Ichthyodiversity of the Bangshi river , Savar , Dhaka

Fish diversity of Bangshi river, Savar, Dhaka was studied over a period of two consecutive years (July, 2010 to June, 2012). A total of 48 fish species belonging to 39 genera, 18 families and 8 orders were recorded. Siluriformes was the most dominant order comprising 33.33% of all the number of species recorded, followed by the Cypriniformes (31.25%), Perciformes (14.58%), Clupiformes (6.25%), Channiformes (6.25%), Osteoglossiformes (4.16%), Synbranchiformes (2.08%) and Beloniformes (2.08%). The most dominated species of this study were Ailia punctata, Mystus tengra and Puntius sophore and rare species was Bagarius yarrellii. During the study 29 sp. (40.42%) fish species were found to be locally rare, whereas, only 3sp. (6.25% ) were very common and 16 sp. (33.33%) were common in occurrence. Among the fishes, 52.08% was threatened in which vulnerable, endangered and critically endangered were 20%, 36% and 44% respectively.


INTRODUCTION
Fish biodiversity of a river essentially represents the fish faunal status and their abundance.River conserves and supports comparatively varieties of fish species which in turn supports commercial fishery.Once upon a time, rivers of Bangladesh were rich in fish diversity but, gradually number of fishes was decreasing toward threatened status.According to a report of the International Union for Conservation of Nature (IUCN) in 2000, Bangladesh was a home of 266 freshwater fish species of which, 54 were classified as "threatened" and grouped under the 'Red List' species.Bangladesh being rapidly developing country of the south-east Asia, currently holds 1176 industries that discharge about 0.4 millions m 3 of untreated wastes either directly or indirectly in to the rivers in a day (Rabbani & Sharif, 2005).This increasing industrialization and consequent agricultural revolution have already brought negative impact on the water quality (BCAS, 2004).The Bangshi river, located at Savar of Dhaka district is one of the important rivers in central Bangladesh.Once, the river was the prime habitat for many diversified fresh water fishes.But, now it lost all of the riverine characters including its fish resources.The thing becomes more worsen with the industrial effluents mainly from Dhaka Export Processing Zone (DEPZ) as well as river grabbing, siltation and many more anthropogenic factors.Therefore, present research was aimed to carry out to obtain present status of fish diversity in the Banghsi river, Savar, Dhaka.

MATERIALS AND METHODS
Fish samples were collected and recorded from June to October over a period of two consecutive years from July, 2010 to June, 2012.For this research, four sampling sites namely, St.1 (2355′32″N, 09013′32E), St. 2 (2354′35″N and 09013′51E), St. 3 (2353′45″N and 09013′56E) and St. 4 (2352′54″N and 09013′59E) were selected for getting almost complete record about the available fish species (Fig. 1).From each of these sampling sites, fishes were harvested by local fisherman using different types of nets namely, gill nets, cast nets, lift net (dharma jal) and dragnets were collected.As soon as a new fish species was found, photographs were taken and then preserved in 8-10% formaldehyde.The fishes were brought to the laboratory and preserved finally with fresh formaldehyde in separate jars.Smaller fishes were directly placed in the formalin solution while, larger fishes were given an incision and labeled properly on the abdomen before they were fixed.Identification was done based on keys used by Bhuiyan (1964), Talwar & Jhingaran (1991), Shafi & Quddus (2001), Rahman (2005) and finally recorded in the museum of the Department of Zoology, Jahangirnagar University.All collected data were then used to calculate "Relative Abundance" of a particular fish species" by following the method of Jadhav et al. (2011) with slight modification i.e., the relative abundance of the fish was classified into three categories namely Very common (67-100%), Common (34-66%), and Rare (1-33%) on the basis of their availability in total catch.Consequently, the statuses of recorded fishes were determined following IUCN Bangladesh (2000).

RESULTS AND DISCUSSION
A total of 48 species of fresh water fishes belonging to 39 genera, 18 families and 8 orders were recorded (Table 1).The only variation found in Titas river was 35 species of fish (Ahmed & Akter, 2008), which is fewer than the present findings in the Banghsi river.

Fig. 1 .
Fig. 1.Satellite image of the Bangshi river, Savar, Dhaka, showing the four sampling sites

Fig. 2 .
Fig. 2. Percentage of species composition under different orders recorded in the Bangshi river during July 2010 to June 2012

Fig. 3 .
Fig. 3. Status of recorded threatened fish species in the Bangshi river during July 2010 to June 2012