Oryzias eversi

Overview

The Sulawesi ricefish Oryzias eversi carries its developing eggs externally beneath the female's abdomen until hatching. Courting males turn dark over the belly and rear body, making reproductive behavior a distinctive feature of a dedicated group.

Distribution & habitat

Only one locality is documented: a rainforest-surrounded karst pool near Tilanga in the Salo Sadang drainage of Tana Toraja, South Sulawesi, Indonesia. Clear, still water has a single inlet and outlet. Wild males occurred individually while females gathered near vegetated edges.

Aquarium setup

A group requires a footprint of at least 75 × 30 cm. Sand, worn roots, branches, and leaves provide a naturalistic setting; planted aquaria also work well. Sparse decoration tends to reduce coloration, while dense growth provides juvenile refuge.

Diet & feeding

Offer foods small enough to take easily, combining crushed quality flakes or fine granules with microworms and Artemia nauplii. Adults have been seen grazing hard surfaces, suggesting a possible algal contribution to the wild diet though the natural contribution remains uncertain.

Behaviour & compatibility

Usually peaceful, it is nevertheless too small for many general communities. Other tiny, gentle fishes and suitable freshwater shrimp are options. Eight or more individuals tend to appear more confident, although males spar during courtship. Keep a breeding group by itself and avoid other ricefish species because of hybridization risk.

Sexual dimorphism

Male dorsal and anal rays are elongated, and nuptial darkening affects several fins and part of the body. Females are plainer, with greatly lengthened pelvic fins and a depressed egg-carrying area between those fins and the anal fin. A membrane connecting part of the last pelvic ray to the body occurs in males but not females.

Breeding

Spawning usually occurs early in the day. Dominant males darken and exclude rivals. About 20–30 eggs are released and fertilized together, remaining attached to the female by adhesive threads. Her extended pelvic fins secure them against the abdominal depression until hatching, generally after 18–19 days. She often hides while carrying eggs and does not spawn again during incubation.

Adults usually leave eggs alone but eat free-swimming fry. Separate the carrying female before hatching or transfer fry to a nursery containing parental-tank water. Fine plants and floating cover allow some young to survive in place. Microworms and Artemia nauplii can be taken immediately after free swimming begins.