Introduction

General description

Project description

Sampling methods

Description: 

This survey was conducted in the Masai River Basin, located in the southern part of Johor Bahru, Malaysia, covering 19 sites along urban rivers in the Basin and eight surrounding non-urbanised sites. The Masai River is a 7 km-long main river course that flows into the Johor Straits, with a drainage area of 26 km² (Fig. 1). The Basin is part of the Iskandar Development Region (Iskandar Malaysia), established in 2006 under the 9^th Malaysia Plan and has undergone significant urbanisation. Many of the river channels in the area have been modified with concrete linings, raising concerns about the degradation of the river ecosystem. However, there is a lack of information on urbanisation and biodiversity loss in tropical regions. Therefore, a fish survey was conducted to assess the current state of the fish population in the region. Additionally, comparisons were made with rivers not affected by urbanisation. The fish survey was carried out between 28 November 28 and 2 December 2024.

Figure 1.  

Location of the study sites. The study focused on 27 sites (19 sites belonged to urban area, eight sites belonged to non-urban area).

Geographic coverage

Taxonomic coverage

Description: 

As a result of the surveys, 15 families, 28 genera, 32 species and 3,007 individuals were collected from the 34 habitats of 27 stations. The highest number of species was 10 (sites belonging to the Tiram River) and the highest number of individuals was 756 (site belonging to the Masai River). By contrast, fish were not confirmed in the site belonging to the Masai River. The highest number of individuals found was 1,447 of Poecilia sphenops, which appeared in nine stations.

The orders were Cypriniformes (13 species), Siluriformes (6 species), Cyprinodontiformes (4 species), Perciformes (4 species), Cichliformes (3 species), Anabantiformes (3 species), Beloniformes (1 species), Gobiiformes (1 species) and Synbranchiformes (1 species) (Fig. 2). The families were Cyprinidae (13 species), Cichlidae (4 species), Clariidae (4 species), Osphronemidae (3 species), Poeciliidae (2 species), Actinopterygii (1 species), Ambassidae (1 species), Aplocheilidae (1 species), Bagridae (1 species), Butidae (1 species), Channidae (1 species), Loricariidae (1 species), Oxudercidae (1 species), Synbranchidae (1 species) and Zenarchopteridae (1 species) (Fig. 3).

Figure 2.  

Taxonomic coverage (by order).

Figure 3.  

Taxonomic coverage (by family).

Amongst the species confirmed, Amphilophus trimaculatus (Günther, 1867), Geophagus sveni (Lucinda, Lucena & Assis, 2010), Mayaheros urophthalmus (Günther, 1862), Poecilia sphenops (Valenciennes, 1846), Gambusia affinis (S. F. Baird & Girard, 1853), Poecilia reticulata (W. Peters, 1859), Puntius pentazona (Boulenger, 1894), Cichla kelberi (Kullander & Ferreira, 2006), Clarias gariepinus (Burchell, 1822) and Pterygoplichthys disjunctivus (Weber, 1991) are considered to be invasive species.

According to the IUCN Red List in 2014, the following species were determined as LC (Least Concern): Channa striata (Bloch, 1793), Betta imbellis (Ladiges, 1975), Trichopsis vittata (G. Cuvier, 1831), Dermogenys siamensis (Fowler, 1934), Aplocheilus panchax (F. Hamilton, 1822), Barbodes lateristriga (Valenciennes, 1842), Barbodes rhombeus (Kottelat, 2000), Cyclocheilichthys apogon (Valenciennes, 1842), Danio albolineatus (Blyth, 1860), Esomus metallicus (Ahl, 1923), Parachela maculicauda (Smith, 1934), Rasbora borapetensis (Smith, 1934), Rasbora dusonensis (Bleeker, 1850), Rasbora elegans (Volz, 1903), Rasbora trilineata (Steindachner, 1870), Parambassis siamensis (Fowler, 1937), Oxyeleotris marmorata (Bleeker, 1852), Trichogaster trichopterus (Pallas, 1770), Clarias batrachus (Linnaeus, 1758), Clarias nieuhofii (Valenciennes, 1840) and Monopterus albus (Zuiew, 1793). Additionally, Labiobarbus festivus (Heckel, 1843) is listed as DD (Data Deficient).

Traits coverage

Temporal coverage

Collection data

Usage licence

Data resources

Additional information

The results of this survey identified 23 species of natives in 18 genera and natives in three genera which were not identifiable to species, for a total of 20 native genera. Further, we identified nine species of introduced fish in eight genera and introduced species in one already-seen genus which was not identifiable to species. The comparison of the number of non-native species between urban and non-urban areas revealed that the urban area had an average of 2.8 ± 1.4 species (mean ± standard deviation), while the non-urban area had 0.6 ± 1.2 species. A significant difference was observed in the results of the t-test (Fig. 4).

Figure 4.  

The comparison of the number of non-native species between urban and non-urban areas.

Amongst the non-native species, Poecilia sphenops was the most abundant, with 1,447 individuals captured in the urban watershed, accounting for approximately 48% of the total number of fish collected in this survey. Poecilia sphenops is a species native to Central and South America and from Mexico to Colombia (Ghazi et al. 2019) and is commonly introduced as an ornamental fish (Brito et al. 2013). Known for its high reproductive capacity, a typical characteristic of highly invasive species (Lockwood et al. 2007) and its ability to thrive in turbid environments (Ramírez-García et al. 2017), it is likely that the large number of individuals captured in the urban watershed is a result of these traits.

The next most abundant species captured was Mayaheros urophthalmus, with 430 individuals collected. Mayaheros urophthalmus is native to tropical America (Lardizábal et al. 2020) and has expanded its distribution range to Southeast Asia, including Malaysia (Nico 2007, NG et al. 2018). This species is known for its ability to adapt to a wide range of water temperatures and its tolerance to low oxygen conditions (Schofield et al. 2009, Chelapurath Radhakrishnan et al. 2020), suggesting that the urban river environments studied in this research provide a suitable habitat for its survival. Additionally, Mayaheros urophthalmus is favoured as a food source in Southeast Asia including the study area (Nico 2007, Ordoñez et al. 2015). On the other hand, Pterygoplichthys disjunctivus, originally native to the Amazon River (Armbruster and Page 2006) and widely distributed in the urban rivers targeted in this study, was first recorded in Malaysia in the early 1990s (Anand Prakash et al. 2022) and is currently expanding its distribution range within the country (Olawale Saba et al. 2024). In the urban rivers surveyed, Mayaheros urophthalmus and Pterygoplichthys disjunctivus were confirmed sympatrically, while Pterygoplichthys disjunctivus is typically removed when captured, Mayaheros urophthalmus appears to be released back into the river due to its value as a fishery resource. This suggests that the perceived value of these species as food resources may play a significant role in their proliferation in these environments.

Within urban watersheds, the proportion of non-native species also varied. In areas where urbanisation was concentrated downstream, many sites were dominated by non-native species, while in upstream areas with remaining forests, native species listed on the Red List, such as Parambassis siamensis and Clarias batrachus, were confirmed. This phenomenon, where rare species emerge from the small remnants of non-urban environments within urban watersheds, has been reported in other climate zones as well (Furlan et al. 2012, Wahlroos et al. 2015, Itsukushima and Maruoka 2022, Itsukushima et al. 2024). The conservation of habitats for these rare species and the restoration of these environments to expand their habitats are critical challenges in the natural regeneration of urban rivers. Future studies that clarify the relationship between physical environments, water quality and fish community structures will help develop environmental restoration methods for urban rivers aimed at the conservation and regeneration of native fish species in tropical urban watersheds.

Acknowledgements

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Supplementary material