DNA testing refreshes fish distribution records in Australia and Japan: First genetic confirmation of a recreational catch of Pacific bluefin tuna in Victoria; 126 fish species detected shifting northward in Japanese coastal waters

Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) has confirmed through DNA testing that two large tuna caught recreationally near Western Port Bay in Victoria's Bass Strait in July 2026 were Pacific bluefin tuna (Thunnus orientalis) — the first genetically confirmed recreational catch of Pacific bluefin tuna in the state. The research was reported by the Global Seafood Alliance's Responsible Seafood Advocate on 9 November 2026.

The two fish weighed approximately 165 kg and 131.6 kg respectively and were initially thought to be southern bluefin tuna (Thunnus maccoyii). Experienced angler Dave Standing, Tuna Champions science ambassador Jonah Yick and other anglers noticed unusual morphological features and raised questions about the species identity. Yick said Pacific bluefin tuna and southern bluefin tuna look very similar to the naked eye, but subtle differences in the length of the anal fin and second dorsal fin, skin markings, body shape and average size can be used to distinguish the two.

Standing coordinated the collection of muscle samples, which were passed on through Yick to CSIRO chief research scientist Peter Grewe. Initial DNA screening identified both fish as Pacific bluefin tuna, and subsequent forensic-grade sequencing further confirmed the result. Grewe said he was extremely confident in the result after the secondary forensic-grade sequencing analysis further corroborated the initial rapid species identification test. CSIRO noted that without genetic testing, the two fish would almost certainly have been recorded as southern bluefin tuna.

CSIRO said Pacific bluefin tuna had previously been caught by commercial longline vessels in Victorian waters, but those catches typically occurred farther offshore. This recreational catch suggests the species may occur more frequently in southern Australian waters than previously recognised. Grewe also noted that increased recreational tuna fishing activity may lead to more encounters with infrequently caught species. Yick said the two fish were caught very close to each other, less than 10 km from the coastline, right on Melbourne's doorstep — an astonishing catch.

In Japan, researchers used a different genetic approach to investigate fish distribution on a larger scale. The study, published in Diversity and Distributions, analysed 2,672 environmental DNA samples collected from 316 locations along the Japanese coast between 2017 and 2024. Environmental DNA sampling involves collecting seawater containing genetic material shed by marine organisms, extracting and sequencing the DNA, and comparing it against reference databases to identify species present in the samples. The Japanese study included nearly 1,000 newly collected samples and detected thousands of fish species, of which 126 were found at locations farther north than previously recorded.

These species include commercially important fish such as Japanese scad (Decapterus maruadsi) and blacktip grouper (Epinephelus fasciatus), as well as the mottled spinefoot (Siganus fuscescens), which is associated with damage to seaweed beds. The findings provide new information on fish distribution against the backdrop of rising ocean temperatures altering marine habitats and some species moving to cooler waters.

Timothy Ravasi, head of the Marine Climate Change Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) and senior author of the study, said fishers across Japan have already noticed that the species they catch differ from those of decades ago; this is a problem because people in these regions may not be accustomed to buying, cooking or eating these new fish, and they also cannot prepare dishes of cultural or historical significance because those fish are no longer there. Ravasi also noted that changes in the species available may require new fishing techniques, equipment and knowledge, posing challenges for small family-run fishing businesses.

The Japanese researchers said environmental DNA sampling can complement existing monitoring methods, including field surveys, specimen collection and citizen scientist observations. Ayşe Haruka Oshima Açıkbaş, first author of the study, said Japan's existing genetic reference data played an important role in this research. She said one advantage of applying this method in Japan is that the reference DNA sequences required for environmental DNA analysis — the MiFish primers — were developed in Japan; researchers have invested considerable effort in sequencing local marine fauna, improving the coverage and accuracy of species detection within Japan.

Both studies highlight the importance of combining genetic analysis with information from people working daily on the coast and at sea. Grewe said information from people who work on the water every day is invaluable to scientists.