Bicolor Blenny (Ecsenius bicolor) Breeding Guide

Breeding the bicolor blenny (Ecsenius bicolor): demersal nesting habits of the genus Ecsenius and why larval rearing remains very difficult at home.

Overview

Ecsenius bicolor is a small combtooth blenny (family Blenniidae) from the Indo-Pacific that grows to about 11 cm and frequently enters the aquarium trade (Wikipedia). Like other members of the genus Ecsenius, it is a demersal egg-layer rather than a pelagic spawner. Spawning of Ecsenius blennies has been described as relatively common in aquaria, but for years rearing the larvae through to settlement remained unsuccessful, making home breeding of this species advanced and rarely accomplished.

Sexing

Reliable external sexing of Ecsenius bicolor is not documented in the consulted scientific sources. In the genus, pairing is generally observed only once compatible individuals occupy and defend a nesting hole together, so behavior rather than fixed external markings is the practical guide to identifying a functional pair.

Breeding Setup

Ecsenius blennies perch on and shelter in rock and use crevices and small holes as nest sites. A mature aquarium with abundant live rock, established algae growth for grazing, and small-diameter tubes or holes that a pair can defend provides the structure these fish use for spawning. Stable reef parameters in the ranges reported for the species (temperature roughly 24-27 C, pH about 8.1-8.4) support conditioning.

Spawning Behavior & Trigger

Ecsenius species deposit demersal eggs and tend a nest. Aquarium accounts of bred Ecsenius report that compatible pairs spawn every few days and tend a large nest made up of multiple batches of eggs attached to a surface, with the eggs hatching roughly five days after laying (Reef Builders). The eggs are guarded at the nest site rather than scattered into the water column.

Egg & Fry Care

The principal obstacle is larval rearing, not spawning. The first confirmed rearing of any Ecsenius species (E. gravieri) was reported only in 2014, after decades in which larvae could not be raised, and a second commercial success with E. pulcher was reported in 2024 (Reef Builders). Newly hatched larvae are very small and pelagic, requiring tiny live first foods; published hobby sources indicate copepods such as Parvocalanus crassirostris may be needed before a transition to Artemia nauplii. No routine home protocol for Ecsenius bicolor is documented.

Common Challenges

Even when a pair spawns readily, the bottleneck is the planktonic larval phase: minute larvae, demanding first-food cultures, and a long pelagic period. Successful Ecsenius rearing to date has come from dedicated commercial hatcheries rather than home aquaria.