Marbled Hatchetfish Breeding Guide

Breeding the marbled hatchetfish (Carnegiella strigata): a rarely bred blackwater egg-scatterer, with what is known of sexing, wild spawning and the soft-water conditions involved.

Overview

The marbled hatchetfish, Carnegiella strigata, is a blackwater surface fish that is rarely bred in the aquarium. It is not produced on a commercial basis, and almost all fish offered for sale are collected from the wild, so reliable captive-breeding accounts are scarce. The notes below summarise what the sources actually record.

Sexing

There is little reliable external difference between the sexes. Some specimens grow larger and become rounder-bodied than others, and these are presumed to be adult females; females also tend to have larger abdomens than males. Visual sexing therefore remains uncertain.

Breeding Setup

Any attempt should reproduce the species' natural blackwater conditions: soft, acidic water of low conductivity, stained brown by humic substances, with overhanging and floating vegetation at the surface. Reported maintenance parameters are 20-28 degrees C, pH 4.0-7.0 and hardness 18-179 ppm; the lower, softer, more acidic part of this range matches the blackwater habitat.

Spawning Behavior & Trigger

In the wild the species moves upstream into tributaries and the flooded forest to feed and spawn during the rainy season, indicating that softer, fluctuating water associated with seasonal floods accompanies reproduction. Females lay eggs that fall to the streambed or into vegetation rather than being guarded.

Egg & Fry Care

The eggs are non-adhesive scatter eggs that drop among plants or to the bottom. They hatch within about 36 hours at 25 degrees C. Beyond this, documented fry-rearing detail is not available for this species.

Common Challenges

The principal challenge is that aquarium breeding is essentially unrecorded, so there is no proven protocol to follow. The fish is small, timid and gregarious, best kept in groups of ten or more, and recreating the soft, acidic, seasonally flooded blackwater conditions in which it naturally spawns is difficult to achieve consistently.