No abstract

The spatial and temporal variations of fish assemblages in rivers and streams of Nepal are poorly understood. So, the present study aimed to explore the spatial and temporal variations of fish assemblage structure in Nepal’s West Rapti River. The data were collected during autumn, winter and spring seasons, from October 2018 to April 2019. Fish samples were collected using cast net of 12 mm mesh size. A total of 28 species belonging to 7 orders, 10 families and 19 genera were recorded during the study. The analysis of similarity (ANOSIM) showed no significant difference among the stations and seasons. Based on cluster analysis, two major clusters were observed. The similarity percentage (SIMPER) analysis delineated that Cabdio morar (C14, 13.63%), Barilius bendelensis (C11, 10.32%), Gogangra viridescens (C22, 7.85%), Salmostoma phulo (C17, 7.74%), Labeo gonius (C5, 7.53%), Gagata cenia (C23, 6.45%), Garra gotyla (C6, 5.87%) and Labeo dyocelius (C2, 5.62%) were the most contributing species. The Canonical Correspondence Analysis (CCA) distinctly showed that the environmental variables dissolved oxygen, pH, carbon-dioxide, and water temperature play an essential role in shaping the fish assemblage structure of West Rapti River.

We assessed the correlation of fish assemblages with habitat and environmental variables temporally from July and October, 2019 and January and April, 2020 across 5 study sites in the Phewa Khola stream of Mangsebung Rural Municipality, Ilam, Nepal. We sampled 3571 fish representing 13 species, belonging to 3 orders, 4 families, and 9 genera. An analysis of similarity (ANOSIM) indicated that there is a significant difference between the fish assemblage structure in space (R= 0.833, P= 0.001) but not in time (R= -0.148, P= 0.985). Our habitat study showed that glides, runs, pools and deep pools are the primary habitats contributing to the maximum diversity in the Phewa Khola stream. The canonical correspondence analysis (CCA) affirmed that variables such as pH, water temperature, water velocity, total hardness and dissolved oxygen play an important role in shaping fish species distribution. Results from the similarity percentage analysis (SIMPER) hinted that, 67.08% similarity was found between the months and the major contributing species were Schistura multifasciata (20.61%), Devario aequipinnatus (16.48%), Schistura rupecula (15.65%), Garra annandalei (15.36%), Schistura horai (7.74%), Schistura scaturigina (5.91%), Schistura savona (5.74%), Schizothorax plagiostomus (4.37%), Channa punctata (3.9%), Puntius terio (1.9%) and Neolissochilus hexagonolepis (1.39%). On the contrary, a 76.23% similarity was found between the sites and the major contributing species were Schistura multifasciata (21%), Devario aequipinnatus (16.8%), Garra annandalei (15.89%), Schistura rupecula (15.38%), Schistura horai (7.7%), Schistura scaturigina (5.66%), Schistura savona (4.9%), Schizothorax plagiostomus (4.4%), Channa punctata (3.97%), Puntius terio (2%) and Neolissochilus hexagonolepis (1.43%). Ongoing road development, micro-hydropower generation, the use of poisonous herbicides, illegal electro-fishing, deforestation and water diversion are all found to be major threats to the present fish species of the Phewa Khola stream.

Studies on fish community structure along altitudinal gradients of rivers are lacking in Nepal. This study was carried out to gauge the fish diversity and composition along elevational gradient in Ratuwa River. The altitudinal gradient varies between 70 m to 1300 m. Fish samples were collected based on habitat representativeness from April (spring) 10-18, July (summer) 10-18, October (autumn) 10-18, 2020 and January (winter) 10-18, 2021. A total of 3447 specimens representing 4 orders, 14 families and 36 species were identified. Both fish diversity and abundance of studied ichthyofauna vary with altitudinal gradient. The present study affirmed that fish species of Opsarius bendelisis, Schistura multifasciatus, Garra annandalei, Brachydanio rerio, Aspidoparia morar, and Schistura scaturigina are the major contributory species (>1%) for both space and time spectrums. Fish community structure testing for both to space and time showed significant difference in spatial spectrum (R=0.72, P<0.01) but no significant difference in temporal variation (R=-0.034, P>0.05). The present results hinted that fish assemblage structure varied significantly from low to high elevations, altitude, water temperature, water velocity, dissolved oxygen and pH was found as major influential factors (P<0.05) for species distribution.