When most people think of aquariums, they think of a tank populated with placid, colorful fish swimming around in small groups. And for good reason – the most popular style of aquarium in both the freshwater and marine hobby is the so-called “community” tank, which contains an assortment of peaceful, compatible species living together in harmony. But as long as people have been keeping fish, there have been those hobbyists who gravitate towards species of a very different sort – the predators, fish at the top of the food chain which have adapted to hunt down and capture prey of all sorts. In almost every aquatic ecosystem in the world, there are fish which specialize in preying on other fish or invertebrates, and many of these have developed amazing strategies to do so. From mouths full of razor sharp teeth to remarkable camouflage that can render a fish almost invisible, many predatory fish have a certain appeal which makes them enduringly popular in the aquarium hobby. Not all species are suitable for the average aquarium owner, however, and many require specialized care or grow far too large for all but the largest aquariums to contain. With that in mind, let’s take a look at some of the most popular predators for both freshwater aquariums.
In the freshwater hobby, there are a huge variety of predatory species that are regularly available. Probably the most well-known of these is the Piranha – a complex of species hailing from tropical South America and the source of many fearsome myths. While they certainly live up to their reputation in terms of looks – with their unmistakable rows of serrated teeth – Piranha are often rather shy in the aquarium. Another popular group of freshwater predators in the same order as the Piranha are often referred to as freshwater “barracuda”. Although they have no relation to the super-fast marine predator of the same name, they look similar, with elongated bodies and mouths full of sharp teeth. Another close relative, often called the sabretooth barracuda or vampire tetra, also originates in the Amazon basin where it skewers smaller fish with two massive teeth in its lower jaw. All of the freshwater “barracuda” species can be challenging to keep, and will often only eat live fish.
Many of the popular freshwater predators are species that grow to huge proportions – and quickly. The Arowana, a group of 6 species representing an ancient family of fish, all grow well over 24” in size as adults, and their active nature and tendency to jump have given them a well-deserved reputation as “tankbusters”. Similarly, most species of gar grow to at least 30”, with the largest – the alligator gar (Atracosteus spatula) reaching 8 feet or more in length as adults! Although they lack the prominent teeth of some of the other freshwater predators, there are many catfish species in the aquarium hobby which are voracious predators as well. Probably the two best known of these – the Tiger Shovelnose (Pseudoplatystoma fasciatum) and the Redtail Catfish (Phractocephalus hemioliopterus) both originate from the Amazon in South America where they are popular food fish. Although they may look cute as 2” babies at the local fish store, both species grow very quickly and are known to eat almost anything in their aquariums – including rocks, airstones, even heaters. Although smaller in size than many of its cousins, the gulper catfish (Asterphysus batrachus) lives up to its name by being able to consume fish even bigger than it is – so almost any potential tankmates are at risk.
Not all predators are “monster fish” however – there are quite a few species suitable for medium or even small aquariums. One of these is the pikehead gourami or crocodile fish (Luciocephalus aura), an unusual relative of the gouramis which originates from Malaysia and Indonesia. This fish is a lightning fast ambush predator, and preys on smaller fish in its native habitat. With an adult size of only 6-8”, the pikehead would be at home in a medium-sized aquarium. Another fascinating ambush predator for the smaller aquarium is the Amazon leaf fish (Monocirrhus polyacanthus), which mimic dead leaves so closely that it is often difficult to spot them in an aquarium. These fish have mouths that open extremely wide, creating a suction which pulls in any small fish unlucky enough to get too close. There are even a few species of highly predatory freshwater puffers, like the Congo puffer (Tetraodon miurus) and Hairy puffer (Pao baileyi) which stay relatively small and don’t require a large amount of tank space.
Aquatic predators can make fascinating aquarium fish if their needs are met, but keep in mind that nearly all of them require specialized care and many species grow large. As always, research your fish (especially their adult size!) before bringing them home to ensure they will thrive in your care.