* Japanese name: Tairiku baratanago
* Scientific name: Rhodeus ocellatus ocellatus
* Description: A small freshwater fish in the carp family, native to Taiwan, the rosy bitterling grows to some 6.5cm long. It’s a pretty thing, with a flat silver body touched with green behind the head, blue on the sides and, in the breeding season (March to September), males develop a rosy glow on their flanks, tail and fins. The eye often has a gold-orange iris. A similar species, the native Japanese bitterling, easily interbreeds with the rosy bitterling.
* Where to find them: In ponds, especially farm ponds where mussels are grown, and reservoirs and streams, from southern Honshu to Kyushu and Okinawa. They prefer warmer temperatures from 18-24 C, and areas with dense plant growth. They are tough, and able to survive in water that is low in oxygen. The native Japanese subspecies is now critically endangered, as the rosy bitterling has interbred with it. Conservation efforts are being made to save it. The rosy bitterling was introduced from Taiwan to eastern China, the Korean Peninsula and Japan.
* Food: Pretty much anything. Bitterlings, like other carp, are omnivorous and dig around in the detritus on the pond floor, eating insects and insect larvae that they disturb, also phytoplankton plants and larger plants such as pond weed. The snuffling around on the pond floor throws up clouds of mud, and the bitterling relies to some extent on a keen sense of smell to locate food items, but it will also take anything promising into its mouth, spitting it out if it is inedible.
* Special features: Because they are usually found associated with bivalve mollusks such as mussels, bitterlings were thought to be symbiotic with their shells. In fact, the fish form parasitic relationships with them. When the females spawn, they deposit their eggs inside the shells, attaching the eggs to the gills of the mussel where the developing fish benefit from the oxygen. Two to three fish larvae develop safely inside the mollusks and feed off them, remaining inside for 15 to 30 days until they can swim. Juveniles leave the mussels by the bivalve’s siphon, and are about 7.5 mm long when they brave the open waters on their own.
PHOTO COURTESY OF BIO-IMAGE NET