Among mammals and many other taxonomic groups, body size is positively correlated with the species’ geographic range. Think elephants on their long journeys seeking water, bears hunting over vast lands, or whales migrating from Hawaii to Alaska. The same can be said for at least some groups of fish and has been demonstrated in Catostomids and Centrarchids where larger bodies confer larger home ranges (Pyron, 1999). From our armchairs, we can speculate the same could be true among some South American Characins, and within this very small sample, these elongate Characins all inhabit wide ranges throughout the vast river basins and networks of tributaries of South America.
Widespread throughout the Rio Negro and Orinoco basins in Brazil and northern Peru, Iguanodectes adujai is a blackwater species inhabiting smaller tributary channels. Reaching a maximum length of about 3 inches, these “Slender Tetras” are long and skinny with red eyes that lead into a long red stripe down their sides, yellow pigmentation on their undersides, and a dark caudal blotch. Typically found among dense vegetation and tree roots, they are best kept in planted setups that simulate blackwaters with soft substrate, leaf litter, driftwood, and plants rooted in the substrate, attached to hardscape, and floating. This species is a bit combative, and males will develop a bit of a pecking order with a dominant male showing the brightest coloration. They should be kept in groups of at least 8 to prevent overt intraspecific aggression. Otherwise, they are great options for blackwater community setups and may be housed alongside similarly-sized Characins, peaceful Catfish, and small to medium-sized and non-predatory Cichlids. Interestingly enough, their color and patterning are superficially similar to the Red Striped Tetra, Hemigrammus rubrostriatus. Opportunistic and omnivorous, they eat small invertebrates, filamentous algae, and fallen fruit in the wild and should be provided varied diets in captivity with a large live and frozen component and high-quality dried products with some green matter. Tank waters are best maintained with temperatures between 69°F and 77°F, a pH between 5.0 to 7.5, and a hardness up to 90 ppm.
A gorgeous acrobat, Abramites hypselonotus headstands across the Amazon and Orinoco in Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Venezuela, and Paraguay. Known for their manner of swimming head down and tail up, these “High Backed Headstanders” reach up to 5.5 inches in length, have long pointed bodies with a pronounced dorsal hump, and black marbling over light-colored bodies. Hardy and able to thrive in a variety of habitat types stretched over such a vast range, this species isn’t terribly particular when it comes to tank setups. They do best in tanks with sand or smooth gravel substrate, driftwood or spiderwood, decent filtration, some water flow, and hardy plants with tough leaves, while soft-leaved plants may be eaten. Another omnivorous forager, they eat a variety of benthic items and should be fed live and frozen invertebrates, fruits and veggies, and high-quality sinking pellets. These robust, and slightly nippy schooling Characins do best in groups of 6 or more and may be kept alongside peaceful South American Cichlids, Characins of a similar size and temperament, and Catfish. Graceful and inquisitive, they shine in carefully curated setups with their quirky behavior. Not too particular with regards to water conditions, they may be kept in waters with temperatures of 68°F to 86°F, a pH between 5.5 and 7.5, and a hardness up to 268 ppm.