Otocinclus affinis, commonly known as the Otocinclus catfish or dwarf suckermouth catfish, is a small freshwater fish belonging to the family Loricariidae. These catfish are popular among aquarium enthusiasts for their algae-eating habits and peaceful nature. Here is some information about Otocinclus affinis:

1. Size: Otocinclus affinis is a small fish, typically reaching a maximum size of around 1.5 to 2 inches (3.8 to 5 cm) in length.

2. Appearance: They have a streamlined body with a sucker-like mouth that helps them attach to surfaces. The body is typically translucent with a mottled pattern. The abdomen area is often more rounded in females.

3. Habitat: Native to South America, Otocinclus affinis is found in slow-moving rivers and streams in countries such as Brazil, Colombia, and Peru. They are commonly found in areas with dense vegetation.

4. Behavior: Otocinclus catfish are peaceful and shoaling fish, meaning they prefer to be kept in groups. Keeping them in groups helps reduce stress and promotes more natural behavior. They are known for their algae-eating habits, making them valuable in aquariums for controlling algae growth.

5. Tank Requirements:

   • Tank Size: A minimum tank size of 10 gallons is recommended for a small group of Otocinclus affinis.
   • Water Parameters: They thrive in well-oxygenated water with a pH range of 6.0 to 7.5 and a temperature range of 72 to 79°F (22 to 26°C).
   • Tank Setup: Provide plenty of hiding places and plants in the aquarium, as they appreciate cover. Driftwood and rocks can also be included.

6. Diet: Otocinclus catfish are primarily herbivores, and their diet in the aquarium should include algae and biofilm. If algae levels are insufficient, supplemental feeding with algae wafers or blanched vegetables like zucchini or cucumber is recommended.

7. Compatibility: They are generally peaceful and can be kept with other peaceful fish species. However, avoid keeping them with larger, aggressive fish that may harass or prey on them.

8. Breeding: Breeding Otocinclus catfish in captivity can be challenging. They are egg layers, and reproducing their natural habitat conditions in an aquarium can be complex.

It's essential to note that these fish are sensitive to water quality, so regular water changes and maintenance are crucial for their well-being.