238
Coral Reef Fish
6.4 Aspects of Behavior
Features of behavior are among the most important ecological adaptations
of animals to environmental conditions. They are formed during their
evolution and are fixed in their genetic apparatus the same as their
morphological and physiological characteristics (Wickler 1971). The
behavioral reactions of animals are interconnected with their morphology
and physiology. Among these kinds of ecological adaptations the behavioral
ones are the most mobile during evolutional changes of species adapting to
changes in environmental conditions. This is most spectacularly displayed in
reef fish, which form exclusively dense and varied communities, including a
multitude of interacting species (Barlow 1975).
One of the important behavioral adaptations of reef fish is the rhythms of
diurnal activity, which is peculiar to most of their species. During a 24-h
day, fish shift from a period of active feeding to a period of relaxation.
Among them there are the daytime fish. These fish are active within the
light period of the day, while nocturnal fish are active only at night. A
smaller part of reef fish are active the entire 24 h, and only a few of them
have indefinite diurnal rhythms (Helfman 1978). With the aid of this
adaptation the reef fish fulfills two main aims of their life strategy: to use
optimally the trophic sources of environments and to escape grazing by
predators. The first aim they achieve by their diurnal migrations to places of
foraging and the second by the formation of schools and by hiding in refuges
(Hobson 1973). From the viewpoint of evolution the species of nocturnal
fishes are more ancient compared with the daytime ones, as they are closer
to their perchid ancestors. Among them we find representatives of the most
common reef-fish families Apogonidae, Lutjanidae, and Holocentridae. The
daytime fish are of later origin. They are more specialized in aspects of their
morphology, in their behavioral features and in food preferences. Their
predatory species, like chromises, caesionids, atherinids, gobiids, and
cirrithids, which are adapted to feeding on zooplankton, acquired small
body (Table 6.10). A large part of daytime fish turned to feeding on sessile
plants and animal organisms, like periphyton, macrophytes, corals, and
sedimentary polychaetes, and also on large vagile zoobenthos, which do not
hide in daytime. These kinds of food objects are more accessible to grazing
during the daytime. Among the latter the herbivores Scaridae,
Acanthuridae, Pomacentridae, the corallovores chaetodontids, the feeders
on large benthos Ballistidae, and some of chaetodontid species could be
mentioned. The appearance of the daytime and the nocturnal fish greatly
increased efficiency in the use of available refuge space on reefs. At night,
these are used by daytime fish which feed early in the morning. These
refuges then are ready to be occupied by their successors - the nocturnal fish
which use them for their daytime relaxation (Smith and Tyler 1973; Fig.
6.4). Among fish without any apparemt diurnal rhythm the large piscivorous
Coral Reef Fish
6.4 Aspects of Behavior
Features of behavior are among the most important ecological adaptations
of animals to environmental conditions. They are formed during their
evolution and are fixed in their genetic apparatus the same as their
morphological and physiological characteristics (Wickler 1971). The
behavioral reactions of animals are interconnected with their morphology
and physiology. Among these kinds of ecological adaptations the behavioral
ones are the most mobile during evolutional changes of species adapting to
changes in environmental conditions. This is most spectacularly displayed in
reef fish, which form exclusively dense and varied communities, including a
multitude of interacting species (Barlow 1975).
One of the important behavioral adaptations of reef fish is the rhythms of
diurnal activity, which is peculiar to most of their species. During a 24-h
day, fish shift from a period of active feeding to a period of relaxation.
Among them there are the daytime fish. These fish are active within the
light period of the day, while nocturnal fish are active only at night. A
smaller part of reef fish are active the entire 24 h, and only a few of them
have indefinite diurnal rhythms (Helfman 1978). With the aid of this
adaptation the reef fish fulfills two main aims of their life strategy: to use
optimally the trophic sources of environments and to escape grazing by
predators. The first aim they achieve by their diurnal migrations to places of
foraging and the second by the formation of schools and by hiding in refuges
(Hobson 1973). From the viewpoint of evolution the species of nocturnal
fishes are more ancient compared with the daytime ones, as they are closer
to their perchid ancestors. Among them we find representatives of the most
common reef-fish families Apogonidae, Lutjanidae, and Holocentridae. The
daytime fish are of later origin. They are more specialized in aspects of their
morphology, in their behavioral features and in food preferences. Their
predatory species, like chromises, caesionids, atherinids, gobiids, and
cirrithids, which are adapted to feeding on zooplankton, acquired small
body (Table 6.10). A large part of daytime fish turned to feeding on sessile
plants and animal organisms, like periphyton, macrophytes, corals, and
sedimentary polychaetes, and also on large vagile zoobenthos, which do not
hide in daytime. These kinds of food objects are more accessible to grazing
during the daytime. Among the latter the herbivores Scaridae,
Acanthuridae, Pomacentridae, the corallovores chaetodontids, the feeders
on large benthos Ballistidae, and some of chaetodontid species could be
mentioned. The appearance of the daytime and the nocturnal fish greatly
increased efficiency in the use of available refuge space on reefs. At night,
these are used by daytime fish which feed early in the morning. These
refuges then are ready to be occupied by their successors - the nocturnal fish
which use them for their daytime relaxation (Smith and Tyler 1973; Fig.
6.4). Among fish without any apparemt diurnal rhythm the large piscivorous