ROBERTO LONDONChauliodus sloani: bioluminescent fish at a depth of 500 meters ROBERTO LONDON
There is no point in looking for a Myctophidae on the fish stand in the market. Even if you ask for it by its popular name lantern fish, it won’t be any use. With a length of from 5 to 10 centimeters and one thing in common with glow-worms their body is covered with organs that produce light, the representatives of this family of fishes live during the day in deep waters, of up to 1,500 meters, along the Brazilian coastline. At night, they migrate to the surface, in shoals. That is when they are devoured by big fish like tunas, which indeed are an option for lunch, 2 to 3 meters long. Much more is known today about the lantern fish as a result of two complementary enterprises, both funded by the Ministry of Science and Technology (MCT): one linked to the Nuclei of Excellence Support Program (Pronex), which began five years ago to assess the diversity of the fauna in fish in Brazil, and the Assessment of the Sustainable Potential of Live Resources in the Exclusive Economic Zone Program (Revizee), started in 1997 with the aim of proposing forms of exploitation that do not threaten the survival of the more commercially exploited species (see Pesquisa FAPESP 43).
The book Peixes da Zona Econômica Exclusiva da Região Sudeste-Sul do Brasil [Fish from the Exclusive Economic Zone of the Southeastern-Southern Region of Brazil], published by USP’s publishing house (Edusp) with the findings of the Revizee team, has brought unprecedented data about 185 species of fish from the depths that were ignored in the Catálogo das Espécies de Peixes Marinhos do Brasil [Catalog of Brazil’s Species of Marine Fish], published by the Zoology Museum of the University of São Paulo (USP). With these two works, the number of known species of Brazilian marine fish has more than doubled. If there were 578 in 1941, the date of the previous survey, today there are 1,297 species, listed one by one in the catalog.
At first sight, the fish from the Brazilian coast call attention for the contrast in sizes from the tiny and colorful gobiidae, with less than 1 centimeter in length, found in coral reefs, to the whale shark (Rhincodon typus), with up to10 meters. They live along the 8,000 kilometers of the Brazilian coast, in the rocky seaboard, the coral reefs, in the regions of the high seas close to the surface, or in the depthswithout any light, like the lantern fish, studied in great detail by Andressa Pinter dos Santos, a postgraduate student at USP’s Oceanographic Institute and one of the authors of the book Peixes da Zona Econômica Exclusiva [Fishes of the Exclusive Economic Zone], coordinated by José Lima de Figueiredo, from the Zoology Museum at USP. “Lantern fish are the most abundant vertebrates of the oceans”, she says, after studying 37 of the 77 species found on the Brazilian coast.
Representatives of the Myctophidae family, they are recognized today as having a high ecological value for being at the base of the food chain in other words, for serving as food for species with a commercial value, like tuna (Scombridae family) and squid (Illex argentinus ), or even for whales. There are other regions of the planet with smaller territorial dimensions and an even greater diversity of species, such as the archipelagoes of Hawaii, but the quantity of endemic exclusive – species of the Brazilian coast is respectable: there are 123, equivalent to 10% of the total of species. This group includes even large sized fish discovered recently, like the Dasyatis marianae stingray. With a diameter of 1 meter, this species lives over the bottoms of reefs or pebbles, in shallow waters, at a depth of no more that 30 meters, and it was described only in 2000.
It was also three years ago that biologists from the Zoology Museum and from the Smithsonian Institute, of the United States, reported the discovery of a new species, Clepticus brasiliensis, a very peculiar fish, also endemic to Brazil. The tail fin of the males, longer than the body itself, with some 30 centimeters, sports long filaments whose function is unknown. Clepticus brasiliensis is a selective picker of plankton, the set of tiny organisms that float on the surface of the sea and find themselves at the base of the marine food chain other species of fish that also feed on plankton swim with their mouths open and filter the food. The most intriguing thing is that this Clepticus is a sequential hermaphrodite: they are born female and part of them the proportion is not yet known are transformed into males after becoming adult. If one of the dominant males of the group dies, just one female turns into a male, takes over the post, stops producing ova and starts to produce spermatozoids.
Among the still more recent findings are the new representatives of the Apionichthys genus, which remained unidentified for some 30 years in the collection of the Zoology Museum and of other museums, until they were studied by Tamar da Costa Ramos, who is studying for a doctorate under Naércio Aquino Menezes and coordinated the catalog. Ramos discovered three new species, described this year: Apionichthys menezesi, A. rosai and A. seripierriae, which live today in rivers of the Amazon Basin, but are descendants of marine ancestors. They are fish that, like flounders, to which they are related, have their two eyes and the body colored on one side only and thus succeed in camouflaging themselves. “They live buried or half-buried in the sand, and their predators do not see them”, Menezes reports. Seen from above, even when they are swimming, the Apionichthys blend into the riverbed, because of the dark color of the upper side of their body.
Paradigm undone Previously, for a lack of detailed information about the diversity of marine fish, it used to be thought that the Brazilian fauna of reef fishes was practically identical to that of the Caribbean sea, for both of them being tropical and neighboring areas. This theory was scuttled for once and for all last year, when Rodrigo Moura finished his doctorate at USP?s Biosciences Institute, with support from FAPESP, showing the differences between the fish that live in the coral reefs of the coast of Brazil and those of the Caribbean, seen before as being identical, mainly because of the patterns of colors on their bodies. “The levels of endemism in the Brazilian reefs are four times higher than those of the Caribbean, where 95% of the Atlantic reefs are”, explains Moura, a co-author of the catalog, who is working today in Caravelas, on the coast of Bahia, as a biologist with Conservation International Brazil.
If one idea has died, another is gaining strength: it is clearer that the Amazon separates the populations of marine fish, by pouring fresh water over 100 kilometers beyond its mouth. “The Amazon works like an effective barrier to the dispersion of fish”, Moura comments. According to him, it is not impossible to cross this obstacle, but many species have to overcome it at a slow rate, which makes possible the differentiation of species to the north and to the south of the mouth. The results from Revizee make it clear that it is impossible to increase in any significant and non-predatory way the quantity of the marine catch. “Brazil’s coast is poor in commercial species, different from Peru, which enjoys ample stocks of anchovies, due to the cold marine currents that run close to the continent”, says Menezes. “And the worst of all is that the stocks of the most exploited species have been exhausted.” According to him, shoals of sardines (Sardinella brasiliensis) are rare today, after previously having constituted one of the country?s main fishing resources, as a result of predatory fishing, added to local environmental variations. The blackfin goosefish (Lophius gastrophysys), once disdained in commercial fishing, began to be fished intensively a few years ago, because its flesh was regarded as delicious, and today the populations of this fish are in headlong decline.
The Project
Knowledge, Conservation and Rational Use of the Diversity of Fauna of Brazil’s Fish; Coordinator Naércio Aquino Menezes Zoology Museum/USP; Investment R$ 1,051,000.00 – Pronex (CNPq)
