Today I learned that an interesting characin had been imported, as the ‘Brazilian algae eater’, or to ichthyology, Apareiodon machrisi, from the clearwater Tocantins-Araguaia basin of north-eastern South America. This is a pretty and charismatic fish, with interesting and useful feeding behaviours, that grows to almost 6 centimetres or a bit more than 2 inches long, and rarely as large as 7 and a 1/2 centimetres, or about 3 inches. Sometimes it is called a round-nosed characin, which is a ‘posh word’ meaning the same thing as a tetra, for this animal is, in fact, a species of tetra. Sometimes this and related species are labelled as ‘darter characins’ although a number of different, often unrelated, and in many ways dissimilar fishes are called ‘darters’ in the English language, so I would rather be more precise. The similar La Plata algae eater from subtropical Paraguay, A. affinis, has appeared sporadically in the aquarium trade, as have certain other, related species. (It isn’t exactly clear how these fish are identified to a species level taxon, other than by their source at collection.) It does seem that in the aquarium trade, the genus Apareiodon are commonly labelled as ‘algae eaters’, a descriptor that is more commonly used for unrelated and geographically separated, but strikingly similar, fishes from Asia, the more familiar genus Crossocheilus that has long been a staple in our tropical aquariums.
Although they are unrelated to the Asian algae eaters, which are cyprinoids or carp, these characins or tetras do look quite similar to them, and share the same foraging behaviours. In different continents, different guilds of freshwater fishes have evolved in parallel to fill the same niches. In tropical to subtropical South American rivers, tetras are dominant in the same kinds of niches that are occupied by small carp species, in analogous Asian environments. Not surprisingly there have evolved similar ‘algae eaters’ among both the New World tetras and the Old World carp – small and slender, grazing algivorous fishes with underslung mouths, shaped by their parallel natural environments; they even have a similar stripe on their sides. Similar convergent evolution exists regarding land animals, explaining the unrelated kinds of vultures and anteaters, as well as the similarities of certain marsupial and placental mammals on different continents. Fish are not relegated to the past, as is implied by their false status as ‘lower vertebrates’; like mammals and birds, they evolve vibrantly to meet challenges. (If in doubt, notice that the Apareiodon sp. have the expected, fleshy, tetra-type apidose fin, behind the fore dorsal fin, which all carps lack.)
Specifically the Brazilian algae eater belongs to a clade among the tetras, that is called the scrapetooths; indeed, their anatomy is adapted to the demands of their grazing habits. Although have never seen anything peer reviewed about the diets of any Apareiodon species, they are reportedly omnivorous grazers, consuming different kinds of algae, pieces of vascular plant, and some benthic invertebrates. It has been suggested that their ingestion of any vascular plant tissues is accidental and incidental only, because it is reportedly limited to swallowing the periderm or ‘skin’ of the plant. They possess mobile, pedicellate upper teeth, and other craniodental traits, as a result of natural selection for this bottom grazing mode of feeding, There is no need to doubt that this species will consume algae effectively in the aquarium. As captive fishes they are unfussy as to which foods they accept, but they should be expected to eat from the bottom. They should also be housed in numbers because they are of a gregarious nature, and they seem completely peaceful in a community aquarium, The genus are mainly found in well oxygenated, flowing waters with a rocky substrate, from which they scrape their food, although I have also seem them reported to use areas with a sandy substrate also, though in the vicinity of rocks. Thus in the aquarium they should have access to both types of substrate, and be maintained in clear and well oxygenated water, that is slightly acidic to neutral with a tropical tank temperature, and ideally with some flow.
