Invasive aquarium fish threatens biodiversity in Laguna’s Lake Sampaloc

MANILA, Philippines — A bright golden aquarium fish has become an invasive threat to biodiversity and aquaculture in Lake Sampaloc in San Pablo City, Laguna, researchers said.

“It is increasingly taking an outsized role in both the natural ecosystem and local aquaculture operations,” said the researchers from the Ateneo de Manila University – Department of Biology and the Ateneo Aquatic and Fisheries Resources Laboratory.

They documented the widespread presence of Flowerhorn cichlids (Amphilophus spp.) in the volcanic crater lake, noting that this “fenced and feral” status is intensifying pressure on native biodiversity and poses potential risks to public health.

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Introduced originally through the aquarium trade, the fish escaped into the lake when a strong typhoon hit.

As early as 2016, fish assemblage surveys already documented their increasing presence.

Researchers Hannah Nicole Gasmen and Dr. Janice Ragaza discovered that the species “are no longer merely escaped ornamental fishes, but have become integrated into local aquaculture through intentional retention and sale.”

This has a sharp impact on native species, they said, as Flowerhorns, known for territorial aggression, tend to monopolize breeding grounds and feeding sites.

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Consequently, the native Ayungin (Leiopotherapon plumbeus), once a common local staple, is now rarely encountered, and is listed as Vulnerable by the International Union for Conservation of Nature.

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“Flowerhorns also display remarkable adaptability to a wide range of environmental conditions,” they said.

While the lake is affected by nutrient runoff, microplastics, and trace organic pollutants linked to untreated sewage, household runoff, and aquaculture practices, the species’ phenotypic plasticity enables it to thrive and dominate in these anthropogenically stressed waters.

Beyond charting the Flowerhorn’s spread, the researchers highlighted broader threats, including pollution, habitat degradation, declining native fish populations, and public health concerns.

Previous research has shown that Flowerhorns can host Paracapillaria philippinensis, a zoonotic parasite that can cause serious illness in humans, including intestinal capillariasis—an infection that can lead to abdominal pain, chronic diarrhea, and malnutrition.

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“The species may serve as a possible reservoir of parasites, pathogens, and contaminants, providing a strong foundation for future ecological, parasitological, and aquaculture research aimed at developing evidence-based management strategies for invasive Flowerhorn populations,” Gasmen explained.

To help manage Flowerhorn populations, the researchers proposed a possible circular economy model: Harvesting invasive Flowerhorns and converting them into aquafeed, provided the biomass is screened for parasites, contaminants, and microbiological safety.

Gasmen also points to the Aquatic Species Invasiveness Screening Kit (AS-ISK) as a promising tool for assessing invasion risks of non-native freshwater fishes, as demonstrated in a 2024 study of Lake Naujan.

“Applying AS-ISK to Lake Sampaloc and other Philippine lakes could help identify high-risk species early and inform targeted management actions,” she said.

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For Gasmen, “protecting and sustaining our aquatic ecosystems requires a collaborative approach among communities, research institutions, and policymakers.” /apl