Alien Fish Threaten Indonesia’s Freshwater Biodiversity, New Study Warns
The spread of alien fish species in Indonesia’s rivers, lakes, and reservoirs is emerging as a major ecological concern. A study by Faqih Baihaqi from the Department of Fisheries, Faculty of Fisheries and Marine Sciences, Universitas Padjadjaran, and Shafira Bilqis Annida from the Marine Tourism Study Program, Vocational School, Universitas Padjadjaran, analyzes the ecological consequences of these biological invasions. Published in 2026 in the Indonesian Journal of Contemporary Multidisciplinary Research (MODERN), the research synthesizes scientific evidence showing how introduced fish species are reshaping freshwater ecosystems and threatening native biodiversity in Indonesia.
The findings matter because Indonesia is one of the world’s megabiodiversity countries, with exceptionally rich freshwater fish diversity and many endemic species found nowhere else on Earth. However, the increasing introduction of non-native fish—often linked to aquaculture, fisheries development, and the ornamental fish trade—is altering ecological balance in inland waters across the archipelago.
Freshwater Ecosystems Rich but Vulnerable
Although freshwater ecosystems cover less than one percent of the Earth’s surface, they host a disproportionate share of global biodiversity. Indonesia’s inland waters—including rivers, lakes, wetlands, and reservoirs—support hundreds of unique fish species shaped by the country’s complex geological and archipelagic history.
This diversity also makes Indonesian freshwater ecosystems highly sensitive to biological invasions. When species are introduced outside their natural range, they may disrupt ecological relationships that have evolved over thousands or millions of years.
Introductions occur for several reasons. Many non-native fish are brought into Indonesia intentionally to improve aquaculture production, strengthen fisheries, or control certain aquatic organisms. Others enter ecosystems through aquarium releases or accidental escapes from fish farms.
While these species often provide economic benefits, their long-term ecological effects can be severe.
How the Research Was Conducted
To understand the scale of the issue, Faqih Baihaqi and Shafira Bilqis Annida conducted a systematic literature review of peer-reviewed scientific studies published between 2000 and 2025.
The researchers searched major academic databases including Scopus, Web of Science, and Google Scholar, collecting studies related to alien fish species and their ecological impacts in Indonesian inland waters.
The research process followed several steps:
- Identification of relevant scientific publications
- Screening of titles and abstracts for relevance
- Full-text evaluation using strict selection criteria
- Extraction of ecological impact data from eligible studies
- Thematic analysis to identify common patterns across regions
Instead of statistical meta-analysis, the study used qualitative narrative synthesis to interpret patterns of ecological impacts reported in different ecosystems.
This approach allowed the researchers to consolidate fragmented scientific evidence into a comprehensive national perspective.
Alien Fish Species Widely Established
The review identifies several non-native fish species that have become widely established across Indonesian freshwater systems. Among the most commonly reported are:
- Nile tilapia (Oreochromis niloticus)
- African catfish (Clarias gariepinus)
- Common carp (Cyprinus carpio)
- Armored catfish (Pterygoplichthys pardalis)
- Red devil fish (Amphilopus species)
Many of these species were originally introduced to improve aquaculture production or increase fishery yields. Over time, however, they escaped or were released into natural ecosystems, where they established wild populations.
These fish often possess traits that make them successful invaders: rapid growth, high reproductive rates, flexible diets, and strong environmental tolerance.
Key Ecological Impacts Identified
The study highlights several recurring ecological consequences linked to alien fish invasions in Indonesia.
- Competition with Native Fish: Non-native species often compete with indigenous fish for food and spawning habitat. Because many invasive species have flexible diets and fast reproduction, they can outcompete native populations.
- Predation on Local Species: Predatory alien fish can feed on eggs, juveniles, and smaller native species, especially in isolated ecosystems where local species have not evolved defenses against new predators.
- Habitat Modification: Bottom-feeding invasive catfish disturb sediment while searching for food. This activity increases water turbidity and damages spawning grounds used by native fish.
- Changes in Food Web Structure: The introduction of highly adaptable omnivorous fish can simplify aquatic food webs by replacing specialized species with generalist communities.
- Genetic Impacts: In some cases, hybridization between introduced and native fish species can dilute genetic diversity and threaten unique evolutionary lineages.
Together, these impacts can reshape entire aquatic ecosystems.
The Risk of Biodiversity Homogenization
One of the most significant long-term consequences identified in the study is biotic homogenization.
This process occurs when diverse ecosystems gradually become dominated by the same widely distributed invasive species. As a result, unique local species decline or disappear, and different regions begin to look ecologically similar.
In Indonesia, this trend is particularly concerning because many freshwater fish species are endemic to specific lakes or river systems. Losing these species would mean the permanent loss of unique genetic and ecological heritage.
Balancing Fisheries Development and Conservation
The researchers emphasize that alien fish introductions are closely linked to Indonesia’s efforts to strengthen food security and rural livelihoods. Aquaculture expansion and fisheries enhancement programs have contributed significantly to national fish production and economic development.
However, unmanaged introductions can create long-term ecological costs.
Faqih Baihaqi of Universitas Padjadjaran notes that the challenge lies in balancing economic benefits with biodiversity protection. Evidence-based management strategies are needed to prevent invasive species from spreading uncontrollably while maintaining sustainable fisheries production.
Policy and Management Recommendations
Based on the synthesis of scientific evidence, the study proposes several policy priorities:
- Strengthen ecological risk assessments before introducing non-native fish species
- Improve biosecurity protocols in aquaculture facilities to prevent escape events
- Establish monitoring programs to detect invasive species early
- Integrate fisheries policies with biodiversity conservation frameworks
- Support long-term ecological research on invasion impacts
Such measures could help Indonesia protect its freshwater biodiversity while still benefiting from aquaculture and fisheries development.
Why the Study Matters
Indonesia’s freshwater ecosystems are among the most biologically rich in the world, yet they are also among the most vulnerable to environmental change.
Alien fish invasions add a new layer of ecological pressure to ecosystems already affected by habitat degradation, pollution, and hydrological modification.
Without proactive management, the gradual loss of endemic fish species could undermine both ecological stability and the cultural heritage associated with Indonesia’s inland waters.
Author Profiles
- Faqih Baihaqi, S.Pi., M.Sc.: Faqih Baihaqi is a researcher at the Department of Fisheries, Faculty of Fisheries and Marine Sciences, Universitas Padjadjaran. His research focuses on freshwater ecology, fisheries management, and biological invasions in aquatic ecosystems.
- Shafira Bilqis Annida, S.Pi., M.Sc.: Shafira Bilqis Annida is affiliated with the Marine Tourism Study Program, Vocational School, Universitas Padjadjaran. Her academic interests include aquatic ecosystem management, marine and freshwater tourism sustainability, and biodiversity conservation.
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