There is a myth that fish will only grow according to their tank size. Unfortunately this is not true and there are many fish which grow too large for standard aquariums. Collectively, these are known as the 'Tank Busters'
Every fish keeper is aware of the myth that a fish will only grow depending on the size of its environment, and too many fish keepers still believe this. The simple fact is that a fish that naturally grows to 45cm will not stop at 10cm, regardless of the size of its environment.
Such fish, if kept in aquaria that are too small, may not quite reach their full size, and may grow in a distorted manner, but they will still grow. It is important then, for the welfare of the fish, that it is given a suitably sized environment. Big fish need big tanks, and that should be the final word.
How big is big
Selecting a suitably sized tank to house big fish depends not only on the fish's eventual size, but also on its character and attributes. A sedentary catfish, which might spend much of its natural life either waiting in chosen spots for the opportunity to feed, or resting while digesting a meal, will not need lots of swimming space. These types of fish can be kept in aquaria quite comfortably around three times the fishes length.
Other species are more active, and require swimming room and hiding spots in order to become comfortable and feel safe in their surroundings. Fish like silver sharks (up to 30cm) and silver dollars (up to 15-20cm), both of which are shoaling species and should be kept in groups, will need a tank around 150cm (5 foot) when fully grown. This tank is around 5-6 times the length of the fully-grown fish and will house a shoal of up to six of each with room for a few large pieces of bogwood. A 5-foot tank might house a couple of groups of these peaceful shoaling fish; the story is slightly different when it comes to the more territorial fish
Making your mark
Many of the Central American Cichlids are ideal candidates for big fish aquaria, sporting characters and intelligence that make them a joy to keep. Unfortunately, part of their endearing character is due to their territorial tendencies.
These large cichlids, which include the well known Oscars, Jack Dempsey's and Jaguar Cichlids are a difficult bunch to mix together and two big fish which do not like each others company will often result in the weaker, or less aggressive fish, being bullied and stressed to the point of no return. Fish that have been raised together tend to fare better, but to keep these fish you are looking towards a very big tank with very few fish, and a long-term commitment to their care.
On the plus side, many of the larger Synodontis and Suckermouth catfish such as the common Plec can be mixed with these large cichlids without many problems. The catfish will need hiding spots and dark areas to rest, so a few large pieces of bog-wood are ideal. Rocks should be used with care as the larger cichlids do have a tendency to move objects around, presenting a possible safety hazard.
Not all of the big specimen fish are aggressive however, and there are plenty of big fish that can be kept together as individuals. Some of the larger cichlids are peaceful enough to be kept in a community and these include the Severum Heros severus
(20cm), the colourful Quetzal Cichlid Theraps synspilus
(30cm), and the Triangle Cichlid Uaru amphiacanthoides
(25cm) These fish can also be kept with the larger shoaling barbs, Silver Sharks, and Silver Dollars. To create a community however, you will need to look at tanks in the 180cm (6 foot) or more range. The Giant Gourami (Osphronemus goramy
) is another large peaceful fish that can be kept with other large fish, but this particular 'giant' can grow to 70cm in the wild, and 50-60cm in aquariums.
Many of the brackish fish species can reach quite a significant size and make an interesting community of fish in large tanks, especially when the tank is aquascaped to mimic a mangrove, with lots of twisted roots and a sandy substrate. Monos, Scats and Archerfish will all reach 25-30cm and can be mixed with silver or orange Chromide Cichlids, whilst Shark Catfish (Arius sp.) will scavenge around the substrate and depending on the species, can reach up to 50cm.
Avoid at all costs
There are a few fish that have characters and sizes that make them wholly unsuitable for all but the biggest tanks. The best example of this is the midwater-swimming pangassius, sometimes called 'Shark Catfish', a common name that is shared with the silver Arius sp. mentioned above.
Pangassius live in large open rivers in the wild and can reach sizes in excess of 120cm (four foot), although they usually only reach around 30cm in aquariums. Pangassius are particularly nervous fish and will dart and flee at the slightest disturbance, unfortunately this means they often damage themselves in the aquarium and are really only suited to public aquaria size tanks of around 300cm (10 foot) or more.
A fish that requires an even bigger tank when fully grown is the Redtail Catfish that will grow to sizes in excess of 100cm. Similar sizes of tank are required for Arowanas, which are unfortunately still available as juveniles in many shops. Whilst it is possible to keep some species in large tanks, the most common type, the Silver Arowana (Osteoglossum bicirrhosum) will grow up to 100cm in aquariums, and even bigger in the wild.
One more fish to avoid is the Black Shark (Labeo chrysophekadion), which will grow to 60cm and depending on the individual, may aggressively bully virtually any fish.
Black Sharks, Pangassius, Arowanas, and Redtail Catfish are simply too large or troublesome to be kept in home aquariums and no responsible shop should be selling these fish to the general public. If you find such fish fascinating, then look them up, read about them, see them at a public aquarium, but don't cause them to suffer by keeping them in tanks that are too small.
Feeding big fish
Apart from the size of the aquarium, the biggest mistake many fish keepers make when keeping large fish, is too feed them too frequently. Although some of the more active barbs, silver sharks, and silver dollars will benefit from daily feeding, for most large fish, daily feeding could eventually bring an early death.
Most aquarium fish will eat far more than they need to, and many big fish, most notably the Oscars and other cichlids will learn to 'beg' for food from their owners, even when they don't require nutrition.
As with any fish, to feed big fish properly you need to look at their natural diets. Fish like Silver Dollars and Uaru's are mainly herbivorous, feeding on vegetation, fruits and seeds. This suggests that they are grazers and need regular feeds high in vegetable matter, as well as a little meat based foods. Larger cichlids like Oscars however, are predators and feed almost exclusively on meaty foods, namely other fish.
Meat eaters generally eat large amounts of high protein foods, but only every few days or so. If they are fed such foods on a daily basis they will accumulate dangerous fatty deposits and produce more waste, causing long-term damage to the fishes health and decreasing water quality or demanding more powerful filtration.
Variety is the key to feeding; almost all big fish will take proprietary pellet foods as a basic diet but this should be matched with foods tailor made to the fishes diet. For semi-herbivorous fish this could include plant matter, vegetables (shelled peas, lettuce, cucumber) or algae based dried foods. For carnivores there are a number of meaty foods available from most fish shops including shrimps, cockles, and mussels, as well as specially designed dried foods. Feeding predatory species on live 'feeder' fish is unacceptable on ethical grounds, and will not provide the correct nutrition or essential vitamins and minerals found in dried foods.