Research Article PatternsofFishAssemblage,Growth,andDietCompositionina Tropical River between Two Cascading Hydropower Dams LeeNyanti , 1 Chen-Lin Soo , 2 Afina-Yian Chundi , 3 Elsa-Cordelia-Durie Lambat , 3 Alvinna Tram , 3 Teck-Yee Ling , 3 Siong-Fong Sim , 3 Jongkar Grinang , 3 Tonny Ganyai , 1 andKaren-Suan-PingLee 1 1 Research and Development Department, Sarawak Energy Berhad, Kuching 93050, Sarawak, Malaysia 2 Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah, Jalan UMS, Kota Kinabalu 88400, Sabah, Malaysia 3 Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan 94300, Sarawak, Malaysia Correspondence should be addressed to Chen-Lin Soo; qianlin1112@gmail.com Received 11 December 2020; Revised 27 January 2021; Accepted 1 February 2021; Published 18 February 2021 Academic Editor: Agoes Soegianto Copyright © 2021 Lee Nyanti et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Construction of cascade dams has been shown to have impacts on fish assemblages and biodiversity. Yet, there is no literature on fish assemblages in the Murum River that connects the cascading Bakun and Murum dams in Sarawak, Malaysia. Hence, study on this modified ecosystem is necessitated to better understand the effects of the cascade dam construction on fish fauna. For this, fish samples were caught at five stations located along the river during both dry and wet seasons. Environmental parameters were taken concurrently with fish sampling. Length-weight relationship, condition factors, and diet composition of selected fish species in the river were also determined. e present study demonstrated that there are indications of the impact of cascading dams on the formation of a complex ecosystem in the Murum River, that is, changing from the shallow downstream of the Murum Dam to the deep transitional and inundated zone of the Bakun reservoir. e transitional zone in the Murum River exhibited the lowest fish species diversity, richness, and evenness during the dry season due to low pH and DO coupled with high turbidity. e biological indices improved when the water quality improved during the wet season. On the contrary, the diversity and evenness indices at the inundated tributary station decreased remarkably during the wet season, likely due to the migration of fish during the onset of the rainy season. is study showed that Barbonymus schwanenfeldii has a wider feeding habit which contributes to its higher distribution and abundance in the Murum River. e growth patterns of B. schwanenfeldii, Cyclocheilichthys apogon, Hampala macrolepidota, Lobocheilos ovalis, and Osteochilus enneaporos were better during wet than dry season. Overall, the condition factor of all native fish species in the Murum River was in poor to fair condition, whereas the exotic species, Oreochromis mossambicus, exhibited excellent condition (K value > 2) for both seasons. e increase in the number of O. mossambicus coupled with its high condition factor indicates biological intrusion and a potential threat to the native fish species in the Murum River. Continuous monitoring is essential to detect in-time risk issues associated with environmental degradation and biological invasion in this regulated and inundated river ecosystem. 1.Introduction Physical structures such as dams and reservoirs were made to fulfil man’s needs for the purposes of power generation, flood control, recreation, agriculture, and industry. Dam im- poundment inevitably modifies the natural regime of its downstream rivers and has resulted in environmental degra- dation [1–3]. e fluctuations of flow and environmental conditions could lead to alteration of aquatic biodiversity in the downstream river [4]. Nyanti [5] demonstrated that the downstream river of the tropical Batang Ai Dam is extremely shallow and slow flowing when the power generation is halted, and no water is discharged from the powerhouse, which has subsequently reduced the fish abundance in the river. In ad- dition, seasonal changes in the hydrology of the downstream river could also lead to differences in fish assemblages [6]. Hindawi International Journal of Ecology Volume 2021, Article ID 6652782, 10 pages https://doi.org/10.1155/2021/6652782