FISH DIVERSITY OF RAPTI RIVER, CHITWAN, NEPAL

Abstract

The present study was conducted in Rapti River of Chitwan District located between latitudes of 27°20’ to 27°52’N and longitudes of 83°55’ to 84°52’E. The field visit was conducted from 23rd February to 28th June, 2020. Samples were collected from four stations, i.e. Manahari, Lothar, Kumroj and Sauraha for fishes and physicochemical parameters such as water temperature, DO, water velocity and pH. Fishes were collected with the help of well-trained local fisherman, by using a cast net of varying mesh sizes (6mm, 2cm). A total of 36 fish species were collected belonging to 5 orders, 11 families and 24 genera. The Cypriniformes was the dominant order with 24 species representing 65.71% of the total collection, followed by Siluriformes (8 species, 22.85%) and Anabantiformes (2 species, 5.7%). Each of Beloniformes and Synbranchiformes was collected a single species representing 2.85 % respectively. The highest species richness (9) was recorded at Kumroj and lowest species (3) at Manahari in rainy season. Similarly, the highest species richness (8) was recorded at Manahari and the lowest species (4) at Sauraha in winter season. The Shannon-Wiener’s diversity index was high at Kumroj (1.588) and low at Manhari (1.055) in rainy season. It is high at Kumroj (1.588) and low at Lothar (1.298) in winter. In rainy season, the highest Simpson diversity index (0.75) was found at Sauraha and the lowest (0.611) was at Lothar. In winter, the highest Simpson diversity index (0.768) was found at Kumroj and the lowest (0.702) was at Lothar. In rainy season, the highest Margalef’s index (2.09) was found in Kumroj and the lowest (1.243) was at Manhari. In winter, the highest Margalef’s index (2.164) was found at Sauraha and the lowest (0.965) was found at Lothar. Dissolved oxygen was recorded as the highest (11.5 mg/l) at Manhari and lowest (8.3 mg/l) at Sauraha in winter season. The dissolved oxygen was comparatively lower in rainy season which ranged from 7.4 mg/l (Sauraha) to 9.8 mg//l (Lothar). The Redundancy Analysis (RDA) showed a strong positive association between species like Barilius barila, B. bendelisis, B. modestus, C. jaya, and T. tor with DO. C. chagunio was found to be negatively associated with pH and the remaining species however showed the average association. It is evident that systematic research on regular interval of time basis is crucial to have more reliable data on fish diversity status. Long term research covering more seasons and more water quality parameters is highly recommended in this river in future.