Habitat Ecology and Shellfish Diversity of River Burhi Gandak, North Bihar, India

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INTRODUCTION
I ndia is endowed with abundant water resources in the form of river 29000 km, reservoirs 3.15 million ha, lakes 0.72 million ha, backwater and lagoons 0.9 million ha, estuaries 0.3 million ha, floodplain wetlands 0.2 m ha, which provides a wide range of opportunities for the growth and development of fisheries sector (ICAR-CIFRI, 2019). The Ganga River system is one of the largest riverine systems in India and its combined length is 8047 km. Gomti, Ghagra, Gandak, and Burhi Gandak rivers are the major tributaries of this river system (Ayyappan et al., 2011). India has rich resources of shellfishes include 2,934 crustacean species (2,430 species of saltwater and 504 species of freshwater crustacean), 5,070 molluscan species (3,370 species of saltwater and 1,700 species of freshwater) (Jena and Gopalakrishnan, 2012). Shellfish are the crucial members of the phylum Arthropoda and Mollusca, which have the biosphere's highest animal biodiversity. The biodiversity index examines the abundance and distribution of distinct species and species richness to further detail society makeup. These indexes help determine the uniqueness and genetic richness of species in a given society (Grace, 2013).
Bihar has significant freshwater resources for the development of fisheries The Burhi Gandak river originated in Chautarwa Chaur near in West Champaran district of North Bihar. The Burhi Gandak river basin is bordered on the north by the Himalayas, on the south through Ganga River, on the east through Kosi River, and on the west through the great Gandak river, which forms the Gandak's eastern boundary. The Burhi Gandak river has the area of catchment 12,500 sq km, with 10,150 sq km in Bihar and the rest in Nepal. The river abundantly flows through India and it is an important perennial river of North Bihar (Singh et al., 2018).

Study area
The present biodiversity investigation was conducted in Burhi Gandak River, North Bihar to study the variation in distribution and abundance of shellfish fauna for a year from July 2020 to June 2021. Motihari (site 1), Muzaffarpur (site 2), and Khagaria were the study locations (site-3). Three sites totaling about 100 km each make up the entire study area (about 300 km). Three of these study stations are positioned upstream (site-1), in the middle stream (site-2) and in the lower stream, respectively (site-3). A global positioning system (GPS) was used to map out the locations of the sampling sites.

Sampling methods, data collection and taxonomic identification
The shellfish samples were collected in the morning between 5.30 am to 10:00 am every month from July 2020 to June 2021, with the help of local fishermen by using traditional boats and locally man-made nets like bamboomade traps (Ghana) and Pelni Jaal to catch the freshwater prawn and crabs and other species like snails, mussels are picked by hands. The collected specimens were identified by using standard taxonomic keys (Ramakrishna and Dey, 2007;Jayachandran, 2001).

Habitat ecology parameters of Burhi Gandak River
Habitat ecological parameters such as river depth, width, flow rate, river substrates, aquatic vegetation and river riparian cover were recorded in the field by using cloth tape, bamboo poles, rope, thermocole and by visual inspection (Table I). The river substrate, aquatic vegetation and riparian cover play an important role in abundance and distribution of shellfishes. These ecological parameters were observed through visual inspection and mean range calculated by using SPSS version: 22.0 Software.

Shellfish faunal diversity indices analysis
The data was collected on monthly basis from all sampling stations and then recorded the total number of specimens from each sampling station (Table II). The all biodiversity indices of shellfish were calculated by Shanon-Weiner diversity index (H'), Margalef's richness index (d), Pielou's evenness indices (J'), Simpson index (1-Lambda), Taxonomic diversity (Δ), Taxonomic distinctness (Δ*), Average taxonomic distinctness (Δ+), Variation in taxonomic distinctness (ᴧ+) and total phylogenetic diversity (sPhi+) were used to calculate by computer software package PRIMER V6.1.9 developed by the Plymouth Marine Laboratory, United Kingdom (Clarke and Warwick, 2001).

RESULTS
During the study time a total 12 species of shellfish belonging to 4 orders, 9 families and 10 genera were recorded from Motihari, Muzaffarpur and Khagaria. Identified shellfishes comprised of 5 species of crustaceans (3 species of freshwater prawns and 2 species of crab under 2 orders, 2 families and 3 genera) and 7 species of molluscs (5 species of snails and 2 species of mussels under 2 orders, 7 families and 6 genera). Higher species abundance was observed at Muzaffarpur and the maximum numbers of species were observed in the monsoon season. The average river width of Motihari sampling site was 102.77±11.58 m, Muzaffarpur sampling site was 87.14±12.24 m and Khagaria sampling site was 87.34±10.17 m. The average maximum river depth of River Burhi Gandak was 13.55±1.21 m in Khagaria followed by Muzaffarpur (12.06±0.99 m) and Motihari (8.62±0.99 m). The average maximum flow rate of Burhi Gandak River was 0.74±0.11m/s in Motihari, 0.65±0.10 m/s in Muzaffarpur and 0.55±0.11m/s in Motihari. The river substrates were mostly muddy, sandy, rocky and clay content found in all three sites. The higher abundance of aquatic vegetation was observed in Muzaffarpur, while the observed riparian cover was dense at Muzaffarpur.

Habitat ecological parameters
The habitat characteristics like river width, depth flow rate, substrate, aquatic vegetation and the riparian cover were investigated during the study period. The recorded river width was high (67.13 to182.88 m) in Motihari followed by Muzaffarpur (56.38 to 179.83 m) and Khagaria (65.53 to 167.64 m) which is higher than the earlier report as Johnson and Arunachalam (2009) observed 9.1 to 80 m in river width Western Ghat streams while Johnson et al. (2012) observed 54.6 m in Ken River, Madhya Pradesh. The maximum river width was observed during July 2020 and low in June 2021 in the river Burhi Gandak. The increase in water depth started from the monsoon season and was high during July to August. The highest depth of water (7.31 to 21.33 m) was recorded in Khagaria and minimum (3.04 to 12.19 m) in Motihari which was higher than the earlier reports as Johnson and Arunachalam (2009)  .54 m/s mean flow rate in Pinder river, India. As a similar report was observed by Sarkar et al. (2010) for Danio, Ompok, Bagarius are attracted to fast-moving water with high flow and depth. There was a positive association between habitat parameters and shellfish abundance in all sites. The high flow rates were reported in the monsoon season and lower in the winter season. The river substrate is highly muddy, sandy clay and rocky while Pati et al. (2012) observed the Sartoriana spinigera freshwater crab likes to live in sandy clay in the pond and canal of Odisha. The Maximum number of aquatic vegetation (6) was observed in Muzaffarpur as compared to Khagaria (5) and Motihari (4). River riparian cover was recorded maximum at the middle stream and low in the lower stream of river Burhi Gandak. Such as earlier reports Annawaty et al. (2016) observed the freshwater prawn Caridina species found in slow-flowing to virtually stagnant water, sandy muddy bottom with aquatic plants roots and dead leaves is the most preferred habitat, while Johnson et al. (2012) observed some species like Danio rerio and Rasbora daniconius chiefly affected by the altitude of river, riparian cover. A similar report Bhat (2004) observed small stones and rocks were associated with species like Mystus malabaricus, Oreochromis nashii, while more sand and silt substrate was associated with species like Glossogobius giuris, and Puntius ticto and Mastacembelus armatus species were found in high riparian vegetation in Western Ghat, India.

Species diversity, richness, distribution and abundance
The present research was conducted from July 2020 to June 2021 for 12 months duration in the Burhi Gandak river to study variation in distribution and abundance of shellfish from the Burhi Gandak River. A total 12 species of shellfish have been recorded belonging to 4 orders, 9 families and 10 genera which which is lower than the earlier records of Prabhakar and Roy (2008) who recorded 20 species of molluscs and 10 species of crustacean from the Kosi river of North Bihar; Rao (2001) recorded 15 species of molluscan, and 04 species of crustacean in the upper stretch of river Ganga; Ramesha et al. (2013) observed 19 species of freshwater bivalve belonging to 3 families and 5 genera in Cauvery river, India, Waghmare and Kulkarni (2015) observed 15 molluscs species which includes 9 species of Bivalvia and 6 species of Gastropoda in Lendi River, Maharashtra, Wagh et al. (2019) reported 30 species of molluscan fauna comes under 2 categories, 6 orders, 12 family and 17 genera from river Ghaggar in Maharashtra. Raghunathan and Valarmathi (2007) recorded 10 species of freshwater prawns and crabs from a paddy field in Singaperumalkoil, Chennai, which is less than the shellfishes recorded during present study. The average taxonomic distinctness index (Delta+) estimated 12 months was 90.61.
The Shannon-Wiener species diversity data was calculated according to month and sampling sites during the study period. Among the studies of Burhi Gandak river the higher H' value for the overall studied period ranged from 2.40 to 2.50 in Muzaffarpur followed by 2.30 to 2.50 in Motihari and 2.35 to 2.47 in Khagaria which is higher than the earlier records such as Soomro  (Table III). Sudhan (2017) estimated lower value of of Delta + index ranged from 71.21 to 90.14 in Pechiparai reservoir. The mean phylogenetic index is calculated by dividing the total phylogenetic diversity index by the number of species, and it reflects the taxonomic width or overall taxonomic path length. The total phylogenetic diversity index (sPhi + ) calculated was 860 in all sampling sites, seasonwise and monthwise. Sudhan (2017) observed phylogenetic diversity index ranged from 890 and 1966 in Pechiparai reservoir. Pavinkumar (2014) recorded higher phylogenetic diversity value in selected three estuaries of Tamil Nadu namely Manakudy estuary, Korampallam-Thermal estuary and Punnakayal estuary. Cluster analysis is useful for determining the natural grouping of samples, inside a group being more similar to one another than samples from separate groups (Clarke and Warwick, 2001). Bray-curtis similarity based on counts in all three sampling sites. The Bray-curtis similarity analysis of all three sampling stations given in Figure 1. Motihari performed 87% similarity with Muzaffarpur and 92% with Khagaria as same as Muzaffarpur performed 87% similarity with Motihari and 90% with Khagaria and also Khagaria performed 92% commonality with Motihari and 90% with Muzaffarpur. The group in the dendrogram was formed between Motihari and Khagaria with 92% similarity. While comparing similarity between all three sampling sites based on mothwise, seasonwise and sitewise. The monsoon and post-monsoon show 99% similarity and post-monsoon and pre-monsoon shows 97% (Fig. 2). During the study time the higher species abundance was observed at Muzaffarpur (2169 individuals) followed by Khagaria (2089 individuals) and Motihari (1767 individuals) and the maximum numbers of species were observed in the monsoon season. The diversity index was calculated for Motihari, Muzaffarpur and Khagaria sampling stations. The Shanon-Weiner diversity index ranged from 1.30 to 1.50 from all three stations. The Pielou's evenness ranged from 0.90 to 1.00 in Motihari, Muzaffarpur and Khagaria. The Magalef's species richness index (d) varied between 2.0 to 2.30 in all three stations. According to the hierarchical clustering, the highest similarity was observed for Motihari and Khagaria (92%) and the lowest between Muzaffarpur and Motihari (87%). While the season wise post-monsoon shows 99% similarity. According to seasonwise maximum similarity between season was 99.65% similarity between monsoon and post-monsoon season and minimum similarity season was 97.22% between post-monsoon 2020 and premonsoon 2021. The average taxonomic distinctness index was 90.61 in all monthwise, seasonwise and sitewise also.

O n l i n e F i r s t A r t i c l e
Icthyodiversity of River Burhi, India  The total phylogenetic diversity index calculated was 860 in all three sites. Shellfish diversity, richness and evenness showed a similar trend at all the sampling sites.
Higher river width was observed at Motihari followed by Khagaria and Muzaffarpur and maximum river depth and flow was recorded at Muzaffarpur. This could be the reason for higher species abundance at Muzaffarpur compared to other 2 sampling sites The current study provides a valid information pertinent to the shellfish assemblages in the Burhi Gandak river and this information is used to evaluate future species populations. Industrial waste, domestic waste and agricultural runoff were some of the major threats to habitat and diversity of shellfish fauna in the river Burhi Gandak. The study also suggests that the evaluation of the river primary economic benefits might show the precise effectiveness and trigger after actions for developing laws, rules and regulations into place. The habitat of Burhi Gandak needs to be conserved because this river basin harbours a diverse group of freshwater finfishes and shellfishes. University, Pusa, Bihar, India, and the Dean, College of Fisheries Dholi, Bihar, India for providing the necessary resources and supporting the study.

Funding
Funding was provided by RPCAU-College of Fisheries Dholi, Bihar by providing PG merit university fellowship.

IRB approval ethical statement
IRB Approval have been given by the advisory committee members and all the procedures were carried out according to the institutional guidelines.

Statement of conflict of interest
The authors have declared no conflict of interest.

O n l i n e F i r s t A r t i c l e
Icthyodiversity of River Burhi, India