In this paper we describe some aspects of the reproduction and development of secondary sexual characters of Bryconamericus iheringii, based on the analysis of 194 females and 210 males collected monthly in the rio Vacacaí (30 o 21'34"S and 54 o 18'48"W), from April 2001 to March 2002. The reproductive period occurred from September to January (spring and summer in the Southern Hemisphere), as described for other characids of the same area. The absolute fecundity mean was 933.71 ± 303.10 oocytes, and the relative fecundity mean was 0.36 ± 0.08 oocytes per mg of total weight, being the species a multiple spawner. There was no correlation between the values of GSI and variation of biotic (stomach repletion and hepatosomatic indexes) and abiotic data (rainfall, day length and temperature) but we suggest that these factors can influence the reproduction of the species acting as "starters" of the beginning of gonadal maturation. Fin-ray hooks consist in a sexually dimorphic character of the species. Well developed hooks were found mainly in mature males, during the reproductive period and in the largest individuals.Neste trabalho são descritos aspectos da reprodução e do desenvolvimento de caracteres sexuais secundários em Bryconamericus iheringii. Foram analisados 194 fêmeas e 210 machos coletados mensalmente no rio Vacacaí (30 o 21'34"S e 54 o 18'48"W), de abril de 2001 a março de 2002. O período reprodutivo ocorreu de setembro a janeiro (primavera e verão no hemisfério sul), como descrito para outros caracídeos da mesma região. A fecundidade absoluta média foi de 933,71 ± 303,10 ovócitos e a fecundidade relativa média foi de 0,36 ± 0,08 ovócitos por mg de peso total, sendo a desova do tipo parcelada. Não houve correlação entre os valores de IGS e a variação dos dados bióticos (índices de repleção e hepatossomático) e abióticos (pluviosidade, fotoperíodo e temperatura) mas sugere-se que estes fatores possam influenciar na reprodução da espécie, atuando como desencadeadores do início da maturação gonadal. Ganchos nas nadadeiras ventrais e anal dos machos consistiram em caracteres de dimorfismo sexual da espécie. Ganchos bem desenvolvidos são encontrados principalmente em machos maduros, durante o período reprodutivo e nos maiores indivíduos.

Reproduction of Bryconamericus stramineus was described based on the analysis of 208 females and 166 males collected monthly in the Rio

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Some aspects of reproduction in two species of Mimagoniates, M. microlepis (Steindachner 1877) and M. rheocharis Menezes & Weitzman 1990 are herein described. Samples were taken monthly from January 1998 to February 1999 in two streams in the locality of Maquiné, Rio Grande do Sul, Brazil. Results from the analysis of hundreds of specimens of M. microlepis and M. rheocharis in two investigated sites indicated mature specimens and peaks of the gonadosomatic index (GSI) along the year. There was a negative and significant correlation between M. microlepis male’s GSI and water temperature. Females of the latter species and both sexes of M. rheocharis, in turn, showed no correlation with any of the tested parameters (relative stomach weight, day length, rainfall). Absolute and relative fecundity are lower than in externally fertilized species of Characidae. Maximum oocyte length was 1.14 mm for M. microlepis and 1.02 mm for M. rheocharis and both species were characterized as total spawners based on the type of oocyte development estimated through oocyte size analysis. Features like non-seasonal reproductive period, low fecundity, and insemination may indicate adaptive advantages, which may enhance the chance of survival even with low energetic investment and improved fertilization.

Aim In the present work we describe and analyze the diet of a small characin species, Piabarchus stramineus, from the Ibicuí River, Uruguay River Basin, southern Brazil. Methods Samples were collected monthly from April 2001 to March 2002 with seine net. All fish were measured, weighed, and had its stomach extruded for gut content analysis. Months were grouped in seasons and fish were classified within three standard length classes (SLC). We tested for possible alimentary differences between the different seasons of the year and standard length classes. Results The analysis of the content in 301 stomachs identified 27 food items and low to intermediary niche breadth. The main food item/category was allochthonous insects, regardless of the seasons, and P. stramineus can be classified as an insectivorous species. We observed no food overlap between smaller and larger fish (SLC1 and SLC3). On the other hand, we observed food overlap between small and intermediary fish (SLC1 and SLC2) and between intermediary and large fish (SLC2 and SLC3), evidencing a transition in food consumption along size classes. A temporal variation in diet composition was also observed among size classes. Thus, different sized fish differed in their diets, with smaller fish feeding mainly on cladocerans (SLC1 and SLC2) and larger fish (SLC3) feeding mainly on allochthonous Diptera and Hymenoptera. Conclusions The species diet varies in time (seasons) and such variation is different in each size class. Allochthonous food items were important in the diet of the species in the different developmental phases, especially for larger fish, with autochthonous items also important, especially for smaller fish. The allochthonous food items are strongly related to the ciliary forest; thus, we emphasize the importance of the conservation of such environments.