Navigobius dewa is a beautiful and sensational species of Ptereleotrine dart fish that was first discovered and described in 2009, with specimens coming from Kagoshima Bay, in the south of Japan. The distinct features of Ptereleotrine fish is seen in its slender body shape, but its characteristic deeply forked tail and other unique traits landed it in a genus all on its own – Navigobius. Navigobius dewa is the only member of its monotypic genus, but careful observations of both aquarium and wild specimens may prove that more than one Navigobius exist, and if that is true, then we could be looking at new additions to this genus.
Let us first take a look at the original Navigobius dewa, the true to type species. N. dewa is slender, purple-pink in base coloration with neon raver like highlights on all its unpaired fins. The spectacular tripped out colours makes this species one of the most beautiful of all the related Ptereleotrine fishes. In N. dewa, the double dorsal fins are rather straight edged, with very short almost indiscernible cirri. Take note of the dorsal fin coloration , being purple with transverse yellow bands. The anal fin and tail bear the same characteristic purple and yellow horizontal markings.
In the wild, N. dewa favours moderately deep waters with open sandy substrate. In typical Ptereleotrine fashion, they often group together and hover just above the substrate. These are quite skittish and shy, and will duck for cover in presence of danger. N. dewa is found from 45m (150ft) to 60m (200ft), and possibly deeper.
A second species of Navigobius occurs in Japan, which has been erroneously identified as N. dewa. At first glance in the wild, and in general pictures, they do look rather similar. However in close scrutiny, the difference between this second Navigobius species and N. dewa is quite clear.
The main difference lies in colour as well as fin morphology. In this unknown, Navigobius cf. dewa, the dorsal fins are clear and without the intense neon purple and yellow markings. It lacks the yellow transverse band, but instead, possesses a broken line-spot pattern at the base. Another noteworthy characteristic is the presence of larger, distinct cirri at the top of the dorsal spines. The rounder, larger dorsal fin gives this species a more flamboyant appearance, but is less gaudily coloured as compared to the type N. dewa.
In July 2014, we received a pair of Navigobius from Koji of BlueHarbor. Back then when we wrote about it, we had also made the mistake of calling it the true N. dewa. Looking back now and comparing the pictures in closer scrutiny, it is clear that our specimens were not the true N. dewa. Again, the rounded and larger dorsal fins with the lack of purple and yellow transverse bands points to Navigobius cf. dewa.
In September 2014, we ran into another aquarium specimen. This one however, rather shockingly, was collected outside of Japan. The Philippine specimen was the first of its kind to come out from there, and again, we made the mistake of labelling it Navigobius dewa. Looking at this fish in closer detail now, it is quite clear that it is not N. dewa. The lack of the characteristic purple and yellow lines, the larger dorsal fin all points towards N. cf. dewa. So while N. cf. dewa indeed has a range extension outside of Japan, it appears that the true Navigobius dewa is still a Japanese endemic, and has so far not been recorded outside of its known range.
A third Navigobius appears to exist, but there has been not much information on where it is found or how deep it is recorded in. Presumably Japan, the third Navigobius species bears the same overall characteristics as the other two in the genus. However unlike the other two Navigobius species, this one appears to have a very spiky first dorsal fin.
The coloration in this third Navigobius is also very unlike the other two. Its dorsal fins and tail are highlighted in blue, instead of the usual purple and without any yellow coloration. The anal fin is clear and appears to be unmarked. The defining characteristic of this species has to be remarkably spiked first dorsal fin, which differs the most compared to the other two.
Without any actual specimens to examine, and with only pictures to look at, we can only make assumptions based on colour differences and physical morphology. Meristics, DNA and other information obtained through live specimens would be key to finding out if these two Navigobius species are indeed new. The possibility that Navigobius may lose its status as being a monotypic genus may not be too far fetched after all. A collage of all the pictures above is provided below for ease of comparison.