Breeding Rosy Bitterling

How to breed Rhodeus ocellatus: the female lays eggs inside a living mussel via a long ovipositor, the male fertilises in the gill cavity, and juveniles emerge after weeks.

Overview

The Rosy Bitterling (Rhodeus ocellatus) is an East Asian bitterling occurring from the Amur River basin to the Pearl River basin. Like other bitterlings it has a highly specialised reproductive strategy that depends on living freshwater mussels, with males turning rosy in the breeding season.

Sexing

Females develop a unique pipe-like ovipositor roughly as long as their body during breeding. Males change to a reddish, sometimes purple, colour during the spawning season to attract females, making the sexes easy to tell apart when in condition.

Breeding Setup

House a living freshwater mussel in the tank as the obligatory spawning site. The active spawning period runs from March to September, so a cool seasonal temperature regime supports breeding condition in this temperate-to-subtropical species.

Spawning Behavior & Trigger

The female uses her ovipositor to place eggs on the gill of the mussel, usually two or three eggs at once, and the male fertilises them by spawning into the mussel's gill cavity immediately afterwards. A female normally lays repeatedly at six- to nine-day intervals, about ten times in a season.

Egg & Fry Care

Eggs hatch after about three days, when the juveniles are about 2.8 mm long, and they develop within the mussel's gills for roughly 15 to 30 days. The juveniles then swim out from the margin of the mussel's excurrent siphon at around 7.5 mm.