Shane's World Right Arrow Reproduction Right Arrow Triggering reproduction with the Walking Catfish (Clarias batrachus) • Article © Wolfgang Ros, uploaded September 29, 2007

Love at first sight?
Love at first sight?

Introduction
I already had reported the spawning of my Walking Catfish pair here and in Datz 7/2004 ("Successful spawning of the Walking Catfish in the aquarium", p. 12-15). At that time and without my intervention they catfish spawned four times in a period of only five months. Then their interest in reproduction suddenly disappeared for some time and didn't wake again as several months passed.

What had happened? Was the spawning season for the animals, at least in my aquarium, at the end? Were there otherwise any magic dates? The couple was still in top form: Male, like female, remained e avaricious eaters and did not show any deviations in their behaviour at all. Also unchanged was their bond as a pair. The initial parameters for another spawning seemed to me to be favourable, but obviously there was a lack of certain something to trigger again the courting that previously was so often observed and initiated another reproduction event.

Patience pays off
Certainly I still had in mind the breeding reports, primarily concerning species of Corydoras, in which it is recommended that the aquarist imitates the rainy season largely because the spawning season of the animals falls in this season. Therefore at first I started to exchange a third of the tank contents for such cool water that the previous water temperature of about 25 dropped to 22°Celsius. However the result was rather disappointing. Although the Walking Catfishes started again to swim behind one and another more often, I didn't observe the typical courting before spawning, much less the real reproduction. At least the supply of cool fresh water alone could not be the decisive factor.

Male piebald Walking Catfish Female albino Walking Catfish
Male piebald Walking Catfish Female albino Walking Catfish

An alternative discussed in an Internet catfish forum, namely just reducing in the water level about ten centimetres under maintenance of the usual temperature of 24° degrees Celsius was also fruitless.

Further attempts of which I brought respectively additional factors into the game and varied them, finally provided the desired result - my Walking Catfish pair spawned once more: In the morning at eight o'clock the female after many hours of courting laid eggs; a number of further matings which dragged on up to the early afternoon followed over about six hours. At the first and nearing the end of each spawning act only about 100 eggs were laid; within the hours between this, however, it was at least 500 or more.

During this spawning about 500 eggs are laid
During this spawning about 500 eggs are laid

With on average about 200 eggs per mating and at least four matings per hour, this 40cm long female therefore dropped almost 5000 eggs! This is remarkable, as the female had only grown by about two centimetres in the length over the three-quarter-year since she produced a total of around 1000 eggs. Though the animal had strongly grown in girth over this time and seemed obviously more massive than before, this indicates that eggs must have formed constantly over the intervening time. However they would not have been laid without the started changes, but I will come back to that later.

In the meantime after another three (approximately monthly) successful tests of the same "recipe", I have arrived at the conclusion that reproduction specifically of Walking Catfish can be triggered in relatively short intervals of few weeks if the following framework of conditions are created or changed gradually. They simulate the natural environmental changes at large in the native countries of these animals, especially during the monsoons with their long continually strong rains and resulting flooding.

All factors combined lead to spawning in inundated areas like paddy-fields, in which the water (due to the lower levels) quickly warms to 28 or even 30°C. There the mature animals, which previously lived in very different waters, are presented with a feeding area which is rich at insect larvae, worms and so on and also where their offspring will also find food plentiful in addition to finding shelter more readily. The experiences described here can presumably also be used for other Clarias species, if not even transfer to some other catfish families or at least motivate the reader to ponder a little in this direction.

Male viewed from above Female viewed from above
Male viewed from above Female viewed from above

General conditions
At first the tank size must be correct of course: If one wants to spawn a pair of Walking Catfish then the aquarium should hold at least 500 litres! Then one must have sexually mature animals. Even if my Clarias batrachus pair spawned for the first time at a length of almost 30 centimetres, the beginning of sexual maturity might lie considerably under this mark, at about 20 centimetres. Either you safely have a pair already at this size or you have to find such a pair for yourself from a group of either four or five animals, and then you have to work out where the extras are.

If one is not able to distinguish the sexes due to their appearance - the female is more corpulent and more massive than the male even out with the spawning season - one can observe the differences in animals of about 20 centimetres due to the form of their genital papilla. The male's is longer and tapered to the end - like a wizard's hat, the female's however is short, stubby and oval.

Male viewed from above Female viewed from above
Male viewed from above Female viewed from above

Barbels to barbels
"Barbels to barbels": If you have a bonded pair, both partners will show the feeling of togetherness

A harmonious couple will be looking to keep close proximity to each other. The animals conspicuously seek physical contact. They mostly rest in such a way so as they keep in touch via the fins or barbels.

Preparations
Initially the animals are kept for about three months at a water temperature of at most 23°C. This temperature might be rather at the lower limit but still should be still unproblematic for most tankmates. Avoiding a high water temperature for a relatively long time will make the sensitivity of the catfishes correspondingly increase in terms of reacting quickly with a first spawning at a later warming and change of other substantial factors.

At this time one should refrain from offering living food and confine foods to cichlid sticks, tablets, "Forelli" and similar. The animals also should get food only once a day and then only so much food so that they are always still hungry. The usual water changes of about 25 per cent have to be carried out like always in regular distances.

Important changes
Following these twelve weeks the animals should then be fed particularly well and alternatively with their favourite live food like tubifex or earthworms! If one only offer frozen food even with bigger specimen provided red mosquito larvae are suited quite well. In any case you should feed daily now three times.

As an aside, it appears that what the animals favour eating the most depends on which food was given to them in their youth. So Clarias batrachus keepers confirmed that animals raised in aquaria to which exclusively prepared food had been fed from the first months of life soon ate one of those again particularly greedily. This food - whether food tablets, sturgeon pellets or cichlid sticks - they are able to "recognize" even after a long time. In such a way, captive raised Walking Catfish clearly prefer prepared food even over live food which they have never bben fed until it is offered as a trial later in life.

Parallel to the change in feedign regime, a generous 50% water change is carried out within the next few days. The newly added cooler water can even lead to another, merely short-term, reduction in the temperature of about one to two degrees. Feigning an inundated area is made possible by using a good product for water preparation and only filling the aquarium up again by about 85 per cent of the total volume and lowered again by about ten per cent on the day after the water change. Thereafetr the water level is only 45 centimetres in a 60 centimetre high aquarium. Anyway, if the aquarium is only 50 centimetres high, then a lowering at five centimetres each in these two steps to about 40 centimetres is recommended. The filter output should lie above the surface so that the water can audibly flow well into the tank from above. To increase the water current at the surface, a further internal filter should be placed if necessary to increase.

Male viewed from above Female viewed from above
Male Clarias batrachus eating an earthworm Female eating "Forelli"

After mother nature has cooled the water with the rains and we've analogously dropped the temperature to the described 21 to 22°Celsius, it's then time to, in the end, increase the temperature to 28°C gradually within the next three days. Due to this warming, the resulting more active way of life accompanying with that the increasing appetite of the animals grows, they should be further fed extensively with their favourite food.

Male viewed from above Female viewed from above
Pair in a tank with lowered water level and increased temperature, the female seems to develop more and more eggs each day.

First spawning preparations
Due to being offered rich live food and especially induced by fresh water, the lowered water level and then the increased temperature, the female soon gets visibly gravid and (preferably in with the lights turned off), the pair will start courting. An important prerequisite for this may be the changed water supply mechanism: The water pouring from filters outlets above the water line creates pearls of oxygen pearls as it enters the water and creates noises akin to those made by monsoon rain. The perception of these noises also should have signaling effect for the animals.

Courting Courting
Courting of my Walking Catfish pair in the evening (with light turned off) "Nuzzling" is also part of courting

Many a reader may smile now but this effect still can be strengthened by a background noise like loud music for one to two hours a day; these sounds in connection with the stronger flow are apparently an indication to the catfishes that the rainy season with its monsoon thunderstorms and eventual bursting of riverbanks is imminent or has already started.

Both partners intially start with digging activities which are clearly different from those observed when the animals rummage the bottom for food: They are concentrated on a certain location, namely the spawning site and are mostly accompanied by wafting movements of the pectoral and tail fins which become particularly obvious when the male is digging the shallow pit.

Digging the spawning pit Digging the spawning pit
Both partners of the Walking Catfish pair are digging the pit.

Digging for food however - except naturally for the place underneath the usual feeding spot - is carried out more or less aimlessly throughout the entire tank, here the head and the first body third or so is drilled into the sand or gravel ground.

Digging for food Digging for food
By comparision, this is just diggging for food.

If the pit is dug, the first matings follow but no eggs are delivered yet. From time to time the animals take breaks of several hours up to a few days which are interrupted by intense courting and more matings again and again. These "fake" matings might accelerate the formation of further eggs.

The first matings are dry runs The first matings are dry runs
The first matings are dry runs without producing any eggs.

The end game!
As soon as eggs in a sufficient number have developed and the female shows herself once more ready for mating, the spawn finally is ejected after further looping entabglemtns, contortions and embraces. The eggs adhere to the substrate and to avoid a loss of them to fungus, especially at the high water temperature, it is advisable to add an anti-fungal product. In addition, it's not a bad idea to adjust the heater down by one or two degrees.

Fewer eggs are produced at first Fewer eggs are produced at first
Fewer eggs are produced at first

Even with such precautions a larger percentage of eggs succum to fungus particularly after about fifteen hours. Due to the profusion of the fungussed eggs - from the estiamged five thousand eggs, only about a tenth hatched and therefore over four and a half thousand threatened to ruin the water - this creates water cloudiness which only can be resolved with very good filtration. I warn against a water change in this phase. Due to the disturbances connected with that, it can be that the male does not return to the spawning site and stops the care of the offspring, the clutch is then ruthlessly exposed to potential predators. Already a couple of Botia lohachata or Chromobotia macracanthus were able to unerringly track down and eat the few young fish hatched out.

The very high contingent of fungused eggs produced by my pair could be explained by the fact the spotted male was developed from hybridization and its fertiligy restricted. The number of the eggs from which young fish can develop even after fertilization then would already be very low, however this is an assumption. Under circumstances such as the change of other water parameters or use of another anti-fungus agent product has brought better results; further improvement however this requires additional tests.

Some of the large number of eggs at the bottom of the shallow pit The first eggs after 12 hours become fungused
Some of the large number of eggs at the bottom of the shallow pit The first eggs after 12 hours become fungused

It appears to be certain that the eggs of Clarias batrachus are generally more susceptable to fungus. A British aquarist reported to me of a coincidental spawning of his pair of semi albino Walking Catfish; there a large portion of the eggs also were also fungussed after twenty hours and only a few fry hatched out. With an experimental attempt carried out 1990 in Indonesia to transport the eggs of Walking Catfishes (here it can only have been the wild form) into aquaria and to let them develop in captivity, separated from the parent animals, there was explicit mention of the fungal infection of the jelly-like mass which surrounds the eggs. In an abstract given at FishBase/LarvalBase it is recommended to dip the eggs immediately after spawning for five minutes in a one per cent sodium sulphite solution, to rinse them three times in tap water and only then move them to a separate hatchery tank. So fungus can be avoided. However, this procedure may be left to these persons, who actually want to raise young animals in a larger number and who are already prepared, from the outset, to have this responsibility later.

Flexible females
It becomes apparent that the female is able to control the number of the eggs released per spawning event. Only this can explain that the very same animal will deliver "only" a few hundred to at most a thousand eggs and then only four weeks later however can expel a couple of thousand eggs. Presumably not only the intervals play here a role between the spawning procedures after which a longer pause leads to a higher number as described in the case with five thousand eggs at the beginning. Even if such a high number of eggs can theoretically be expelled in the course of a day because they are already available, it is not automatically inevitable that the female must deliver the maximum yeild. In fact further circumstances like water-level or temperature and the other fish kept together with the Walking Catfish are of importance. If the water values are not optimal for the female, if she feels disturbed by tankmates or looks at other fish as possible predators, then she will only deliver a lower number of eggs, possibly merely the "minimum number" of eggs, whereas in good conditions she will lay all eggs during the spwanings of a given day.

Some of the large number of eggs at the bottom of the shallow pit The first eggs after 12 hours become fungused
Here the female feels very secure - about five thousand eggs in total are laid during the day.

Water level raised again, then it was again lowered, after two more changes the pair spawned again
Water level raised again, then it was again lowered, after two more changes the pair spawned again.

Some notes
If pairs do not come into reproductive mood despite starting the described changes it is highly recommended to further best feeding and to keep the temperature set last of 28°C for four to five days with additional water changes (a third) at which the water level rise and fall by about 15 per cent.

As recently as with the hatching of the fry the female returns a few times to the edge of the nest. It comes to rapid movements of both animals there. The male tries to push the female away immediately by "rebelling" vertically in front of his partner, taking a threatening attitude with an open mouth and beating with the tail fin against the body of the female. However, since the aggressiveness of the female sharply heightens at the same time, it can be that especially when pursuing other fish, she strays unintentionally into the immediate nest area whose guarding is the sole job of the male. He will then fend off the female with hectic, extremely fast swimming movements. These are carried out with such ferocity and speed that, especially larger fish, can sustain injuries to the fins and barbels mainly from collisions with tank decor.

Female spawning copiously
Trouble brewing.

However the keeper does not have to worry much about this behaviour. Clarias batrachus, like many catfishes, is a hardy and robust species that is seldom affected by illnesses. Injuries to the fins will heal completely after few weeks. Even damaged and almost entirely lost barbels can regenerate in a similar timeframe. The fish are more delicate to injuries affecting the skin. These can become infected quickly and heal comparatively slowly even with the best water care and with the use of a special additive product designed to protect the fish's mucous layer.

If the couple has stopped the care of the brood after a few days, the temperature can be gradually lowered to about 24°Celsius again. After a break of some weeks one can keep this value as the exit temperature following another change of the factors stimulating reproduction.

Sexually mature but younger animals can more frequently reproduce in comparison with fully-grown specimen and do so with about four week less of a break between spawning events; though the total number of eggs per spawning event with older females is higher - about double. Since my pair are only two years old and at 40 centimetres, not quite fully-grown, in the end attainable numbers from eight to then thousand eggs should be realistic.

So, what is the maximum size of the animals in the aquarium? At least the albino and piebald specimens that are offered now and then in the ornamental fish trade usually don't get much bigger than 40 centimetres in size and according to feedback from other Walking Catfish keepers even after many years do not exceed the 45 centimetres mark (in one case however there is reported a specimen of 52 centimetres). Therefore, these larger catfish are different from the predatory catfishes of South America who nearly all get bigger than one can keep (at least in the long run) in a one and a half up to two metres long tank.

Full grown pair Full grown pair
Full grown Clarias batrachus pair - both partner are swimming and resting mostly together

Summary
It is likely that Walking Catfish that are spawned as food fish in ponds in warmer climates will simultaneously spawn as a large group. It is probable that all of the sexually mature females will spawn, triggered only by using the "natural" methods described here. An artificially initiated mating in the conventional meaning by means of intra-muscular injection of hormones with the female is not inevitably required with Clarias batrachus if one wants to spawn them at a particular pre-determined time.

Surely it is not advisable to persuade the animals to continually spawning by constant change of the factors influencing their reproduction. Spawning too often provoked in this way may, in the long run, weaken them. Appropriate use of these triggers makes sense even if adult pairs have not reproduced yet at otherwise optimal conditions.

DATZThis article was first published in April 2006 in the German publication: "Die Aquarien und Terrarienzeitschrift" (Datz) 59 (4): 33-37. Our thanks apply here for the Datz editorship and their editor-in-chief, Rainer Stawikowski, who gave us kind permission to publish this article on PlanetCatfish. Published here is the original text; only some photos have been updated and new ones added. © Copyright text and photos, Datz.


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

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