Lake Kutubu Rainbowfish Breeding Guide
How to breed Melanotaenia lacustris: conditioning, alkaline spawning water, daily egg-laying on mops, 7-12 day hatch and surface-feeding fry.
Overview
Melanotaenia lacustris is a plant-spawning rainbowfish endemic to Lake Kutubu in the Kikori River system of Papua New Guinea, where it is one of 13 endemic fish species. It is a continuous spawner that deposits small batches of adhesive eggs over a period of weeks rather than in a single event, which makes it accessible to intermediate aquarists willing to harvest eggs regularly.
Sexing
Males are larger and more brightly coloured and develop a noticeably deeper body than females as they mature. When ready to spawn, males display to one another almost constantly and develop an orange patch above the gill flaps, while conditioned females become noticeably plumper with eggs.
Conditioning
Condition the adults as a group in a separate aquarium with plenty of live and frozen foods. Heavy feeding brings the females into spawning condition; readiness is indicated by the females filling out and the males displaying intensely to each other.
Breeding Setup
- Spawning tank at least 30 inches (76 cm) long, no substrate needed
- Slightly hard, alkaline water around pH 7.5
- Temperature 72-75°F (22-24°C)
- Small air-powered filter for oxygenation
- Fine-leaved plants such as java moss, or nylon spawning mops as an egg-receiving medium
Spawning Behavior & Trigger
A small rise in temperature often induces spawning. The selected pair spawns over a period of several weeks, laying batches of eggs each day. Eggs are attached to plants or mops by a small thread.
Egg & Fry Care
Adults eat their own spawn, so eggs should be removed regularly to a separate rearing tank. The eggs hatch in 7-12 days depending on temperature. Newly hatched fry stay very close to the surface and require infusoria-type first foods, graduating to free-swimming foods such as brine shrimp nauplii after about a week. Avoid sinking foods, which the surface-oriented fry will not reach.
Common Challenges
The two main difficulties are egg predation by the adults, addressed by daily egg harvesting, and the small mouth size of the surface-dwelling fry, which makes a steady supply of infusoria essential during the first week. This species is also Endangered in the wild, so captive breeding helps relieve collection pressure on the natural Lake Kutubu population.