Description
Species Overview
The Aru IV Gertrude’s Spotted Blue-Eye Rainbowfish (Pseudomugil gertrudae) is a small, highly active rainbowfish known for its brilliant blue eyes, translucent body, and beautifully patterned fins. Mature males are especially impressive, developing elongated fins covered in dark spots that they spread while displaying to females and competing with other males.
This particular form originates from the Aru Islands population of Pseudomugil gertrudae and is commonly referred to in the aquarium hobby as Aru IV. Rather than relying on size or intense body color to stand out, these fish put on a show through constant movement and fin displays. Keeping several males together can actually make the aquarium more interesting, as they regularly posture and display without the serious aggression associated with many territorial fish.
Aru IV Gertrude’s Spotted Blue-Eyes are social fish and should be kept in a group rather than individually. A larger group also allows their natural social behavior to develop while spreading attention among multiple fish. Their small adult size makes them particularly well suited to planted nano and community aquariums with other peaceful species.
We offer Tank-Bred and USA Bred options when available. Both provide the same beautiful Aru IV form of Pseudomugil gertrudae, with the source clearly identified so you know which option you are purchasing.
What We Love About This Fish
Brilliant blue eyes and dramatically spotted fins that become especially noticeable when males display
Males regularly flare and spread their fins toward one another, creating fascinating activity without the intense territorial aggression of many display fish
Small adult size makes them an excellent choice for heavily planted nano and peaceful community aquariums
Available as Tank-Bred and USA Bred options, with the source clearly identified when available
Quick Care Guide
Care Level: Easy to Moderate
Temperament: Peaceful and Social
Adult Size: Approximately 1.25 to 1.5 Inches
Diet: Omnivore (Micro Pellets, Crushed Flakes, Frozen Foods, and Small Live Foods)
Minimum Tank Size: 10 Gallons
Swimming Zone: Middle to Upper
Social Behavior: Active Shoaling Fish
Group Size: Keep at least 6, with larger groups preferred when aquarium space allows. Keeping multiple males encourages their impressive fin-spreading and display behavior.
Source: Tank-Bred / USA Bred options available when listed
Scientific Name: Pseudomugil gertrudae
Purchase Size: Approximately 0.75 to 1.25 Inches
Recommended Water Parameters
Temperature: 72° to 79°F (22° to 26°C)
pH: 6.0 to 7.5
GH: 5 to 15 dGH
KH: 2 to 8 dKH
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: Ideally below 20 ppm
Aru IV Gertrude’s Spotted Blue-Eye Rainbowfish are adaptable to a reasonable range of water chemistry, but they do best when conditions are clean, stable, and well oxygenated. Avoid making frequent adjustments simply to reach an exact pH or hardness value.
Good filtration and regular water changes are particularly important for these small, active fish. A mature aquarium with consistent water quality provides a much better environment than one where parameters fluctuate, even when those fluctuations remain within the recommended range.
