Gobiodon okinawae Breeding Guide

Gobiodon okinawae is a tiny coral-dwelling goby that lays eggs on Acropora branches under male care. This guide covers its bidirectional sex change, the documented captive spawn and why its 2 mm larvae are so hard to rear.

Overview

Gobiodon okinawae is a small western Pacific coral goby ranging from southern Japan, including Okinawa, to the southern Great Barrier Reef (Wikipedia). It reaches about 3.5 cm and roosts in the outer branches of Acropora corals in sheltered lagoons, often in groups of 5 to 15 individuals. Its small size and coral-perching habit make it a candidate for dedicated breeding projects in mature reef systems.

Sexing

The species is a bidirectional protogynous hermaphrodite: when two individuals of the same sex settle together, one changes sex to form a breeding pair (Wikipedia). Because sex is flexible, fixed external sexing is unreliable, and pairs are formed simply by housing two compatible fish together and allowing one to transition.

Conditioning

Conditioning is built on stable reef water and regular small carnivore feeds such as enriched mysis, baby brine and finely chopped marine foods offered about twice daily. A settled pair with a coral or branched structure to claim shows the perching and territorial behaviour that precedes spawning.

Breeding Setup

A breeding setup provides branched Acropora or comparable branched structure on which the pair can perch and deposit eggs. In a documented captive spawn the parents laid eggs on a dead Acropora skeleton, which was then removed for separate incubation (Reef Builders). A mature, stable reef tank with calm flow and good water quality supports the pair.

Spawning Behavior & Trigger

Eggs are laid in circular bands around coral branches in masses of up to about a thousand, and the male fertilises and guards them until hatching roughly five days later (Wikipedia). In the De Jong Marinelife captive account a clutch of 50 to 200 eggs on an Acropora skeleton showed about a 90% hatch rate (Reef Builders).

Egg & Fry Care

Newly hatched larvae are only about 2 mm and too small for rotifers or Artemia nauplii, so the captive protocol used copepod nauplii, cryo-preserved barnacle larvae and ciliates with greenwater, in a black round tub at a stable 26 °C under an 18:6 photoperiod (Reef Builders). Larvae stayed in the water column for nearly 40 days, with metamorphosis around day 40 and tradeable 1 cm size by about 80 days post-hatch.

Common Challenges

The decisive challenge is first feeding: at 2 mm the larvae cannot take standard rotifers or brine shrimp, so failure to supply suitable copepod nauplii and ciliates is the usual cause of total loss. The long pelagic phase of around 40 days also demands sustained water quality and consistent micro-food culture.