Escaped Ornamental Fish Threaten Philippine Lake Ecosystem

Escaped ornamental aquarium fish have integrated into a local ecosystem in the Philippines, but scientists say they may be threatening the native biodiversity of the lake.

Flowerhorn cichlids – human-bred hybrid fish prized for their bright-gold colour and prominent head humps – are believed to have escaped from breeding facilities into Lake Sampaloc, which sits in a volcanic crater, during a typhoon.

The lake’s main farmed fish is tilapia, which supports local food production and commerce. Research by Hannah Nicole C Gasmen and Dr Janice A Ragaza of Ateneo de Manila University has found that flowerhorns are being incorporated into the existing aquaculture system because, like tilapia, they can survive difficult conditions. Flowerhorns that have established wild populations and entered tilapia cages are sometimes kept and sold into the ornamental trade, while some local people stock them intentionally.

The research, however, suggests that intentional stocking and sale could expand an already established invasive population.

The 104-hectare (260-acre) Lake Sampaloc is already strained by sewage, household runoff, aquaculture nutrients and plastic waste, making it especially vulnerable to invasive species. Flowerhorns thrive in its eutrophic, polluted waters and compete for food, shelter and breeding grounds. The native ayungin, or silver perch, once a common catch, has become increasingly rare and has been classified as endangered by the International Union for Conservation of Nature.

“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. “Cichlids are particularly successful in adapting. They are a textbook example of how new phenotypes can arise very quickly.”

Concerns were also raised about potential parasites. Some flowerhorns in captivity have been found carrying Paracapillaria philippinensis, a roundworm capable of infecting humans. Some people have been observed fishing for flowerhorns recreationally and incorporating them into their cooking. The parasite has not been found in Lake Sampaloc’s flowerhorns, but the researchers advise against promoting the fish for human consumption.

The study also highlights a much wider issue, according to Collins. “This is just one lake in the Philippines, but the release of species outside their natural ranges is a major contributor to biodiversity loss worldwide.”

Dr Noël Juvigny-Khenafou, a lecturer in aquatic environmental science at the University of Stirling who was not involved in the research, noted that climate change may also intensify the problem. “Climate change may alter where aquaculture takes place and what species people are able to raise,” he said. “That could mean production shifting between regions and more non-native species being introduced into new places.”

He said the research raised interesting questions: “What does that mean for the native species? What does that mean for the function of the ecosystem? Is the introduced species leading the ecosystem towards collapse, or is it simply becoming part of a new ecological community?”

The researchers proposed long-term solutions including stronger pens, finer mesh, overflow barriers, routine inspections and community-led monitoring. They also suggest that invasive fish could be harvested for use in aquafeed, subject to screening for pathogens, heavy metals and microplastics.

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