ABSTRACT
This study aimed at analyzing the influence of different levels of environmental integrity of streams of the Ivinhema river basin (Mato Grosso do Sul State, Brazil) on the diet of A. altiparanae. Samplings were performed from July 2001 to November 2011 at 101 sites, using sieves, seining and gill nets, and electrofishing. Streams were classified into three levels of environmental integrity. We analyzed 664 stomachs with the methods of frequency of occurrence and volumetric analysis index, combined in the Importance Index (AI). The species was omnivorous, with predominance of allochthonous resources. At the least impacted sites, the most representative resource was allochthonous plant material; and in the altered sites in the rainy period the most consumed item was allochthonous arthropods. On the other hand, at the most impacted sites in the dry period there was a lower consumption of allochthonous plant material and allochthonous arthropods, compared with other levels of environmental integrity considered, with higher consumption of autochthonous arthropods. The results evidenced that in the least impacted sites there was greater contribution from allochthonous resources, probably because these environments show a more preserved riparian forest.
ABSTRACT
The aim of this study is to describe the diet and the feeding activity of Pimelodella cf. gracilis in Amambai river, Mato Grosso do Sul State, Brazil, along the four seasons of the year. For this, the stomach contents of 232 individuals were analyzed and their Stomach Fullness Index was calculated. The results indicate that this species is omnivorous and generalist, so it consumes feeding items of several origins, such as plant material, terrestrial and aquatic insects, mollusks, fish scales, sediments and non-identified material. Notwithstanding this, the plant material was predominant in the diet along the whole year, indicating that Pimelodella cf. gracilis tends to herbivorous habit. The composition of the basic diet changed seasonally, so we observed that allochthonous items have their importance increased in the warm and rainy seasons. Besides this, we also observed seasonal shifts in the feeding activity, probably due to climactic (temperature and precipitation) and physiological factors (reproductive cycle).
Esse estudo teve como objetivo descrever a dieta e analisar a atividade alimentar de Pimelodella cf. gracilis no rio Amambai, Estado de Mato Grosso do Sul, ao longo das quatro estações do ano. Para tanto, analisou-se o conteúdo estomacal e calculou-se o Índice de Repleção Estomacal de 232 indivíduos. Os resultados obtidos demonstram que essa espécie é onívora e generalista, pois consome itens alimentares de origens diversas, tais como material vegetal, insetos terrestres e aquáticos, moluscos, escamas de peixes, sedimentos e material não-identificado. Apesar disso, o item material vegetal foi predominante na dieta ao longo de todo o ano, demonstrando que, embora onívora, essa espécie apresenta tendência à herbivoria. A dieta básica mostrou variações sazonais em sua composição, pois observou-se que alimentos alóctones têm sua importância aumentada nas estações mais quentes e chuvosas. Além disso, também foram registradas alterações sazonais na atividade alimentar, possivelmente influenciadas por fatores climáticos (temperatura e pluviosidade) e fisiológicos (ciclo reprodutivo).
ABSTRACT
The aim of this study is to describe the seasonal variations of condition factor and of the gonadal development cycle of Pimelodella cf. gracilis in Amambai River (MS, Brazil). The length and weight of 232 individuals were measured to calculate the Allometric Condition Factor. For the females (n=162), we also obtained the ovarian weight and the gonadal maturity stages in order to calculate the GSI and the relative frequency (%) of this stages at each season of the year. Results indicate that the highest GSI values were registered in spring and summer. Thus, we concluded that the spawning season of this species occurs between October and April. However, it was not possible to identify more precisely when this event occurs. The highest values of condition factor were observed in summer, as a probable consequence of the more intensive feeding activity that individuals demonstrate during the spring.
O objetivo deste trabalho é descrever a variação sazonal do fator de condição e do ciclo de desenvolvimento gonadal de Pimelodella cf. gracilis no rio Amambai, Estado de Mato Grosso do Sul. O comprimento e o peso de 232 indivíduos foram obtidos para cálculo do Fator de Condição Alométrico. Para as fêmeas (n=162), obtivemos, ainda, o peso e o estádio de maturação dos ovários, para cálculo do IGS e da freqüência percentual desses estádios em cada estação do ano. Os resultados obtidos indicam que os maiores valores de IGS correspondem às estações primavera e verão. Com base nisso, conclui-se que o período de desova da espécie está compreendido entre os meses de outubro e abril, embora não tenha sido possível determinar com maior precisão quando esse evento ocorre. Os maiores valores do fator de condição foram observados no verão, como possível conseqüência da maior atividade alimentar que os indivíduos apresentaram durante a primavera.