The Japanese dragonet, known as ‘YAMADORI’ in Japan, which means a bird that lives in the mountains, might have earned this name due to its unique appearance.
Text and Photo by Keigo Kawamura
The Japanese dragonet (Neosynchiropus ijimae) is believed to be endemic to Japan, ranging from Hokkaido to northern Kyushu. It is often seen around the Izu Peninsula, where I usually dive.
Adult male Japanese dragonets grow to about 10cm in length and have large dorsal fins, while adult females are about 5cm long and their dorsal fins do not grow as large. They can be seen in rocky areas at a depth of 1 to 10m, sandy areas surrounded by rocky reefs and sandy areas close to rocky reefs. They are not typically found in coral reef areas. In Kawana on the Izu Peninsula, one of my fields, they are often seen at a depth of 3 to 7m. As they are benthic fish, they feed on small benthic crustaceans and plankton. Because they have a small mouth, they cannot eat large organisms.
About 10 to 15 years ago, Japanese dragonets were common. However, they are now rarely seen on the west side of the Izu Peninsula, although they are still present in the northern part of the east side. The decline in their population is undeniable. Outside of the Izu Peninsula, they seem relatively easy to see at diving points on the Miura Peninsula, Boso Peninsula and the Sea of Japan side. Because they live in rocky areas covered with seaweed and camouflage themselves with the seaweed, they will lose their habitat as the seaweed dies due to rising water temperatures.
The Japanese dragonet is known among Japanese divers for its unique reproductive behaviour, but it is not well-known worldwide. This is partly due to the Japanese diving style, where many diving sites on the Izu Peninsula close at 4:30 p.m. for fishing. Since Japanese dragonets become active only after 5:00 p.m., their behaviour is visible only on days when sunset diving is specially permitted.
Japanese Dragonet behaviour is quite similar to that of mandarinfish, which is well-known to many divers. Mandarinfish stay deep in the coral during the day and emerge before sunset to actively eat and spawn. Female Japanese dragonets hide in the shade of rocks during the day and are rarely seen. Males can be seen even during the day in early summer. It is very rare to see juveniles. Spawning behaviour takes place from the end of May to early July.
During dives around sunset, the first task is to locate the males. These males, at about 10cm in size, move around actively, so they are easy to find. Males have their own territory and take turns visiting females living within that area. When they meet a female, they become excited – the spots on their body surface, their fins begin to shine blue, and they characteristically open their dorsal fins multiple times to appeal to the female.
Also, when they meet other males within their territory, they open their dorsal fins to warn each other off. As with other fish, the larger male wins, but if the males are roughly equal in size, they may start biting each other. The defeated male must leave the area.
Because multiple female mandarinfish live in close proximity, several females may agree to spawn with one male. However, female Japanese dragonets are scattered over a wide area, so spawning behaviour is one-on-one. If the female agrees, they will slowly rise together and the female will begin to release eggs about 40–50cm above the bottom. When they reach the peak of their ascent, the male releases sperm and the two separate at an incredible speed. The male then heads to another female and spawning continues until sunset.
Approaching a mating pair with a camera just as they start to rise can interrupt the spawning, causing the female to return to the bottom. However, in my experience, even if you approach a couple that has risen about 30cm, spawning often continues.
When shooting such scenes, it is recommended to use a red torch because the spawning behaviour will stop if a bright white torch is used for illumination. Modern mirrorless cameras can often focus and shoot without additional illumination. By the time it becomes difficult to focus the camera in the very dark water after sunset, the spawning behaviour is almost over. Even though the eggs are released near the peak of the ascent, they are very difficult to see them in the camera’s viewfinder. The sperm is released so quickly that timing the shutter is nearly impossible, making the camera’s high-speed continuous shooting function invaluable for capturing these moments.
In conclusion, the Japanese dragonet is a remarkable species with distinct reproductive behaviour and ecological requirements. However, due to environmental changes and limited observation opportunities, their population is declining, highlighting the need for conservation efforts to preserve their habitats. The unique behaviour of these fish, especially their spawning rituals, offers a captivating glimpse into the underwater world for those fortunate enough to witness it.
By promoting the conservation imperative and sharing insights into the intricate behaviours of species like the Japanese dragonet, we cultivate a deeper understanding of marine life’s diversity, reinforcing our commitment to protecting marine environments for future generations.
