The Natural History of an Aquarium Legend
Article Written By Aquatic Specialist: Gary Rolfe.
There are thousands of species of freshwater tropical fish in today’s aquarium hobby, but in my opinion, there has always been one that has stood alone. One species of fish that has become the icon of aquaculture, royalty of the fish world and king of the aquarium. The Discus.
Strictly speaking that is not 100% true, there are actually 3 species of Discus. All are very closely related, in fact they are all in the same genus, Symphysodon. Ichthyologists have agreed that we have Symphysodon aequifasciatus and Symphysodon discus, but there is still debate over the name of the third species. It may be Symphysodon tarzoo, or it may be Symphysodon haraldi, for the purpose of this article it doesn’t really matter. We’ll just use ‘Discus’ to cover all three species respectively.
Discus are native to the Amazon river in South America. There are many different biotopes within the Amazon system, Discus inhabit the lowland lakes, tributaries and floodplains. These are the areas of slow moving water and heavy vegetation. Heavy amounts of vegetation decaying in the water releases tanins and stains the water brown. This type of water is often referred to as blackwater.
Blackwater is naturally very soft and relatively acidic. Soft water by nature has a low mineral content. Minerals in the water neutralise acids, resisting change to the water’s pH, this is known as the water’s buffering capacity. Because of blackwater’s lower ability to buffer against pH changes, maintaining the correct water conditions for Discus in an aquarium has always been more of a challenge when compared to keeping harder water species. But with a combination of water softening technology and a relative acclimatisation of captive bred Discus to harder water, this challenge is now well within the grasp of most experienced fishkeepers.
Discus are perfectly adapted to their natural environment. Like the more common Angelfish (Pterophyllum scalare) Discus have a laterally compressed body shape, hence their common name. Why would this be beneficial to the Discus? Well, every year during the wet season, the Amazon’s water level rises significantly causing it to break it’s banks and flood the surrounding forest. The discus’ thin shape allows it to slip and glide through the mass of tangled roots and branches as the Amazon’s fish inhabit the flooded forest. This seasonal environment reveals exciting new foraging grounds for the grazing Discus.
Discus are omnivorous fish, the stomach contents of wild caught Discus have been examined by ichthyologists, revealing both plant and animal matter. Their digestive system is relatively short for their size suggesting that they pick at small food items, but on a regular basis. Their feeding behaviour in the aquarium has also confirmed this and experienced Discus keepers will feed their Discus small items, such as granules, at least 2-3 times per day. This allows Discus to fully digest their food with minimal waste and none of the health problems associated with over-feeding.
A wild Discus’ natural prey consist of small crustaceans, worms and even small fish, even though they are not the most adept predators in the river! It’s hard to say whether they are actively eating plants or if they are just ingested as a result of grazing on invertebrates, but the nutrition gained from these plants should also play a part in their aquarium diet. Luckily, granules high in both animal and plant protein, specifically engineered to meet the nutritional needs of Discus are now available.
Discus are a member of the Cichlidae family, the cichlids. Cichlids are renowned amongst freshwater fish for their excellent parental care. Discus are no different, in fact they take parental care one stage further and have a rather unusual method for raising their babies. Before the eggs hatch, the parents will attentively fan the eggs with oxygen rich water and guard them from predators. Once hatched the Discus parents will start producing a nourishing mucus through their skin that the babies will feed on for a few weeks. This mucus has been compared to mammalian milk as it has been shown to contain valuable antibodies that boost their babies’ immune systems.
I’ve always been a believer in understanding the origins of your pet fish in order to give them the best environment possible. This is never truer than with Discus, create the right physiological conditions and provide a good quality diet and you can achieve something special within the fishkeeping hobby. You can keep the king of aquarium, the Discus.