Big-Spot Otocinclus (Otocinclus macrospilus) Care Guide
Otocinclus macrospilus is a tiny dwarf suckermouth catfish from the upper Amazon, a shy, shoaling algae grazer best kept in groups of six or more in mature tanks.
Compiled by Aquairi from published sources · Published · Updated
Overview
Otocinclus macrospilus is a dwarf suckermouth catfish of the family Loricariidae (subfamily Hypoptopomatinae), commonly called an "oto." It is one of the smallest aquarium loricariids, reaching only about 3.5 cm. It is frequently mislabelled in shops as O. affinis or O. vittatus.
Taxonomy
- Family: Loricariidae
- Scientific name: Otocinclus macrospilus
- Subfamily: Hypoptopomatinae
- Common synonyms: Macrospilus Oto
Habitat
The species is endemic to the upper Amazon, principally in Peru, with some records extending into Colombia and Ecuador. Otos live in shoals in small streams and well-oxygenated river margins, clinging to wood, stones and broad-leaved plants where they graze the surface film. The genus possesses an air-breathing duct, an adaptation to low-oxygen conditions.
Tank requirements
- Minimum tank volume: 60 L (16 gal)
- Adult size: 3-4 cm (1.2-1.6 in)
- Temperature: 22-26 °C (72-79 °F)
- pH: 6-7.5
- GH: 2-12 °dGH
- Group size: ≥6 individuals
- Lifespan: 8-12 years
Diet
The diet is algae-based, dominated by diatoms and aufwuchs (the film of algae and micro-organisms on submerged surfaces). It does best added to a mature, planted tank with a steady supply of soft green algae and biofilm; vegetable foods such as cucumber, courgette and spinach, plus algae wafers, supplement this. Small live or frozen foods are taken only sparingly.
Compatibility
The fish is very shy and retiring and is easily outcompeted for food, so it needs peaceful tankmates. It is a strongly social shoaler and should be kept in groups of at least six. It is plant-safe and combines well with small tetras and Corydoras.
Breeding
Spawning occurs in a T-position similar to Corydoras, with eggs scattered among plants and on the glass; the genus lays adhesive eggs and does not guard them. Large weekly water changes with cooler water appear to help trigger spawning.
Otocinclus macrospilus Breeding Guide
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.