Study warns growing flowerhorn presence threatens Laguna biodiversity, public health

A study found that the increasing presence of the flowerhorn fish in Lake Sampaloc, a volcanic crater lake in San Pablo City, Laguna, poses potential risks to biodiversity and public health in surrounding communities.

Researchers from the Ateneo de Manila University Department of Biology and the Aquatic and Fisheries Resources Laboratory said fish surveys had already confirmed the presence of the flowerhorn cichlid in the lake as early as 2016.

The golden-hued fish was originally introduced through the aquarium trade before reportedly escaping into the lake during a major typhoon.

“[The] species are no longer merely escaped ornamental fishes, but have become integrated into local aquaculture through intentional retention and sale, indicating that human activities may continue to reinforce their persistence and spread,” researchers Hannah Nicole Gasmen and Dr. Janice Ragaza said.

Territorial aggression

Flowerhorn cichlids are known for aggressive territorial behavior, often monopolizing breeding and feeding areas, which makes it difficult for native species to survive and reproduce.

The native Ayungin fish (Leiopotherapon plumbeus), once a common local staple, is now rarely seen and is listed as “Vulnerable” by the International Union for Conservation of Nature (IUCN).

Researchers also noted that flowerhorns are highly adaptable to varying environmental conditions.

“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,” Ateneo said.

Parasite host

The growing flowerhorn population also raises public health concerns.

Ateneo said previous studies found the species can host Paracapillaria philippinensis, a parasite that can cause intestinal capillariasis in humans, leading to abdominal pain, chronic diarrhea, and malnutrition.

“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 said.

Researchers also called attention to other threats such as pollution, habitat degradation, and declining native fish populations.

Proposed solutions

Researchers proposed a circular economy approach, including harvesting invasive flowerhorns and processing them into aquafeed, provided they are screened for safety.

“[It starts with] harvesting invasive dlowerhorns and converting them into aquafeed, provided the biomass is screened for parasites, contaminants, and microbiological safety,” Ateneo said.

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

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

The researchers believe that addressing the flowerhorn invasion requires a unified effort.

“Protecting and sustaining our aquatic ecosystems requires a collaborative approach among communities, research institutions, and policymakers,” Gasmen said.

Ateneo published the study in March 2026. —VBL, GMA News