STUDY ON THE PRESENT STATUS OF ENDANGERED FISHES AND PRODUCTIVITY OF TEESTA RIVER CLOSEST TO BARRAGE REGION

Received 23 November, 2020 Revised 28 December, 2020 Accepted 30 December, 2020 Online 24 January, 2021 -----------------------------


INTRODUCTION
Teesta is one of the longest rivers of the northern part of Bangladesh and makes a total run of about 170 km from its entrance into Bangladesh to the Kamargani Mouza of Gaibandha where it merges with Brahmaputra River just south of Chilmari Thana of Kurigram district. The Teesta dependent area covers almost the entire greater Rangpur district which includes Lalmonirhat, Nilphamari, Gaibandha, Kurigram and Rangpur, located in the north-eastern part of the country (Islam et al., 2014). Teesta river has great importance for bearing country's largest irrigations project. Teesta Barrage is located on Teesta river at Duani in Hatibandha upazila of Lalmonirhat district. The barrage is a 615 m long concrete structure fitted with 44 radial gates having a discharge capacity of 12,750 cusec of water. At the right bank of the barrage a canal is taking off 280 cusec of water for irrigation. A flood embankment of about 80 km has also been constructed for the provide protection from flood to the adjoining areas. This was designed to provide irrigation water, flood protection and drainage facilities for 749000 ha of cultivated land. The gross benefited area of the Teesta barrage project is 750,000 ha, of which 540,000 ha is irrigable. The Teesta Barrage is the largest irrigation project in the country which spreads over seven districts in greater Rangpur, Dinajpur and Bogura. Transboundary Rivers have long been a source of enormous tension between riparian states (Asaduzzaman and Rahman, 2015). The report of World Commission on Dams, (2000) noted that large dams and diversion projects can led to the loss of forests and wildlife habitat, aquatic biodiversity and can affect downstream floodplains, wetlands, reveries', estuarine and adjacent marine ecosystem.
Bangladesh has vast productive fresh water resources with diversified macro and micro aquatic flora and fauna. Out of 260 freshwater fishes in Bangladesh, over 140 species have been classified as 'small indigenous species (SIS)'. Currently, diversity and abundance of several SIS has tremendously reduced due to some stressors dominantly by over fishing, dryness and anthropogenic activities (Wahab, 2003). IUCN-Bangladesh, (2015) reported that about 64 freshwater fish species are under threats of extinction and this scenario is worsening as the threatened fish species are greatly influenced by climate change-oriented warming, massive bed siltation, pollution etc. Although several small fish species have now apparently disappeared and become endemic in the major parts of Bangladesh, still different threatened fishes are locally available in different rivers of North Bengal especially in Teesta river Amin et al., 2019). On the other hand, plankton is one of the most essential characteristics of the aquatic ecosystem for maintaining its stability and a means of coping with any environmental change therefore plankton community structure observation may be used as a reliable tool for biological monitoring studies to assess the pollution status of aquatic bodies (Hambright and Zohary, 2000). The diversity of species, amount of biomass and abundance of plankton communities as well as benthos can be used to determine the health of an ecosystem and evaluation tool for the health status of a river ecosystem (Yazdian et al., 2014). Therefore, this research work has been conducted to know about the current status of endangered fishes, productivity and health status of the studied river ecosystem including seasonal variations near to Teesta barrage region.

Site selection
The study was carried out for a period of four months from July, 2018 to April, 2020. The proposed research work was designed to collect fish and plankton sample from the upstream and downstream regions of Teesta barrage in Teesta river. For plankton sampling six different sampling sites three upstream and three downstream were selected to collect water and sediment sample from the river ( Table 1 & Figure 1). Samples were collected from all selected site fortnightly.

Fish sample collection
To collect fish sample from upstream and downstream site fishermen using seine net (Berjal) were called for collection of fish as well catch information. Net hauling was performed by fishermen around three hours and collected fish samples were then identified through their various morphometric and meristic characteristics. The taxonomic studies of fish were done according to (Rahman, 2005;Talwar and Jhingran, 1991). Then fish species were systematically classified according to fishbase database, Bangladesh Species Database (bdspdb) and Integrated Taxonomic Information System (ITIS). Recorded data were then sorted and tabulated. Conservation status of fishes was confirmed was determined by following the database of IUCN Bangladesh (2015) and Bangladesh Species Database (bdspdb).

Collection and preservation of plankton and Benthos
Plankton samples were collected from sub-surface water of each sites of Teesta river by using plankton net (mesh size, 0.04 mm) for the qualitative and quantitative study of plankton. Ten liters of water samples were passed through the plankton net. Then the collected sample was preserved by marking with site number, sample number and date of the data collection immediately in plastic bottles with 10% formalin solution for the further study. Sediment-samples were collected with the help of Ekmen Drager. Both the plankton and sediment samples were taken to the laboratory of Fisheries Biology and Genetics Department of Hajee Mohammad Danesh Science and Technology University (HSTU) using ice-box for further study. Electron microscope was used to identify the plankton samples whereas benthos samples were identified by eye observation.

Analysis of plankton and benthos
Qualitative analysis Taxa of plankton were identified to genus level with the help of taxonomic keys from the text book of (Babar and Haworth, 1981; Bellinger, 1992;Pontin, 1978;Lind and Brook;1980) with magnification of 10 × 0.25 under binocular microscope.

Quantitative analysis
For quantitative study of plankton Sedgewick-rafter chamber was used. The used rafter-chamber ( Figure 2) was 50 mm long, 20 mm wide and 1 mm deep. The total area of the bottom was approximately 1000 square mm and total volume was 1000 cubic mm.

Present status of endangered fishes in Teesta barrage region of Teesta river
The natural water bodies of the Northwest part of Bangladesh were blessed with small indigenous fish species. Although, the availability of indigenous fishes is declining due to various man-made and natural stressors nationally, most of the threatened fishes of Bangladesh are available in different natural waters of Rangpur and Dinajpur districts. There were 50 species recorded as available endangered fish of barrage region of Teesta river (Table 2). Those species belongs to order Cypriniformes (20), Perciformes (6), Mastacembeliformes (3), Osteoglossiformes (2), Channiformes (3). Siluriformes (11), Clupeiformes (2) and one species each from the order Symbrachiformes, Tetraodontiformes and Beloniformes. It is obvious that Cypriniformes the most dominant order both in number and species followed by Siluriformes, Perciformes, Channiformes, mastacembeliformes, osteoglossiformes, Clupeiformes, Symbrachiformes, Tetraodontiformes and Beloniformes.

Available plankton and benthos in the studied river
Planktonic flora and fauna ( Figure 2) determination revealed that comparative higher density of plankton (n >11500 per liter) as well as more number of planktonic flora (>21 nos.) and fauna (>9 nos.) were found in the early monsoon and monsoon season (April-September).
On the other hand, comparative lower density (n<10000 per liter) and less number of both phytoplankton (<11 nos.) and zooplankton (<7 nos.) were reported in the pre-monsoon season (January-February). Akter et al., (2018) recorded phytoplankton density was found the maximum and the minimum in the dry and wet season, respectively in the Jamuna River that supports the present findings. Again Malik and Bharti, (2012) found that the plankton density was highest during summer-winter and lowest during monsoon in the Sahastradhara stream as the current research said. A total of 30 species of plankton had been recorded from the barrage region of Teesta river of which 21 species (70%) were phytoplankton and 9 species (30%) were zooplankton. Among the phytoplankton, there were 9 species of bacillaryophyta (43%) representing the dominant phytoplankton group followed by charophyta (19%), chlorophyta (19%), cyanophyta (9%) and dinophyta (10%) ( Table 3 and Figure 3).

Figure 2. Planktonic concentration of Teesta river detected in the study period
The common phytoplankton in the Teesta riverine ecosystem (barrage region) in monsoon season were Asterionella, Biddulphia, Ceratium, Clostridium, Cosmodismus, Chlorella, Cyclotella, Dinophysis, Fragillaria, Melosira, Micrasteria. Navicula, Oscillatoria, Pediastrum, Scenedesmus, Spirogyra, Spirunila, Surirella, Synedra etc (Table 4). According to Hossain et. al., (2017) most of the above mentioned planktonic flora were available in the riverine ecosystem. Relative lower and higher numbers of plankton availability found in the pre-monsoon (December-January) and pick monsoon season (July-September) respectively indicated that both diversity and abundances of planktonic flora and fauna were importantly influenced by seasonal variation particularly for thermal change. These findings suggested that Teesta riverine ecosystem was more productive during pre-monsoon and monsoon season. Sixteen species of benthos belongs to class Gastropoda, Bivalvia, Branchiura and Insecta (Table 5)     Asterionella Navicula Tabellaria Fragilaria Surirella Biddulphia

DISCUSSION
Among the recorded species of this findings, 5 species were found nearly threatened (NT) globally reported by IUCN (2015). According to IUCN Bangladesh, 2 species critically endangered (CR), 13 species endangered (EN), 8 species vulnerable (VU) and 5 species were categorized as threatened. There is a very scarce information on the status of fish biodiversity of Teesta river has not been studied till date. Khan et al., (2013) stated, 42 fish species belonging to 7 common groups were identified from the Teesta river which was lower than the present findings. Sarker, (2018) noted that 77 SIS species alone from Teesta river which was much higher than our report. Ali et al., (2014) described 53 species of fish from Chitra river. Parvez et al., (2017) mentioned 55 freshwater fish species were from Dhepa river. According to the information provided by the fishermen, over 40 threatened fishes were currently available in barrage region of Teesta river (Table 3) from where some showed abundant in the studied river although these fishes are rarely available nationwide. During winter season (December-January) the studied river contained less water when local people prepared Katha (fish shelter with tree branches) and at the pre-monsoon season (February-March) they caught fish indiscriminately from the katha. Fishermen also informed that almost similar fish species were found in the upstream and downstream poles of Teesta barrage. It is important to note that several critically endangered fishes such as: bagair (Bagarius bagarius), chenua (Sisor rabdophorus), ghaura (Clupisoma garua) etc. are reported to be available in the barrage area of Teesta river.
The presence of more plankton during early monsoon and monsoon and less in the pre-monsoon or winter indicated that Teesta riverine ecosystem was more productive in early monsoon and monsoon might be due to increased temperature and rainfall. The finding also agreed with Shafi et al., (1978), Patra and Azadi (1985), Chakrabarty et al., (1995), Khan et al., (1998). Bacillariophyceae (Diatoms) was found to be dominant group of phytoplankton by Jha et al., (2014) in Manakudy estuary, Ishaq and Khan (2013) in the Jamuna River. A study on Halda river recorded the phytoplankton population belong to classes Chlorophyceae, Cyanophyceae, Bacillariophyceae and Myxophyceae (Patra and Azadi, 1985). Shafi et al., (1978) reported the availability of higher percentage composition of phytoplankton (76.0 -93.6%) from the Meghna river. In the present investigation phytoplankton formed 65.6% of the total plankton abundance. Akter et al., (2018) noted 9 species of phytoplankton dominated by Bacillariophyceae in the Jamuna River which is more or less similar to the present findings. Ahsan et al., (2012) described 19 taxa of phytoplankton in Ganges-Meghna river system route. The group of phytoplankton belonged to Chlorophyceae (7 taxa), Bacillariophyceae (6 taxa) and Cyanophyceae (6 taxa). The present findings of teesta river showed 9 Bacillariophyceae spp., 4 Chlorophyceae spp. and 2 Cyanophyceae spp. reflects the similarity. Other relevant study conducted by Amin et al., (2019) in the Kanchan river of Dinajpur district noticed almost similar findings. On the other hand, 11 zooplankton contained the dominant group cladpcera (37%) representing 4 species followed by rotifer (27%), copepod (18%) and crustacean larvae (18%) (Figure 4) (2003). According to the study findings, Teesta barrage region associated riverine ecosystem consisted with 5 groups of phytoplankton and 4 groups of zooplankton (Table 3 and Table  4). This study also distinguished the available planktonic flora and fauna in the upstream and downstream regions of Teesta barrage in Teesta river. According to the result (Table 3) little more phytoplankton genera were found in the upstream region than the downstream region whereas opposite scenario was visualized in case of zooplankton availability. This may be the impacts of water flow and upwelling.
Benthic invertebrates provided about 60% of the total natural food items for aquatic animals and also play an important role in sediment-water interaction through their burrowing and feeding activities. The investigation of benthic fauna in the Teesta river showed that the riverine ecosystem near to barrage contained 16 species of macro-benthos (Table 5) Azrina et al., 2006) mentioned that macrobenthos were the basic components of the aquatic chains of rivers and ubiquitous in all aquatic ecosystems and showed sensitivity towards aquatic pollution. The findings of this study demonstrated that the availability of the threatened fishes are reducing gradually in the Teesta river although some endangered and critically endangered fishes are still commonly available. The monitored productivity indicators particularly the availability of planktonic flora and fauna showed comparative better condition in early monsoon and monsoon season than pre-monsoon and late monsoon.

CONCLUSION
The Teesta is a productive river having a great potentiality to conserve the fish biodiversity. But the situation is getting degraded gradually due to various natural and manmade causes. The findings of this study demonstrated that the availability of the threatened fishes are reducing gradually in the Teesta river although some endangered and critically endangered fishes are still commonly available. The monitored productivity indicators particularly the availability of planktonic flora and fauna showed comparative better condition in early monsoon and monsoon season than pre-monsoon and late monsoon season. Finally, it can be concluded that it is very essential to take all effective necessary actions to provide good productivity and to conserve the ichthyodiversity of Teesta river that would also be helpful to conserve the commonly available endangered and critically endangered fishes of Teesta river.