Ichthyofaunal diversity of Senkhi stream, Itanagar, Arunachal Pradesh: a comparative status between 2004–05 and 2018–19

: An investigation was conducted during 2018–19 after a time span of 13 years in the Senkhi stream, an important hill stream that flows through western corner of the capital city, Itanagar. The present study aims to compare decadal changes in ichthyofaunal diversity, status, and abundance with reference to the impact of increasing urbanization in the capital city. The ichthyofaunal diversity assessed presently is restricted to 37 species spreading over 30 genera under 13 families which include four species more, not reported in the past. Thus, of the 37 species recorded, 33 species only could be compared, and noticeably resulted ultimate reduction of 14 species belonging to 11 genera under 10 families from the study area. It indicated that nearly 64% decline in fish abundance within stream zone under urban area and about 46% reduction in undisturbed area. The present study hitherto revealed the alarming rate of decline in fish diversity and also unfolded key factors responsible for crucial decline of fish diversity along with the possible mitigation measures.


INTRODUCTION
Biodiversity is essential for stabilization of ecosystems and protection of overall environmental quality (Ehrlich & Wilson 1991). Freshwater fish are one of the most threatened taxonomic groups (Darwall & Vie 2005) because of their high sensitivity to the quantitative and qualitative alteration of aquatic habits (Laffaille et al. 2005;Sarkar et al. 2008;Kang et al. 2009). Conservation of fish diversity and associated habitats is a great challenge (Dudgeon et al. 2006). Conservation measures to mitigate the impact of the pressures have largely been slow and inadequate and as a result populations of many of the species are declining rapidly. The Himalayan region in India has been identified as one of the 36 biodiversity 'hotspot' areas of the world (https://www.conservation. org) where the state of Arunachal  constitutes 60.93% of the region and is characterized in having varied topographical features that forms a huge watershed network provided with numerous aquatic habitats. There are 2,500 species of freshwater fishes that have been recognized in the Indian subcontinent out of which 930 are categorized as freshwater species (Jayaram 2010) and 1,570 are marine (Kar 2003;Vijaykumar et al. 2008). Fishing is a common recreational activity and fish is a good source of protein required for a good health. The tribal populace of the state of Arunachal Pradesh are fond of fish and practice fishing and harvesting seasonally from streams and rivers by employing traditional fishing gears and traps as common property resource. However, depletion of the aquatic biodiversity is gradually increasing due to use of modern contraptions in most of the streams and rivers of Arunachal Pradesh (Chaudhry & Tamang 2007;Tamang & Shivaji 2012). A glimpse of such non-conventional methods of fishing using inverter and battery had once been highlighted in the local news (Arunachal24. dated 24 September 2020) operating within D'Ering Wildlife Sanctuary (DEWS).
Senkhi is an important and lonely hill stream, one of the tributary of upper Brahmaputra River and is the prime source of water for people inhabiting Itanagar that caters about 70% of drinking water to urban populace. The stream originates from about 7 km inside dense forest fed by merging various small drainages, before entering a beautiful valley popularly known as 'Senkhi Valley' in the north. The freshwater stream moves downwards traversing urban areas like Chandranagar, Police colony, IRBN colony and subsequently meets with Chimpu stream near IRBN firing ground. Thereafter, it forms a contiguous water body with Pachin and eventually confluences with Dikrong river at RCC bridge, Doimukh, covering about 30 km towards east. It consists of varied microhabitats ranging from deep water to fastflowing riffles. The substratum comprised of medium to large boulders, pebbles, cobbles, and sand. Density of medium to large boulders are higher upstream than downstream. Sand and mixture of various colored gravels are dense towards lower reaches after Jullang village and density of sand increases thereafter up to Doimukh, through twin capital Naharlagun. On account of having varied physiographic features, the stream harbours a good number of fish diversity.
As far as ichthyofauna of the state is concerned, McClelland (1839) seemed to be the earliest pioneer worker followed by Chaudhuri (1913), Hora (1921, Jayaram (1963), Jayaram & Mazumdar (1964), Srivastava (1966), Dutta & Sen (1977), Dutta & Barman (1984, 1985, and Sen (1999). The first compilation of fish fauna of the state was made by Nath & Dey (2000) who listed a total of 131 species, followed by Bagra et al. (2009) Tamang et al. (2006;2007a; had also reported first distributional record of three fish species: Pseudolaguvia shawi, Balitora brucei, Glyptothorax telchitta for the state and one new species Erethistoides senkhiensis from this stream. Therefore, the stream also acts as an important habitat for ichthyological research. Chaudhry & Tamang (2006) had also reported practicing of non-conventional method of fishing like using of chemicals, electrocution and it has been being continued by many people since long time. Thus to validate the current status of ichthyofaunal diversity of the stream, the present study has been conducted, so that the information may be used for restoration of the ongoing situation. Besides, the paper aims to highlight the major key factors responsible for rapid depletion of fish population in the Senkhi stream along with necessary policy decision to be taken for conservation and mitigation of the stream.

MATERIAL AND METHODS
The reinvestigations were conducted after a time span of 13 years from 02 September 2018 to 22 September 2019. Two sampling sites were selected in Senkhi stream with a gap of about 3 km in between J TT Site-I consists of large to medium sized boulders, pebbles and cobles with low quantity of sand deposit, width of stream narrow causing high pressure water during monsoon. Site-II: Stream gradually becoming wider towards downstream, and stream bed consists of large number of pebbles, cobbles, gravels, and sand, but few numbers of large boulders, placed collectively at beginning, middle and end of the site. Overall, it somewhat resembles with plain stream of Assam. However, both the sites mostly share gravelly bed which characterized true hill stream habitat. Random sampling was carried out weekly after dusk from 1800 to 2200 h using a cast net with radius of 2.30 m and 7 x 7 mm mesh size. Sampling in site-II was done in other alternate day. Weekly samplings were restricted to four weeks in a month. The frequency of occurrence of each species was calculated based on the numbers of occasions the species were collected during the samplings. Finally the data of total catch frequencies (%) of species encountered from two respective sites were compared and each result was compared with data of 47 species of the past record (Tamang et al. 2007b), prior to total number of species encountered in each site. Samplings were carried out covering various microhabitats such as shallow to deep and moderate to torrential flowing water. The collected samples were brought to laboratory of Rajiv Gandhi University for identification. The identification of fishes was confirmed following Talwar & Jhingran (1991), Nath & Dey (2000), and Darshan et al. (2019) and subsequently deposited in Rajiv Gandhi University Museum of Fishes (RGUMF). Trophic niche model may be useful for assessing altered as well as less altered fish habitat of the tropical rivers. Trophic niche of the species were recognized examining morphology of mouth, body shape and paired fins. Species having inferior mouth, cylindrical or dorso ventrally flattened body or horizontally situated paired fins are considered as bottom feeder, whereas terminal to sub-terminal mouth with compressed body are categorized as column feeder and upturned mouth with compressed body as surface feeder. The five previously misidentified species were rectified and fourteen name of species were revised and upgraded (indicated by symbol # and ** respectively in Table 1) following "Eschmeyer's Catalogue of Fishes, 2019. The catch frequency of common (91-100%) and abundant (81-90%) as per Tamang et al. (2007b) were used as standard norms of frequency scale (Table 2). Thus, % catch frequency with respect to species richness is computed as Abundant: 91-100%, Common: 81-90%, Frequent: 61-80%, Occasional: 31-60%, Sporadic: 15-30%, Rare: 05-14%, Extremely rare <05%. The conservation status of the encountered species were categorized following IUCN Red List of Threatened Species (2019-3).

RESULTS AND DISCUSSION
The ichthyofaunal diversity in the present study is restricted to 37 species belonging to 30 genera under 13 families, including additional four species   Figure 3). With regard to 14 disappeared species, presently it is unwise to consider them as extinct as they may be existing in undisturbed upstream habitat far beyond study sites inside Senkhi valley or other drainage system within the vicinity of Itanagar Wildlife Sanctuary. Therefore, at present, species diversity is raised to 50 species excluding one exotic species Oreochromis mosssambica, which had been reported earlier.
Comparative analysis between two sites (Site-I: urban area) and (Site-II: undisturbed area): Of the total 37 species collectively encountered, distribution of 31 species were common in both sites except for six species. The comparative analysis of total catch frequency obtained from 37 species, showed 467.1 and 682.2 in site I and site II respectively, resulting deduction of 215.1, i.e., 31.5% catch frequency in Site-I than Site-II. This is the point in fact which shows that % catch frequency in Site-I is lower, since it is being situated in urban disturbed area compared to Site-II (Table 2). Of the remaining six species, four species-Danio rerio, Bangana dero, Chanda nama, and Parambassis rangawere only caught in Site-II and two species-Opsarius tileo and Anguilla bengalensis-in Site-I. This may be due to habitat preferences, as Danio rerio, Chanda nama and Parambassis ranga are typically occurs in slow moving water of the plain, characteristics somewhat familiar with Site-II. However, Bangana dero occurs in plain as well as upstream. So, may be due to water contamination, it migrated to lower reaches. The occurrence of Opsarius tileo and Anguilla bengalensis in Site-I is genuine as Opsarius tileo occurs in both the habitat in hill streams. This may be due to low population density, occasionally caught in the past study too. So, Opsarius tileo might not have caught during sampling in Site-II. Anguilla bengalensis was accidentally caught during flood.
The comparative analysis of 33 species (excluding 4 additional species) with those of 47 species of Tamang et al. (2007b) showed respectively 1295.9 and 457.5 total catch frequencies resulting in deduction of 838.4, i.e., 64.7% in Site-I and similarly total catch frequencies 1295.9 and 697.6 respectively which depicts decline of total catch frequency 598.3, i.e., 46.2% in Site-II. This clearly indicates drastic decline of abundance of fish fauna in the study sites. Further, the data of comparative analysis between two sites also revealed 64.7-46.2% = 18.5% relatively more decline in urban area than undisturbed area, except Neolissochilus hexagonolepis, Botia rostrata and Tariqilabeo latius which showed 5.8%, 11.6%, 1.9% higher, respectively (Table 2 and Figure 1). Only one species Opsarius bendelisis showed cent percent catch frequencies in both sites as well as in the past. This indicates that Opsarius bendelisis is the most dominant and adoptive species in the stream.
The percent declining trend of each species in descending order are as follows (

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3% are Data Deficient (DD), 5% Not Evaluated (NE), and Endangered (EN) each ( Figure 4). The 14 disappeared species mostly belong to LC category, i.e., 11 species and 1 species to NT, DD, and NE (Table 1). However, in case of local abundance, these species fall under extremely rare (8), rare (4) and occasional (2) categories (Table 2). In the case of ecological trophic niche is concern, it is found that majority of the species are belong to bottom feeder represented by 19 species (51%), followed by 14 (38%) column feeders and four (11%) surface feeders ( Figure 5). The percent catch frequencies of each species and availability status are presented in Table   2. The species under extreme threats are: Amblyceps arunachalensis recognized as 'Endangered' among all, followed by Neolissochilus hexagonolepis, Schistura devdevi, Balitora brucei, & Anguilla bengalensis as 'Near Threatened', and Botia rostrata & Cyprinion semiplotum as 'Vulnerable'. In the present study four species-Erethistoides senkhiensis, Barilius vagra, Anguilla bengalensis, and Amblyceps apangi-were additionally caught. Erethistoides senkhiensis was doubted to be a new species in the past study and not included in Tamang et al. (2007), and later published as a new species (Tamang et al. 2008). Though, as per     present study it seems to be locally a rare species and consequently considered Data Deficient in IUCN Red List of Threatened Species. The population density of Barilius vagra seems to be very low and might not have caught in the past study. Even in the present sampling its catch frequency is rare in upstream (Site-I) and sporadic in downstream (Site-II). Anguilla bengalensis was accidentally caught during flood. Moreover, its population seems to be very low as they mostly lives under hollow gaps of large boulders or rocks which is rarely seen in the study sites and is usually inappropriate and difficult to catch by castnet because of its robust and slippery body. Amblyceps apangi mostly hide beneath pebbles and cobbles and usually not comes in castnet, but sometime occasionally entangle, which may be the reason it could not be sampled in the past study.
Altogether the result of the present reinvestigation prior to disappearance of 14 species and drastic decline in catch frequencies within a time span of thirteen years broadly revealed rapid dwindling of existing fish fauna in the study sites primarily due to human intervention on various aspects.
On the backdrop of human interaction in the stream we gathered the information from dwelling people using unstructured questionnaire along with physical observation throughout the study sites. In fact the major key factors that has seriously jeopardized the stream ecosystems leading to sharp declination of fish fauna 1. Electro-fishing: Electric fishing was frequently observed in the study site-I and rarely in Site-II. Chaudhry & Tamang (2006) had already reported the practicing of nonconventional method of fishing like using of chemicals (lime and bleaching power) and electrofishing in the Senkhi stream. This is basically operated during winter season (November-February) when water level comes down and intensity of current becomes more effective. Electro fishing is mostly dreadful to bottom dwelling fishes like species belonging to genera Glyptothorax, Garra, Schistura, Aborichthys, Channa, Anguilla, Mastacembelus, Pseudolaguvia, Olyra and Amblyceps as members of these genera live inside boulders and cannot escape or run away immediately when electric rod is run over the boulders. Besides, eggs, fish larva, juveniles, crustacean (crab and shrimp), various aquatic insects, and zooplankton which are prime food for growing larval fishes are also destroyed. Such fishing technique enables easy and more collection in short time with less effort (Image 4). However, using of chemicals was not observed as reported earlier, mainly due to siltation of organic wastes.
2. Water contamination: Being a solvent the water gets polluted very easily and causes various water borne internal and external diseases. Water contamination has been observed mostly in urban area within study site-I which covers Police colony, Chandranagar, and IRBN colony. Discharge of untreated domestic savage into the stream is one of the key factors responsible for water contamination and habitat degradation in Senkhi stream.
3. Sewage disposal: The study site is primarily fed by a major perennial drainage that brings all sorts of organic and inorganic wastes far off Ganga market places (ca 3 km) and other surrounding areas during heavy floods (June-August). Our field observation throughout

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the study sites and at the time of sampling, has led to identification of the following sewage wastes mostly in Site-I (urban area): (i) Organic wastes (vegetable): cabbage, cauliflower, tomato, peels of potato, onion, long guard, and pumpkin; radish, green lettuce, french bean, soya bean, bitter guard, brinjal, ladies finger etc.; fruits: spoiled apple, banana, orange, lemon, pineapple and its peels; dead animal: pig, dog, cat, poultry bird were occasionally seen entrapped between boulders and sometime on marginal area of the stream, and intestine, skull, bony jaws of commercial cattle were frequently seen in the stream bed; (ii) Inorganic wastes: all sorts of cold drink plastic bottles and packets were seen densely accumulating among the boulders towards banks and middle section of the stream; footwear: plastic, foam, rubber, nylon and leather shoes and slippers; other items include large number of wrapped polythene bag, commercial fish thermocol box, plates, plastic sheets, vinyl carpet, cement bags, rubber pipe, pieces of tin sheet, umbrella, helmet, vehicle tyre, blanket, plastic sheets, plastic ball etc. Siltation of organic and inorganic debris over stream bed seen till premonsoon season; (iii) Human waste: typically human faecal matter is known to spread many water borne diseases to human like diarrhoea, typhoid, cholera, polio, hepatitis, and skin borne diseases. Some direct disposal of wastes have been seen within study Site-I as well as along the main drainage mentioned above. 4. Habitat degradation and disruption of riparian vegetation: Habitat alteration was more commonly seen in the lower reaches of the stream near Jullang village and beyond it. This was extraction of bed materials like boulders, cobbles, pebbles, gravels, and sand for developmental activities (Image 3a). This mining operation seems increasing due to increase in demand for developmental activities within capital city and its vicinity. Ecologically viable riparian vegetation have been replaced by residential houses and walls creating fish habitat congested, unsuitable and threatening mostly in Site-I (Image 3b). Habitat loss is also seen by displacing heavy boulders towards stream banks by JCB machine to protect from flash flood devastation. Moreover, due to disruption of aquatic ecosystem, one sustainable recreational angling, practiced especially for Cyprinion semiplotum using bamboo rod, nylon line and loops were entirely disappeared which was popular in the year 1995-1998 (personal observation).

CONCLUSION
In modern days management of fish diversity and its relevant habitats is a great issue and challenges (Dudgeon et al. 2006). Fresh water fish are one of the most threatened taxonomic groups (Darwall & Vie 2005) because of their high sensitivity to the quantitative and qualitative alteration of aquatic habits (Laffaille et al. 2005). One of the regular visible sign of development efforts in Itanagar, the capital, is the rapid urbanization and spreading of settlements which have adverse effect on stream ecosystem and its fauna. Much of the upstream areas near by Senkhi valley have already low vegetation cover consequences to low water discharge in the stream. Therefore, adoption of all above mentioned activities would only aggravate the already existing problems, first by destruction of the minimal viable population and secondly, by the destruction of the habitat itself. It has been observed that Senkhi stream harbors a good number of fish diversity. However, most of the fish fauna are freshwater bottom feeders which are very sensitive to ecosystem alteration. It was observed that anthropogenic activities may be the sole reasons responsible for the worsening condition of the Senkhi stream ecosystem. Hence, this might have resulted serious fish stock depletion and disappearance of 14 species in the present catch.
The fish are staple diet of the tribal folklore and an important source of protein required for the hardworking tribal communities of the state. Hence, sustainability of fish harvesting must continue for future generations. One can emulate examples from the state itself, where the tribal customary laws protect the flora and fauna in their own village area.
Keeping in view all above mentioned issues and overall result of the present study suggests urgent adoption and implementation of the following conservation strategies and mitigation measures by the concerned state government departments/ nongovernment agencies/ local volunteer organizations: i. Disposal of organic and inorganic wastes into the stream should be banned. ii.
Disposal of human wastes directly into the stream should be replaced by safety tank. iii.
Illegal and unscientific methods of fishing should be strictly band.
iv. Construction of residential houses and walls closely attached to stream banks should be avoided by laws. Moreover, the hilly regions are prone to flash flood and land slide which is risky to life.
v. Creation of awareness campaign among www.threatenedtaxa.org The Journal of Threatened Taxa (JoTT) is dedicated to building evidence for conservation globally by publishing peer-reviewed articles online every month at a reasonably rapid rate at www.threatenedtaxa.org. All articles published in JoTT are registered under Creative Commons Attribution 4.0 International License unless otherwise mentioned. JoTT allows allows unrestricted use, reproduction, and distribution of articles in any medium by providing adequate credit to the author(s) and the source of publication.