RESUMEN
The Nile Tilapia, Oreochromis niloticus, and the Congo Tilapia, Tilapia rendalli, are important members of the African cichlids, and have been introduced to many Brazilian lakes and reservoirs. These species exhibit a large feeding flexibility and may modify their habits during their growth. In the Barra Bonita reservoir, these species are well adapted, representing more than 80% of fish. This study aimed to analyze ontogenetic variation with regard to the diet of these species in this important reservoir. Samples were taken monthly, from March 2007 to February 2008, in Anhembi, São Paulo State. Both species were analyzed by grouping individuals according to size classes. The coexistence of these species was observed in this environment, to which fish were introduced, as well as discreet differences in diet, being that Oreochromis niloticus was considered as an detritivorous, since the detritus was constant in the diet of almost all size classes, and presents some changes in its diet according to the different size classes. While T. rendalli may was defined as herbivorous, and the contribution of food resources to the diet of T. rendalli seems to be different from that of O. niloticus along the size classes.
RESUMEN
The aim of this study is to characterize some population biology parameters of P. squamosissimus, A. altiparanae and S. maculatus, the dominant fish species of the Santa Bárbara River, a tributary of the Nova Avanhandava Reservoir, low Tietê River. Fish samplings were performed monthly between September/2002 and August/2003, using gill nets with different mesh sizes. Females of all species have larger standard lengths than males (Mann-Whitney, p
The aim of this study is to characterize some population biology parameters of P. squamosissimus, A. altiparanae and S. maculates, the dominant fish species of the Santa Bárbara river, a tributary of the Nova Avanhandava reservoir, low Tietê river. Fish samplings were performed monthly between September/2002 and August/2003, using gill nets with different mesh sizes. Females of all species have larger standard lengths than males (Mann-Whitney, p 0.0001), and are more frequent in superior size classes (Kolmogorov-Smirnov, p 0.0001). All populations presented isometric growth, but differences between males and females were observed. Only P. squamosissimus presented a gender ratio different from 1:1, with a higher proportion of males (1:2, 2, p 0.05). The onset of gonadal maturation occurs at 15 cm in P. squamosissimus, 9 cm in S. maculates and at 8.9 cm in A. altiparanae. In all species populations, the adults predominate over juveniles. The allometric condition factor (K) of P. squamosissimus and S. maculates presented higher values in the periods from March-May and June-August, and A. altiparanae in the period from March-May (Kruskal-Wallis, p 0.05). These results indicate that the populations successfully exploit the lentic environment, and present life cycle tactics adapted to their particular means of environment occupation.
RESUMEN
Monthly collections of fishes using a trawl net were carried out from August 1996 to December 1997 with the objective of evaluating the composition and diversity of fish species in the littoral area of the transition zone between Veados Stream and Jurumirim Dam (Upper Paranapanema River, São Paulo State). Diversity and similarity indices of ichthyofauna at the sites were determined and correlated with abiotic factors such as dissolved oxygen, temperature, pluviometric precipitation and hydrological level. Twenty-six (26) fish species (the majority small-sized) of the family Characidae (Tetragonopterinae and Cheirodontinae) were registered. Representatives of the orders Siluformes, Gymnotiformes, Perciformes and Synbranchiformes occurred in lower abundance. Significant differences were found in the site diversity indices, but not in the abiotic factors. Significant correlations between the abundance of the ichthyofauna and the variations in the abiotic factors were not detected. The presence of fish larvae in the samples indicates the importance of the transition zone as a reproduction area of the fish species registered in this study
Com o objetivo de avaliar a composição e a diversidade de espécies de peixes da área litorânea do trecho de transição entre o Ribeirão dos Veados e a represa de Jurumirim (alto rio Paranapanema, SP), foram realizadas coletas mensais de peixes com rede de arrasto, no período de agosto de 1996 à dezembro de 1997. Índices de diversidade e de similaridade da ictiofauna entre os locais foram determinados e correlacionados com alguns fatores abióticos (oxigênio dissolvido, temperatura, precipitação pluviométrica e nível hidrológico). Foram registradas 26 espécies de peixes, sendo a maioria de pequeno porte da família Characidae (Tetragonopterinae e Cheirodontinae). Em menores abundâncias, ocorreram representantes das ordens Siluriformes, Gymnotiformes, Perciformes e Synbranchiformes. Diferenças significativas entre os índices de diversidade nas estações foram encontradas, mas entre os fatores abióticos não foram detectadas. A composição faunística de peixes entre as estações foi similar. Não foram detectadas correlações significativas entre a abundância da ictiofauna e as variações dos fatores abióticos. A presença de larvas de peixes nas amostras indica a importância da zona de transição como área de reprodução, de refúgio e de alimentação das espécies de peixes que sustentam os níveis tróficos superiores da teia alimentar desse biótopo