Fish and Their Habitats in North-East India Biodiversity Hotspot

Studies revealed rich biodiversity of fishes in North-East (NE) India biodiversity (BD) hotspot region. Fish habitats portrayed both lotic and lentic systems having different types of microhabitats and substrata in different stretches. Various limnological and ichthyological studies were done on Sone Beel wetland of national importance. Various studies were done on the zooplankton of different wetlands. Integrated Fish farming with fish and pigs have been found to a profitable venture. Occurrence of parasites have been reported from fishes in various wetlands. The dreadful EUS fish disease has been killing innumerable fishes of this region rendering many of them endangered. Attempts are being made to manage and conserve the fishes of the region through Community Based Fisheries Management (CBFM) involving the stakeholders from the grass root level.


Introduction
Various kinds of studies were done, since last four decades, on the Fishes and their habitats in the North-East (NE) region of India covering fish and non-fish biodiversity, aquaculture (AQC) and Fish disease. The wetlands and rivers were studied about their habitat inventory (HI). The NE India is a hotspot of biodiversity. The hills of this region give rise to many torrential hill streams, which lead to big rivers that finally become part of the Ganga-Brahmaputra-Barak-Chindwin-Kolodyne-Gomati-Meghna system [1]. Studies from 1979 to 2019 in the major rivers of Mizoram, Tripura and Barak drainage, revealed the occurrence of 42 ,42, 31, 25, 36, 9, 14, 23 species of fishes in rivers Tuirial, Kolodyne, Karnafuli, Mat, Tlawng, Tuirini, Serlui and Tuivai respectively in Mizoram 28 22, 53 and 22 ichthyospecies in rivers Manu, Khowai, Gomati, and Feni respectively in Tripura and 65, 61, 54 and 32 species of fishes in rivers Barak, Jatinga, Sonai and Dhaleswari respectively in Assam [2].
HI parameters of the rivers revealed mostly `fall', `cascade' `riffle-pool' types of micro-habitats mainly in their upstream rheophilic stretches in the hills; and, sometimes, in the midstream stretches. Accordingly, fall and cascade regions portrayed mostly bedrock and boulders, while the riffle-pool regions mainly depicted cobbles and gravels. These micro-habitats and substrata are important breeding grounds for the hill stream fishes, which have been undergoing irreparable losses due to human intervention and the fishes not finding a substratum for anchorage (with suckers, etc.), are often lost to oblivion being driven away by the fast torrents of the hill streams thus, causing colossal loss to the rheophilic biodiversity. Aquatic sanctuaries are essential in certain stretches of the rivers to protect the coveted fishes [2].
India has c 67,429 number of wetlands covering an area of c 4.1 million. The NE India Biodiversity (BD) hotspot region is blessed with several wetlands locally called `Beel (perennial), Haor (seasonal floodplain) and Anua (river-formed oxbow type). These constitute c 81 % of the total lentic area (0.12 x 10 6 ) in Assam [1]. Sone Beel (3458.12 ha at FSL) situated at 23 m MSL between 92 o 24' 50" -92 o 28' 25"E and 24 o 36' 40" -24 o 44' 30" N is one of the biggest wetlands in Asia. It has shallow plate-like basin and low volume development 0.15, shore development 1.69,....etc. its shoreline 35.4 km gross volume 101.54 x 10 6 m 3 and its mean depth 0.29 m. Its area diminishes to 409.37 ha at DSL. Sone Beel has continuous inlet (max flow 33.91 m 3 sec -1 ) and outlet (max. flow 87.03 m 3 sec -1 ) channels. The latter acts as a spillway to limit retention of excess water storage. There is retention of higher silt load in the lake through the inlet (max350.0 mg lit -1 ) in contrast to low expulsion through the outlet (max. 216.0 mg lit -1 ).

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The turbidity ranged from 20.56 TU to 185.54 TU. The overall thermal trend of the lake depicted a state of isothermy. The water temperature varied from 18.7 to 32.3 o C, pH 6.02 to 7.9; DO 2.6 to 5.9 mg lit. -1 , FCO 2 0.9 to 14.5 mg lit. -1 and TA 25.0 to 76.0 mg lit. -1 . The solubility of DO ranged from 9.4 to 11.9 mg lit. -1 while it % saturation varied from 32.3 to 74.4%. As an index of dissolved salts, the conductivity of Sone water was low. The lake soil was quite unproductive with pH ranging from 5.02 to 5.9, OC 0.25 to 1.74 %, available phosphorus ranging from 0.15 to 1.93 mg 100 g -1 and available potassium from 1.62 to 24.8 mg 100 g -1 . The phytoplankton depicted 47 forms with density varying from 10 to 5308 units lit -1 The zooplankton contained 19 forms with density ranging from 6 to 380 units lit.  [4]. Still further studies revealed that, E4 (Hills Evenness) and E5 (modified Hills Ratio) for Malini Beel and Narsingtola Pond portrayed an even distribution of zooplankton species (rotifers, cladocerans and copepods). Margoles diversity index revealed 6.66, 6.7, 6.43, 6.95 and 6.1; Shannon-weiner index revealed 1.97, 1.92, 2.08, 2.51 and 2.36; and Sheldon's index revealed 1.22, 1.28, 1.45. 1.67 and 1.7 respectively for Salchapra Anua, Madhura Anua, Sat Beel, Malini Beel and Narsingtola pond [5].
AQC has been an age-old practice among the fish farmers of the region. Integrated Fish Farming (IFF) practice involving Fish Culture with Livestock rearing holds great promise and potential for augmenting production of animal protein, betterment of economy and generation of employment in rural India. Studies were done on IFF practices in 4 IFF farms each in villages Silcoorie (fishery with poultry) and Irongmara (fishery with piggery) in this region. Study revealed that, total annual profit in four IFs in village Silcoorie were Rs, 2, 40, 000.00; 3, 85, 000.00; 37,000.00 and 1, 40, 000.00 respectively while those in 4 [6,7].
Notwithstanding the above, EUS has been causing largescale mortality among the freshwater fishes since 1988, initially affecting four species of fishes very widely. Our study revealed fluctuation in the intensity of the disease in relation to species affected. Large haemorrhagic cutaneous ulcers, epidermal degeneration and necrosis followed by sloughing of scales are the principal symptoms of EUS. Low total alkalinity (TA) could be pre-disposing `Stress factor'. Sick fishes show low haemoglobin and polymorphs, but high ESR and lymphocytes. Communicative nature of EUS revealed variation in time gap between fish and infection in different species. Inoculation of microbes in the test animals did not reveal of any sign of ulcerations for two years. Bacterial culture revealed occurrence of haemolytic E. coli, Aeromonas hydrophila, Pseudomonas aeruginosa, Klebsiella sp, Staphylococcus epidermitis in the surface lesions as well as in the gut, liver, gills, heart, kidney and gonads of sick fishes, all of which have been found to be sensitive to Chloramphenicol, Septran, Gentamycin, etc. • Unceasing customer service Track the below URL for one-step submission https://juniperpublishers.com/online-submission.php microscopically identified as the primary a etiological agent of EUS. Further studies in this regard are being conducted [8].
Recent studies revealed the detection of Ranavirus infection in cultivated carps of North-East India [9]. Attempts had been made to deal with management of water bodies and their fish resources through Community-Based Fisheries Management (CBFM). CBFM could be said to be a modus operandi to empower the community to manage their resources in a sustainable manner and to conserve the natural wealth for future [10].

Conclusion
Ichthyological surveys revealed rich diversity of fishes in rivers of NE India. However, there have been destruction of fish habitats Limnological studies portrayed usual trend of physicochemical parameters of water in the various wetlands. EUS have been devastating the fishes. Fish parasites have been adding to this dimension. However, Integrated fish farming and management of the resources by CBFM have been trying to improve the situation.