The Moon Princess Kaguya and Her Dartfish

To many of us westerners, Japan is a magical place, full of legends, myths and tales that most of us have no knowledge of. For example, the epic Taketori Monogatari or “Tale of the Bamboo Woodcutter” is the story of a Moon Princess, sent to earth as a penance. She is named Kaguya Hime. The tale ends in sadness, and you can read it yourself if you like by just googling the title. In the world of aquarium enthusiasts, there is a gorgeous dartfish named Kaguya's Dartfish (Navigobius kaguya). Kaguya's dartfish has a line of circles along its gorgeous dorsal fin and, it could represent a moon phase chart (very, very loosely). As a result, and as a nod to Japan where this fish was originally found, this Dartfish got named for the princess in the story above.

While these fish aren't new to the deepwater divers of Japanese waters, they hadn't been described for science until 2017. Since that time, another population of them has also been found in the Philippines, though they are still among the rarest of Dartfish available to aquarists. They come from deepwater, the shallowest fish we know of was 137 feet deep, and we don't really know yet how much deeper they can actually go! They're usually found above sandy or silty areas, or areas with low reef and rubble cover.

These stunning little fish never get much bigger than two and a half inches long and as such, don't need a huge aquarium for keeping them. A small group of three to five could be kept in a tank as small as 40 gallons, though we'd suggest a little bigger. Tanks should have a soft sand bed with a small grain size to emulate their natural environment. Rock work should offer plenty of cover while leaving a lot of open space, especially in the top half of the tank for these fish to hover in the current. Flow should be strong, and you'll have to balance this with the small grain size of the sand to keep the sand on the bottom of the tank. Dartfish got their name for their incredibly fast swimming in short distances especially when startled or in response to threats. You should always cover an aquarium with Kaguya's Dartfish in it to prevent them from launching themselves out of the tank on accident. Lighting for these displays should be dim, especially initially as these fish are timid and come from very dark environments. The lighting should have a strong actinic component to really make Kaguya's colors shine. They can be acclimated to brighter light over time.

Dartfish spend their day suspended in current, eating whatever comes along. As a result, they burn through a lot of energy and are always eating! This is likely the biggest challenge in keeping them, they are very shy to start with, which makes them hide during feedings, and they need to be fed often. We suggest feeding them at least three times a day, and more would be better. Luckily, they aren't that picky about what they eat, so you should be able to get food into them with some patience. Navigobius kaguya is a small fish, and they'll need small foods. Here we use Gamma foods, and like to feed them the Rotifers, Copepods, finely chopped Prawn and all the different infused Brine that Gamma offers. We're also introducing them to the sinking pellets from Nutramar, and getting them on food like this makes a huge difference in keeping them as these pellets have a broad nutritional spectrum, and are protein dense so you can feed a little less. It also allows aquarists to use an auto-feeder for some of the scheduled feedings.

This feeding style also makes them good candidates for reef tanks as they don't do any grazing and will be low risk to pretty much all your invertebrates. While you could keep a single Dartfish, they'll be much bolder and acclimate much more quickly if you keep at least three. In regards what other fish would make good tankmates for Kaguya's Dartfish, you need to look for other fish that are small, peaceful and docile. Cardinals like Pajamas or Banggai are great options, smaller peaceful Clowns like Ocellaris would work, but we'd caution you about having a host anemone for the same reason you cover the tank, Dartfish can dart right into a strong Anemone (great food for the Nem, terminal for the Dart.) Pencil Wrasses would be great as would many Halichoeres and Macropharyngodon Wrasses. Avoid large and boisterous fish like Triggers and Tangs, as they'll scare your Dartfish into hiding, especially at feeding times. Also avoid anything that could make a snack of the diminutive Kaguya's.

Navigobius kaguya loves stability. It is not going to matter if your display has a specific gravity of 1.021 or 1.026, as long as the number you choose doesn't change. Shoot for a pH that doesn't fluctuate more than .2 and always stays between 8.0 and 8.4. Consistent water changes will help with this and will also help keep your nutrients low. These fish will do best in slightly cool tanks, shoot for somewhere in the low to mid 70s.

All Dartfish are beautiful things, and a group of them hovering about in an aquarium makes an amazing display that too few people go for. When it comes to Kaguya's Dartfish, they definitely belong in the discussion when we're talking about the most gorgeous Darts. They're also ticking the rare-fish box in a serious way and so these could be just the showpiece you were thinking about for your smaller reef tank! Never thought about Kaguya's Dartfish? Now's the time, stop by your Local Fish Store and see the fish that was named for a mythical Japanese Moon Princess.