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The Banded Knife Fish, Gymnotus carapo, features both in my copy of the venerable Innes book, and in the Braz Walker pocket book. Both authors make similar statements regarding this fish, which is a suitable candidate for the experienced 'big fish' keeper looking for something challenging, unusual and imposing to look at.

The range of this fish is considerable in the wild, from Guatemala, through Guyana, into the Amazon region, and this means of course that the fish prefers soft, slightly acidic water. However, it is unbelievably tough, according to both authors, though as Braz Walker succinctly and eloquently states: "Withstands abuse and overcrowding amazingly, which is no excuse for trying". It should, therefore, be adaptable to a wide range of water conditions, though salt should be avoided as it is an exclusively freshwater fish.

The Gymnotids are unusual anatomically, in that all of the internal organs are very strongly compressed forwards in the body, to the extent that the urogential and anal vents are almost behind the head. The part of the body (including the head) forward of the long, rippling anal fin accounts for only 15% of the total length of the fish, and it is in this restricted space that it packs its internal organs. Like the Knife Fishes of the Notopteridae, this is a tailless fish, relying exclusively upon its anal fin for propulsion. Unlike the Notopterids, however, which belong to a completely different Order, Gymnotus carapo and the other, much more rarely encountered members of the Family Gymnotidae, have no dorsal. The pelvic fins are also absent, the pelvic girdle having atrophied over millions of years of evolution, and the only paired fins present are the pectorals. Altogether, a most unusual body design, but one which allows the fish to swim backwards with the same finesse with which it propels itself in the more usual forward direction.

Another unusual feature of the fish, and one which accounts for a fair amount of its toughness, is its ability to supplement gill respiration by breathing atmospheric air. I am not currently in a position to say whether this is done via the gut, as in Corydoras catfishes, or via a supplementary respiratory organ such as that found in the Labyrinth Fishes, but breathe atmospheric air it can, and thus it needs an aquarium design facilitating this.

Gymnotus carapo inhabits reed and submerged root tangles in small creeks during the daytime, becoming more active and moving into larger water bodies during twylight hours. It can navigate in dark conditions, thanks to it being one of those weakly electric fishes that generate an electric field for sensory and navigation purposes, and consequently, it is advised NOT to house one of these fishes anywhere near a hi-fi system or a PC, whose electric fields would stress the fish. An aquarium for this fish should, ideally, be furnished with bogwood root tangles mimicking those found in its natural habitat, along with thickets of reed-shaped plants such as Giant Vallisneria. Initially, while adapting to the aquarium, it will spend much time hiding in these, but becomes bolder as it learns that daytime is the more likely time for the appearance of food in the aquarium. Like numerous other crepuscular fishes, this species should be adapted gradually to a daytime feeding régime via the 'lights out' feeding method. Lighting should be subdued, and additional shade provided by large floating plants such as the Water Lettuce, Pistia stratiotes. Temperature range is reported as 21°C to 28°C.

The hardiness of this fish means that it will forgive occasional management lapses or the odd aquarium catastrophe, and survive remarkably well in circumstances that would see off many other fishes, but given its appetite, and its size, high-quality filtration should be considered mandatory, so that its toughness is not unduly pressed into service. However, the species has several negative attributes, which I shall now come to.

First, the fish reaches 2 feet in length. And, instead of being stunted by a small aquarium, will simply outgrow it. Therefore large quarters are called for right from the word 'go'. A 6 foot aquarium should be considered as a baseline setup for this fish.

Second, the fish is viciously aggressive toward other fishes. Including other members of its own species. Which means it is destined to be the lone occupant of a species aquarium. If mistakenly housed with other fishes, it will rapidly turn the aquarium into a species aquarium by eating the other inmates. Live fishes form a considerable proportion of its diet in the wild, and for long-term maintenance, sacrifice of other live fishes will be periodically required, making this an ethically problematic species for several aquarists. Earthworms will be devoured ravenously, as will carefully prepared and scraped beef heart and other meaty foods. The bad news is that keeping more than one specimen together is likely to result in disaster, as the species has, lamentably, a well-developed cannibalistic streak that is also present in many of its more rarely encountered relatives. Adult specimens, with jutting lower jaws, even look vicious. A large adult is also capable of administering a painful and severe bite to an aquarist's arm, should the aquarist fail to be watchful during aquarium maintenance, which means that this is NOT a fish to be kept in an environment where children can gain access to it unsupervised. The fish has a large mouth even as a juvenile, and adults possess an air of menace in their appearance that is not even remotely deceptive: this is one of those fishes whose mean looks signal a mean temperament. In the wild, this is an efficient 'stealth predator', relying upon dim lighting, its electric navigation and sensory capability, and a well-developed ability to launch a lightning attack seemingly from nowhere, to provide it with a bountiful living. One of those "Don't mess with me" fishes that attracts a handful of dedicated (and affluent!) enthusiasts.

Because of its aggressive nature, and its complete intolerance of other aquarium occupants, except in the colossal setup of a large public aquarium or aquatic biology laboratory, the species has not been reported as having bred in captivity, an exercise that would be impractical in a home aquarium setup. Most other fish species will breathe a sigh of relief upon hearing this! As a result, this is a fish that will principally appeal to the 'oddball specialist' - I sense that both Shinigami and Toirtis will take a liking to it, but I would caution anyone else to give this fish a wide berth unless they are prepared to live with its size, bad temper and large appetite. For those who are prepared to expend the effort, however, this curiosity has a certain appeal: a strange fish with a strange body shape, an unusual anatomy, atmospheric respiration and electric navigation thrown in for good measure. One for the specialist, but one that, despite its minus points (which are brought into sharp relief if unwisely housed with other fishes!), has a peculiar appeal, dare I say, even a certain charm?



Panda Catfish fan and keeper/breeder since Christmas 2002

Great article i love reading yours there packed full of info great job. Glad to see you frequent the boards more often.


==fish1