Delicate blue-eye
Pseudomugil tenellus
The delicate blue-eye (Pseudomugil tenellus) is a small, active blue-eye from northern Australia and nearby regions. It inhabits warm, often densely vegetated billabongs, swamps and slow streams. The name “Arnhem Land blue-eye” refers to a familiar part of its range, but related blue-eyes can look similar; buy fish with a dependable identification and locality. Adult males develop longer, conspicuously patterned fins. This is a peaceful shoaling fish, but its small size and fine-food requirements make it unsuitable with large or pushy tankmates. A mature, oxygen-rich aquarium, stable warm water and a group of at least eight provide a sound starting point.
Plan your aquarium →At a glance
- Temperature
- 25–32 °C
- pH
- 5.5–7.5
- GH
- 5–20 °dGH
- Aquarium length
- At least 75 cm
- Minimum aquarium volume
- At least 68 L
- Adult size
- Up to 5.5 cm
- Group size
- At least 8 individuals
- Temperament
- Peaceful
About this species
Pseudomugil tenellus Taylor, 1964 is recognised as valid by Eschmeyer’s Catalog of Fishes and belongs to Pseudomugilidae. Its type locality is a large billabong near Oenpelli in Arnhem Land. The fish is small and slender; males usually have longer, more colourful and patterned unpaired fins than females. Pale spots along the mid-lateral scales become more evident with age. Do not confuse it with Pseudomugil gertrudae or P. signifer: trade names such as “delicate” and “blue-eye” are not always applied consistently. FishBase and Seriously Fish report about 5.5 cm standard length, which excludes the caudal fin.Natural habitat
The species is recorded from northern Australia, including the East Alligator River catchment and separate Queensland localities, as well as nearby parts of New Guinea and the Aru Islands. It occurs in vegetated swamps, billabongs, floodplains and slow-flowing streams. Conditions vary considerably with place and season. Brackish habitats are also reported, but salt is not required for normal aquarium care; the fish can be kept in freshwater. Do not treat field measurements as universal aquarium settings. Choose a stable, well-aerated freshwater aquarium.Aquarium and layout
Seriously Fish recommends considering a footprint of at least 75 × 30 cm, about 68 litres gross, as a starting point. The length gives a shoal room to swim and males space to display. Keep at least eight together and favour more room rather than a tiny nano tank. Plant the back and sides, add floating cover and roots, but retain open surface swimming space. Gentle to moderate flow and good oxygenation suit its habitat. The species is sensitive to water-chemistry swings: introduce it only to a biologically mature aquarium and maintain it regularly. A close-fitting lid helps prevent escapes.Water conditions
For routine care, Seriously Fish gives 25–32 °C, pH 5.5–7.5 and GH 5–20 dGH. The species account also cites higher local field measurements; these are not a recommendation to keep aquarium water at such extremes long-term. Keep chosen conditions stable and acclimate new fish gradually. No specific KH target is sufficiently supported. Although the fish tolerates a broad salinity range, marine salt is unnecessary in an ordinary freshwater aquarium. Avoid rapid temperature and pH changes and provide mature filtration.Behaviour and group size
The delicate blue-eye shoals, mainly in the upper water, and takes small food particles from the surface. It is generally peaceful. Males spread their longer fins during courtship; keep a group rather than a single fish or isolated pair so social behaviour is more evenly expressed. Large predators, fin-nippers and fast feeders may cause stress or food competition. Assess tankmates by adult size, behaviour, swimming zone and feeding style, not merely similar pH or temperature. A species-focused aquarium is a prudent choice when suitable small companions are unavailable.Feeding
In nature it feeds on floating or suspended zooplankton, phytoplankton, algae and small invertebrates; the mix changes seasonally. In the aquarium, offer small floating complete flakes or microfoods that fit its mouth. Supplement with small live or frozen prey such as Daphnia, Artemia nauplii or other appropriately sized microfoods. Give several small portions and check that smaller or subordinate fish can swallow them. Food sold for “tropical fish” is not automatically small enough. Remove leftovers to maintain water quality.Breeding
The species scatters adhesive eggs among fine plants or on a spawning mop and provides no parental care. Adults may eat eggs and larvae. For planned breeding, use fine-leaved moss or a mop, inspect it regularly and move eggs if desired to a clean, gently aerated rearing container. Aquarium spawning may occur through the year; Seriously Fish reports 24–28 °C as a spawning condition. This is not a reason to keep routine maintenance water above the normal care range. Start fry on food small enough for them and keep water exceptionally stable.Suitable products
Recommended staple foods
Tropical Supervit Basic 100ml
Complete flakes can serve as dry food when crushed very finely; check that this small fish can swallow the particles and supplement with suitable live or frozen microfoods.
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Tropical Dafnia 100ml
Dried Daphnia are only a supplementary prey item and must be small enough; offer small portions alongside complete staple food.
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Sources & review
This care guide draws on several specialist sources and was last checked on .