* Japanese name: Ruri-Yoshinobori
* Scientific name: Rhinogobius sp.
* Description: Gobies have a slender body with a rather large head, bulbous eyes, fleshy cheeks and a full-lipped mouth, giving them something of a cartoon appearance. Males have shining bright blue spots on their cheeks and body. The gorgeous, lapis lazuli-colored spots are not present on the female or on young fish, but another identifying feature is a Y-shape connection between the caudal (tail) fin and the body. The blue goby grows up to 10 cm long.
* Where to find them: In fast-flowing streams from Honshu to Kyushu. If you are paddling in a stream, you may find that the gobies gather around your feet. Perhaps they like the shelter. They prefer warmer waters, so they will not be found in cold mountain streams. Blue gobies are fairly unusual in the goby family for being adapted to survive in freshwater. Most species are salt-water fish.
* Food: As omnivores, gobies eat algae, worms, insect larvae and tadpoles. Gobies are highly important as prey items themselves: Many other larger fish rely on gobies as their main food source.
* Special features: There isn't an official name in English for this fish (goby being a general term), and even the scientific species name is apparently not yet decided (hence the sp.). One potential name I'd suggest is the "lady-boy fish." That's because some fish researchers have noticed that some of the males of this species mimic females. Occasionally male fish are found that look like females, in coloration and morphology. Other female-mimics are more malelike, so there is a spectrum of morphology and appearance among the female-mimics, with some males looking very much like females and others only looking slightly like them. Female-mimics lack the beautiful blue spots on the body and cheeks. Now, why do they do it? On the few lady-boy fish that have been studied, the males that mimic females have been found to have larger testes than "normal" males. They might look like females, but they are most decidedly male when it comes to sperm production. This suggests that mimics are "pretending" to be females so they can hang out with real females and then mate with them unexpectedly. When a female lays her eggs and her partner male is preparing to fertilize them, the sneaky mimic can suddenly release a large amount of sperm over the eggs, swamping that of the "real" male.