Invasive Flowerhorn Cichlids Threaten Biodiversity in the Philippines’ Lake Sampaloc

Ornamental flowerhorn cichlids—bright-gold, hump-backed hybrids bred for the aquarium trade—have escaped into Lake Sampaloc, a 104-hectare (260-acre) volcanic crater lake in the Philippines. Researchers Hannah Nicole C. Gasmen and Dr Janice A. Ragaza of Ateneo de Manila University report that the fish now coexist with the lake’s primary aquaculture species, tilapia, and are being sold in the ornamental market and occasionally stocked intentionally. Their presence coincides with the lake’s existing stressors: sewage, household runoff, nutrient-rich aquaculture effluent and plastic waste, creating conditions that favor invasive generalists.

The Guardian

Lake Sampaloc’s eutrophic, polluted waters enable flowerhorns to outcompete native fish for food, shelter and breeding sites. The native ayungin (silver perch), once abundant, has become increasingly rare and is listed as endangered by the International Union for Conservation of Nature. Researchers also note that some captive flowerhorns harbor *Paracapillaria philippinensis*, a roundworm capable of infecting humans, though the parasite has not yet been detected in the lake’s wild population. The study underscores that human-degraded habitats are especially vulnerable to invasions by adaptable cichlids.

The Guardian

Gasmen emphasizes a collaborative response, urging communities, research institutions and policymakers to work together to protect aquatic ecosystems. Dr Noël Juvigny-Khenafou of the University of Stirling highlights climate change as a potential amplifier, suggesting shifting aquaculture zones could exacerbate invasive-species risks. The researchers propose that harvested invasive fish might be repurposed for aquafeed, provided they are screened for pathogens, heavy metals and microplastics.

The Guardian

Conservationists warn that continued intentional stocking and commercial sale could expand the invasive population, further endangering the ayungin and other native species. The possibility of parasite transmission to humans adds a public-health dimension to ecological worries.

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• “Human-degraded habitats are generally the most vulnerable to invasion, and they are typically invaded by generalist species, said Rupert Collins, a senior curator of fish at London’s Natural History Museum.” — Rupert Collins, senior curator of fish, Natural History Museum, London

The Guardian

• “Cichlids are particularly successful in adapting. They are a textbook example of how new phenotypes can arise very quickly.” — Rupert Collins, senior curator of fish, Natural History Museum, London

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• “Climate change may alter where aquaculture takes place and what species people are able to raise,” — Dr Noël Juvigny-Khenafou, lecturer in aquatic environmental science, University of Stirling

The Guardian

• “Protecting and sustaining our aquatic ecosystems requires a collaborative approach among communities, research institutions and policymakers,” — Hannah Nicole C. Gasmen, researcher, Ateneo de Manila University

The Guardian