Breeding Petrochromis trewavasae

Breeding guide for Petrochromis trewavasae, a maternal mouthbrooding Lake Tanganyika rock-grazer with high aggression and bloat risk on protein.

Overview

Petrochromis trewavasae is a large algae-grazing cichlid endemic to Lake Tanganyika, where it lives on shallow rocky substrates and feeds by scraping the biocover (aufwuchs) from rocks. FishBase records a maximum length of about 18 cm and confirms that females brood their young in the mouth, making this a maternal mouthbrooder. Within the genus Petrochromis, breeding follows a consistent pattern, so closely related species such as P. famula provide a reliable model for captive reproduction.

Sexing

Sexual dimorphism in Petrochromis is subtle. As documented for the genus on Seriously Fish, mature males tend to be more colourful and develop pointed dorsal, anal and pelvic fins, while females remain plainer. Reliable visual sexing usually requires adult, well-conditioned fish, and many breeders rely on observing spawning roles to confirm sex.

Conditioning

Petrochromis are specialised rock-grazers and must be fed a diet high in fibre and low in protein. Excess protein is associated with digestive disorders in this group, so conditioning should centre on vegetable-based foods such as spirulina flake and blanched greens, with only sparing use of richer items. Maintaining a colony in spacious, well-filtered, well-oxygenated water supports the steady condition needed for spawning.

Breeding Setup

Because of their adult size and aggression, these fish require very large tanks with a rocky aquascape providing open grazing surfaces and broken sightlines. A single male with several females is the typical breeding configuration; intraspecific aggression is intense and is best diffused by keeping the colony with robust tankmates rather than alone. Hard, alkaline water within the temperature range of 24-27 °C suits the species.

Spawning Behavior & Trigger

Spawning follows the maternal mouthbrooding pattern typical of the genus: the female takes the eggs into her mouth, where they are fertilised, and then carries the developing brood. Good water quality and steady conditioning on the correct herbivorous diet are the main triggers. The dominant male defends a grazing territory and courts receptive females within it.

Egg & Fry Care

Based on the closely related P. famula, the female carries the brood for around four weeks and does not feed during this period. Released fry of Petrochromis are large and accept adult-sized foods almost immediately, growing quickly when fed frequently. As with conditioning, fry and adults should be kept on a fibre-rich, low-protein diet to avoid digestive problems.

Common Challenges

The two principal challenges are aggression and diet-related disease. Intraspecific aggression can be severe in species-only setups, so adequate volume and tankmate diversity are essential. Feeding too much protein risks the digestive bloat that the genus is prone to. Sexing difficulty and the slow maturation of these long-lived fish also make breeding an advanced undertaking.