Porthole Rasbora

Geographic Origin and Biotope: Endemic to the blackwater peat swamps and flooded forests of insular and peninsular Southeast Asia. This is an extreme habitat, with water dark as strong tea, incredibly low pH (below 5.0), and a total absence of hardness due to immense amounts of decaying organic material.

Taxonomy and Morphology: Cyprinidae. Unlike the average for its genus (which sits around 4-5 cm), this is a true giant, approaching 13 centimeters (5.1 inches) in length. The body is a narrow torpedo shape, with a large, sharply upward-angled mouth, the perfect evolution for surface hunters.

Social Behavior: Very active and peaceful toward similarly sized fish, but frighteningly fast. Being an opportunistic predator, it will swallow anything that fits in its mouth. Moves predominantly in the upper layers. It remains a gregarious fish that must be kept in schools (at least 6, ideally 8-10).

Coloration and Sexual Dimorphism: Antique silver or dark copper base. It takes its name from the characteristic lateral pattern: instead of a solid line, two narrow parallel black lines run along the flank, merging into a series of round spots forming a chain or 'porthole' motif. Females are noticeably plumper and deeper-bodied; males are streamlined torpedoes, with warmer, coppery reflections.

Tank Setup: Being lightning-fast giants, they demand XL tanks (absolute minimum 120-150 cm / 48-60 inches in length). This fish STRICTLY requires a Blackwater biotope: almost zero light, tangled driftwood, dried leaves on the bottom to release tannins, and floating plants to shield the surface. Heavy glass lid: a 5-inch muscle-bound fish will smash through light netting or thin plexiglass if it jumps.

Feeding and Diet: Omnivorous macro-predator. Devours commercial surface food with unheard-of ferocity. Prefers large prey such as chopped earthworms, jumbo bloodworms, krill, and dried/live crickets dropped on the water's surface.

Water Quality: This is its greatest limitation: it cannot tolerate hard, alkaline tap water. It requires pure reverse-osmosis water, extremely soft (GH 1-5), and decidedly acidic (pH 4.5 - 6.5). Temperatures between 22 and 26°C (72-79°F). Highly sensitive to ammonia spikes.

Compatibility and Cohabitation: Terrible choice for a general community tank with small fish. It will eat Neons, dwarf rasboras (Boraras), or guppies. Excellent for tanks with large Asian peat-swamp fish, such as medium Loaches, large Gouramis (e.g., Pearl Gouramis), and large Asian Cichlids.

Aquarium Reproduction: Very rare in captivity due to the tank size required for spawning and the extreme acidic parameters needed to condition the female. They are free-spawners and, naturally, will devour the eggs if hungry.

Risks and Diseases: They stress out, fade, and fall ill from lethal bacterial/fungal infections if kept in hard, neutral, or alkaline waters. Fatal leaps from the tank due to their hyperactivity.