Historia natural de peixes do Pantanal : com destaque em habitos alimentares e defesa contra predadores

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

This study deals with the natural history of fish of the Pantanal, espcially the feeding habits and means of defence against predators that these animals possess. The field studies were carried out in lagoons, vazantes (drainage channels) and corixos (lake outlets) that are found alongside the Transpantaneira Highway, in the Poconé region of the Pantanal, Mato Grosso (16° 30 S 56° 45 W) and in similar places of the Barão de Melgaço region of the Pantanal in the district of Saint Antonio de Leverger, Mato Grosso (16° 06 S, 55° 50 W). The field trips were successive and encompassed the three main periods of the Pantanal: the rainy season, the period of draining and the dry season. The data was collected from the month of September 1986 to May 1999, in a total of 1325 hours of field comments, of which about 70% was during the draining period, about 10% in the rainy season and 20% in the dry season. The habits of the fish were studied during sessions of natural observation during their feeding times (diurnal or nocturnal). The species of fish observed and their behavioural sequences were recorded in pencil on boards of white PVC. The underwater observations were carried out in locations where the water depth was between 0.5m and 1.7m, with a minimum of disturbance to the animals. The studied species of fish were divided into four large feeding categories: herbivores, carnivores, omnivores and detritivores. The means of finding food was divided into ten categories: rovers, waiter hunting, stealth hunting, scavenging, searching, skin-scraping, grazing, trimming/cutting, deep diving and deep searching. The food items were identified by sight by disarming them during the observation sessions or by examination in analyses of the stomach contents with the aid of a stereomicroscope and an optical microscope. The mechanisms of defence against predators were studied by means of direct observation of inter-species interaction, during diving sessions. The period of reproduction of the fish was studied by following the reproductive migrations that the rheophilic species perform in the rivers at the beginning of the rains, mainly for the larger species. For the recognisably lacustrine species, the reproduction period was observed through the change of their normal colours and during the care of the offspring. Collections were carried out using nets, fine sieves and, occasionally, hooks. The collections in the river Piraputanga were carried out during three consecutive days, encompassing several different phases of each 24 hour cycle. The samples are stored at the Museum of Zoology of the University of São Paulo (MZUSP), the Museum of Natural History of the State University of Campinas (ZUEC) and of the Laboratory of Vertebrates of the Department of Biology and Zoology, Institute of Bioscience of the Federal University of the State of Mato Grosso (UFMT). In the Pantanal there are 263 recorded species of fish. In the study of fish communities along a small stretch of the river Piraputanga, I registered 74 species. This demonstrated that in this reduced area there was an occurrence of about 30% of the total of existing species in the Pantanal. This can be considered not as a fortunate coincidence, but rather as proof of an environment with a substantial wealth of species. The wealth of fish in the Pantanal may be a result of the rich variety of environments, that provide shelter and food. The trophic composition and means of feeding, in the groups of fish, can vary from specialised predators to generalised herbivores. Numerous types of feeding interactions occur between fish of the high Pantanal, exemplified by the various morphology types and means of obtaining food and exploring the environrnent, characterising carnivorous fish (some Characidae, Pimelodidae, Cichlidae), herbivores (a Anostomidae, some Characidae, some Cichlidae), ornivores (Anostomidae, some Characidae) and detritivores (Curimatidae, Prochilodontidae). Fish, due to their abundance, are frequent prey in the aquatic environrnents of the Pantanal. For this reason, they possess numerous anti-predatory defences. Anti-predatory mechanisms in fish of the Pantanal include primary defence such as camouflage (mento Catoprion, Hoplias cf. malabaricus, Crenicichla spp., Astronotus ocellatus, Potamorrhaphis eigenmanni) and imitation (young Piaractus mesopotamicus, imitating Pygocentrus nattereri; Corydoras hastatus imitating Serrapinnus spp.; Bujurquina vittata, imitating Satanoperca pappaterra); and secondary defence such as escape (the majority of the species), intimidation (Pimellodela gracilis, Satanoperca pappaterra, Astronotus ocellatus) and retaliation (Crenicichla lepidota, Cichlasoma dimerus). The defensive mechanisms described here act in conjunction and possibly diminish the strong influence of the fish-eating predators in the Pantanal. The reproductive methods of the fish in the Pantanal are defined by the time of the rains, that begin in the month of October, for the rhoephilic species such as Brycon hilarii, Piaractus mesopotamicus, Mylossoma spp.. The Erythrinidae, some lesser Siluriformes, Cichlidae and Synbranchidae reproduce in the system of lagoons. However, there are species whose reproductive processes are unknown, not in so far as the reproductive period is concerned, but in terms of how their preferred environments and their physiology. Some groups offish stand out in the Pantanal, the diurnal (Pygocentrus nattereri and Serrasalmus spp., Mylossoma spp., and diverse Cichlidae) and the noctumal (Pseudoplatystoma spp., descalvadensis Cynopotamus kincaidi and Roeboides, Eigenrnannia virescens and Rhamphichthys hahni). In the Pantanal, the fish play a role of great importance for the maintenance of the system, and as a source of food for several other types of vertebrates, as is the case of fish-eating birds that depend on fish throughout the whole of their life cycle

ASSUNTO(S)

defesa peixe habitos alimentares

ACESSO AO ARTIGO

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