Black-Axil Chromis (Chromis atripectoralis) Breeding Guide

Chromis atripectoralis is an oviparous Indo-Pacific chromis that lays demersal eggs adhering to the substrate, guarded and aerated by the male. Its pelagic larvae make home rearing difficult.

Overview

Chromis atripectoralis Welander & Schultz, 1951, the black-axil chromis, is an Indo-Pacific species ranging from the East African coast to French Polynesia and north to the Ryukyu Islands, reaching about 12 cm total length. It is nearly identical to C. viridis but bears a small black mark at the base of the pectoral fin. FishBase records it as oviparous with monogamous pairing during breeding, following the family's demersal-spawning, male-guarded pattern. IUCN assessed it as Least Concern in 2022.

Sexing

No reliable external sexing character is documented for C. atripectoralis in the consulted sources, and the species is broadly monomorphic. As in the closely related C. viridis, the nest-preparing, guarding individual is the male during reproduction.

Conditioning

A species-specific conditioning protocol is not documented. C. atripectoralis is planktivorous (trophic level about 3.1), feeding on copepods, amphipods and larvae and forming large aggregations above staghorn Acropora; a varied diet of small marine planktonic foods conditions a peaceful group. Maintain stable reef parameters within the recorded ranges (temperature about 24–26 °C, pH 8.1–8.4) and keep it as a school.

Breeding Setup

Provide open rock and rubble near branching coral, echoing the species' coral-thicket habitat, so a dominant male can establish and clean a nest patch. The family pattern has the male clear the area of algae and invertebrates. Keeping a group raises the chance of a pair forming; this is a relatively peaceful chromis.

Spawning Behavior & Trigger

Specific spawning triggers for C. atripectoralis are not documented. In Pomacentridae, ritualised courtship precedes spawning; the female lays a string of sticky eggs attached to the substrate and the male fertilises them externally. FishBase confirms the eggs are demersal and adhere to the substrate and that males guard and aerate them.

Egg & Fry Care

The male guards and aerates the clutch through incubation. At family level, eggs hatch over about two to seven days into transparent larvae roughly 2–4 mm long that enter a pelagic phase; late-stage larvae are strong swimmers documented at about 21.6–25.2 cm per second. This planktonic stage is the principal barrier to captive reproduction.