Axelrod's Bloodfin Tetra

Geographic Origin and Biotope: Rio Negro basin in Brazil and Orinoco in Venezuela/Colombia. Inhabits dark forest streams (blackwater) and flooded forests (Igapó) rich in plant organic matter.

Taxonomy and Morphology: Axelrod's Bloodfin (Brittanichthys axelrodi). Dwarf characin (max 3 cm / 1.2 inches). It is one of the fish with the most pronounced male dimorphism: they possess a complex, hook-shaped (or spine-like) caudal gland protruding from the base of the fin.

Social Behavior: Peaceful, but often frightened. A school of at least 10-12 specimens is essential. Males engage in frequent "displays" puffing their fins to intimidate each other or to court females.

Coloration and Sexual Dimorphism: Olive-gray to translucent body. The name "bloodfin" comes from the blood-red bases of the dorsal, anal and caudal fins. Females lack the complex glandular hook (caudal hook) typical of males.

Aquarium Setup: Minimum 60 cm (24 inches). A very strict blackwater biotope is ideal: fine silica sand, twisted branches, a dense carpet of dry leaves (Catappa or Oak) to release humic acids. Very weak light and floating plants are mandatory.

Diet and Feeding: Micropredators. They often disdain industrial dry feeds at first. Wean them with vinegar eels, brine shrimp nauplii, copepods (Cyclops) and live or frozen daphnia to ensure long-term health.

Water Quality: Fragile and delicate. Does not tolerate nitrogenous pollutants or hard waters at all. Needs a very acidic pH (5.0-6.5) and minimum conductivity (GH 1-5). Well-matured water and regular changes with osmosis.

Compatibility and Tankmates: Easily overwhelmed by frantic companions. Insert only with other placid nano-characins (e.g. Tucanoichthys, dwarf Nannostomus), pygmy Corydoras and Otocinclus.

Aquarium Reproduction: The exact role of the males' caudal hook is a mystery, but presumably serves to hold the female. Spawning occurs by releasing eggs randomly in very dark waters. Raising is very difficult due to the smallness of the fry.

Risks and Diseases: Most specimens are wild-caught. They heavily suffer the stress of transport and adaptation to tap water: rigorous quarantine recommended.