Why are you here? Strange DNA finding for 2025 Yadoriki Stream

 

The eDNA study for Yadoriki Stream 寄沢 completed the 4th year in 2025. The species found in the specimen indicated nice environment for the source of Kanagawa’s tap of water. The aquatic creatures which left their DNA in the stream were the ones that could live mainly in unpolluted water. It’s good news. Several interesting things came up. Mr. Hasebe for Kanagawa Environmental Research Center, who analyzed the specimen, found the amount of nucleobase was larger from the water collected in April, compared with that for November. Though humans love to dive in fresh water in mid-summer, the amount of nitrogenous base during summer is smaller than for April and November.

Yadoriki Stream in autumn

When we remember the life cycle of water insects, it would be a predictable conclusion. Many of them, including EPTs (Ephemeroptera, Plecoptera, Plecoptera; their existence can suggest the level of water quality), leave water by the end of spring as adult mayfly, stonefly, caddisfly, dragonfly, … They spend hot summer on land to find partners, to mate and to lay eggs in water for the next generations. When humans enjoy specimen “hunting” in summer, many waterborne bugs have already left their cradle water.

Yadoriki Stream in mid-summer.
Surprising, it contains the smallest nucleobase.

In autumn, tiny nymphs come out of the eggs. As they move around in water, they will leave tiny bits of their DNA in the stream. Since the absolute number of such water bugs is larger during fall than for summer, we can catch their DNA bits more. But they are still babies if not remaining in eggs. In April, many of them are now bigger final-instar larva ready for the launch pad to leave water as adults. The amount of DNA they shed in water would be bigger than for fall or summer. Mr. Hasebe said the next research agenda would be to verify these hypotheses and to think about the meaning of it for the evolving ecosystem under climate change. We citizens keep on draining water in regular way and send it to the lab. Easy. Let us see how it will turn out.

A larva of Nemoura is eating
a larva of Tipulidae.
And we made them fixed
in alcohol …

Having said that, there is a strange finding. This year, Yadoriki Stream contained DNA for Japanese crucian carp. It’s an endangered species, endemic to Japan, nay, to Lake Biwa 琵琶湖 and to Yodo River 淀川. These two large water systems in Kansai 関西 are, I would say, not mountain streams, but have relatively gentle flow. The carp should love such environment and must be perplexed by rapid current of Yadoriki. Why there? We naturally concluded somebody has introduced them from far Kansai Area. The carp is important ingredient for traditional meals in Kyoto 京都 and Osaka 大阪. People farm them for culinary reasons. Endangered ones are the fish in wild environments. Biologically speaking, wild and cultivated ones are the same species. It’s easy for somebody to bring it to mountainous Yadoriki beyond Hakone 箱根. Maybe that person expected fun to fish crucian carp in Yadoriki. (By the way, to fish in Yadoriki Stream, you need an official license. Otherwise, you’ll be defined as “thief” by the police.) Or, s/he may have nobler intention of “restoring the population of endangered species.” Er, well.

Fishing carp here? No way!

From the fish’s point of view they have moved in an environment VERY different from their ideal home. We can simply expect many will die out quickly before leaving the next generation. Let us pray for them … Or there might be stronger individuals that could survive quick water flow. The next question is, does Yadoriki Stream have sufficient ecosystem that could sustain voracious appetite of the carp? The fish can grow 30cm long within 3 years and reach 60cm or more at the adult stage. If they eat up all the algae and the other animal-based feed, what would happen to the local tiny creatures of Yadoriki stream, such as mayfly, et al? It may not happen, but we must be watchful in any case.

Eggs for montane brown frog
recently in Yadoriki Stream.
They would be gorgeous meal
for carnivorous larger animals, such as carps.

If the release turns out to be successful, it will contribute to saving endangered species in wild. But there is a high possibility in such a case the ecosystem of Yadoriki would be different from the place before the arrival of the carp. Is this a desirable outcome for environmental management in water sources? I simply wonder …

If you find environmental issues in Kanagawa Prefecture, please make contact with

Kanagawa Natural Environment Conservation Center

神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/