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The hidden fish of the upper Paraná

A broad survey of biodiversity discovers new species of fish in the streams and headwaters of the upper Paraná basin

A portrait of some of the streams and headwaters of the upper Paraná basin shows that the biodiversity of freshwater fish life in São Paulo is much greater than previously supposed. In just 3 kilometers of narrow watercourses,  researchers from the University of São Paulo (USP) at Ribeirão Preto, discovered no less than 10 new species.

In the 30 sections of streams in São Paulo already studied (on completion there will be 66), 58 species have been collected – quite a large number, considering that the last study of the streams of the whole of the Upper Paraná system, a much larger area than the State of São Paulo, counted 71 species. Of the 58 already found, 17% are new and are being described in detail.

There are undoubtedly others awaiting the researcher Ricardo Macedo Correa and Castro, of the Biology Department of the Philosophy, Science and Arts School of Ribeirão Preto – University of São Paulo (FFCLRP-USP), who is running the project, Diversity of Fish in the Streams and Headwaters of the Upper River Paraná Basin in the State of São Paulo/Brazil, financed by FAPESP.

Castro was also one of the coordinators of the diagnosis of the biodiversity of vertebrates in São Paulo (including fish), part of the Biota/FAPESP Program, launched in March 1999. It involved around 300 specialists in mapping biodiversity. In charge of the survey and the study of the ichthyofauna of the country’s various regions, he assembled around 30,000 specimens, which formed the nucleus of the future Natural History Museum of the Biology Department of the FFCLRP-USP. His discoveries give an idea of what is still to be found throughout Brazil.

Abundant yet unknown
The most abundant species of stream fish studied is the yellow-tailed-minnow or the yellow-tailed astyanax, a small fish about 80 millimeters long, which had been identified for some time as the Astyanax bimaculatus. In studying it, however, Valdener Garutti, of the Biosciences, Arts and Exacts Sciences Institute (Ibilce) of the São Paulo State University (Unesp) in São José do Rio Preto, and Heraldo Antonio Britski, of USP’s Zoology Museum, discovered that it was in fact a new species.

Found only in the basin drained by the Upper Paraná and also called the tambiú, the yellow-tailed-minnow is often used as live bait for larger fish, such as the tucunaré (Peacock bass) and traíra (also known in English as  Tiger fish, South American Snakehead). Now recognized as different it was baptized with a name inspired by its habitat: Astyanax altiparanae.

As it is the so far numerically dominant species – it was found in 25 stretches and accounts for 16% of the samples and 39% of the weight of the fish collected – the yellow-tailed-minnow was chosen as the symbol of the project. The species is successful in occupying spaces: its habitat ranges from small headwater streams to the main channels of the larger rivers of the Upper Paraná system and the great lakes of the hydroelectric plant dams.

“As it was to be expected, the fish is omnivorous, tending to eat insects, but it is able to eat practically any food available”, explains Castro. Besides this, it spawns several times a year, which helps it swift multiplication and renewal of the population.

Evolutionary isolation
Nineteen samples were collected from the sub-basins of the rivers Aguapeí, Peixe and the Pontal of Paranapanema another unknown minnow, belonging to the subfamily Tetragonopterinae of the family Characidae. It is also small – around 50 millimeters long – and it is being described by Castro. He had already collected the new species, for the time being, called Astyanax sp. n. (the letters indicate that it has no definitive name), but there are too few of them for proper study and description.

Like the other minnows in the subfamily, this one seems to be omnivorous, tending to feed on insects. Everything suggests that it is diurnal, finds its food mainly by sight, and is only found in the Upper Paraná basin. If it really is endemic to this basin, its existence, like that of the other fish endemic to the region, will be one more piece of evidence of the possible evolutionary isolation of the local fish in relation to the rest of the River Plate basin (which besides the Paraná, includes the river Paraguay and Uruguay basins).

Endemic species
The abundant yellow-tailed-minnow is the exception among the stream fish, most of which are few in number and live in confined areas. This is the case of the Planaltina sp. n., another new species being studied: 20 of them, collected in the São José dos Dourados sub-basin, are being analyzed by Naércio Aquino Menezes, of USP’s Zoology Museum, and Stanley Howard Weitzman, of the Fish Division of the National Natural History Museum of the Smithsonian Institution in Washington (USA). This fish of the Planaltina genus is about 30 millimeters long and belongs to the subfamily Glandulocaudinae of the family Characidae, the males of which inseminate the females in a still unknown manner, with “packets” of spermatozoids.

Also typical is the small, shelled Corydoras sp. n., only five samples of which were collected in the sub-basins of the Pardo and the Mogi-Guaçu rivers. It measures 30 millimeters and is being studied by Castro in partnership with Marcelo Ribeiro de Britto of USP’s Biosciences Institute. A scavenger type of fish, it eats small insect larvae buried in the fine sand of the stream bottoms. Castro says that, because of the position of this species on the evolutionary scale, his study is likely to lead to important changes in the classification of the Callichthyidae family, one of the largest among South American freshwater fish.

In his opinion, these discoveries are a strong sign that there really was a long period of evolutionary isolation of the local fauna in relation to the rest of the River Plate system. It may indicate that there are many endemic species seriously threatened with extinction by environmental change. Hence, in tracing the diagnosis of the biodiversity in São Paulo, the Biota/FAPESP program is an essential step towards establishing a conservation plan.

Why streams
There is a reason for the choice of streams for the survey: relative to the size of the area, they are the richest environments in fish biodiversity. Castro calculates that half the species of fresh water fish in South America live in streams. Not the large commercially important fish like the dorado (Salminus maxillosus) or the sorubim, (psedoplatystoma coruscans) but small fish measuring up to 15 centimeters long, which generally move only short distances and form isolated populations.

They are the least studied freshwater species and their survival depends on environmental factors to which they have adapted over millions of years. They feed almost exclusively on vegetation on the river banks – leaves, small fruits, flowers – as well as land dwelling insects that fall into the water, aquatic insect larvae, other invertebrates that also feed on these materials, and twigs that fall in the water. They are usually very sensitive to temperature and light changes and to variations in the water level, and these conditions also depend on the vegetation.

This rich and complex environment has been brutally changed. In the State, no more than 8% to 9% of the original vegetation remains, essentially concentrated in the Mar mountain range. In the interior of the State, the streams flow through extensive plantations, pastures, and towns, where domestic garbage and a broad range of pesticides are thrown in them.

“This environmental degradation has a catastrophic effect on the number of species”, says Castro. Proof of this is that the richest point so far found is a small stream in the Upper Paranapanema that crosses a farm where there is still 73% native vegetation. Twenty-three species were found there. In the Aguapeí and the Peixe sub-basins, where much of the forest has been destroyed, the average number of species collected per stream was only 12 to15.

The survey of ichthyofauna that Castro is coordinating involves more than six researchers, two biological technicians and 19 students.By the time it is completed in 2002, the project is expected to cost R$ 368,000 plus US$ 2,200 financed by FAPESP. The analysis of the results will produce a large database, with environmental information on the streams, statistics, descriptions of new species, and data on the evolutionary relationships between species based on morphological and genetic analyses, including studies on migratory movements. Much of these data, including photographs, will be available on the Internet, to be used by professors, students, environmentalists, and the general public.

Positive balance
The 35 kilograms of fish collected so far are in the new building of USP’s Ichthyology Laboratory at Ribeirão Preto (Lirp), expanded and improved through the program’s budget. There are 8,710 fish samples, classified in six orders, 17 families, 44 genera, and 58 species. When the analysis of the material is complete we will be able to discover the entire population of each stretch studied and have information on the population of each species, its size, age structure, biomass, feeding habits (from studying the contents of its stomach), and even whether or not it has migratory habits. The study will also give good clues as to how some species evolved, Castro expects to assemble information to help create a system for measuring the biotic integrity of these streams, with indices showing critical points for starting conservation programs. He also believes that this work will help change people’s mentality to avoid the extinction of many species. “No great value is attached to these species because they have no commercial importance. But people forget that, like man and other vertebrates, they are the end product of a unique evolutionary process, taking billions of years, which will never be repeated”, he points out.

An adventure in the woods

A good diagnosis of fish fauna does not depend on scientific knowledge alone. It demands acceptance of hard work. The toughest part is collecting the fish, which begins with a full day’s journey in a small four-wheel-drive pick up truck specially bought for the purpose.

After swallowing a lot of dust on local dirt roads, they arrive at small village just in time to find somewhere to sleep. Comfort is not a priority. The following day, as soon as the sun is up, the five researchers set off in search of somewhere with the right characteristics for collection – a minimum amount of conservation around a stream. It is not easy. They need to ask the owner’s permission. The owner is not there… These are just the first difficulties.

When finally everything is in order regarding the place, the manual work can begin. Unloading the equipment from the car which is some distance away, setting up the tables and nets, measuring the stream, setting up the generator, switching on the electrodes, analyzing the water, getting samples from the bottom and samples of the vegetation, taking photographs of the place.

Then it is time to surround the fish. Two nets are set up, at about 100 meters from one another, so as completely to isolate the stretch of river. To ensure the greatest efficiency, the stretch is swept three times upstream with an electric fishing device producing a discharge of 220 volts in the water. This stuns the fish completely, making it easier to collect them, but it is dangerous for the collectors. Two more manual sweeps are done with a net and than a final one with two big sieves, to catch the fish hidden under the vegetation.

After a meal of instant noodles, the fishermen begin organizing the material collected. First, the fish are separated and the samples of the material for genetic analysis are collected. Then, the samples are plunged into a formalin solution to conserve all their characteristics, including the contents of the stomach. The fish are photographed on the spot and packed for the return journey.

When it starts to get dark, it is time to dismantle the equipment and return to the inn. “We arrive with our clothes wet, covered in mud, smelling of fish, literally rotten”, describes Castro. Working at this pace, the researchers manage to do three day’s collecting at different points.

Whenever possible, they take a day off to rest and clean up and to reorganize the equipment. They do more than three consecutive day’s collecting and finally, generally ten days and 2,500 kilometers later, they are back in Ribeirão Preto, with several kilos of fish in their baggage, covered with insect bites, dead tired and happy with their findings.

Ricardo Macedo Correa e Castro, 45 years old, professor and co-responsible for the Ichthyology Laboratory of the Vertebrate Zoology Sector of the FFCLRP-USP and researcher associated with the Fish Division of the Zoology Department of the  Smithsonian Institution (Washington, EUA). A graduate in Marine Biology  (1977) and Zoology (1978) at the Federal University of Rio de Janeiro, he completed his master’s degree (1984) at USP’s Biosciences Institute. He was a Pre-Doctoral Fellow (1986 and 1987) at the Smithsonian Institution and did his doctorate at USP (1990).

The Project
Fish Diversity in the Streams and Headwaters of the Upper Paraná River Basin in the State of São Paulo/Brazil (nº 98/05072-8); Modality Auxílio à Pesquisa – BIOTA; Coordinator Ricardo Macedo Corrêa e Castro; Investment: R$ 368,142.27 plus US$ 2,212.65