240
organ developed on their second and fourth gills.
They help the fi sh to obtain oxygen from the air.
They belong to a large group of catfi sh (order
Siluriformes, family Clariidae) which is found all
over Africa and Southeast Asia. They are long
cylindrical fi sh with a broad fl attened head and
generally terminal mouth. The name ‘catfi sh’ is
derived from the presence of four pairs of long
sensitive barbells around the mouth almost similar to the vibrissae of a cat. These barbels are
probably used for locating food in dark muddy
waters. Most of them are predators living on a
variety of other animals including fi sh.
Concomitant to above, the equivalent catfi sh
of North America belong to the family Ictaluridae
which includes the blue catfi sh ( Ictalurus furcatus ) and the channel catfi sh ( I. punctatus ). The
latter is of considerable commercial importance
and is grown in ponds and raceways. It may grow
up to >20 kg and is highly prized by anglers.
15.5.7 A Few Aspects of Wetland
Fishery
Fish in our studied wetlands in India are common
to those found in many wetlands in Asia and
Africa. Some are near the limits of their geographical distributions. Crossocheilus burmanicus are at the northern limits, while Tor khudree
are near the southern limits (Beckere 1983 ; Kar
and Sen 2007 ). Adult Wallago attu, Sperata
seenghala, etc., could be keystone piscivore
(Carpenter and Kitchell 1987 ; Kar 2007a , b ) with
an ability to limit the abundance of forage fi sh.
Some of the carps are effective zooplanktivores,
which are capable of changing the size and species composition of zooplankton communities
(Kar and Dey 2000 ).
At present, the fi sh assemblages generally
have a dwindling species richness as compared
to other lentic bodies of the region having
almost similar morphometry (Kar 2005d ). In
some of the wetlands where sport fi shery is
active, the fi sh population structures refl ect the
effects of exploitation in the form of fi shing
and sports (Kar 2007a , b ). Effect of high fi sh
densities (mainly due to irrational recruitments) could also be depicted in the anomalous
growth rate, feeding behaviour, etc., of the
fi shes (Dey and Kar 1990 ; Kar 2007a , b ). In
some wetlands, strong competition amongst
different species could also shape diets through
resource partitioning. Prey resources and, thus,
the community structure of the lower trophic
levels in these wetlands refl ect the effects of
intense predation pressure by fi shes.
Diets are generally analysed as frequency of
occurrence (FO), the % of fi sh in a sample that
ate a particular food item, % number (%N), etc.
In this connection, relevant literature are also
consulted (NBFGR Manual 2000 ; Kar 2007a , b ,
2012a ). Studies revealed carnivory in fi shes like
W. attu and S. seenghala and herbivory in fi shes
like Labeo rohita and Catla catla (Kar 2007a , b ).
Planktivorous fi sh generally feed on larger
and more prominent zooplankton (Patgiri et al.
2002 ). Statistical relations between fi sh consumption and cladoceran biomass and length
are obscured by a fact that they depend on the
species involved. Further, there are, sometimes,
potential links between population’s interactions, community structure and ecosystem
processes.
There is, generally, considerable variation in
minnow catches from year to year. Catches are
usually high during late summer and monsoon. It
declines generally from autumn. There is rich
catches also during the winter, particularly from
the fi shing centres (Kar 1990 , 2000a , b , 2007a ,
b ). Comparison of length frequency distribution
before and after monsoon indicated that mean
lengths were generally signifi cantly greater than
the early summer population (Kar 2007a , b ).
Further, high temperature in epilimnion during
summer may reduce the activities of fi shes during
that period. This, probably, reduces the vulnerability of such fi shes to passive fi shing gears such
as the cast net.
Certain exotic fi shes like Cyprinus carpio,
Hypothalmichthys molitrix, Ctenopharyngodon
idellus and Oreochromis mossambicus are introduced in the natural and cultivated wetlands by
the fi sh farmers in many Asian countries. These
exotic fi shes generally replace the indigenous
fi shes, which indicates that introduction of exotic
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes
organ developed on their second and fourth gills.
They help the fi sh to obtain oxygen from the air.
They belong to a large group of catfi sh (order
Siluriformes, family Clariidae) which is found all
over Africa and Southeast Asia. They are long
cylindrical fi sh with a broad fl attened head and
generally terminal mouth. The name ‘catfi sh’ is
derived from the presence of four pairs of long
sensitive barbells around the mouth almost similar to the vibrissae of a cat. These barbels are
probably used for locating food in dark muddy
waters. Most of them are predators living on a
variety of other animals including fi sh.
Concomitant to above, the equivalent catfi sh
of North America belong to the family Ictaluridae
which includes the blue catfi sh ( Ictalurus furcatus ) and the channel catfi sh ( I. punctatus ). The
latter is of considerable commercial importance
and is grown in ponds and raceways. It may grow
up to >20 kg and is highly prized by anglers.
15.5.7 A Few Aspects of Wetland
Fishery
Fish in our studied wetlands in India are common
to those found in many wetlands in Asia and
Africa. Some are near the limits of their geographical distributions. Crossocheilus burmanicus are at the northern limits, while Tor khudree
are near the southern limits (Beckere 1983 ; Kar
and Sen 2007 ). Adult Wallago attu, Sperata
seenghala, etc., could be keystone piscivore
(Carpenter and Kitchell 1987 ; Kar 2007a , b ) with
an ability to limit the abundance of forage fi sh.
Some of the carps are effective zooplanktivores,
which are capable of changing the size and species composition of zooplankton communities
(Kar and Dey 2000 ).
At present, the fi sh assemblages generally
have a dwindling species richness as compared
to other lentic bodies of the region having
almost similar morphometry (Kar 2005d ). In
some of the wetlands where sport fi shery is
active, the fi sh population structures refl ect the
effects of exploitation in the form of fi shing
and sports (Kar 2007a , b ). Effect of high fi sh
densities (mainly due to irrational recruitments) could also be depicted in the anomalous
growth rate, feeding behaviour, etc., of the
fi shes (Dey and Kar 1990 ; Kar 2007a , b ). In
some wetlands, strong competition amongst
different species could also shape diets through
resource partitioning. Prey resources and, thus,
the community structure of the lower trophic
levels in these wetlands refl ect the effects of
intense predation pressure by fi shes.
Diets are generally analysed as frequency of
occurrence (FO), the % of fi sh in a sample that
ate a particular food item, % number (%N), etc.
In this connection, relevant literature are also
consulted (NBFGR Manual 2000 ; Kar 2007a , b ,
2012a ). Studies revealed carnivory in fi shes like
W. attu and S. seenghala and herbivory in fi shes
like Labeo rohita and Catla catla (Kar 2007a , b ).
Planktivorous fi sh generally feed on larger
and more prominent zooplankton (Patgiri et al.
2002 ). Statistical relations between fi sh consumption and cladoceran biomass and length
are obscured by a fact that they depend on the
species involved. Further, there are, sometimes,
potential links between population’s interactions, community structure and ecosystem
processes.
There is, generally, considerable variation in
minnow catches from year to year. Catches are
usually high during late summer and monsoon. It
declines generally from autumn. There is rich
catches also during the winter, particularly from
the fi shing centres (Kar 1990 , 2000a , b , 2007a ,
b ). Comparison of length frequency distribution
before and after monsoon indicated that mean
lengths were generally signifi cantly greater than
the early summer population (Kar 2007a , b ).
Further, high temperature in epilimnion during
summer may reduce the activities of fi shes during
that period. This, probably, reduces the vulnerability of such fi shes to passive fi shing gears such
as the cast net.
Certain exotic fi shes like Cyprinus carpio,
Hypothalmichthys molitrix, Ctenopharyngodon
idellus and Oreochromis mossambicus are introduced in the natural and cultivated wetlands by
the fi sh farmers in many Asian countries. These
exotic fi shes generally replace the indigenous
fi shes, which indicates that introduction of exotic
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes