Japanese medaka

About

Japanese medaka (Oryzias latipes) is one of those species with a resume that puts most fish to shame. It has served as a model organism in biological and genomic research for over a century, and in the mid-1990s became the first vertebrate ever to mate in space. In the wild it occupies shallow, slow-moving waters across Japan, Korea, China, and Vietnam, from rice paddies and marshes to coastal tide pools, where it tolerates a surprisingly broad range of salinities. That adaptability carries over into the aquarium, where it proves fairly forgiving once conditions are dialed in. It's a small, loosely schooling fish that does best in groups of eight or more, where individuals display more natural behavior and males show off their temporary color darkening during courtship. Community options are limited by its specific water preferences, so suitable tankmates are relatively few. Small surface-oriented or brackish-tolerant species tend to work best. Breeding is genuinely rewarding: females can produce adhesive egg clusters nearly every day when healthy, and the eggs hang briefly from the female before being deposited among fine-leaved plants. Beyond the wild type, a golden ornamental strain is widely traded, and a transgenic glowing form exists in several colors. Though the latter is banned in the EU and best avoided. A fish with real character and a fascinating backstory.