Shane's World Right Arrow Catfishology Right Arrow The Eel-tail banjo catfish Platystacus cotylephorus • Article © Ingo Seidel, uploaded September 13, 2008

Translation by Kate McKay

Introduction
In the huge order of the catfish species (Siluriformes) we find a great number of different reproductive strategies which to a great extent display adaptability to their natural living conditions. Apart from the species who do not look after their brood at all, the spectrum of behaviour types ranges from open brooding/incubation and cave brooding which far and away the majority of catfish practice, as far as mouth brooders in the family of Ariidae (Sea catfish) and Bagridae (Spine catfish) and a small group of South American Armoured catfish (Loricariidae) who carry their clutch around with them in lips which form into a mouth pocket. Hardly any strategy for the care of young is unutilised somewhere. As well as foam nest building, which we find in the armoured catfish (sub family Callichthyinae) there are even species, among the Spine catfish of the family Bagriidae, who nourish their offspring with an 'egg food' or secretion which they excrete from their skin. Even brood parasitism is known within this order in the family of squeaker or featherbeard catfish (Mochokiidae).

Platystacus cotylephorus`
1. Dark variant of the Whip catfish (Platystacus cotylephorus) with speckled tail

Platystacus cotylephorus
2. Dark brown Whip catfish with brightly coloured tail

Platystacus cotylephorus
3. There is also a reddish brown P. cotylephorus with a bright coloured tail

Platystacus cotylephorus
4. Dark brown specimen with light brown front

A very unusual form of brood care is found in a few representatives of the Family Aspredinidae in the so called Banjo (English) or Frying pan (German) catfish whose distribution is restricted to the continent of South America. This group hitherto only known to aquarists through a few of the species, is at the moment divided into two sub families Bunocephalinae and Aspredinidae. The latter consists of four only species which are distributed between three genera Aspredo, Aspredinichthys and Platystacus. It is known that the females of these fish carry their young with them under their abdomen. The species are otherwise extremely similar in appearance and possess an extremely long tail-'stalk' which has earned them the name of 'Whip’ (German) or ‘Eel-Tail’ (English) catfish' The anal fin is also remarkably long and is supported by more than 50 rays.

The Aspredinidae have a very wide distribution in the north and east of South America and occur there in the lower reaches of the rivers near the river mouths (into the sea) as well as along the coast. And so the Platystacus cotylephorus which we examine here is more closely is distributed in Brazil, French-Guyana, Guyana, Surinam and Tobago as well as in Venezuela. It is a matter therefore of fish which can comfortably tolerate strong variations in the salinity of the water. Often we would encounter all four species in the same biotope which is most remarkable in view of their apparently almost identical way of life.

Platystacus cotylephorus habitat
5. The Whip catfish are indigenous to the estuary regions of the rivers of South America. Shown here is the Essequibo river in Guyana.

Platystacus cotylephorus habitat
6. As an adaptation to the strong fluctuations in water levels many of the plants of the estuaries have stilt-like roots.

The differentiation between the sexes in the adults is relatively simple in P. cotylephorus. The males are easily distinguished from the females by the thread like lengthening on the first ray of the dorsal fin. This distinguishing feature between the sexes was apparently unknown in the scientific field for a long time since a related species Aspredinichthys filamentosus has this feature to thank for its species name.

Female Platystacus cotylephorus
7. Female of P. cotylephorus

Male Platystacus cotylephorus
8. Males have a flag like elongated dorsal fin.

Care of the Whip in the aquarium
The care of the elegant whip catfish in the aquarium gives little problem. I was able to observe among other fishkeepers that these fish can be kept for years in pure fresh water without any addition of salt at all. Since I lack exact measurements from the wild I naturally have great difficulty in giving you recommendations as to salinity. The broad distribution of these creatures along the North West coast of South America shows that the fish obviously can swim unharmed through the saltwater of the Atlantic Ocean to reach neighbouring river systems. Experiences from the Ornamental fish Wholesale trade have shown that the fish thrive well with the addition of 2g/litre of salt. The water temperature should be between 25 to 29°C. While dry food preparations will be accepted only after a short period of acclimatisation, a diet of live and frozen food is recommended. The various insect larvae Daphnia, brineshrimp, Mysis or also other shrimps will be gladly eaten. Whip Catfish despite their size of a maximum of 32-35 cm are totally peaceful aquarium fish, although I would like to warn against allowing them to be kept with any fish which are too small and which could possibly be regarded as food. Any fish possibly kept as companions should not be able to do the relatively defenceless whip catfish any harm, which would normally be a concern especially with all territorial fish. From time to time these fish swim with snakelike movements through open water, however, most of the time they spend on the bottom, appearing only occasionally to dig themselves under the substrate, a behaviour which is unlike many other relatives in the Aspredinidae. Burial it seems is their preferred mode of rest and they only seldomly look for hiding places. I have not so far been able to detect any sign of aggressive behaviour within the species, which also means that there is no reason why these fish couldn't be kept in larger numbers. Admittedly, one should in any case offer these fish appropriate space.

A few observations on reproduction
Sands (1984) in his five part monograph on catfish was the first to show to the world the whip catfish which carried its eggs under its abdomen. The illustrated specimen had obviously been caught and exported while caring for its brood. Sands had apparently discovered the nursing creature in a shop and documented the incident. Unfortunately he gives only sparse information on the species of catfish.

Since that time, whenever I saw a Platystacus in a shop, I always looked at it more closely than usual and closely inspected the abdomen of imported fish. I hoped one day to be lucky enough as to be able to observe this unbelievable brooding behaviour. Finally it came to pass that I came across a job in an ornamental fish Wholesalers and from then on of course came into contact with these fish more often. And in fact one Thursday morning my hopes were fulfilled, when yet another consignment of roughly 35 Whips arrived from Macapa, Brazil. Among the 15 or 20 cm specimens there was one which had four gigantic eggs of about 4mm hanging by threads from under its abdomen.  It was a female which was not difficult to identify because of the comparatively short dorsal fin. Unfortunately for me the timing of the arrival of this import was totally inconvenient. I had a weekend appointment for which I had to set off that afternoon. Not knowing whether there would be anything left of the eggs on my return or whether the water conditions were anywhere near right for the development of the eggs, I took the female home with me and transferred her to a, luckily, empty 50 x 30 x 30 cm tank (water temp 28 C; ph 7.5; electrical conductivity 890 microS/cm). The eggs appeared to be well developed already so I was afraid that the young would hatch during my absence and would possibly be eaten by the female. So, I put an extremely large helping of white insect larvae in the tank which the female was supposed to eat instead of her young. So much for planning. When I got home on the Sunday, of course the first thing I did was look at the Platystacus tank and I was in luck. True, three of the four eggs had disappeared and no young were to be seen in the tank. However, one of the eggs was still hanging from its mother's abdomen and seemed to have developed further as the dark embryo was clearly recognisable through the eggshell. Now I had the chance to record this event in photographs and it was clearly not one moment too soon as two days later the egg had disappeared from the abdomen. Luckily after a few searches of the floor of the tank I found it and transferred it to a small hanging compartment with mesh walls. After a further 24 hours an already well developed fry with yolk sac attached hatched out of the egg. Already it must have been about 18mm. After 2 or 3 days the yolk sac was exhausted and the 'baby' began to eat at only 22mm in length. As a starter food I gave him Artemia nauplii and fine grindal worms. He seemed to love both. Although he had at first seemed to thrive very well and in the days following gained in length very well, he died unexpectedly after roughly two weeks. I am not able to say what the cause was. I suppose that it was either the wrong nutrition or a lack of salt in the water. Even though this story did not of course have a 'Happy Ending', I was nevertheless overjoyed to have had the opportunity to observe this very interesting occurrence.

Platystacus cotylephorus`
9. Female Whip catfish with an egg under the abdomen.

Platystacus cotylephorus
10. On closer examination many more "attachment structures" can be seen on the sides of the abdomen.

Platystacus cotylephorus
11. Shortly before hatching the embryo can be seen through the egg shell in every detail.

Platystacus cotylephorus`
12. Freshly hatched yolk-sac larvae already at least 22mm long.

Platystacus cotylephorus
13. P. cotylephorus young, roughly 10 days old.

Until now P. cotylephorus has not to my knowledge successfully been bred in the aquarium. To do this is one of the projects I would like to tackle in the not too distant future. But that only seems to me to make sense if I can first of all clear up the question of what living conditions these creatures breed under in the wild. The fact that they only breed once a year in a particular place (I was able to get this information from Le Bail et al. 2000) supports the theory that they require special conditions for breeding. Whether a drop or an increase in salinity of the water triggers spawning or some completely different factor, I do not know. I hope that at some time I will some across someone who can give me this information. Any information on this subject would be gratefully received by myself as well as all involved in the catfish hobby.

Scientific Information
Although the Whip has been known for a long time (the species Aspredo aspredo was described as early as 1758 by Linnaeus and Playstacus cotylephorus in 1794 by Bloch), there are today still many unanswered questions about these interesting fish. Bloch (1794) established the genus Platystacus (meaning 'Flat-lovers') initially for four species, of which only P. cotylephorus, the 'Plate carrier' has remained in the genus today. He had already noticed some remarkable 'suckling nipples' or 'little plates' on the abdomen of the largest of the specimens available to him, and so he writes: "When one looks at these nipples with a magnifying glass one finds that they are flattened, and for the most part stand on a stalk. Not only the whole underside of the abdomen but also the lower side of the abdominal fin is covered with them. Some of these nipples lie quite flat to the skin, others on short stalks and still others on longer ones. They resemble the plates of the cuttlefish". From the fact that in the second specimen examined by Bloch the 'little plates' only lay flat and that in both of the other specimens were not in evidence at all, Bloch concludes erroneously: "From this it seems probable to me that the purpose of these nipples is for attachment during mating and therefore they are not yet developed in the younger specimens".

In reality these plates, which are also called cotylephorum, represent the device by which the developing embryos attach themselves, Wetzel, Wourms & Friel (1997) examined these more closely and explained that a convergent development had taken place between “skin brooders” of a certain salt water fish of the genus Solenostomus (Ghost Pipefish) from the symbiosis with sea needles. In these fish however the cotylephorum are only found on the abdominal fins which are merged together. In P. platystacus they consist of a stalk of about 1.6mm long and 0.2 mm wide which seems to develop on the female on the epidermis on the abdomen and on the fins ending in a membrane which eventually covers the egg shell. Between 3 and 5 blood vessels pass through the stalk as well as the membrane. How the eggs reach their point of attachment has not been explained up till now. Burgess (1989) maintains that in the spawning season spongy tentacles develop on the abdomen of the female. After spawning they supposedly lower themselves onto the clutch, whereby the eggs are attached to the egg stalks. Unfortunately Burgess does not offer any proof or source for these observations.

Pterobunocephalus depressus
14. The banjo catfish of the genus Pterobunocephalus,
which also have very long tails, carry their young under their abdomen.
Here P. depressus from Peru.

Another matter of controversy is the reason and purpose of the 'suspension' of the eggs on these stalks. Sands conjectures that the Whip catfish females carry the eggs around with them so that they can take the eggs away from the brackish waters of the lower reaches of the rivers further upstream to areas of fresh water where the young can grow in safety. This hitherto unverified hypothesis appears however to be very improbable, since there are numerous species of catfish who undertake 'spawning journeys' in order to spawn in the upper reaches. Why then should the Platystacus transport their eggs the whole way there attached under the abdomen when they could much more easily and safely lay them there as others do? The favoured explanation at the moment for the arranging of eggs on stalks under the abdomen is the necessity to ensure a sufficient supply of oxygen to the embryos. Presumably this is an adaptation to the oxygen poor conditions of muddy brackish regions. Because the eggs are arranged loosely on stalks under the abdomen, there is a constant flow of fresh water over them and because of the blood supply to the egg shells and stalks further provision of oxygen to the eggs is made possible.

As you can see there remains much to observe and explore about these fish which is why they simply fascinate me. There is however one thing I have not yet mentioned. There is in fact also a small group of freshwater banjo catfish and it has only been discovered very recently that they have a similar reproductive biology. Friel (Internet, Tree of Life) observes that the females of Pterobunocephalus also carry their eggs under their abdomen. True, this genus hangs its eggs directly under the abdomen and not on stalks. The genus consists at this time of only the two species P. depressus and P. dolichurus. These are relatively small banjo catfish of 10 cm length at the most with a similarly extremely long tail spine. In the last few months as well as P. depressus, two more new species have been imported to Germany from Peru. It remains to be seen whether these fish will prove to be breedable in aquarium conditions. To try this will be one of my future projects. Should I be lucky in this I will certainly report on it here at some time.

Bibliography

  • Bloch, M. E. (1794): Naturgeschichte der ausländischen Fische. Achter Theil. J. Moreno & Co., Berlin. 486 S.
  • Burgess, W. E. (1989): An atlas of freshwater and marine catfishes: a preliminary survey of the Siluriformis. TFH publications, Neptune City, 784 S.
  • Le Bail, P.-Y., P. Keith & P. Planquette (2000): Atlas des Poissons d´eau douce de Guyane. Tome 2 — Fascicule II, Siluriformes. Muséum National d´Histoire Naturelle, Paris.
  • Sands, D. D. (1984): Catfishes of the World, Volume Four, Aspredinidae, Doradidae & Loricariidae. Dunure Publications, Scotland.
  • Wetzel, J., J. P. Wourms & J. Friel (1997): Comperative morphology of cotylephores in Platystacus and Solenostomus: modifications of the integument for egg attachment in skin-brooding fishes. Env. Biol. of Fishes, 50: 13-25.
  • Wyman, J. (1859): On some unusual modes of gestation. Amer. J. Sci., 77: 5-13.


There is further information on this species on the Cat-eLog page.

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