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Illegal gold mining in West Kalimantan has led to the formation of Serantangan Lake, a post-mining void with potential for freshwater resources, tourism, and agriculture. However, mercury contamination and degraded water quality pose significant ecological and public health risks. This study evaluated the lake's water quality using macrozoobenthos as bioindicators across three stations representing varied environmental conditions. The research was conducted from December 2024 to February 2025. A total of 1,078 macrozoobenthos individuals were collected, representing 14 genera, 14 families, and 9 orders. Diversity indices revealed the highest biodiversity at Station I (H' = 1.13, E = 0.98) and the lowest at Station III (H' = 0.42, E = 0.37), which was adjacent to active mining. Dominance index (D) and Family Biotic Index (FBI) further confirmed poor ecological conditions at Station III (D = 0.41, FBI = 8.6), indicating very poor water quality. Physicochemical measurements showed elevated mercury levels (up to 0.0027 mg/L) and BOD (up to 12.6 mg/L), with transparency, mercury contamination, and hardness significantly correlated with macrozoobenthos abundance and diversity. Canonical Correspondence Analysis (CCA) and Principal Component Analysis (PCA) revealed distinct macrozoobenthos assemblages influenced by environmental parameters.

Macroinvertebrates are often used for monitoring water quality of rivers. The presence of macroinvertebrates in river ecosystems is influenced by physical, chemical and natural conditions. The aim of this study was to compare the macroinvertebrates community in three rivers of Jawa Island, Indonesia. The abundance, composition and taxa richness of macroinvertebrates community in Brantas River (the largest river in East Java) and Opak-Progo Rivers (two large rivers in Special Region of Yogyakarta) were described for comparison. The macroinvertebrate communities were sampled using surber at ten stations in Brantas River, six stations in Opak River and four stations in Progo River. One-way ANOVA tests revealed significant differences in temperature, pH, dissolved oxygen (DO) and current velocity (p < 0.05) among rivers but, it was not in case of chemical oxygen demand (COD). Based on Post Hoc test using LSD, Brantas River had significantly different environmental parameters compared to the other two rivers. Brantas River showed a rich and diverse macroinvertebrate fauna comprising 45 genera of 29 families and 11 orders. While in Opak River 39 genera of 21 families and 7 orders were found, and in Progo River 55 genera of 29 families and 10 orders were obtained. Of the three rivers, Brantas River showed the highest abundance of macroinvertebrates. The number of taxa richness among three rivers was not significantly different. The differences in environmental parameters seemed to be the factors causing the difference in composition, abundance and taxa richness of macroinvertebrates of these three rivers.

This study refers to the general reproductive biology of Osteochillus waandersii, and provides information about the sex ratio, gonad development stages, gonado-somatic index (GSI), length at maturity, fecundity, and growth pattern. The fish samples were collected monthly, between March and August 2018, from the Landak River, Kalimantan Province, Indonesia. A total of 234 specimens were collected using gillnets and dipnets, 136 males and 98 females, resulting in a 1.39:1 sex ratio, which is significantly different from the expected ratio of 1:1 (P<0.05). Males reached sexual maturity at a lower size than females, with a length at first maturity estimated at 137.9 mm for males and 140.3 mm for females. Analysis of the macroscopic and histological observations showed that testicles could be classified into four stages: immature, maturing, mature and spent. The GSI ranged between 1% and 9.54% and 1% and 11.67% for males and females, respectively. The ovaries were classified into five stages: immature or resting, maturing, mature, ripe, and spawned-recovering. The absolute fecundity varied from a minimum of 2130 to a maximum of 13640 eggs and a mean of 7165 eggs, corresponding to fish with total length between 145 to 177 mm and a weight between 30 to 67 g.