236
latitudes), the Garo–Rajmahal gap might have
become a few hundred metres higher than the sea
level, and that colder climate might have favoured
increased precipitation with less evaporation and
greater run-off in streams like Narmada and Tapti
along Satpura–Vindhya. These conditions might
have favoured the spread of torrential fi shes from
the region of Assam Himalayas to Peninsular
India across the Garo–Rajmahal Bridge.
15.5.3 Some Concepts Related
to Fish Community Ecology
15.5.3.1 The River Continuum Concept
It was originally proposed for aquatic invertebrates. It predicts that there is an upstream–
downstream gradient of changing physical
conditions and associated biotic changes
(Vannote et al. 1980 ). It has been postulated
that species assort themselves along environmental gradients, like pH and temperature. In
general, it has been found that species diversity
increases from upstream to downstream regions
in streams. According to Lowe McConnell
( 1975 ), this is due to the fact that habitat diversity also increases along the stream gradient in
the same fashion. However, this happens in
such a way that most of the upstream habitat
types also occur in the downstream sections. In
addition, detritus and plankton richness also
seems to increase downstream which may lead
to greater diversity in the higher trophic levels.
Certain studies on African stream fi sh communities (Toham and Tuegels 1997 ) revealed the
occurrence of distinct pattern in the longitudinal zonation of species with a sequential shift
in species compositions and also an increase in
species diversity along the stream gradient.
Further, spatial segregation of fi shes is said to
be infl uenced by environmental and physical
characteristics of the lotic and lentic waterbodies, like width, depth, current velocity and substrate types (Toham and Tuegels 1998 ) as well
as certain biotic characteristics like canopy
cover, occurrence of dead wood, leaves and
aquatic plants. These are known to infl uence
habitat features like depth and stream current
(Angermeier and Karr 1983 ) and also said to
enhance invertebrate production (Benke et al.
1984 ) which could serve as fi sh food.
15.5.3.2 The Habitat Guild Concept
There is diversity of habitats in stream ecosystems.
Each of them harbours diverse and distinct types
of fi sh communities. The Habitat Guild Concept
attempts to explain this observation. It implies that
species–habitat associations are strong and are
forged by adaptations of the fi sh communities to
their surrounding habitat as well as interactions
between each other (Taylor 1996). Such a view has
been tested and found to be true in comparative
studies of fi sh communities in riffl e and pool habitats in some of the rivers of Oklahoma and
Arkansas. It was found that these communities differ in a number of attributes, like species richness,
composition, abundance patterns and responses to
changes in environmental gradients (Taylor 2000 ).
However, riffl e and pool communities are linked
by a continuous gradient, at a very local scale; and
species may use both these habitats at different
parts of their life cycles as well as at different seasons (Schlosser 1982 ). Nevertheless, some of the
juvenile fi sh may prefer riffl es to pool habitats as
they provide the required kind of food and fl ow
patterns necessary at a particular stage of their
growth, whereas the same species may prefer pool
habitats at later parts of their life cycle. Thus, generalised concepts, like the Habitat Guild Concept
may not hold true at all levels of observation and
would depend on the relative abundance of pool
and riffl e habitats within a river stretch. There have
been some observations on size-related differences in habitat use by many species where smaller
individuals of some species occur in faster-fl owing
waters than their larger conspecifi cs (Toham and
Tuegels 1997 ).
15.5.4 An Account
of the Ichthyospecies
Zoogeographically , FW fi sh have been classifi ed
differently by different workers, although the classifi cation made by Myers ( 1949 ) have been found to
be useful and widely accepted. The FW fi sh of
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes
latitudes), the Garo–Rajmahal gap might have
become a few hundred metres higher than the sea
level, and that colder climate might have favoured
increased precipitation with less evaporation and
greater run-off in streams like Narmada and Tapti
along Satpura–Vindhya. These conditions might
have favoured the spread of torrential fi shes from
the region of Assam Himalayas to Peninsular
India across the Garo–Rajmahal Bridge.
15.5.3 Some Concepts Related
to Fish Community Ecology
15.5.3.1 The River Continuum Concept
It was originally proposed for aquatic invertebrates. It predicts that there is an upstream–
downstream gradient of changing physical
conditions and associated biotic changes
(Vannote et al. 1980 ). It has been postulated
that species assort themselves along environmental gradients, like pH and temperature. In
general, it has been found that species diversity
increases from upstream to downstream regions
in streams. According to Lowe McConnell
( 1975 ), this is due to the fact that habitat diversity also increases along the stream gradient in
the same fashion. However, this happens in
such a way that most of the upstream habitat
types also occur in the downstream sections. In
addition, detritus and plankton richness also
seems to increase downstream which may lead
to greater diversity in the higher trophic levels.
Certain studies on African stream fi sh communities (Toham and Tuegels 1997 ) revealed the
occurrence of distinct pattern in the longitudinal zonation of species with a sequential shift
in species compositions and also an increase in
species diversity along the stream gradient.
Further, spatial segregation of fi shes is said to
be infl uenced by environmental and physical
characteristics of the lotic and lentic waterbodies, like width, depth, current velocity and substrate types (Toham and Tuegels 1998 ) as well
as certain biotic characteristics like canopy
cover, occurrence of dead wood, leaves and
aquatic plants. These are known to infl uence
habitat features like depth and stream current
(Angermeier and Karr 1983 ) and also said to
enhance invertebrate production (Benke et al.
1984 ) which could serve as fi sh food.
15.5.3.2 The Habitat Guild Concept
There is diversity of habitats in stream ecosystems.
Each of them harbours diverse and distinct types
of fi sh communities. The Habitat Guild Concept
attempts to explain this observation. It implies that
species–habitat associations are strong and are
forged by adaptations of the fi sh communities to
their surrounding habitat as well as interactions
between each other (Taylor 1996). Such a view has
been tested and found to be true in comparative
studies of fi sh communities in riffl e and pool habitats in some of the rivers of Oklahoma and
Arkansas. It was found that these communities differ in a number of attributes, like species richness,
composition, abundance patterns and responses to
changes in environmental gradients (Taylor 2000 ).
However, riffl e and pool communities are linked
by a continuous gradient, at a very local scale; and
species may use both these habitats at different
parts of their life cycles as well as at different seasons (Schlosser 1982 ). Nevertheless, some of the
juvenile fi sh may prefer riffl es to pool habitats as
they provide the required kind of food and fl ow
patterns necessary at a particular stage of their
growth, whereas the same species may prefer pool
habitats at later parts of their life cycle. Thus, generalised concepts, like the Habitat Guild Concept
may not hold true at all levels of observation and
would depend on the relative abundance of pool
and riffl e habitats within a river stretch. There have
been some observations on size-related differences in habitat use by many species where smaller
individuals of some species occur in faster-fl owing
waters than their larger conspecifi cs (Toham and
Tuegels 1997 ).
15.5.4 An Account
of the Ichthyospecies
Zoogeographically , FW fi sh have been classifi ed
differently by different workers, although the classifi cation made by Myers ( 1949 ) have been found to
be useful and widely accepted. The FW fi sh of
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes