Otocinclus macrospilus Breeding Guide

Breeding the Big-Spot Otocinclus (Otocinclus macrospilus): a Corydoras-style T-position spawner that scatters eggs with no parental care. Sexing, triggers and fry care.

Overview

Otocinclus macrospilus, the Big-Spot or Tailspotted Oto, is a tiny algae-eating loricariid endemic to the upper Amazon in Peru, with records from Colombia and Ecuador, reaching about 3.5 cm. It has been bred in captivity but spawning is difficult and uncommon. Despite the cave-spawner label sometimes applied, the documented behaviour is a Corydoras-style egg scatterer with no parental care.

Sexing

Per Seriously Fish, females appear noticeably broader in body when viewed from above compared with males, the difference being clearest in mature fish in spawning condition. There are no strong external differences beyond body width.

Conditioning

Condition a group (the species should be kept in groups of at least 5-6, preferably more) on abundant biofilm and vegetable matter; Seriously Fish recommends fresh foods such as courgette and cucumber slices and blanched spinach, plus dried algae wafers and Spirulina tablets, with small live/frozen foods as a supplement. A mature, biofilm-rich tank is important.

Breeding Setup

Use a mature, planted tank with fine-leaved plants and clean glass for the scattered eggs; a base of at least about 80 cm is suggested for a group. Seriously Fish gives 21-26 degrees C, pH 5.5-7.5 and hardness 1-12 degrees H. Excellent water quality and abundant grazing surfaces are essential.

Spawning Behavior & Trigger

Spawning follows the Corydoras-style T-position, in which the male grasps the female between his pectoral fin and body. Rather than concentrating eggs, the fish scatter them among fine-leaved plants and along the glass, after which they fall. Large water changes with cooler water are the key trigger; the presence of other breeding species (such as Corydoras) may also stimulate spawning.

Egg & Fry Care

There is no parental care; eggs are simply released and fertilised. The eggs are very small (around 1 mm), transparent to slightly yellowish and sticky, and hatch after a few days. The newly hatched fry are extremely small and feed on the fine algae and biofilm present in the tank; finely crushed Spirulina flakes can supplement them.

Common Challenges

Getting the fish to spawn at all is the first difficulty, and the minute fry then require abundant micro-algae and biofilm to survive, so a mature, food-rich tank with excellent water quality is essential. The lack of parental care means eggs and fry are vulnerable to being eaten or to poor conditions.