The water quality parameters are depicted in Table 1 and the data regarding the fish composition of the Ranganadi river presented in the Table 2, Fig 1 and 2. The survey revealed occurrence of 76 species of fish belonging to 9 orders, 26 family and 54 genera. On the basis of species composition, the Cypriniformes order were dominant having 36 species followed by siluriformes with 18 species, followed by Perciformes, Synbranchiformes, Anabantiformes and Clupeiformes respectively 10,4,3 and 2 numbers of species. Only 1 species from the order Anguilliformes, Beloniformes and Tetraodontiformes were recorded during the study period.
@table 1
The water quality parameters and bionetwork of a particular water body have vital role in the growth and development of fish and ichthyofaunal diversities
(Akhter et al., 2021). Such a way, temperature is viewed as one of the most important factors which effects the fish composition of that area. The water temperature recorded during the survey ranged from 15.2-26.5 (°C) which is suitable for the sustainability of the fishes recorded in the eastern Himalayan region
(Sehgal, 1999).
Another important parameter of water is transparency which helps to assess the quality, transparency is directly related to dissolved oxygen content, sunlight penetration and plankton and macrophyte growth
(Boyd and Lichtkoppler, 1979). During the study period, a range 16.7-34.6 cm transparency has been recorded which is give the impression to be adequate for fish health
(Bhatnagar and Devi, 2013). However, seasonal variation of transparency is very much distinct in the river basin.
The water level of Ranganadi river found to be in the range of 36-175.8cm throughout the year from hilly stream of Kimin (Arunachal Pradesh) till the confluence (Assam) with the Subansiri river at the downstream. This diverse range of water level implies presence of hill stream species like
Glyptothorax telchitta,
Batasio batasio, Erethistes pusillus to big catfishes such as
Wallago attu,
Sperata seenghala and Indian Major Carps. The records of current flow of riverine water varies seasonally, with the advent of monsoon and monsoon period current flow increases drastically in the study sites. Although, the water current rate is provoked from the reservoir of the Ranganadi dam built on the upstream of the river. However, environmental flow is prominent in the all the study sites.
pH ranged in the study sites from 7.07 to 7.45, which indicates a healthy hydrogen ion concentration in the water bodies. According to
Michael (1969), survival and growth of the fish species is best in the range of 7.3-8.4 which indicates it is in safe array.
Concentration of dissolved oxygen (D.O.) is one of the most important parameters of water which indicates the physical and biological processes prevailing in water. Comparatively higher range of D.O. was recorded during the monsoon season due to assimilation of water by heavy wind action and mixing of monsoon rains. During the investigation, the D.O. was found to be in the range of 6.21-8.91 mg/L. Higher content of dissolved oxygen level may be attributed to the hilly fast-flowing region of the Ranganadi river
(Hamid et al., 2020).
According to Swann (1997), that fish can endure concentrations of 10ppm of free Carbon Dioxide on a condition that, D.O. concentrations are high and water supporting good fish populations usually contain less than 5 ppm of free CO2.
Bhatnagar et al., (2004), suggested 5-8 ppm is vital for photosynthetic activity; 12-15 ppm is sublethal to fishes and 50-60 ppm is fatal to fishes. Therefore, it is evident that free carbon dioxide in water supporting good fish population should be less than 5 mg/L. During the investigation, the range of Free Carbon dioxide from 4.1-4.7 mg/L from which it signifies that it is apposite for the ichthyofaunal species.
The hardness of water is principally dependent upon by the content of calcium and magnesium salts, combined with bicarbonates and carbonates with sulphates, chlorides and other anions of minerals
(Devi et al., 2017). Hardness range of 35-80 mg/L said to be beneficial for fishes
(Jhingran, 1988). The hardness level in the Ranganadi river basin during the study period was 50.25-81.44 mg/L.
Total dissolved solids (TDS)
The solids present in the water in the dissolved state which consists of inorganic salts and dissolved materials. TDS content below 400 mg/L is regarded as appropriate quality for better growth and survival for the aqua faunas
(Munni et al., 2013). The TDS content ranged 24.4-47.9 mg/L during the survey.
Total Suspended Solids (TSS)
Indicator of the measure of wear and tear that took place in the upstreams. The TSS parameter ranged from 100.1-252.4mg/L during the yearlong survey. With the advent of pre-monsoon and monsoon season rise in TSS trends is very distinct which can be positively co-related with the increase precipitation, high sediment load, deterioration and mixing of rainwater
(Bailung and Biswas, 2021).
Various previous studies on ichthyofaunal diversity and physico-chemical properties of water have been conducted in and around upper Brahmaputra basin and its tributaries,
Bakalial et al., (2014), conducted studies on the nearby Subansiri river, which recorded 204 species from 34 families 101 genera. Also, investigation conducted by
Boruah and Biswas (2002), lead to listing of 167 fish species from the upper Brahmaputra basin of north-east India. Considering the facts in regard of nearby waterbodies of Brahmaputra River, the fish composition of Ranganadi river is seems to be affected because of some anthropogenic factors like Hydel project, rampant fishing in an unsustainable matter which involves electrode fishing, lethal lime fishing
etc. Similar effects on fish community because of man-made factors can be seen in the recent reports of
Limbu et al., (2021) and
Shao et al., (2019) conducted respectively Nepal and China.
