Peruvian Amazon river
Aerial view of a meandering river in the rainforest of Peru. If you look closely, two oxbow lakes are visible towards the center of the image. One is considerably "darker" than the other, but both are isolated from the main channel of the river.
A biotope aquarium is set-up to simulate a natural habitat. The fish, plants, water chemistry, light conditions, and tank furnishings are similar to those that can be found in a specific natural setting.
OXBOW LAKE IN SOUTHWESTERN PERU
The southeastern part of Peru is arguably the most biodiverse place on the planet. This biological wealth extends to the river systems found in this tropical rainforest environment.
This biotope profile will look specifically at two oxbow lakes found along the Madre de Dios and Tambopata rivers in the Madre de Dios river system upstream of Puerto Maldonado.
Virtually all lakes in this part of the Amazon are oxbow lakes. An oxbow lake is a crescent-shaped lake formed when a river changes course. In lowland Amazonia where soft alluvial soils dominate, meandering rivers gradually shift due to erosion and sediment deposition. Oxbow lakes typically form when loops in the river become so extreme that the main channel erodes a new straighter route, leaving the river bend apart from the river. As time passes, the oxbow lake becomes increasingly distant from the main channel. Water conditions change as the water stagnates.
The characteristics of an oxbow lake generally depends on its age. Younger oxbow lakes may be "flushed" by river currents, especially during the flood season. These lakes tend to be slightly more turbid (less transparent) and less acidic than older lakes more distant from the river channel.
Oxbow Lake Characteristics
Depth: Oxbow lakes generally range in depth from 16 feet (5 meters) during floods to less than 6 feet (2 m) at low water.
Thermal stratification: Oxygen and temperature tend to decrease with depth in lakes due to thermal stratification whereby cooler waters do not mix with warmer waters. Thermal stratification is more common in older, more isolated oxbow lakes.
Temperature: According to Amazon Headwaters, a book on the rivers of southeastern Peru, the average temperature of oxbow lakes is 76-80 degrees Fahrenheit (24.6-26.6 degrees Celsius). Oxbow lakes are generally warmer than nearby river channels and shaded forest streams. Temperature rises during the low water period.
Water chemistry: According to Amazon Headwaters, the pH of oxbow lakes ranges from 5.4-6.8 while conductivity is 40-68. pH and conductivity rise during the low water period, possibly due to "increased phytoplankton production." Water transparency also increases at this time.
Substrate: The substrate consists of mud with overlaying organic matter and vegetation in varying states of decomposition. There is a fair amount of submerged wood.
Other wildlife: Both oxbow lakes are inhabited by families of giant river otters. Giant river otters are the top predators in these ecosystems, feeding on 5-10 kg of fish per day. Other non-fish predators of resident fish are primarily birds. Tambopata (650 species) and Manu (1000 species) are incredibly rich with bird life.
Underwater shot of Bladderwort (top) and Victoria cruziana (bottom)
Bladderwort, Utricularia foliosa is especially abundant in this habitat.
Oxbow lakes in this region have considerable aquatic plant growth. Most conspicuous are free-floating plants including Eichhornia, Pistia, Salvinia, Victoria cruziana, and Bladderwort (Utricularia foliosa), which grows densely and extensively in the lakes. Amazon sword plants (Echinodorus sp.), Vallisneria, Panicum, and Hymenachne were also present, though in lesser numbers. According to Amazon Headwaters, there are about 35 species of "aquatic herbs and shrubs that are characteristic of floodplain lakes of the rio Madre de Dios lowlands."
Surrounding vegetation: The oxbow lake is surrounded by reeds. There are thick floating plants where the lake narrows.
Tank size will depend on the type of fish you plan to keep in your biotope aquarium. If you are going with smaller tetras, catfish, and Apistogramma then you can use a smaller tank than if you plan to go with larger cichlids and characins.
Current: Direct filter outflows to minimize current. Oxbow lakes are quite still.
Lighting: Bright overhead lighting. You can moderate lighting with some floating plants if desired.
Layout: Dense planting along the sides and rear of the tank with open swimming areas. Wood can be used as well.
Substrate: Fine gravel or sand is acceptable since you probably don't want to use decaying leaf matter and mud which is naturally found in this biotope.
Other notes: You might consider using some peat moss in your filtration system to reduce the pH and soften the water. Peat moss can also mimic the slightly tea-colored water conditions that result from the inflow of blackwater streams.
Fish suitable for aquariums
The rio Madre de Dios probably has more than 600 species, many of which have yet to be described according to Amazon Headwaters. Detritus-feeders, invertebrate-feeders, and seed- and fruit-eating species are abundant in the system.
The aquarium fisheries trade began in the department of Madre de Dios in 2002 according to Amazon Headwaters. The book says the rio Madre de Dios headwaters regions has advantages when compared with aquarium trade fisheries in other parts of the Amazon, namely that the seasonal high water period is "neither too deep nor too long to prevent aquarium trade fisherman from working during the rainy season. Elsewhere in the Amazon Basin aquarium trade fisheries largely stop during the flooding season." Further, the rio Madre de Dios watershed had a large number of endemic species, some of which are small and decorative enough to be attractive as aquarium fish. The book lists the following genera as promising for the aquarium trade: Abramites, Corydoras, Pterolebias, Apistogramma , Crenicichla, Mesonatua, Carnegiella, Gymnocorymbus, Hemigrammus, Tyttocharax, Tyttobrycon, Pyrrhulina, Ancistrus, Hypostomus, Pimelodella, and Pimelodus.
The following fish were observed by boat in the oxbow lakes of the rio Madre de Dios (near Manu National Park) and the rio Tambopata (Tres Chimbadas lake):
Mesonauta festivum was the most obviously abundant fish as viewed from the boat. Bloodfins and Moenkhausia were also common. Hatchetfish were found near reeds along the shoreline, while a stingray was seen partially buried in a muddy beach area.
FRESHWATER FISHES OF THE TAMBOPATA NATIONAL RESERVE
Compiled by Mario Napravnik
Cachoro, Pike characin
Two spotted Astianax Silvery tetra
Blotch tailed bario
Sabalo cola roja
Tail light tetra
Cheirodon ait. notomelas
Black widow, Skirt Tetra
Head and tail light tetra
Red tailed flag tetra
Knodus aff. beta
Knodus aff. moenkhausii
Leptagoniates aff. pi
Spot tailed Moenkhausia
Black piranha, Spotted piranha
Fire mouth piranha
Sardina, Narrow Hatchetfish, sapanama
Bristly mouthed tetra
Short finned trahira
Fasaco, Tiger fish, trahira
Banded Knife fish
Ghost Knife fish
Spoted knife fish
Atinga, Marbled Eel
Tambopata Flag Cichlid
Jurupari, Eartheater, Demon eartheater
Smooth banjo catfish
Zungaro, Gilded catfish
Salton, Gilded catfish
Dorado, Gilded catfish
Bumble bee cat
Doncella, Shovelnosed catfish
Parasitic catfishes, Pencil catfish
Armored Catfish, Corydoras
Shirui, Slender Armored Catfish
Coridora, Sharp nosed corydora
Shirui, Port hoplo, Atipa
Plecostomus, Sucker catfish
Dwarf sucker catfish
FRESHWATER FISH AVAILABLE FROM PUERTO MALDONADO, PERU DISTRIBUTOR Aquarium Gone Wild Peru lists the following fish as being locally available in the Madre de Dios region.
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