A pioneering study has unveiled a powerful new tool for marine conservation and fisheries management: the application of environmental RNA (eRNA). This technique researchers to monitor ribonucleic acid in water samples to infer the physiological behaviour of fihs, such as spawing, as it happens.
The research, published in the scientific journal Scientific Reports, suggests that this straightforward water test could revolutionise how biologists track marine life, providing an essential “real-time” of species’ reproductive cycles.
Previously, the main non-invasive technique was environmental DNA (eDNA), which is effective for identifying a species’ presence but limited when it comes to inferring dynamic biological activities. The use of eRNA overcomes this crucial limitation.
The breakthrough lies in the identification of the klhl10 gene, a specific genetic marker for gametes (sex cells). Its concentration in the water increases markedly during mating attempts. This marker acts as an “activity indicator”, confirming the release of egg or sperm.
Applications in Aquaculture
One of the most impressive aspect of this low-cost technique is the speed – only a few hours pass between taking a water sample and detecting the marker. This swift turnaround has clear applications for aquaculture, ranging from reproduction to health monitoring such as breeding optimization, allowing assessment of whether breeding fish are responding correctly to hormonal or environmental induction protocols, precisely pinpointing the moment of spawing in hatcheries.
The test can also measure stress genes (e.g. those related to heat or poor water quality) before fish exhibit visible symptoms, allowing for rapid adjustments to husbandry.
Using eRNA markers specific to pathogens or the immune response could enable fast disease detection.
In the wild, the technique offers the potential to locate natural spawning grounds of pelagic species like sardines, a long-standing scientific challenge.
But limitations remain. For now, the system faces hurdles before widespread commercial applications. The most significant is the instability of the molecule: RNA is far more susceptible to degradation than DNA, complicating the logistics of sample preservation in the field.
Another key aspect that requires attention is standarisation and marker development. Current eRNA extraction methods are more sensitive to contamination and less robust than eDNA protocols, necessitating further development before large-scale adoption.
Reference:
Aminaka, Y., Wong, M.KS., Yada, T. et al. The use of environmental RNA for inferring fish spawning behavior. Sci Rep 15, 37559 (2025). https://doi.org/10.1038/s41598-025-23861-8
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