Dieta da Raia-elétrica Narcine brasiliensis (Olfers, 1831) (Elasmobranchii: Narcinidae) na costa sul do Estado de São Paulo
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Data
2020-03-20
Autores
Laranjeira, Maria Eduarda Alves
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Universidade Estadual Paulista (Unesp)
Resumo
A raia-elétrica N. brasiliensis ocorre do sudeste do Brasil ao norte da Argentina, apresenta de pequeno a médio porte e atinge comprimento máximo de 49 cm. Essas raias são geralmente encontradas em substrato lodoso, composto por areia fina, onde o movimento de protrusão da mandíbula é mais eficiente, facilitando também a sucção das presas. Exemplares de N. brasiliensis são capturados acidentalmente nas regiões sudeste e sul do Brasil, sendo muito suscetíveis às ações antrópicas predatórias. Apesar de ser uma espécie abundante ao longo da costa brasileira, há um conhecimento escasso sobre vários dos seus aspectos biológicos. Estudos relacionados a este gênero concentram-se em distribuição, reprodução, abundância das espécies e em sua dieta, a qual é composta principalmente por crustáceos e anelídeos marinhos, poríferos, equinodermos e sipunculas. O objetivo deste estudo consistiu em analisar o conteúdo estomacal de exemplares de N. brasiliensis, a fim de caracterizar sua dieta na costa sul do Estado de São Paulo, visando obter uma lista de itens alimentares identificados ao menor táxon possível e a proporção geral dos grandes grupos de presas de sua dieta; bem como avaliar a dieta em relação à ontogenia e sazonalidade, além de identificar os principais componentes anatômicos do trato digestório. A dieta de N. brasiliensis na região de estudo foi composta por cinco grandes grupos: Classe Polychaeta, Classe Sipunculida, Ordem Decapoda, Ordem Stomatopoda e Ordem Anguiliformes. Os poliquetas 1, da Família Arabellidae, foram o principal componente alimentar dessa espécie nessa região (IRI 32,41%). O poliqueta 2 foi o segundo item mais importante para a dieta desses animais (IRI 12,73%). Já os Sipunculiformes aparecem como o terceiro item mais relevante (IRI 2,14%). Não houve diferenças significativas na distribuição dos itens alimentares entre os sexos, nem entre as classes de comprimento e tampouco entre as estações climáticas. As dietas entre as Classes II e III, e III e IV apresentaram maior similaridade entre si. A dieta de machos e de fêmeas no período de inverno também foi considerada similar. O teste de Pianka demonstrou alta sobreposição de dietas entre machos e fêmeas, e também entre os meses de inverno, o que está relacionado à disponibilidade de presas e ao tamanho dos indivíduos. A espécie pode ser considerada especialista (estenofágica), apresentando dieta composta principalmente por poliquetas o que está diretamente relacionado à sua morfologia corpórea, sobretudo do aparato mandibular, que é especializado para a sucção de presas.
The lesser electric ray N. brasiliensis is distributed from southern Brazil to northern Argentina, it is small to medium sized and its maximum lenght is 49 cm. These rays are usually found in muddy sediment, in which the jaws protusion movement is more efficient, making easier the prey suction. Specimens of N. brasiliensis are accidentally caught in the southeastern and southern regions of Brazil, being very susceptible to predatory anthropic actions. Although it is an abundant species along the Brazilian coast, there is no much information about its biological aspects. Studies related to the gender are focused in distribution, reproduction, species abundance and diet, which is mainly composed by crustaceans, polychaetes, poriferous, echinoderms and sipuncula. The objective of this research was to analyse the stomach content of N. brasiliensis specimens, to characterize its diet on the south coast of São Paulo State, aiming to obtain a list of food items identified at the lowest possible rate and the general proportion of the large groups of prey in their diet; as well as evaluating the diet in relation to ontogeny and seasonality, in addition to identify the main anatomical components of the digestive tract. The diet of N. brasiliensis in the study region was composed of five major groups: Class Polychaeta, Class Sipunculidea, Order Decapoda, Order Stomatopoda and Order Anguiliformes. Polychaetes 1, of the Arabellidae Family, were the main food component of this species in this region (IRI 32.41%). Polychaete 2 was the second most important item in the diet of these animals (IRI 12.73%). Sipunculiformes appear as the third most relevant item (IRI 2.14%). There were no significant differences in the distribution of food items between the sexes, neither between the length classes nor between the climatic seasons. The diets between Classes II and III, and III and IV were more similar to each other. The diet of males and females in the winter period was also considered similar. The Pianka test showed a high overlap of diets between males and females, and also between the winter months, which is related to the availability of prey and the size of individuals. The species can be considered a specialist (stenophagic), presenting a diet composed mainly of polychaetes which is directly related to its body morphology, especially of the mandibular apparatus, which is specialized in prey suction.
The lesser electric ray N. brasiliensis is distributed from southern Brazil to northern Argentina, it is small to medium sized and its maximum lenght is 49 cm. These rays are usually found in muddy sediment, in which the jaws protusion movement is more efficient, making easier the prey suction. Specimens of N. brasiliensis are accidentally caught in the southeastern and southern regions of Brazil, being very susceptible to predatory anthropic actions. Although it is an abundant species along the Brazilian coast, there is no much information about its biological aspects. Studies related to the gender are focused in distribution, reproduction, species abundance and diet, which is mainly composed by crustaceans, polychaetes, poriferous, echinoderms and sipuncula. The objective of this research was to analyse the stomach content of N. brasiliensis specimens, to characterize its diet on the south coast of São Paulo State, aiming to obtain a list of food items identified at the lowest possible rate and the general proportion of the large groups of prey in their diet; as well as evaluating the diet in relation to ontogeny and seasonality, in addition to identify the main anatomical components of the digestive tract. The diet of N. brasiliensis in the study region was composed of five major groups: Class Polychaeta, Class Sipunculidea, Order Decapoda, Order Stomatopoda and Order Anguiliformes. Polychaetes 1, of the Arabellidae Family, were the main food component of this species in this region (IRI 32.41%). Polychaete 2 was the second most important item in the diet of these animals (IRI 12.73%). Sipunculiformes appear as the third most relevant item (IRI 2.14%). There were no significant differences in the distribution of food items between the sexes, neither between the length classes nor between the climatic seasons. The diets between Classes II and III, and III and IV were more similar to each other. The diet of males and females in the winter period was also considered similar. The Pianka test showed a high overlap of diets between males and females, and also between the winter months, which is related to the availability of prey and the size of individuals. The species can be considered a specialist (stenophagic), presenting a diet composed mainly of polychaetes which is directly related to its body morphology, especially of the mandibular apparatus, which is specialized in prey suction.
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Alimentação, Polychaeta, Stomatopoda, Torpediniformes, Feeding