Rainbow shark (Epalzeorhynchos frenatus)

Very — the eternal workhorse of beginner tanks. Hardy, disease-resistant, broadly adaptable (pH 6.0–8.0, 24–27 °C), omnivorous, and helpful with leftover food and algae. The real caveat is conspecific intolerance: one rainbow shark per tank, full stop — multi-shark civil wars exceed anything their size predicts. Kept singly, it's among the most trouble-free utility fish.

The name comes from build and posture: streamlined body, tall dorsal fin, and mid-bottom cruising that genuinely evokes a small shark. It's a true cyprinid (Epalzeorhynchos), zero relation to actual sharks. 'Rainbow' refers to the jet-black body with scarlet fins — the red edging on tail and dorsal, glowing like hot coals in peak condition.

Strongly discouraged. Conspecific aggression in this species tops the utility-fish chart: two in one tank chase, shred fins, and suppress feeding until one dies or is crippled. It's hardwired territory behavior barely mitigated by space or scape — even 1,000 L tanks produce a victor. For the multi-'shark' look, mix different genera (siamese algae eater, otocinclus), which don't read as rivals.

Omnivore: algae, leftovers, detritus, prepared foods. Its scraping ability is mid-tier among utility fish (below siamese algae eaters and otos), handling filamentous and spot algae but largely ignoring BBA and staghorn. Don't buy it as an 'algae solution' — its core value is policing leftovers and substrate organics; algae control is a side gig.

First confirm the target isn't a conspecific (same-size rainbow or red-tailed black shark — that's territory war; separate immediately). If the victim is another species, usual causes: tank too small (territory anxiety — add space), target too colorful or too small (misread as intruder or prey), or underfeeding (hunger-driven aggression). It's typically harmless toward gentle mid-size fish (corydoras, small barbs) and risky for tiny tetras.

150 L is the floor; 150–200 L in practice. Adults reach 10.5–15 cm, swim actively, and defend territory — small tanks under 100 L amplify aggression. Scaping key: provide one cave it accepts as home (under driftwood, stone crevices, a pot). A shark with an established territory attacks measurably less — the central behavior-management trick.

Six to eight years, ten with fine care. It's the long-liver of utility fish — many keepers' sharks accompany the tank from setup to rescape. The formula matches most cyprinids: stable water, measured feeding, a cave to rest in. Unlike small tetras on a two-year rotation, this is a long-term commitment.

Two commonly confused species: the rainbow shark (Epalzeorhynchos frenatus) has red on all fins including pectorals and a slimmer build; the red-tailed black shark (Epalzeorhynchos bicolor, now often Labeo) shows red only on the tail with a taller, deeper body. Temperament is nearly identical — equally intolerant of conspecifics, still one per tank. 'Albino rainbow sharks' (pink body, red fins) are the same species in albino.

Fin redness is a condition barometer; fading usually means: water too cool (below 22 °C, red dulls to orange), diet lacking carotenoids (add astaxanthin-rich food), chronic stress (bullying, poor water, recent move), or age (old fish fade naturally). The first three reverse within two weeks of correction — if yours never reddens, check temperature before swapping foods.

Yes, but not the way you imagine. Rather than sifting sand like a corydoras, it patrols the bottom picking off leftovers and debris — a mobile cleanup service. Its 'cleaning' is active patrolling: enthusiastic about uneaten food, dead fish, and fallen leaves, but powerless against organics inside the substrate. Don't slack on water changes — deep-sand waste still demands changes and gravel vacs.