone size, number of
anemone fish living in the anemones, etc.) to investigate their influence on the
behaviour of A. bicinctus.
After drawing up a behavioural catalogue I started my observations in twenty
minutes intervals at four different depths. In the second half of my studies I
carried our fake-experiments on A. bicinctus to see which contours evoke more
or less aggression to replenish my observation studies. I also prepared three
white-coloured replicas to see how big the influence of the natural colours on
the aggression behaviour is. It was obvious that the colour is an important
trigger of aggression behaviour. In the beginning of my field research I checked
the behavioural patterns of A. bicinctus and then I choose five particular
behaviours: spreading the dorsal fin and pectoral fins, presenting the broadside,
jerk swimming, whipping with the caudal fin and attack. I took notes how often
each of these behaviour patterns were carried out during one twenty minutes
interval and I also took notes against which other reef inhabitants the anemone
fish were aggressive. In the all together 1600 minutes of my observations I
attend 208 attacks of A. bicinctus against other reef inhabitants. There was an
obvious trend of aggression behaviour against Pomacentridae (Reef Perch),
Labridae (Wrasse) and Chaetodontidae (Butterfly fish). Those families are food
and territory rivals, egg and anemone predators. Serranidae (Grouper),
anemone fish predators, were in the fourth place.
A. bicinctus lives in association with five host anemones: E. quadricolor (Bulb
Tentacle Sea Anemone), H. magnifica (Magnificent Sea Anemone), H. crispa (Leathery Sea Anemone), H. aurora (Beaded Sea Anemone) and S. gigantea
(Gigantic Sea Anemone). The number of the anemones in the area has a big
influence on the social organization of anemone fish. In the investigated area,
the number of anemones was a restrictive factor for adult A. bicinctus.
The results showed, that the method of the observations also has an influence
on the behaviour of A. bicinctus. The fish showed more aggression behaviour
when I was snorkelling. They are probably less disturbed without the noise
coming from the diving equipment.
At different depths the composition of the species is varying. This means that at
different depths different enemies occur. The results showed, that the attacked
species vary, not the behaviour of A. bicinctus.
The size of the anemone fish has a big influence on the aggression behaviour.
Not only the number of attacks increases with it, but also the distance at which
enemies are attacked. No attacks from juvenile A. bicinctus were observed. The
frequency rises with the anemone size, as well as the distance at which passing
fish are attacked. A change of the frequency of attacks during the day could not
be proved. A. bicinctus showed before midday the most activity.