Researchers from the Severtsov Institute for Ecology and Evolution Problems, part of the Russian Academy of Sciences, have identified a defense strategy in ivy perch that helps the fish distinguish inedible objects from real food. This insight emerged in a study described to readers by a science journalism outlet covering developments in Russian science. The finding sheds light on how aquatic species adapt to environments where their traditional prey is mixed with unfamiliar, non-nutritive materials, and it highlights the fish’s remarkable ability to screen potential sustenance before committing energy to ingestion.
The rivers and freshwater reservoirs of central Vietnam, where climbing perch regularly inhabit mangrove-fed streams and other shallow ecosystems, are increasingly burdened by plastic waste. The persistence of plastics in aquatic habitats creates a testing ground for how native species cope with altered resources and reproductive opportunities. Notably, the climbing perch has shown surprising resilience in waters contaminated by refuse, raising questions about the cellular and behavioral mechanisms that enable survival under pollution pressures. In particular, researchers explored whether these fish sometimes ingest polystyrene foam, a common heat-insulating material used in many consumer and industrial products, which can resemble edible pellets in size and form. The episode drew attention to the specific granule sizes of expanded polystyrene that most closely mimic the appearance of standard fish feed, prompting scientists to evaluate whether the perch would confuse plastic fragments with their natural diet and what that implies about their sensory processing in the mouth and throat region.
To investigate, the team designed an experiment offering three choices to the climbing perch: a conventional food pellet, a piece of plastic, and a mixed option containing both food and plastic. They relied on video capture to record the fish’s behavior as it approached and sampled the options, focusing on the sequence of contact, handling, and eventual ingestion or rejection. The observations showed a clear preference pattern: when presented with a pure food pellet, the perch consumed it first, before any consideration of plastic. Yet, when the mixture appeared, the fish directed attention to both targets, engaging with the edible component and the plastic concurrently. This behavior revealed not a simple avoidance of plastic but a nuanced decision-making process that weighs taste, texture, and the tactile feedback from particles held in the mouth.
During the trials, the fish often grasped plastic fragments with the same precision used for food, momentarily holding them in the oral cavity. However, the organisms consistently refrained from swallowing the plastic, suggesting the presence of a real-time intraoral assessment mechanism. A researcher associated with the project explained that the fish use taste receptors and other sensory cells within the oral and oropharyngeal cavities to evaluate captured items, effectively performing a quick texture and flavor check before any risk of choking or nutrient loss. In several instances, deformed pieces of plastic broke into smaller fragments, yet none of the materials were swallowed, underscoring a sophisticated sensory veto that protects the animal from consuming non-nutritive substances.
These findings point to a functional system of intraoral testing in climbing perch. The mechanism appears to combine gustatory input with tactile feedback from the oral cavity, enabling the fish to discriminate between potential food and foreign matter even when the latter closely resembles edible particles on the surface. The study’s authors emphasize that such intraoral testing likely involves chemoreceptors and sensory cells distributed in the mouth and throat, which together form a rapid evaluative loop that informs feeding decisions. This integrative sensory check is crucial in environments where plastic debris is commonplace, providing a potential behavioral buffer against costly mistakes in nutrient intake.
In this context, the researchers concluded that the perch could differentiate plastic from food objects during the trial, even when traces of edible material were present on the plastic’s exterior. The ability to separate nutritious items from non-nutritive substitutes is seen as contributing to the species’ ongoing survival amid plastic-laden waterways in Southeast Asia. The observed behavior highlights a broader question about whether other aquatic animals possess similar rapid-assessment capabilities, a hypothesis that invites further comparative research across ecological communities to determine how widespread such intraoral discrimination might be and what its ecological consequences are for feeding strategies in polluted habitats.
Overall, the work suggests that adaptive sensory processing in the mouth and throat may play a key role in how fish navigate a world filled with mixed signals about food availability. The climbing perch’s cautious approach to plastic, combined with decisive swallowing of genuine nourishment, illustrates a resilient strategy that supports foraging efficiency under environmental stress. Scientists anticipate that additional studies, including controlled trials across different water qualities and species, will help clarify whether these intraoral checks are common across other fish and what evolutionary pressures shape such behaviors in polluted aquatic ecosystems.