Abstract:

Nullah Aik and Nullah Palkhu, tributaries of Chenab River, Pakistan were studied to assess the impacts of environmental factors on diversity and distribution of fish species at 18 sites on, from September, 2004 to April 2006. A total of 1506 fish specimens were recorded from 14 sites whereas zero fish capture was recorded from four sites located in close vicinities of Sialkot city. Highest species richness and abundance diversity indices Shannon and Simpson were recorded during post monsoon season as compared to pre monsoon. In case of spatial distribution highest diversity indices were recorded from upstream site of Nullah Aik and down stream of Nullah Palkhu during post monsoon season. Most of the fish species were restricted to upstream of Nullah Aik during pre monsoon while rest of sites did not showed significant fish distribution. To evaluate the relationships between species abundance and environmental variables in longitudinal zones of streams, Canonical correspondence analysis CCA was used. Out of 13 variables such as stream morphology Stream flow, depth and flow , physicochemical parameters DO, COD, turbidity and NO3- and metals Na, Ca, Fe, Pb, Cr, Ni and Cu used for the explanation of species distribution data Ordination analysis with the direct gradient technique of the CCA was performed to study the association of these environmental parameters to species composition. CCA identified overall three groups upstream fishes, downstream fishes and evenly distributed fishes. Fish assemblage at upstream sites was comparatively stable through out the year; however, downstream of studied streams severely affected during pre monsoon. Present study is a major step in exploring the structure of fish assemblage in Nullah Aik and Nullah Palkhu. It would be helpful in efforts for protection and rehabilitation of habitat and conservation of fish assemblage at local and regional level

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