Tropical fresh water is usually cloudy and either coffee coloured from humic substances, or milky from sediments (white water rivers). However in some regions of the world the water is extremely finely filtered by a geological feature before it flows out as a spring: This occurs in the north-east of Florida (Ginnie Springs, Crystal River etc.) and in the southwest of Brazil. The karst ground in these areas acts as a gigantic fine filter which produces water which is completely crystal clear and allows visibility of over 50 m underwater!
Following the first part of the JBL expedition to the Amazon region, the team travelled from Manaus via Brasilia to Cuiaba in the federal state of Mato Grosso. From Cuiaba the trip went further north by bus to Bom Jardin. We checked into an ecolodge (www.hotelbomgarden.com.br) and from there the JBL research team drove to the various clear water springs as well as rivers and lakes in the area.
Still on the day of arrival we sought out the Rio Triste in order to catch a first glimpse of the fauna. After the brown-black waters of the Amazon region, the sight and especially the views underwater were simply unbelievable: shoals of tetra with thousands of individuals make up the background for large Leporinus, piranhas and tropical cichlid. Plecos were scraping at the wood and above the water lush tropical vegetation flourished. Sometimes the scenery seemed almost artificial, nature is rarely that beautiful and perfect.
Behavioural studies and other ethological experiments are only really possible in clear water. But before the team set off underwater, the usual obligatory water analyses had to be carried out: the pH-value now measured between 7.3 and 7.4, the CH was 10 and led to a high conductivity, depending on the river or lake, of between 356 and 388 µS/cm.
On the second day we went to a clear lake which is well known for its piranha stock. In order not to stir up too much sediment on the shore, the boats went to the middle of the lake, which was just seven metres in depth, from where we snorkelled and dived. Contrary to the rivers, scuba diving was also possible in the lake, which offered even better possibilities for observations. We were simply able to lie on the ground of the lake between the spread-out algae and observe large black and white Southern sailfin catfish (Liposarcus anisitsi), as well as demon eartheaters (Satanoperca pappaterra), or watch the hunting behaviour of the pike characin (Acestrorhynchus pantaneiro), which develop clever hunting strategies in order to isolate single small tetra from huge shoals. In the centre of the lake piranhas appeared singly and less frequently, but in the shore area, often underneath clumps of floating plants, large piranhas could be found. Unlike in all the horror stories, they remained shy and kept their distance.
The two highlights of this part of the trip were planned for following day: freshwater stingray are said to be found in the Rio Salobra and night snorkelling was planned. The fish species we encountered were similar to those of the previous waters. But with a little practice, dwarf cichlid (Apistogramma trifasciata), armoured catfish (Corydoras polystictus), twig catfish and various predatory tetra could be spotted. Only fresh water stingrays were nowhere to be found. As all the team members were carrying out observations in the river throughout the day and in their enthusiasm several of them ignored instructions and stirred up sediment, we waited a while and continued our search in the late afternoon. And finally: after 4 p.m. various participants were able to find stingray. The stingray (Potamotrygon falkneri) could mostly be found in the sandy areas of the riverbank, rarely between foliage and never in stone or wood regions. If you approached carefully, the fish allowed you to get as close as less than 30 cm away. If this distance was crossed, there was no aggressive behaviour, simply an escape reaction or slow retreat. Unfortunately the stingray could not be observed foraging or feeding. It is assumed that they feed on the frequently seen shrimp and ground-dwelling fish. During the day they probably would not have a chance to catch these creatures, but by night they must be able to succeed without any problems.
An hour after dusk it was finally time: night snorkelling was on the agenda and everything was fervently checked and batteries were replaced to give us more light. It is amazing every time to see how darkness changes perception. Although the team had already dived in the river several times, it seemed completely unfamiliar to everybody. Only the glow of the water-tight lamps lit up the field of vision. Many fish lay asleep on the ground or stood motionlessly between the plant roots by the riverbank. Several fish species were positioned upside-down in the wood â€“ an unusual sight! At first everyone was deceived and thought they were seeing completely different fish than during the day. But it turned out to be the night-colouring of the fish, which rarely looks like their daytime colouring. 40 cm long banded knifefish (Gymnotus spec.) could now be found in the bank area, which had previously not been sighted during the day.
On the final day in Mato Grasso a hike through the rainforest was planned, which led to a waterfall with a clear lake and stream. Luckily many helpers had been organised in advance to help transport the compressed air cylinders, lead weights and analysis equipment. The first glance underwater was a little sobering: the same large tetra (Brycon microlepis) as on the previous days and many Ancistrus catfish on the rocks. But then there was yet another highlight: a catfish species that was unknown even to the catfish specialist Stiev Lorenz. He had even dragged along the catfish atlas by Ingo Seidel and was feverishly searching, in vain, for a fitting picture. Perhaps a new discovery? The team was definitely the first team of aquarium specialists to visit this spot and to dive with compressed air. By means of the catfish pictures taken, the subsequent identification will now take place in Germany and everybody is of course hoping to have discovered a new species, or at least a local variation!
< 0.05 mg/l
GH / KH:
GH / KH:
GH / KH: