The diversity of fish species in an transition zone between the River Paranapanema and the head mouth of the Jurumirim Reservoir was evaluated. Fish samples were collected from October 1995 to September 1996, by experimental fishing (gill-nets and sieve), in three marginal shallow lagoons and two channel river zones. Gill-net collections resulted in 21 taxons of native fishes. Detritivorous Characiformes such as Steindachnerina insculpta were predominant. Sieve collections resulted in 31 taxa and the Tetragonopterinae subfamily was the/most representative group, which included small species as Cheirodon stenodon. The equitability index characterized the high heterogeneity of fish numeric abundance, reflecting the dominance of a few groups. A significant relationship between biotic and abiotic variables was indicated by the first canonical function. In comparison with other regions of the drainage basin, the ecotone zone studied indicated a higher species richness and, in the case of some species, fishes in all stages of development. This study demonstrated the necessity to preserve the ecological zone for the fishing and fishery management in the reservoir.

Histochemical, ultrastructural and morphometric methods were used to study growth patterns of red, pink and white muscle fibres and their relation to body weight and total length in the fast-growing freshwater fish Piaractus mesopotamicus Holmberg. The correlations amongst body weight, body length and diameter of red, pink and white fibres were low. From 10-15 to 40-50 cm, body weight increased 102.7 times, while the diameter of each type of fibre increased by factors of 0.94, 0.74 and 0.70, respectively. Muscle fibres revealed different morphological and histochemical stages of maturation. The frequencies of < 20 microns fibres of red, pink and white muscle tissue in the youngest and oldest classes were 64.5 and 11.0, 38.2 and 7.7 and 24.0 and 1.4%, respectively. In 30-40 cm fish, the frequency of < 20 microns fibres in the red and pink tissue was 24.5 and 25.5%, while in the white tissue it was 11.5%. During sexual maturity (40-50 cm), the recruitment of < 20 microns fibres in white muscle was 1.4%. Muscle fibres of this species showed continuous growth by both hyperplastic and hypertrophic mechanisms, and hyperplasia was particularly active in the juvenile phase.

No abstract

SEM RESUMO

The ichthyofauna of the Taquari River, one of the main tributaries of the South Pantanal, has been studied since the 1970s; however, there is a gap on the studies about the ichthyofauna present on the small adventitious streams of this highly dendritic system. These streams are small tributaries that flow directly into large rivers (mainstem), at least three orders greater in magnitude. The aim of this study was to analyze the structure of the ichthyofauna of five adventitious streams of the Upper Taquari River, South Pantanal, evaluating its temporal variation (dry and wet season) and the relation to the habitat characteristics and the conservation of the streams. Thirty-seven species were collected, from which 14 are exclusive to the Paraguay River basin, one species [Apteronotus albifrons (Linnaeus, 1766)] could represent a new record for this basin, and six species need taxonomic confirmation. The analysis indicated only the existence of spatial variation in the ichthyofauna structure of the streams sampled, with the similarity patterns related to the distance between the streams and to their conditions of conservation. The stream with greater size and preserved riparian forest was the one with the highest values of fish diversity and evenness. On the other hand, the stream with the smallest percentage of riparian forest and highest proximity to urban area presented the lowest diversity. The small size of these adventitious systems should serve as protection against large predators, which have their access to those areas hampered by their own size. Otherwise, the mainstem may also act as source of dispersal of small-bodied schooling fishes to the adventitious streams, where the greater heterogeneity of habitats and the presence of riparian vegetation should offer shelter and food supply for small species.