Harold's Otocinclus Care Guide - Aquarium Setup, Diet & Breeding

Harold's Otocinclus is a tiny suckermouth catfish with a compact body, a flattened underside and a broad, sucker-shaped mouth adapted for clinging to solid surfaces. Its body is usually olive, brownish or grey, with darker markings that help it blend into stone, wood and leaf litter. The fins are translucent and may show subtle dusky patterning.

Parotocinclus haroldoi is native to the São Francisco River basin of eastern Brazil, South America. It inhabits shallow freshwater streams and tributaries with clear, oxygen-rich water and surfaces covered in algae and biofilm.

A group should be given an established aquarium of at least 60 litres, with a footprint around 60 × 30 cm or larger. Use smooth sand or fine rounded gravel, plenty of driftwood, broad-leaved plants, smooth stones and shaded areas where algae and biofilm can develop. Strong filtration, excellent oxygenation, gentle water movement and stable, mature conditions are particularly important; avoid adding these fish to a newly set-up or biologically immature aquarium.

Up to 4 cm (1.6 in) in adult length; females are usually slightly larger and deeper-bodied than males.

This species naturally grazes on algae, aufwuchs and microorganisms growing over submerged surfaces. In an aquarium, provide regular access to algae and biofilm alongside sinking algae wafers, spirulina-based foods and softened vegetables such as courgette, cucumber or blanched spinach. Offer occasional high-quality omnivore foods, but make sure the fish receive enough vegetable matter and are not expected to survive on algae alone.

Harold's Otocinclus is peaceful and best kept with other small, calm community fish. Suitable companions include small tetras, rasboras, peaceful danios, dwarf pencilfish, small Corydoras and other non-aggressive South American community species. Avoid large, boisterous or predatory fish, fin-nippers and territorial bottom dwellers that may outcompete or harass this delicate catfish.

Harold's Otocinclus is an egg-scattering catfish that may spawn in a mature, well-established aquarium when it is well fed and kept in good condition. The pair or group deposits small adhesive eggs on plants, wood, rocks or aquarium glass, with hatching usually occurring after several days. Remove the adults or protect the eggs from other fish, and raise the tiny fry in an aquarium rich in algae, biofilm and suitably fine foods. Captive breeding is possible but not as routinely documented as breeding in some other small loricariid catfish.

Females tend to be broader through the abdomen and noticeably deeper-bodied when viewed from above. Males are generally slimmer and may have a more obvious genital papilla, although sexing young or poorly conditioned fish can be difficult.