Article © Ingo Seidel, uploaded June 28, 2010.

All images by the author

In September 2006 I travelled to Surinam for the first time with my friend Peter Debold, who has often accompanied before on my travels within South America. Because two other friends had called off at the last minute, this time we were forced to try to investigate the fish fauna of the river Surinam on our own. All things considered we were very satisfied with the outcome of the trip. We succeeded in finding a fish we had dreamed of catching for years and we managed to bring back a good number of them to Germany. Since then I have managed to breed the Boeseman's Catfish (Corydoras boesemani) in the aquarium and have already been able to pass the first youngsters on to friends. I wanted therefore to take the opportunity as early as possible to report here on this interesting catfish species.

Our Journey
Surinam is the smallest and least populated country in the continent of South America; it is situated in the North East of the continent between the neighbouring countries of French Guyana, Brazil and Guyana. The population is an eclectic mix of people with different origins. Until 1975, the country was a Dutch colony which is why Dutch is still spoken here and it is not unusual to find Europeans. We discovered that Surinam is one of the most pleasant countries to travel in. Even in the remotest areas we were treated by the locals as one of their own. Often in many other countries we become a village attraction - half the village gathers around us while we attempt to catch fish but this never happened in Surinam. As well as this, we were able to make ourselves understood in English almost everywhere, another great advantage over other South American countries. The climate differs considerably from that in other parts of South America too. There are two dry seasons per year; a smaller one in the months of February and March and a somewhat longer one from August to September. The best time to travel for catching fish is therefore September to November.

We had thoroughly planned our trip in advance. We had applied for a visa from the Surinam Embassy in Amsterdam and had rented a house in Paramaribo via the internet for our stay. We had booked two trips to the interior of the country. The main travel organiser for such trips is a company called Mets in Paramaribo which has a representative in Switzerland. Since nearly the entire population of Surinam lives on the coast and there are next to no roads into the interior, we also booked a flight to the upper reaches of the Surinam River where the home of the Corydoras boesemani lies. The typical habitat of the species is found near Awarradam, on the Gran Rio River, a tributary of the Surinam. This is where we set out to reach on the 1st of September 2006 onboard a small plane. We had previously acquired a licence from the Ministry of Agriculture and Fishing for our trip and had rented a boat with a boatman for two days from Mets.

The flight to the interior on a small plane lasted about an hour. We had very soon left behind the populated strips of coastline and were flying over the dense rainforest which still covers 80% of the land here. During our flight though, the negative effects of civilisation could be clearly seen in places, for example the giant bauxite mines which we could easily spot from the plane, or the van Blommestein-Meer, a gigantic reservoir which dams the middle of the Surinam river. However we finally reached the small landing strip on the Gran Rio River, the destination of our journey. From here we would be taken by boat half an hour upstream to the Awarradam Camp which is on an island in the middle of the river near the rapids of the same name.

The Corydoras of the Surinam River
Five species of cory have been identified up till now from the system of the Surinam. Before the construction of the enormous dam the Dutch carried out large collections of fish in many areas in order to catalogue the fish fauna of Surinam. As a result of this, numerous new species were described. Nijssen (1970) lists for the lower and middle reaches of the river the species Corydoras octocirrhus (=Corydoras geoffroy), C. aeneus and C. punctatus. Evidence of the latter two species was also occasionally found in the upper reaches. Admittedly they are not found there so often now. From the upper reaches the two species Corydoras boesemani and Corydoras nanus were also described. This is C. boesemani’s main area of habitat while C. nanus has its typical home near Awarradam. However, in all of the collections in this area only two specimens were found, whereas there often seemed to be more found in the Lucie River (upper Corantijin River System). We had hoped then to find the species there, but little did we know that we would be lucky enough to find them here.

1. Semi adult C. punctatus in the aquarium	2. We searched in vain for C. nanus (Gran Rio)
3. C. boesemani (Upper Suriname River)	4. C. aeneus is also supposed to be found in the upper reaches of the Surinam,here is a specimen from the lower reaches.

Ecology of the catfish in this region
For two days we travelled up and down the Gran Rio River and looked for catfish. We came across Corydoras boesemani again and again. However we almost always saw only small groups of the fish and their behaviour often makes catching them very laborious. In little tributaries, called creeks, the fish disappeared like lightning among the leaves which in most places completely cover the ground. Not only that but it is not much fun fishing in these creeks. Since the creeks are mostly slow flowing the river bed was very muddy so we typically sunk quite deep when actually in the water. On the bank of the Gran Rio, shoals of these fish prefer places where the branches reach into the water. It was just as difficult to catch even a single fish here. Finally we went from sand bank to sand bank, getting out of the boat to look out for bigger swarms. In the end we had a lucky strike. At two sandbanks about half an hour apart we came across largish groups consisting of hundreds of juveniles. As a rule the fish were roughly 12-15mm long. We managed to net a good number of them trawling with a seine net. We took these fish back to camp distributed them into several boxes. They had to stay in these for the next few days while we fetched fresh water from the river every morning and evening and did almost complete water changes. We managed to get around 70 healthy specimens back to our accommodation in the capital and of those we took about 50 back to Germany with us. The rest we left with an exporter in Paramaribo we had got to know while we were there.

5. The Gran Rio in the upper Surinam River System is the typical habitat of C. boesemani	6. The Awarradam rapids in the Gran Rio
7. On substrate like this we came across large C. boesemani in smallish groups	8. A large number of juveniles wriggling in the net

Capturing Corydoras punctatus turned out to be considerably more difficult. Although this species has already been collected and distributed in the hobby by Werner Seuss a few years ago, I was very keen to bring back a few of these to breed since they seem to have completely disappeared from German aquariums since then. This species is to be found in great numbers in the lower reaches of the Surinam River. Near Awarradam however, we only managed to find small groups in a few places and these finds were mostly in fast flowing sections where catching them is simply not possible. We didn’t manage anything at all here with the trawl net so we were forced to catch the fish individually with two large landing nets. In two days we succeeded in catching a total of 10 specimens of medium size. All of these though arrived safe and sound in Paramaribo and later in Germany.

We could not find any other species in Awarradam. The catfish we caught in the Gran Rio were caught almost exclusively during the daytime. Our fishing trips on the sandbanks during the night brought none of this kind of success, although I have to say that these trips were not carried out nearly as meticulously and thoroughly by us as the daytime ones. The Gran Rio is a river of clear waters with very soft, slightly acidic water. We took the following water measurements on the 3rd September 2006 in the afternoon: Temp 28.4°C: Ph 6.65, Conductivity 11 µS/cm.

9. Sank bank where we found large numbers of C. boesemani juveniles

10. Young male C. boesemani shortly after collection

Care of Corydoras boesemani in the aquarium
After the successful import of the fish they settled in with no real problem. In a mix of mains and reverse osmosis water (conductivity roughly 400) the new arrivals from Surinam thrived splendidly in temperatures between 24 and 27°C. Since the fish which were predominantly still juveniles must unavoidably go though a period of starvation during transport I knew that absolutely optimum care in the first days was crucial to their future development. For this reason I fed the little catfish several times a day to begin with on Brineshrimp nauplii, tubifex and tablet food. As well as this I did partial water changes as often as possible. So in the next few days I had only two casualties from the group of young fish to complain of. They probably died of the stress of the journey, the starvation phase or the move, happily however, the remaining fish had developed a bulging girth after a few days. They were also faintly coloured with only a barely noticeable dark markings. They grew rapidly then and were soon 2cm long and had developed colouring similar to the adult fish. I was now able to pass some of the fish on to friends.

As well as the juveniles I had also been able to bring home three adult Corydoras boesemani. They were evidently one male and two female. The largest specimen, a female, had a total length of 45mm. The males seem to remain a little smaller, are more slender and have a somewhat higher dorsal fin as well as a stronger colour. The behaviour that the fish display in the wild was also to be seen in the aquarium. While the juveniles scurried with little fear across the tank in a swarm to search for food, the adult fish did not venture out of their hiding place even once to eat. I regularly had to reach into the tank and cajole the fish out of their hiding place even to get a look at their faces. I was not familiar with such behaviour in other similar species. From its characteristic body shape and markings, Corydoras boesemani obviously has a close relationship to Corydoras bondi with which other species from the north east of South America could be said to be related, such as for example C. coppenamensis, which also live in Surinam, C. breei and C. sipaliwini as well as C. sp “Mazaruni” (C150) from Guyana.

Successful Breeding
I undertook my attempts at breeding with fish in a tank of 50 x 30 x 30 cm which was set up with plenty of hiding places and a Hamburg filter with air lift. On the bottom of the tank was a thin layer of fine soil and very similar to the conditions in the wild. I had arranged and few cleaned oak and beech leaves on the tank floor.

It was quite a while before I had got the fish conditioned to the point where I would allow myself to hope that breeding of this species in the tank was possible. My travelling companion Peter Debold had thankfully provided me with a second large male for my breeding trials, so that I was now in possession of two mature pairs. Also the fish had survived my move to new premises unscathed. Meanwhile with greatly increased feeding with Tubifex, live red and white mosquito larvae as well as enchytraen the fish were bursting at the seams. The female was noticeably gravid. I took this as a cue to increase the frequency of water changes. So now I changed about ¾ of the water every two days with fresh water of the same quality which was approximately 2 or 3 degrees cooler.

On the evening of the 4th of August it was finally time. By accident I discovered an egg on the side wall of the breeding chamber. It was a little more that 2mm in size, in this respect it was comparable to the eggs of C. sterbai and C. aeneus. On closer inspection I soon found a second and a third. When I removed the objects from the tank I was able to collect a total of 32 eggs but only two of these seemed to be developing. The others were already white and dead. From then on with further intensive water changes the fish spawned about once a week but I never manage to observe the spawning. The 30 or so eggs so far had been mostly laid hidden under stones and plant roots but the favourite place was on the leaves that were lying around. This must also be the favoured place for laying eggs in the wild.

The eggs were moved each time into a bowl of clean fresh water. To reduce bacteria I also added some Acriflavin. Once a day, the dead eggs were collected, the container cleaned and the eggs put into fresh water. At 24-25 degrees the fish hatched after 4-5 days. The young fish had a yolk sac to begin and it was the same length of time again before this was consumed and they began to eat. The first food I offered was newly hatched brine shrimp nauplii which were eaten straight away. Growth was going noticeably quicker now. At first the fish have fine markings similar to many other young catfish. The dark eye stripe as well as a dark spot at the base of the dorsal fin are formed. Only after several weeks are the typical elements of the markings of Boesemans catfish to be seen.

While only two fish hatched out of the first eggs there were many more from following spawnings. The upbringing of the fish carried on with no problem. Juveniles of various ages grew up well together without the older fish interfering with the development of the younger ones. After a while frozen Cyclops and tablet food were taken as additional food.

Since then I have managed to get the first eggs from a second group of fish which have since grown to adulthood. Admittedly the clutch was significantly smaller. So, apparently C. boesemani is not a difficult species to breed and although it appears to be not particularly productive, it certainly can be maintained as a hobby fish by breeding without a problem. Because this fish is so attractive we should have no fear that it will quickly disappear from out tanks again as has happened in the past to some imported Corydoras.

Bibliography
Nijssen, H. (1970): Revision of the Surinam catfishes of the genus Corydoras Lacepede, 1803 (Pisces, Siluriformes, Callichthyidae). Beaufortia, 18(230): 1-75.

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

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