Threadfin Petrochromis
Petrochromis trewavasae
Cichlidae
About
The threadfin petrochromis is a slender, algae-grazing cichlid endemic to the rocky shallows of Lake Tanganyika, where it patrols sunlit boulders and rasps the biofilm and filamentous algae known as aufwuchs from every surface. Reaching around 18 cm, it wears fine trailing fin extensions that give the fish its name. Behind that elegant look lies one of the hobby's most combative herbivores: it is relentlessly territorial and especially aggressive toward its own kind, so it is kept as a large colony in a big, hard, alkaline tank so that no single individual becomes a target. Its specialised long gut makes it dangerously vulnerable to bloat, demanding an almost fat-free vegetable diet and strict discipline at feeding time.
Care
Advanced Tanganyikan for very experienced keepers only. House a colony of 8 or more in a large tank of 450 L or more (150 cm+ footprint) with sand, open rock and hard, alkaline water at pH 8.4-8.8. Spread aggression across many fish and feed a strict low-protein, plant-based diet to prevent bloat.
Diet
Dedicated aufwuchs herbivore that scrapes algae from rock. Feed spirulina flakes, vegetable granules and algae wafers only; keep protein minimal and avoid rich foods, as this species bloats very easily.
Tankmate compatibility
Possible with care (127)
Avoid (144)
Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Telling males from females
What works for this species, most reliable first.
- Extended finsStrong · from about 8 months, and later in a suppressed male
On many cichlids and killifish the male's dorsal and anal fins draw out into trailing points as he matures, while the female's stay rounded.
- VentingA hint only · only on a mature fish, easiest when she is in breeding condition
The method breeders use when the answer has to be right. Hold the fish upside down in a wet hand or soft net and look at the two openings ahead of the anal fin. The forward one is the anus; the one behind it is what you are reading.
- Adult sizeA hint only · only across animals of the same age
In many cichlids, catfish and loaches one sex simply grows larger — usually the male, though there are well-known reversals.
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Frequently asked questions
- What tank size does a Threadfin Petrochromis need?
- A Threadfin Petrochromis needs an aquarium of at least 450 litres (118.9 US gallons) with a footprint at least 150 cm (59.1 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Threadfin Petrochromis need?
- Threadfin Petrochromis does best at 23–27 °C (73.4–80.6 °F), pH 7.8–9 and a general hardness of 8–20 °dGH.
- What group size does a Threadfin Petrochromis need?
- Threadfin Petrochromis is a social species — keep a group of at least 8 so natural behaviour emerges and stress stays low.
- Is the Threadfin Petrochromis suitable for beginners?
- Threadfin Petrochromis is a demanding species best attempted with some experience — it needs stable, closely watched conditions to thrive.