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The estimated mean intestinal coefficients of Leporinus friderici Bloch, 1794 and L. taeniofasciatus Britski, 1997, from the Upper Tocantins River, central-western Brazil, were 1·25 0·15 and 1·14 0·07, respectively. The external surfaces of the lips have taste buds. The histological structure is composed of four layers: mucosa, submucosa, muscular, and serosa. No muscularis mucosa is detected. The oesophageal epithelium is stratified in L. friderici and pseudostratified in L. taeniofasciatus, the latter with PAS+ basal cells and eosinophilic apical cells. A thick layer of adipose tissue was found within the submucosa. Leporinus taeniofasciatus has a sphincter separating the cardiac and fundic portions of the stomach. In both species, gastric glands are present in the stomach, except in its pyloric portion. The pyloric caeca possess a simple columnar epithelium with brush border and three types of goblet cells. Rodlet cells were found in L. friderici. The three portions of the intestine showed no histological differences. Anatomical and histological features of the digestive tract are consistent with the omnivorous habit of both these species. 2001 The Fisheries Society of the British Isles

Electrofishing adequacy was tested as a technique to obtain quantitative data of coastal stream fish populations and communities in the Southeast of Brazil. Seven field trips, between July/94 and July/95, were done in 5 localities of the Ubatiba fluvial system (Maricá, RJ). Seventeen species, among the 22 collected, had their numbers estimated through the Zipping method, the model used to test the sampling methodology. At each field trip, three removals with electrofishing were done in each locality and, according to the number of obtained species at each locality/field trip, we analysed 315 cases. Nineteen cases, among 315, showed failure condition. Estimates were significant (p < 0.01) in 96% of the studied cases. Non-significant cases were obtained for rare species due to over and randomly efficient electrofishing in 63.3% and 36.4% of the cases, respectively. No correlation was found between catchability and the estimated number of individuals and/or environmental characteristics. High values for sampling efficiency (> 85%) were found for all estimates. An experimental analyses were done for one locality and, the comparison between the estimates for 3 and 6 successive removals showed a mean error and a standard deviation of 5.5% and 2.1% respectively. Therefore, it can be concluded that electrofishing was an efficient method for quantitative data analysis of fish populations and communities in the Ubatiba fluvial system.

Aspects of the reproductive biology of Astyanax janeiroensis in the Ubatiba river in Maricá, RJ, Brazil were evaluated in order to ascertain whether the strategy adopted by the species is causally related to environmental variables. Specimens were collected on a monthly basis from October 1994 to September 1995, through electrofishing. The Sex ratio was not significantly different from the expected frequency of 1:1 (G = 1.29; p > 0.50); nonetheless, considering three standard length classes, significantly larger numbers of females were recorded for the higher SL class (G = 11.07; p < 0.01). Size at first maturation showed no significant differences between sexes. Length-weight ratio analyses showed negative allometry for males and isometry, for females. Length structure was significantly different between sexes, suggesting that females are larger than males (D = 0.027, p < 0.01). Reproductive specimens were recorded during nine months of the annual cycle. Seasonal variations of reproductive specimens belonging to two different standard length classes displayed an asynchronous behavior, with larger specimens having a longer reproductive period and smaller ones reproducing for fewer months during the annual cycle. High values of fecundity (F), varying from 3169 to 18714 oocytes, were recorded for fish of 9.1 and 10.2 cm lengths, respectively. The correlation between weight and number of oocytes/unit of weight was positive, indicating that larger specimens produced more eggs.Keywords: stream-dwelling fish, coastal stream, reproductive biology. RESUMOBiologia Reprodutiva de Astyanax Janeiroensis (Osteichthyes, Characidae) do Rio Ubatiba, Maricá, RJForam analisados aspectos da biologia reprodutiva de Astyanax janeiroensis do rio Ubatiba -Maricá, RJ, afim de discutir se a estratégia adotada possui alguma relação de causalidade com as variáveis ambientais. Os espécimens foram coletados mensalmente, entre outubro 1994 e setembro 1995, mediante pesca elétrica. A proporção sexual não diferiu significativamente do esperado 1:1 (G = 1.29; p > 0.50); mas, considerando-se 3 classes de tamanho distintas, foi registrada diferença significativa, com predomínio de fêmeas, na classe de maior tamanho (G = 11,07; p < 0,01). O tamanho médio da 1 a maturação não apresentou diferença significativa entre os sexos. A análise da relação entre o peso e o indicou alometria negativa para os machos e isometria para as fêmeas. A estrutura de tamanho foi significativamente diferente entre os sexos sugerindo que as fêmeas alcançam tamanho superior ao dos machos (D = 0,027, p < 0,01 exemplares de maior tamanho reproduzindo durante um maior intervalo de tempo e os exemplares menores com reprodução restrita a alguns meses do ciclo anual. Altos valores de fecundidade foram registrados, variando de 3169 a 18714 ovócitos para peixes de 9,1 a 10,2 cm, respectivamente. Análises de correlação, entre peso total e o número de ovócitos/unidade de peso, apresentou correlação positiva e indicou que os espécimes maiores produzem mais ovos.Palavras-chav...

Length-frequency analyses showed that male HypostomuS ufinis are bigger than femalcs, but H. luetkeni showed no such differences. The sex ratio was estimated at 1 : 1 for both species.The temporal variation of sex ratio indicated a decrease in the male population when GSI was at its maximum value, suggesting that males are less prone to capture during the spawning season. According to the decrease of males during the reproductive period, paternal behaviour is proposed for both species. H. ufinis reached sexual maturity at a smaller size than H. luefkeni. Considering the length weight relationship and the mortality rate of the reproductive females in both species, the physiological consequences of delay or precocity of the first maturation are discussed. 9' 1995 Thc Fisherics Socicty of the British Isle.;Kcy words: size structure; sex ratio; onset of maturity; Hypostomus spp.; Brazil

ABSfRACf. SPATIAL OCCUPATlON, FEEDlNG AND REPRODUCfIVE PERIOD OF NO SPECIES OF CORYDORAS LACÉPEDE (SILUROIDEI, CALLICHTHYIDAE) COEXISTENTS lN THE ALAMBARI RIVER (BOTUCATU, SÃO PAULO). Patterns of spatial occupation, feeding, and reproductive period of two species, Corydoras aeneus and Corydo ras gr. earlae (Siluroidei, Callichthyidae), coexistents in the Alambari River (Botucatu, São Paulo), were studied. High diet overlap, partial spatial segregation, and well differentiated reproductive strategies were verified. These findings do not permit to evidence the occurrence of competitive interactions between the analysed species. KEY WORDS. Siluroidei, Callichthyidae, spatial occupation, feeding; reproductive period o estudo da partilha de recursos entre espécies de uma comunidade pode fornecer dados importantes para o conhecimento da natureza das relações interespecíficas entre espécies coexistentes (SCHOENER, 1974).Durante estudo sobre a distribuição longitudinal de peixes em riachos da região de Botucatu (São Paulo), CARAMASCHI (1986) registrou Corydoras gr. carlae como espécie constante no trecho médio e Corydoras aeneus como constante nos trechos médio e inferior de alguns cursos d'água. Foi constatada, portanto, coexistência das duas espécies no trecho médio desses rios, o que motivou o estudo da partilha de recursos entre elas.Assim sendo, neste trabalho são apresentados os resultados da análise da segregação espacial e alimentar, bem como aspectos da reprodução, de Corydoras gr. car/ae e C. aeneus coexistentes em um riacho daquela região.

Brycon gouldingi and B. falcatus were the most abundant and widespread of five species of the genus captured in a sampling study encompassing 5 years (1995)(1996)(1997)(1998)(1999)(2000) in the upper Rio Tocantins, where the river was impounded by the Serra da Mesa hydroelectric dam. Given that impoundments constitute a disturbance to which species will show demographic and biological responses, we assessed such responses of these two omnivorous fishes, whose genus is regarded as vulnerable to impoundments. Both species increased greatly in numbers during the initial reservoir filling period. Brycon gouldingi had higher abundance values than B. falcatus in all sampling months, except in the pre-impoundment period. Both species showed a significant weight increment relative to body length during the time they remained in the reservoir. No reproductive individuals of B. gouldingi were recorded in the study area, but those few of Brycon falcatus were found in both wet and dry seasons, suggesting a more opportunistic strategy of reproduction. Both species were omnivorous and overlapped broadly in diet. The proportions of dietary items, however, varied in relation to fish size class and water dynamics (lotic versus lentic sites). Terrestrial arthropods composed a larger proportion of the diet of smaller-sized individuals and those from lentic sites, whereas seeds and fruits contributed more to the diet of both larger-sized individuals and those from lotic environments. Except for fish and aquatic heteropterans, which were consumed mainly in the reservoir, all other food items were allochthonous, indicating the dependence of these two species of Brycon on the terrestrial environment. The two species responded similarly to the alterations imposed by the impoundment of the upper Tocantins, although reproduction/recruitment pattern was slightly different between species. As observed in other regions of Brazil, impoundments and deforestation appear to produce negative cumulative effects on species of Brycon. These impacts call for greater efforts to conserve and manage members of this diverse and widespread genus.

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