Northeast India has rich freshwater fish diversity which is attributed to past geological history and the Himalayan orogeny which played an important role in the speciation and evolution of groups inhabiting mountain streams. The region is criss-crossed by numerous rivers belonging to the three major drainage systems: the Barak–Brahmaputra, the Kaladan and the Chindwin. About 100 species of fish have been described from the region by workers from India, as well as from other countries. Fish survey tours have been organized in the past 30 years in the different river systems of the region. Our survey resulted in the description of more than 50 new species of fish. As many as 40 species of fish are endemic to the Chindwin drainage and 22 to the Brahmaputra basin. The fish fauna of the Kaladan is poorly explored. Of the fish species in the Brahmaputra basin, 34% have not been evaluated for IUCN red list criteria, while in the Kaladan, 48.2% have not been evaluated.
The map used in Abell et al., 2008 of Earth's freshwater ecoregions, based on the distributions and compositions of freshwater fish species and the major ecological and evolutionary patterns, is a useful resource for underpinning global and regional conservation planning efforts. Northeast India refers to the easternmost region of India consisting of the contiguous states of Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura, Sikkim, and parts of North Bengal. The region is criss-crossed by numerous rivers belonging to the three major drainage systems: the Barak-Brahmaputra, the Kaladan, and the Chindwin. The Brahmaputra drainage area includes Arunachal Pradesh, major parts of Assam, including the Cachar district, Sikkim, North Bengal, Meghalaya, Tripura, and parts of Nagaland, Manipur, and Mizoram. The Kaladan drains the southern part of Mizoram, while the eastern parts of Manipur and parts of Nagaland are drained by the Chindwin.
According to Abell et al. (2008), the northeastern part of India encompasses four freshwater ecoregions: the Ganga Delta and Plain, Middle Brahmaputra, Chin Hills–Arakan Coast, and the Sittaung–Irrawaddy (Figure 1).
The fish fauna of the Eastern Himalaya region may be subdivided into three drainage-based geographic units: (1) The Ganga–Brahmaputra drainage, that flows in the Ganga Himalayan Foothills, Ganga Delta and Plain ecoregions, and the Upper and Middle Brahmaputra; (2) The Chindwin–Irrawaddy drainage in the Sittaung–Irrawaddy freshwater ecoregion; (3) The Kaladan drainage and a number of short drainages along the western face of the Rakhine Yoma of Myanmar in the Chin Hills–Arakan freshwater ecoregion (Figure 2).
Northeast India has rich freshwater fish diversity. The diversity is attributed to the past geological history, i.e. the collision of Indian, Burmese, and Chinese plates, and the Himalayan orogeny which played an important role in the speciation and evolution of groups inhabiting mountain streams (Kottelat, 1989). The evolution of freshwater fish of the region has also been studied in relation to the evolution of river drainages in this part of the world utilizing geological evidence. Molecular studies of the fish of this region have shown that current distribution patterns of the freshwater fish of the region may have been due to the vicariance events in the Miocene period (Vishwanath et al., 2011).
About 100 species of fish have been described from the region by different researchers. The earliest available literature on the fish species in the region is that of Hamilton (1822), who described as many as 17 species. Other researchers who have added to the list are: JE Gray, J. McClelland, J. Muller and F.H. Troschel; R.L. Playfair, B.L. Chaudhuri, S.L. Hora and D.D. Mukerji; A.G.K. Menon, E. Ahl, K.C. Jayaram, P. Bararescu and T. Nalbant; S.L. Hora, G.M. Yazdani, A. Singh and P. Banarescu; N. Sen and T. Nalbant, R.P. Barman, A.K. Datta, P. Nath and S.C. Dey; J. Vierke, N. Sen and B.K. Biswas; P. Musikasinthorn, S. Kullander and R. Britz; H.H. Ng, and M. Kottelat.
Fish survey tours have been organized in the past three decades in the different river systems of the region. In this study, fish species were systematically identified which resulted in the description of more than 50 new species of fishes. The majority of the fish species were assessed for IUCN threat criteria. The diversity of the fish in each river and their IUCN threat criteria are given in the paper.
Materials and methods
Fish were collected from different sites of the Barak–Brahmaputra, the Kaladan, and the Chindwin–Irrawaddy drainages using an electro-fishing machine at least twice in each study year, i.e. October–November and March–May. Some areas could not be visited due to inaccessibility. Collection sites were mostly hill streams with forest covers. Fish specimens were also collected from fishermen who used different nets, traps, and local fishing techniques. Collections were also made from the nearby local fish markets.
The fish were preserved in 10% formalin and deposited in the Manipur University Museum of Fishes. Paratypes of newly described fish species have been deposited in the Zoological Survey of India, Kolkata. Catalogued and uncatalogued fish in ZSI, Kolkata, Shillong, and Itanagar, as well as those in different institutes of northeast India were physically examined for the study.
Fish were identified based on morphometric and anatomical study and comparisons were made with types in the ZSI and with the original descriptions of the species. Measurements were made with a dial caliper to the nearest 0.1 mm. Head length and measurements of body parts are given as proportions of standard length (SL). Subunits of head are presented as proportions of head length (HL). Counts and measurements were made on the left side of specimens. General counts and measurements followed Kottelat (2001). For siluroids, the methods of Ng and Lim (1995) were followed, except head length measurements, which were undertaken as a straight measurement of the distance from tip of snout to the most distant point on the opercular membrane. Morphometric analysis for identifying the fish of the genus Schistura were carried out using Menon (1987) and Kottelat (1990); for the genus Garra, Menon (1964) and Kullander and Fang (2004); for the genus Amblyceps, Ng and Kottelat (1998, 2000); and for the genus Devario, Fang (1997) was followed.
Classification of fish followed Nelson (2006). The fish species were assessed for IUCN threat criteria by logging on to the IUCN website and species distribution mapping was completed using Arc View GIS Ver. 3 and MapInfo software during the IUCN Eastern Himalaya Freshwater Fish Assessment. The criteria have been coded as: NE = not evaluated, DD = data deficient, LC = least concern, NT = near threatened, VU = vulnerable, EN = endangered and CR = critically endangered.
Results and discussion
The survey resulted in the identification of 318 fish species under 113 genera and 36 families. A total of 229 species are in the Brahmaputra drainage, 103 in the Chindwin, and 27 in the Kaladan. The list of fish with IUCN threat criteria is given in Table 1.
Twenty-seven species are endemic to the Brahmaputra basin. They are: Amblyceps apangi, A. arunchalensis, Barilius barna, Batasio spilurus, Conta pectinata, Danio rerio, Devario assamensis, Exostoma barakensis, Glyptosternon maculatum, G. manipurensis, Nangra assamensis, Olyra longicaudata, Pseudolaguvia inornata, P. muricata, P. shawi, Pseudecheneis sirenica, Sisor barakensis, S. chennuah, Tor progeneius, Pethia shalynius, Garra kempi, G. naganensis, Nemacheilus pavonaceus, Schistura elongata, S. reticulofasciata, S. papulifera and S. tigrinum.
As many as 41 species of fish are endemic to the Chindwin drainage. They are: Acantopsis spectabilis, Akysis manipurensis, A. prashadi, Amblyceps torrentis, A. tuberculatum, Barilius chatricensis, B. dogarsinghi, B. ngawa, Devario acuticephala D. naganensis, D. yuensis, Gagata dolichonema, Garra compressus, G. elongata, G. litanensis, G. nambulica, G. paralissorhynchus, Glyptothorax chindwinica, G. granulus, G. ngapang, G. ventrolineatus, Hemibagrus peguensis, H. microphthalmus, Lepidocephalichthys manipurensis, Myersglanis jayarami, Mystus pulcher, Neonoemacheilus morehensis, Olyra horae, Osteobrama belangeri, O. cunma, Pseudecheneis ukhrulensis, Psilorhynchus microphthalmus, Pethia atra, P. khugae, P. manipurensis, Rasbora ornatus, Sperata acicularis, Schistura kangjupkhulensis, S. khugae, S. manipurensis and Physoschistura prashadi.
Fish fauna of the Kaladan is poorly explored (Anganthoibi and Vishwanath, 2010). Although more than 200 fish species with about 20 endemics are expected to occur in the basin (Abell et al., 2008), only a total of 27 species have been documented so far. Our survey on this basin resulted in the discovery of 12 new species: Barilius profundus, Batasio convexirostrum, Glyptothorax ater, G. caudimaculatus, G. chimtuipuiensis, G. churamanii, G. jayarami, G. verrucosus, Hara koladynensis, Schistura koladynensis and S. porocephala. Many of our collections from the river are new and are in the process of description. Occurrence of undescribed species of the genus Akrocolioplax (Zhang and Kottelat, 2006), so far monotypic with its type species in the Salween basin in Thailand, is interesting. The high level of endemism in this river basin may be related to the formation of the Kaladan fault and separation of the river from the Ganga–Brahmaputra in the west and from the Chindwin basin in the east.
In the Brahmaputra basin, 42% of species found and in the Kaladan, 16% species of species found have not been evaluated. Although respectively 1, 13 and 34 species have been assessed as CR, EN, and VU in the northeast, only a very few species have been assessed as threatened in the Kaladan (Figure 3). This shows that more studies are required and it is necessary to examine the underlying reasons for the lack of information in greater detail. Many of the species have been recently described from older material or poorly sampled areas. Adequate information on the biology and distribution of these species for accurate assessment is lacking.
Fish fauna of northeast India is still in the discovery survey state. More studies are needed to understand the biology, population trend, nutritional quality, and other criteria, so as to categorize them in respect to threat criteria, value for farm culture, etc. However, freshwater fish in general are facing the threats of five interacting categories: overexploitation, water pollution, flow modification, habitat loss, and exotic species invasion, as well as an additional factor, climate change.
Northeast India has been regarded as the country's future powerhouse. In 2001, the Central Electricity Authority while assessing the hydroelectrical potential of various river basins in the country, found the Brahmaputra basin to rank the highest with capacity for 168 projects and a power production potential of 63,328 MW. However, the construction of dams has been found to have a great impact on freshwater biodiversity (Vagholikar and Das, 2011). For instance, with the construction of the Ithai barrage in the Loktak lake of Manipur, there has been disruption in the migration of fish from the lake and some species have lost their spawning habitats. Species such as Syncrossus berdmorei and Raiamas guttatus that were widely found in swamps, streams, and irrigation canals have been lost from these habitats around the lake (Vishwanath et al., 2011). The proposals for the Kaladan hydel project and the Kaladan multimodal transit transport project for navigation from Kolkata to Kaladan via Sittwe in Myanmar are also of great concern for the freshwater biodiversity of the basin (Vishwanath et al., 2011). All major projects that could impact freshwater systems should be subject to an independent and transparent environmental impact assessment (EIA). The operating conditions of existing dams should be reviewed to ensure that environmental flows are maintained or restored, and technologies should be adopted to mitigate the impact of barrages to migratory fish species (Daniel et al., 2011).
The United Nations has declared the years 2011 to 2020 as the International Decade for Biodiversity. We all should put our best concerted efforts to conserve the freshwater biodiversity. Proper planning and conservation management should be adopted now. Otherwise, it may become too late for freshwater diversity. Developing effective conservation and management strategies for freshwater biodiversity requires documenting declines and extinctions and understanding the underlying causes. Implementation of such strategies depends upon effective communication and engagement among scientists, politicians, and non-governmental organisations. Pragmatic approaches will be needed to ensure that attempts at communication between freshwater scientists and water resource managers, as well as other stakeholders, contribute to planning and problem solving (Richter et al., 2003; Bernhardt et al., 2006) and do not fall on deaf ears. This is a significant challenge, as motivation of the broader community may be neither open nor fair. Conservation typically operates in a world where many players are characterized by dishonesty, self-interest, and even outright hostility to the environment.
The diversity of freshwater fishes in northeast India is attributed to its geological history, drainage patterns and different habitats. These fishes are of great value for food, ornamental, sport and medicinal purposes, but may be exploited. Although the conservation status of the Eastern Himalayan fishes, the majority of which are distributed in northeast India, are available, 27% of these are categorised as Data Deficient. Detailed biological information of these fishes is required to put them under one of the IUCN categories and thus, it is important to reassess and categorize their status so as to take up necessary conservation measures.