Catfish of the Month Right Arrow November 2002


Eel-tail Banjo Catfish, Banded Banjo, Båndet Banjomalle (Denmark), Maulbruetender Hexenwels (Germany), Mottled Eel-tail Banjo Catfish, Whiptail Banjo Catfish - Platystacus cotylephorus   Bloch, 1794

Article © Julian Dignall, uploaded November 01, 2002.

Eel tailed Banjo Catfish are uncommonly but reliably occurring imports. Chief among imports of this small but fascinating group of catfish is the Mottled Eel-Tail Banjo Catfish,Platystacus cotylephorus. The fish, at least for a Banjo Catfish (or Asprenidid), displays attractive patterning and an intriguing shape. Striking features include the random mottling colouration which - especially on mature males - gives the fish the appearance of rusting flaky paint work and a very long, curling, eel tail. In rare fits of exercise, the rays of the anal fin - which runs along the entire underside of this tail - become erect, giving the fish a menacing profile.

Raised parallel lines run along the fishes tail and this feature is most useful in distinguishing this species from the similar Aspredo aspredo. It is perhaps the variance of colouration both between individuals and the sexes in Platystacus which has led to several attempts to synonymize the two genera. Aspredo does not exhibit these rows of tubercules along the tail (you can just see them in the picture below).

Platystacus cotylephorus

P. cotylephorus can be found in coastal areas of north eastern South American rivers that spill into the Atlantic - so is best considered a brackish water fish. It is so adaptable however that it can easily be accommodated in a more traditional amazon style aquarium, though a central requirement from its wild habitat is a soft or light substrate within which it can bury itself. This master of disguise can convincingly disappear from view in such a tank but will not always do so, especially when many other fish are present above it in the water column.

Platystacus cotylephporusReproduction is this catfishes main talking point. Females are sometimes (although very rarely) imported with eggs still attached to the underbelly - see picture to the right. These eggs are attached by minute hair-like threads. Whether these are purely for mechanical attachment or provide some form of nutrient or gas exchange remains to be fully explored. More recently it has been suggested that oxygen is supplied to the eggs via these threads during the term of attachment. Perhaps this would allow the female to continue to bury in the muddy, oxygen starved substrate of a silt laden river mouth. Here the river is wide and flows at a slow pace, allowing some silt to drop out of the water column and provide a perfect home for burying fish.

Other, earlier theories suggest that the threads merely provide a method of keeping the eggs attached to the female as she shields them during migration upstream into purer freshwater. These Banjo catfish are the most adept swimmers in their family and a migratory lifecycle is not unfeasible. However, whether the females migrate into freshwaters with eggs or the young fish do so on their own later, is unreported.

The young hatch and are replicas of their parents at under a week old and less than 8mm long. Microworms appear the best food at this stage. Nothing regarding fully captive reproduction is recorded; solely the hatching of eggs attached to females at import.


Copyright information for the images used in this article can be found on the species' full Cat-eLog page.

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