Care guide · Freshwater · fish

Masked Julie care guide

Julidochromis transcriptus

Photo: Przemysław Malkowski, CC BY-SA 4.0; resized. Photo: Przemysław Malkowski · Source · CC BY-SA 4.0Resized and compressed; no cropping or colour changes.

Julidochromis transcriptus, commonly called the masked or black-and-white Julie, is a small rock-dwelling cichlid from the northwestern part of Lake Tanganyika. Its dark pattern and close association with rocks make it distinctive, but it is not a typical community fish. It needs a stable alkaline aquarium with secure crevices and room to hold a territory. Keep an established pair and take particular care over provenance: the species was assessed as Critically Endangered in 2025. Choose demonstrably captive-bred fish only and avoid animals of unclear or wild-caught origin.

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At a glance

Temperature: 24–26 °C
pH: 8.0–9.0
GH: 9–11 °dGH
Aquarium length: At least 60 cm
Minimum aquarium volume: At least 75 L
Adult size: Up to 7 cm
Group size: At least 2 individuals
Temperament: Territorial

About this species

The masked Julie belongs to the family Cichlidae and is named Julidochromis transcriptus Matthes, 1959. Dark bands and blotches contrast with a pale body; pattern and colour can vary between populations or captive lineages. Seriously Fish reports around 65 mm standard length, while FishBase lists a maximum of 7 cm total length. These are different measurements. ‘Masked Julie’ is the common English name; in shops the fish may also be sold under its scientific name.

Natural habitat

The species is endemic to a small rocky coastal area in the northwestern part of Lake Tanganyika, between Luhanga and Makabola in the Democratic Republic of the Congo. It stays close to rocks, fissures and small caves. Recreate this with several stable rock piles and narrow retreats, rather than loose stones that could collapse. Leave enough open space between rock zones for swimming and maintenance. Sand suits a Tanganyika-style setup, but secure crevices and stable rockwork are the key features for this species.

Aquarium and layout

For a pair, an aquarium at least about 60 cm long and roughly 75 litres is a cautious starting point based on the consulted species and Julidochromis guidance. More floor area and several separate rock caves provide better opportunities to establish territories. Secure heavy rocks on the tank base before adding sand so digging is less likely to destabilise them. Provide reliable filtration and oxygenation without directing harsh flow into the shelters. Do not keep another Julidochromis species or geographic form in the same aquarium.

Water conditions

Aim for stable, hard and alkaline water. AquaInfo gives 24–26 °C, pH 8–8.5 and GH 9–11; FishBase records pH 8.5–9.2 and hardness 8–14. A cautious overlapping guide range is therefore pH 8.5–9 and GH 9–11 °dGH; this is not a reason to alter water chemistry rapidly. The 24–26 °C temperature comes from the species-specific aquarium source. No sufficiently supported KH target is stated here. Test source water and aquarium water and make changes gradually.

Behaviour and group size

Julidochromis transcriptus is territorial around rocks and shelters. Seriously Fish advises keeping it as a pair, while FishBase describes it as usually solitary and territorial. In practice, an established pair is preferable to an arbitrarily assembled adult duo. Provide several crevices so either fish can retreat and the pair does not have to defend one narrow entrance. Matching water values alone do not prove a tankmate is safe. No other individual species is linked to this guide as a verified, guaranteed companion.

Feeding

In nature the species picks small organisms and growth from rock surfaces. Offer varied fine foods in small portions: suitable prepared food can be alternated with small frozen or live foods and foods containing vegetable or algal ingredients. Watch that both fish feed and remove leftovers from crevices. This feeding profile is not an endorsement of a specific brand. No product with a verified current offer and proven species-specific match is linked.

Breeding

The masked Julie spawns in a sheltered fissure or cave and establishes a territory around the site. Make sure the rocks are secure and the entrance is narrow enough to protect the nest. No fixed breeding season, exact clutch size or hatch time is stated because the reviewed sources do not establish a reliable species-specific value. Avoid hybridisation with other Julidochromis species and geographic forms. Its natural range is very restricted and the species is classified as Critically Endangered in the 2025 IUCN assessment; choose traceable captive-bred stock and do not support wild collection.