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In this knowledge hub article, we are looking into greater detail at the different types of predatory fish available in the hobby and how to keep them.

What makes a fish a predator?

A predatory fish is defined as one that hunts or ambushes other animals for food. These can be fish that bite chunks out of their prey; such as members of the piranha family, or consume them whole; such as the red-tailed catfish. Predatory fish are distinct from scavenging species which, while they will consume other fish species, they will do so more opportunistically, feeding upon already dead fish or the remains of someone else’s meal.

Predatory fish groups

Below, we look at some of the more common groups of predatory fish that you may come across in your local specialist aquatic outlet.

Arowana & Gar

Both of these groups of fish are ancient and have lived on earth for aeons. Arowana are native to South America, Africa, Asia & Australasia, whilst gar species are only found in North and Central America.

Arowanas and gars are surface dwelling species and will spend the majority of their time in the search for prey, although they do go about this in quite different ways. Gars exhibit behaviour much more like an ambush predator, lying in wait for prey to come to them before striking. Arowanas are a much more active hunters, constantly on the move in search of prey both below the surface and above – it is not uncommon for arowana to leap from the river and snatch at birds, reptiles, amphibians and even small mammals from overhanging branches. Both these groups also grow very large, with arowana species attaining 120 cms and gars usually growing between 90 cm and 240 cm. Both families have large mouths and can consume very large prey for their size.

Asian Arowana (Scleropages formosus) are an endangered species with legal protection, so they require CITES certificates and microchips to be legal. Many hobbyists have been successful at weaning these species onto a floating pellet. The NT Labs - Pro-f Predator Floating Pellet provides a balanced diet to maintain healthy growth and encourage colour enhancement.

Freshwater Stingray

Freshwater stingray from the family Potamotrygon come from South America and are a beautiful oddball group of fish to keep for the more experienced keeper. Most species in the family grow very large (60 cm disc diameter or larger) and should only be considered if a large enough aquarium is feasible. They spend the majority of their time at the bottom of the aquarium. They are specialists in burying themselves in the substrate if they sense danger. Their eyes protrude from their bodies and their gills are positioned behind the eyes. This allows them to stay buried for extended periods of time with only their eyes and gills on show. For this reason it is imperative that they have a fine grade sand substrate in their aquarium.

As their name implies, this group of fish contain a venomous spine towards the tip of their tail. These spines are shed and replaced on a regular basis so exhibit caution when gravel cleaning as old spines might be buried in the substrate. This venomous spine is not used to attack prey, but rather as a defence mechanism. If threatened, the stingray will flick its tail towards the threat in an attempt to deliver a paralysing dose of neurotoxin. They use their strong muscles in their disc-like body to trap their prey, usually a mixture of molluscs, crustaceans, insects and small fish, underneath their body. They can then manoeuvre the prey towards their powerful jaws. The NT Labs - Pro-f Stingray Pellet provides a complete balanced diet for these amazing fish without the risk of transferring pathogens associated with feeding live foods.

Snakeheads & Bichir

These two families of fish look a little similar and share a few characteristics, but overall are very different animals. Snakeheads occur across Asia and Africa, with sizes ranging from 15 cm to over 100 cm. Both groups share a similar body shape and have very sharp, backwards facing teeth, so any prey caught in their mouths cannot escape. All species are predatory, and all but a few are also very aggressive. They can consume very large prey and should not live with anything smaller than half their size. In the aquarium, most species will accept frozen foods, and with enough persuasion, can sometimes be weaned onto dry pellet.

All snakehead species have a primitive lung that allows them to absorb oxygen from the air, for situations when the water lacks oxygen. These fish are also classified as “obligate air-breathers.”  In other words, although they have gills, they must have access to atmospheric air otherwise they will effectively suffocate.

Bichir (Polypterus) are a group of fish from Africa that on first glance share the similar snake-like body shape of snakeheads. They also have a primary lung that allows them to breath air. They are a bottom dwelling group and vary in size from 35 cm up to 100 cm. When bichir are young, they have external feather gills to help absorb oxygen from the water. Once they approach maturity, these external gills are lost. The popular rope fish/reed fish (Erpetoichthys calabaricus) is also a member of the bichir family. They have an extremely elongated body and have a propensity to escape, so make sure the aquarium is escape proof. They are easily weaned onto dry foods but naturally in the wild would predate on bottom dwelling fish and invertebrates.

African Tigerfish & Vampire Tetra

These two toothy species of predatory fish come from two different continents. Their scientific names have reference to dogs (Hydrocynus - Water Dog and Hydrolycus - Water Wolf). In all likelihood, this reference has been wrongly translated and is more in reference to the large impressive canine teeth they possess that they use to catch and hold on to their prey. African tigerfish, as their name would suggest, hail from the African continent and live throughout Central and Southern Africa.

Vampire Tetra come from South America and are well renowned for their huge canine teeth that are so large, their skulls have evolved to include special slots for the teeth to sit in when they close their mouth. Their prey, usually smaller fish, are impaled on these teeth and then swallowed whole.

Both these toothy fish groups can grow up to 100 cm in length and are only recommended for the very experienced fish keeper. They will often be very fussy with their food and will take great training to feed on frozen.

A miniature predator worth mentioning here is the bucktooth tetra (Exodon paradoxus) from South America. Not a true predator in the wild, they are a lepidophagous (scale-eating) species. In an aquarium environment, they have all the boisterousness of piranhas but stay relatively small at 10-12 cm in captivity. Great care is advised before adding these fish to any set-up - if they don’t receive enough food, they will be more likely to revert to their more instinctive way of feeding in your aquarium!

Eels & Knifefish

The name ‘eel’ applies to many different groups of fish. These include true eel species (moray eels) and eel-shaped fish like the electric eel and the spiny eel. There are few true eel species that live in freshwater, and most are actually brackish species that are mis-sold as freshwater. Spiny eels have an elongated body and live throughout Asia and Africa. They can be told apart from true eels by the presence of front pectoral fins and sturdy fin spines. Spiny eels can grow to between 15 cm – 80 cm and can usually be weaned onto frozen foods with ease.

Electric eels are not actually an eel at all but are a member of the knifefish family. Knifefish live throughout South America (Order Gymnotiformes), Africa and Asia (Family Notopteridae). They usually have a slender, elongated body and are generally predatory. The South American species, including the infamous electric eel, possess electrical organs. They use these specialised electrical pulses to seek out prey, communicate and navigate. The electric eel, capable of producing 800 volts, also use their electricity to stun their prey and defend themselves when threatened. Knifefish can be trained onto frozen food and some can even be weaned onto a good quality sinking predatory food such as NT Labs Pro-f Predatory Sinking.

Catfish

Catfish are a diverse group of fish, with over 4000 species across 34 families. In this article, we are most interested in the predatory species found in the families Pimelodidae and Bagridae.

Both species are characterised with long whiskers and some can grow in excess of 300 cm. Many species are bottom-dwelling and nocturnal, so expect many of these species to spend the day hiding. Popular smaller growing species include the angelic catfish (Pimelodus pictus) and the striped catfish (Mystus vittatus). Larger catfish that are sometimes offered for sale include the red-tailed catfish (Phractocephalus hemioliopterus), the tiger shovelnose (Pseudoplatystoma fasciatum) and the goonch catfish (Bagarius yarrelli). All these species grow to more than 120 cm and are usually only suitable for public aquarium-sized tanks or fishkeepers with indoor ponds! Catfish are one of the easiest groups of fish to wean onto dry pellets. The smaller species would greedily accept NT Labs Pro-f Catfish Pellet. For larger species, NT Labs Pro-f Predator Sinking Pellet provides a good quality staple diet.

What size aquarium do predatory fish need?

This is a very difficult question to answer as predatory species grow to a variety of final sizes. Some species offered for sale are only suitable for public aquaria sized tanks, whilst some remain small and manageable. As a guide, always aim for an aquarium as big as one can fit in the desired space and can afford. A minimum size of 120 cm x 45 cm x 45 cm (4’ x 1.5’ x 1.5’) would give a volume of just under 250 litres. This would not be considered a permanent home for some species mentioned (most species of Arowana for example would need an aquarium in excess of 600 litres long-term) but it would be considered a good starter size.

Most predatory fish require extra filtration to cope with their high-protein diets and messy feeding habits. External canister filters would almost always be recommended. For large predatory fish, it would be recommended to run double the amount required e.g. a 400-litre  aquarium would be best served by filters suitable for 800 litres. Adding a filter booster weekly to the water would help minimise any sudden water quality issues raised by heavy feeding. NT Labs Aquarium Filter Starter is a fantastic blend of live friendly bacteria which will quickly breakdown fish waste, preventing the build-up of toxic ammonia and nitrite. Large weekly water changes would also be recommended, remembering to add NT Labs Aquarium Tap Water Safe to remove any chlorine and chloramine from tap water.

Decorating a predatory aquarium

As previously mentioned, many predatory species of fish are nocturnal or crepuscular (meaning they are most active during night-time or twilight hours.) They appreciate hiding places in the forms of wood or rock caves to feel secure during daylight. Many would also appreciate heavy planting to dapple the aquarium lights. If the species considered are particularly active (e.g. tigerfish), keeping the decor sparse gives maximum swimming space. This will help prevent these very active, fast moving fish from hurting themselves. Stingrays appreciate as much floor swimming space but still like decor. Overhanging decor, or suspending it from the brace bars, allows for interesting designs whilst still providing ample room.

Predatory fish generally will not attack plants as it does not form part of their natural diet. A heavily planted aquarium would provide a perfect biotope for snakeheads or create ambush spaces for knifefish.

Final Thought

The vast majority of the fish we have discussed in this article are not fish to be kept by newcomers to our wonderful hobby. A great deal of time should be spent researching any of these species and consideration should be given to whether you can provide an adequate home based on the adult size and requirements of the species you are interested in. It’s also worth spending time getting to know the more specialist aquatic retailers in your area who will be able to provide you not only with all the advice needed to set-up your aquarium but will also be able to source these fish, settle them in and get them feeding for you.

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