Boraras naevus

A micro-fish originating from the slow-moving, blackwater systems of Asia, the Strawberry Rasbora is adapted to environments rich in tannins, with soft, acidic water and dense vegetation. To successfully keep this species, replicating this natural habitat is key. An ideal aquarium setup includes a soft substrate, plenty of live plants, and the addition of driftwood and dried leaf litter. These elements not only provide security but also help to buffer the water to the preferred acidity and release beneficial compounds. Gentle water flow is crucial, as this species is not equipped for strong currents.

As a shoaling species, its social behavior is a primary consideration for its care. A group is mandatory for their health, reducing stress and encouraging more confident, natural interactions. In a larger, well-structured group, they will actively explore the middle and upper regions of the tank. Their diet is omnivorous with a tendency towards micropredation. In their natural habitat, they feed on small insects, crustaceans, and zooplankton. In captivity, a varied diet is essential and should include high-quality, protein-rich foods like finely crushed flakes, micro-pellets, and a regular supply of live or frozen options. They are also known to graze on biofilm that develops on tank surfaces. Due to their peaceful but timid disposition, they are easily outcompeted for food and stressed by large, boisterous, or overly active tank mates. Suitable companions include other nano rasboras, small tetras, pygmy corydoras, and invertebrates like shrimp and snails. Given their sensitivity and need for stable water conditions, they are best introduced to a mature, fully cycled aquarium.

Boraras naevus is a small-bodied freshwater fish belonging to the family Danionidae. Characterized by a fusiform body shape, this species is morphologically adapted for maneuverability within the complex, densely vegetated aquatic environments of its native range in Asia. These habitats are typically lentic or have low-flow lotic conditions, such as peat swamps and blackwater streams. The water chemistry of these ecosystems is distinct, featuring a low pH and minimal mineral content due to the high concentration of tannins and humic substances from decaying organic matter.

Ecologically, B. naevus functions as an omnivorous micropredator. Its diet consists of minute invertebrates, zooplankton, and algae. It also engages in biofilm consumption, grazing on microbial communities that colonize submerged surfaces, thereby playing a role in nutrient cycling within its microhabitat. Its physiological profile includes a low metabolic rate, low oxygen consumption, and consequently, low waste production. This makes it a low-bioload species in an aquarium setting, but also indicates an adaptation to potentially low-oxygen, nutrient-poor natural environments.

Socially, it is an obligate shoaling species, forming groups as a primary anti-predator defense and for social cohesion. This behavior is critical for its well-being in both wild and captive settings. It is important to note that Boraras naevus is listed as Vulnerable on the IUCN Red List. This conservation status is primarily attributed to habitat loss and degradation from agricultural expansion and other human activities in its native regions, highlighting the need for responsible sourcing and habitat conservation efforts.

Breeding this species is considered moderately difficult and is best attempted by hobbyists with some experience. Success requires a dedicated breeding setup separate from the main aquarium. This tank should contain very soft, acidic water and be dimly lit. Furnish the tank with abundant fine-leaved plants, such as mosses, or artificial spawning mops to provide a surface for egg deposition. The addition of dried leaf litter can help create ideal water conditions and will encourage the cultivation of infusoria, which will serve as the first food source for the fry.

To induce spawning, a group of well-conditioned adult fish should be selected. Conditioning involves feeding them a diet rich in live and frozen foods for several weeks prior to the breeding attempt. While discerning gender can be subtle, males are typically more slender and display more intense coloration, whereas females will appear noticeably rounder and fuller-bodied when gravid. A group with an equal or slightly higher number of males to females can increase the chances of successful fertilization.

This species is an egg-scattering spawner, exhibiting no parental care. The conditioned group is introduced into the breeding tank, where spawning activity usually occurs. Once eggs are laid, the adults must be removed promptly, as they will predate on both the eggs and any resulting fry. The eggs will typically hatch within a few days. The newly hatched fry are minuscule and will initially sustain themselves on infusoria within the tank. As they grow, their diet can be gradually supplemented with progressively larger foods, such as microworms and newly hatched brine shrimp, until they are large enough to accept crushed flakes and micro-pellets.