Diversity and distribution of freshwater fish in mineralized watersheds of the Agno River Basin, northern Philippines

Tenio, KFC ORCID: 0000-0003-1747-1725, Cui, LE, Faustino-Eslava, DV, Guotana, JMR, Padrones, JT, Alejo, KG, Casa, M, Gonzalvo, FIP, Guevarra, EJ, Areglado, RLD, Regalado, MRV, Byrne, P ORCID: 0000-0002-2699-052X, Williams, R ORCID: 0000-0001-6067-1947 and Biles, E ORCID: 0000-0002-7380-1250 (2026) Diversity and distribution of freshwater fish in mineralized watersheds of the Agno River Basin, northern Philippines. Watershed Ecology and the Environment, 8. pp. 248-260. ISSN 2589-4714

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Abstract

The Agno River Basin in the northern Philippines is a region of significant ecological and economic value; however, baseline data on its fish diversity and distribution are poorly documented, limiting effective river basin management. This study provides the first baseline assessment of water quality and fish assemblages (July 2021 and January 2022) across eight sample stations representing diverse land use in the upper and lower Agno River Basin. Diversity indices and spatio-temporal analyses were applied to characterize patterns in both water quality and fish communities. While most physicochemical parameters complied with national and international water quality standards, elevated electrical conductivity was detected near mining zones, and agricultural areas exhibited increased temperatures and reduced dissolved oxygen levels. Most water quality parameters showed significant variability across stations, seasons and interactions effects (p < 0.001). A total of 23 fish species, representing 13 families were recorded, with Gobiidae (84%) and Cichlidae (11%) accounting for the highest abundance. Pseudogobius javanicus and Rhinogobius bucculentus were the most abundant taxa. Notably, no fish specimens were found at the Baloy station, located downstream of intensive mining activity. Species diversity ranged from low to moderate (Shannon index H′ = 0.29–1.62), with low evenness and high dominance, indicating habitat specialization and uneven resource distribution. Non-metric multidimensional scaling (NMDS) (p > 0.05) and species clustering analysis showed similar species composition across sites. Multivariate analyses, including canonical correspondence analysis (CCA) and redundancy analysis, revealed that temperature showed affinities with fish composition and abundance. However, patterns must be interpreted cautiously due to the lack of statistical support (p > 0.05). The findings provide valuable insights into the current ecological condition of the Agno River Basin and highlight the importance of continuous monitoring and comprehensive evaluation of land-use impacts and aquaculture pressures to inform evidence-based, ecosystem-based river basin management.

Item Type:	Article
Subjects:	Q Science > QL Zoology
Divisions:	Biological and Environmental Sciences (from Sep 19)
Publisher:	Elsevier BV
Date of acceptance:	11 May 2026
Date of first compliant Open Access:	11 June 2026
Date Deposited:	11 Jun 2026 09:18
Last Modified:	11 Jun 2026 09:18
DOI or ID number:	10.1016/j.wsee.2026.05.001
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28808

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