Astronotus Crassipinnis - "Fat" Oscar
This article focuses Astronotus crassipinnis, a close relative to the famous Oscarfish Astronotus ocellatus. Crassipinnis was scientifically described by Heckel in 1840 and given the name Acara crassipinnis, but is now considered a member of the genus Astronotus. The name crassipinnis is derived from the Latin words crassus and pinna which means "fat" and "fish" respectively. The species name can occasionally be seen spelled crassipiNis instead of crassipiNNis.
Compared to the popular Oscar, very little is known about Crassipinnis and the information that do exist is often vague or conflicting. Hopefully, we will all be able to learn more about this interesting Astronotus in the future. It is still rare within the hobby and seldom exported from South America, and the regions in which it lives are far from thoroughly explored.
Astronotus crassipinnis habitat
Just like its famous relative, Astronotus crassipinnis lives in tropical South American rivers. Its geographical range does however seem to differ somewhat from that of the Oscarfish because Astronotus crassipinnis has been reported from no more than five different countries: Argentina, Bolivia, Brazil, Paraguay, and Peru. Astronotus ocellatus has a similar distribution, but has also been reported from Colombia, French Guiana, Uruguay, and Venezuela. Interestingly enough, Astronotus ocellatus does not seem to be present in Bolivia. The South American river systems do however need to be more thoroughly explored before anyone can know for sure the exact limits of their respective ranges.
(Since Astronotus ocellatus is a popular food and aquarium fish, it has now been introduced by man to other parts of the world as well, including USA, Puerto Rico, Guam, Cote d'Ivoire, and Singapore, but those countries are not within its native range.)
Examples of locations where Astronotus crassipinnis has been found are Rio Paraguay, Villa Maria and Caisara, Rio Guaporé close to Matogrosso, Rio Negro, and Rio Branco. The species inhabits the Bolivian parts of the Amazon and the Rio Madre de Dios drainage in Peru, plus the Rio Paraná basin in the Rio Paraguay drainage in Paraguay and Brazil.
Size and appearance
While the largest scientifically measured Astronotus ocellatus was 45.7 cm in length, the largest scientifically measured Astronotus crassipinnis was much smaller, only 24.0 cm. (A fish measuring 45.7 cm is almost 18 in long, while 24.0 cm equals 9.44 in.)
Kullander (1986) distinguished Astronotus crassipinnis from Astronotus ocellatus on colour pattern and meristics. (Meristics is an area of ichthyology which relates to counting quantitive features of fish, e.g. the number of fins or scales.) Both species are known to exhibit a variable bar pattern, but Crassipinnis is overall darker than Oscar and its anteriormost light vertical bar is located more anterior than on an Oscarfish. The area where you would find the first light bar on an Oscar is instead decorated with two more or less well-separated dark vertical bars on a Crassipinnis. In addition to this, Crassipinnis does not have the two eye-spots along the base of its dorsal fin that adorns the western Amazonian Oscar.
Astronotus crassipinnis has not been evaluated by the IUCN Red List of Threatened Species. It is a popular food fish within its native region, but quite resilient to harvesting since its minimum population doubling time is within the 1.4-4.4 range.
Keeping Astronotus crassipinnis in aquariums
To begin with, it is important to have - or be prepared to eventually get - a large aquarium. It is true that the largest scientifically measured Crassipinnis was 24 cm / 9.4 in, but this doesn't mean that it must be impossible for this species to grow any larger - there might be even larger specimens lurking in South America unknown to science. Since we still know so little about Astronotus crassipinnis it is best to play it safe and assume that it might one day become as large as an Oscarfish. Also keep in mind that the comfortable life in a well-kept aquarium can make some species grow much larger than they would in the wild.
Try to mimic the South American rivers that Crassipinnis hail from when you decorate the aquarium. You don't have to make an identical copy, but including mangrove roots or similar is a good idea since roots will provide your fish with dark and sheltered spots for resting. Live plants floating on the surface will also be highly appreciated and make your fish feel more at home. Planted plants can also be used, but your Crassipinnis may uproot them so ideally go for robust species.
Since Crassipinnis is quite a messy eater and produces a lot of waste, powerful mechanical and biological filtration is typically necessary even in large and under-stocked aquariums. Even with powerful filtration, it is important to keep an eye on the water quality.
Crassipinnis needs soft water and acidic water with a pH of 6.5-6.9. The species live in tropical South American rivers and the recommended water temperature in the aquarium is 21-28°C / 70-83°F. If you decide to keep the water in the upper part of the range, don't forget that warm water holds less oxygen than cooler water. If your filtration system isn't enough to keep the oxygen level up you can get one or several air stones.