Pseudomugil gertrudae

The Spotted Blue-eye is a small, active freshwater fish known for its stunning appearance and shoaling behavior, making it a captivating aquarium addition. Native to parts of Australia and New Guinea, this species thrives when kept in groups, as it is a natural shoaling fish that feels more secure with company. A small school will display more interesting and natural behaviors. They are quite energetic and can be seen swimming swiftly in the top and middle levels of the aquarium. Due to their active nature and ability to jump, a well-covered aquarium is essential to keep them safely housed.

As omnivores, they are not picky eaters but require food small enough to fit in their tiny mouths. A diet consisting of high-quality crushed flakes, micro-pellets, and supplemented with small live or frozen foods will ensure they receive proper nutrition. These fish have a high metabolism and benefit from several small feedings throughout the day rather than one large one. While they are relatively hardy, they prefer clean, warm water that is soft and slightly acidic, with a gentle current. With a naturally short lifespan, providing them with an optimal and stable environment is the best way to enjoy these beautiful fish for their entire lives.

The Spotted Blue-eye, hailing from the slow-moving, heavily vegetated freshwaters of northern Australia and southern New Guinea, offers a fascinating glimpse into a unique aquatic environment. Its natural habitats, such as swamps, billabongs, and quiet stream margins, are often characterized by dense aquatic plants, submerged wood, and a layer of leaf litter, which stains the water with tannins. Replicating this biotope is key to their long-term health. An ideal aquarium setup should include plenty of fine-leaved plants, such as mosses and stem plants, as well as floating vegetation to diffuse lighting and provide a sense of security. A dark substrate will help accentuate their coloration. Water movement should be gentle, so the use of a sponge filter or a canister filter with a flow-reducing spray bar is highly recommended. A secure, tight-fitting lid is non-negotiable, as these fish are accomplished jumpers.

This is a quintessential shoaling species that must be kept in a group. A larger school not only ensures the fish feel secure but also encourages their most interesting social behaviors. Males will actively compete for female attention by flaring their ornate fins in dazzling displays. Despite these energetic displays, they are exceptionally peaceful towards other species. However, their small size and fast-paced nature mean they should be housed with tank mates of a similar size and temperament that won't out-compete them for food or cause stress. Tank mates like small rasboras, pygmy corydoras, or shrimp are suitable companions.

Catering to their high metabolism is crucial. Their active, constant swimming burns a lot of energy, necessitating multiple small feedings per day. A varied diet is essential for maintaining their health and vibrancy. Offer a base of high-quality micro-pellets or crushed flakes, supplemented frequently with live and frozen foods such as daphnia, baby brine shrimp, copepods, and microworms. Maintaining pristine water quality is vital. Although they produce a low amount of waste individually, their need for frequent feeding and sensitivity to pollutants requires regular water changes and diligent tank maintenance to keep nitrate levels low and the environment stable.

Pseudomugil gertrudae, a member of the family Pseudomugilidae, is a small-bodied fish endemic to the freshwater systems of northern Australia and southern New Guinea. Its classification places it within the order Atheriniformes, sharing ancestry with rainbowfishes and silversides. The species exhibits a classic fusiform body shape, streamlined for its active, pelagic lifestyle predominantly in the upper and middle water column. Morphological analysis reveals a terminal mouth, an adaptation suited for its diet of zooplankton, phytoplankton, and small invertebrates captured from the surface and mid-water.

Significant sexual dimorphism is present. Males are distinguished by their more vibrant coloration and the dramatic extension of their dorsal, anal, and pectoral fins, which are used in complex courtship and territorial displays. Females are more subdued in color with standard, unadorned finnage and a slightly rounder body profile. In its natural ecology, P. gertrudae occupies shallow, slow-moving, and often tannin-stained aquatic environments rich in macrophytes. These habitats are typically soft and acidic, with a substrate of sand, mud, and decaying organic matter. The species' diet and behavior establish it as a micro-predator within its ecosystem.

Physiologically, P. gertrudae is characterized by a high metabolic rate, corresponding to its constant activity and requiring high-energy food inputs multiple times per day. It has a moderate oxygen consumption rate, and while its individual bioload is low, its preference for pristine conditions necessitates excellent water quality and filtration in an aquarium setting. The species is primarily freshwater but demonstrates a degree of euryhalinity, with tolerance for very low salinity levels reported in some populations. According to the IUCN Red List of Threatened Species, Pseudomugil gertrudae is listed as Least Concern (LC), reflecting its relatively wide distribution and stable populations, although localized threats from habitat degradation and invasive species remain a consideration.

Breeding Pseudomugil gertrudae is considered a moderately challenging but highly rewarding endeavor. Success is most often achieved in a dedicated breeding aquarium, which allows for better control over conditions and facilitates the collection of eggs. This tank should be equipped with a gentle sponge filter to prevent fry from being drawn in and contain ample spawning media. Clumps of fine-leaved plants like Java moss or synthetic yarn spawning mops are ideal, as they provide a surface for the adhesive eggs to be deposited.

Identifying the sexes is straightforward. Males possess elaborate, elongated fins and are more intensely colored, while females are plainer with shorter fins and a fuller, more rounded body. To encourage spawning and minimize stress on the females from the males' persistent courtship, a ratio of one male to two or three females is recommended. Condition the group with a rich diet of live and frozen foods for a few weeks to bring them into spawning condition.

This species is a continuous spawner, meaning the female will lay a small number of eggs daily over an extended period. The male will perform a vibrant display, quivering and flaring his fins to entice a receptive female into the spawning medium, where fertilization occurs as the eggs are laid. Since the parents will predate on their own eggs and fry, it is essential to separate them. This can be done by either moving the spawning mops to a separate hatching container every few days or by removing the adult fish after a week of spawning.

The eggs typically hatch within one to two weeks, depending heavily on the water temperature. The newly hatched fry are minuscule and require microscopic food for the first stage of their life. An initial diet of infusoria, rotifers, or a commercial liquid fry food is necessary for the first 7-10 days. As they grow, they can be transitioned to slightly larger foods such as microworms and newly hatched baby brine shrimp. Frequent feedings are critical for the survival and healthy development of the fast-growing fry.