K's Kreature Feature is an educational presentation at our monthly general staff meetings here at the Two Oceans Aquarium, but it’s only right that we extend the knowledge and fun to our readers here on our website. Every month Education Operations Co-ordinator Katja Laingui presents a different animal that we have here at the Aquarium and tells our colleagues more about it. Usually she uncovers some rather interesting facts about the various animals she researches. She also makes sure to entertain her co-workers…
There is a great order of vertebrates called Perciformes or "perch-like fishes". The perciform fishes are the most numerous group of vertebrates on the planet, with more than 40% of all fish belonging to this group. There are more than 10 000 species within this order and species are represented in almost all aquatic habitats. Many of the fish at the Two Oceans Aquarium are Perciformes, but this article is all about the Cape and Natal moony.
Both of these moonies belong to the genus Monodactylus, which means "one finger". This name comes from the fact that the moonies can have very long dorsal and anal fins, making them look like fingers. There are a total of four species of moonies within the "finger fish" genus. Apart from the Cape and Natal moony, there is also a dwarf and African moony. The African Moony can span 30cm from the tip of its dorsal fin to the tip of its anal fin, making it taller than it is long.
The Cape moony (Monodactylus falciformis) is also called the full moony or the oval moony. It is found along our east coast as well as further up the east coast of Africa. There are also populations around Madagascar and in Asia. The Cape moony is oceanodromous, which is a fancy word for an animal that spends its whole life in the ocean. It does, however, also live in estuaries and lagoons, which suggests that it can tolerate slight variations in salinity.
The man who described the Cape moony surely has one of the longest names ever. Bernard-Germain-Étienne de La Ville-sur-Illon, comte de Lacépède was a naturalist and Freemason. You can also just call him La Cépède. He seemed to be a big deal, as he was a member of the Institute of France, a fellow of the Royal Society and a member of the Royal Swedish Academy of Sciences. He also has a street in Paris, a bay in Australia and a very cool looking gecko in Mauritius, named after him. Based on his portrait, it also looks like he was a very chilled dude.
The Natal moony (Monodactylus argenteus) is a much more widely distributed fish. It also has way more common names, probably because it lives in many different waters. The Natal moony is also called the silver moony, round moony, silver batfish, diamond fish, butter fish and butter bream. The meaning of its species name, argenteus, is silver, so silver moony is the most accurate.
The Natal moony is pelagic-neritic. If a fish is pelagic it swims in neither the deep sea nor the surface of the water - it lives somewhere in between. Neritic, on the other hand, is the area of water that is relatively shallow and occurs closer to the coast, before the drop off from the continental shelf into deep ocean. So in short, the Natal moony prefers depths that are not too deep or too shallow and waters that are close to the coastline. Interestingly, it can occasionally be found in freshwater.
The man who described the Natal moony is a bit of a legend. Anyone with a biology background will know this man: Carl Linnaeus, or as he was known later in his life, Carl von Linné. He is the father of our current taxonomic system, the binomial nomenclature. This is the way we classify all living things in this planet, by its genus and species name. There actually is a sloth called Linnaeus’ two-toed sloth with the scientific name of Choloepus didactylus. He was a big deal.
Linnaeus was almost not called Linnaeus, because back in the day the Swedes still followed the primary patronymic naming system, something that the Icelandic still do. Carl Linnaeus was almost Carl Nilsson, because his father’s name was Nils. But Nils decided that he would like his family to have a family name and changed his own to Linnaeus before Carl was born. Another interesting fact about Carl Linnaeus is that he was an advocate for the advantages of mothers breastfeeding their own children. Back in the day, especially amongst the gentry, women could not possibly stoop as low as feeding their own babies, so they used wet nurses instead. Carl obviously knew the health benefits of breastmilk from your own mother and tried to create awareness around that topic.
Luckily for all of the moonies, they are not on the radar of any major fisheries. They are, however, quite popular in the home aquarium industry and are caught for that purpose. The populations seem healthy, with the Cape moony classified as ‘Least Concern’ by the IUCN.
You can check out both of our moony species in the I&J Ocean Exhibit. Hot tip: look for them more towards the surface water, as they like to shoal higher up.