As informações sobre o ictioplâncton são ferramentas importantes para a determinação do período de reprodução que, se associado às variáveis ambientais, permitem inferências sobre os fatores que regulam sua intensidade, início e término. Nesse contexto, o presente estudo visa determinar: (i) a composição do ictioplâncton; (ii) as variações temporais na densidade de ovos, larvas e dos táxons mais importantes; e (iii) a influência de algumas variáveis abióticas e bióticas sobre a abundância destes organismos. As coletas de ictioplâncton foram realizadas no período de abril de 2005 a março de 2006, no rio Ivinhema, bacia do alto rio Paraná (MS/Brasil). Diferenças nas variações temporais do ictioplâncton foram avaliadas por ANOVAs unifatoriais. Análises de Componentes Principais e correlação de Pearson foram utilizadas para avaliar as relações entre densidade de ovos e larvas e as variáveis ambientais. Durante o período estudado, foram capturados 3.341 ovos e 2.896 larvas, sendo que a maior parte foi de espécies de médio e grande porte e que realizam algum tipo de migração reprodutiva. Ovos e larvas apresentaram suas maiores densidades nos meses de primavera e verão, exceto Bryconamericus stramineus que foi mais abundante no inverno. A densidade de ictioplâncton esteve mais correlacionada positivamente com a vazão e a temperatura da água. Contudo, Plagioscion squamosissimus apresentou relação positiva com o aumento do pH e dos organismos zooplanctônicos, enquanto B. stramineus apresentou correlação inversa com a vazão e temperatura da água. Conclui-se que as desovas são mais intensas na primavera-verão, principalmente entre novembro e janeiro, e estão relacionadas aos maiores valores de temperatura e vazão da água. Entretanto, a resposta e a intensidade reprodutiva às variáveis ambientais variam de acordo a espécie.

Information on ichthyoplankton is an important tool in determining reproduction periods that - if associated to environmental variables - allows for inferences about the factors that regulate their intensity, beginning, and ending. In this context, this study aims to establish (i) ichthyoplankton composition; (ii) temporal variations in the overall density of eggs and larvae and among the most important taxa; and (iii) the influence of some abiotic and biotic variables on these organisms' abundance. Ichthyoplankton sampling was undertaken during the period between April 2005 and March 2006 at the Ivinhema River, upper Paraná River basin (MS/Brazil). Differences in the ichthyoplankton's temporal variation were evaluated using unifactorial ANOVAs. Principal Component Analysis and Pearson's correlation were used for the relationships between eggs and larvae densities and environmental variables. A total of 3,341 eggs and 2,896 larvae were captured during the period studied, and most of them were medium-sized and large species that carried out some type of reproductive migration. The highest densities of eggs and larvae occurred during the months of spring and summer, except for those of Bryconamericus stramineus, which was most abundant during the winter. The density of ichthyoplankton was most positively correlated with the water's outflow and temperature. However, Plagioscion squamosissimus was positively related to the increase in pH and in zooplanktonic organisms, while B. stramineus was inversely correlated with water outflow and temperature. The study concludes that spawning is most intense in the spring and summer, especially between November and January, and is related to the greatest values of water temperature and outflow. Nevertheless, the response and reproductive intensity in relation to the environmental variables vary according to the species.

O objetivo deste trabalho foi avaliar o papel de fatores abióticos na ocorrência de larvas de peixes. As amostragens foram realizadas mensalmente em 12 estações (agrupadas em 4 áreas) nos rios Amambaí, Ivaí e Paraná e no reservatório de Itaipu, de outubro de 1994 a janeiro de 1995 (época de desova). Simultaneamente, foram obtidos dados de temperatura, pH, condutividade elétrica, oxigênio dissolvido, nível da água, velocidade da água e precipitação. Análises de Componentes Principais (PCA) e de Correspondência com Remoção do Efeito de Arco (DCA) foram aplicadas para sumarizar os dados abióticos e as densidades de larvas, respectivamente. O rio Amambaí diferiu significativamente das outras áreas em relação aos fatores abióticos. O reservatório de Itaipu diferiu significativamente das outras áreas quanto à composição de espécies, tendo o rio Ivaí também diferido do rio Paraná neste aspecto. A relação entre os eixos da PCA e DCA foi significativa, indicando que os fatores abióticos influenciam as larvas. Por exemplo, Leporinus elongatus preferiu o rio Amambaí, Hypophthalmus edentatus, Plagioscion squamosissimus e Hoplias aff. malabaricus o reservatório de Itaipu e Pimelodus maculatus, Auchenipterus osteomystax e Iheringichthys labrosus o rio Ivaí. Assim, sugerimos que cada espécie seleciona um conjunto de características abióticas em um dado ambiente utilizado como local de desova.

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambaí, Ivaí and Paraná rivers and in the Itaipu Reservoir (upper Paraná River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambaí River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivaí River also differed from the Paraná River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambaí River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivaí River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds.

Este trabalho teve por objetivo analisar a deriva do ictioplâncton em dois canais com diferentes condições de topografia e velocidade de fluxo, entre os estados do Paraná e Mato Grosso do Sul (Brasil). As amostragens foram realizadas no período de outubro de 1995 a abril de 1996, durante ciclos nictemerais. Amostras de água foram coletadas para determinação de algumas variáveis ambientais. A densidade de ovos diferiu significativamente entre os estratos, horários e meses; sendo que em ambos os canais, as maiores ocorrências de ovos foram verificadas entre janeiro e março, com maiores concentrações no fundo durante o período noturno. Com relação as larvas, as densidades diferiram entre os canais, horários e meses. As maiores ocorrências foram observas no canal direito, em ambos estratos, com maior período de captura entre janeiro e março. A superfície dos canais apresentou as maiores densidades de larvas durante o período noturno. A temperatura da água, condutividade elétrica e velocidade de fluxo foram diferentes entre os canais, entretanto, essas variáveis e a densidade de larvas não mostraram correlação, indicando que possivelmente outro fator, esteja influenciando a distribuição do ictioplâncton neste ambiente.

Analysis of drift of ichthyoplankton in two channels in the River Paraná, Brazil, were made. Sampling was undertaken from October 1995 to April 1996 during nychthemeral cycles. Water samples were collected to determine several environmental variables. Eggs densities largely differed to layers, times of day and months. In both the channels, highest occurrence of eggs was detected between January and March; greater concentrations at the bottom, during night. With regard to larvae, densities were significantly different in channels, times of days and months. Maximum occurrences were seen in the right channel, in both layers, with largest capture between January and March. Surface of the both channels presented highest density of larvae during night. Water temperature, electrical conductivity and flux velocity were different in the two channels, however, these variables and larvae density didn't showed correlations. This indicates that there was another possible factor, might be influencing the distribution of ichthyoplankton.

With the purpose of characterizing morphologicaly the larvae and juveniles of Apareiodon affinis (Steindachner, 1879) and to verify their temporal distribution monthly samples were taken at Leopoldo's Inlet, upper Paraná River. The specimens were captured with a conic-cylindrical plankton net of mesh size 0,5mm from March 1991 to February 1992. Soon after identification, the specimens were separeted according to their development (prefle-xion, flexion, posflexion and juvenile) and then the moiphometric analyses were performed. The results showed that the larvae were captured from August 1991 to February 1992, with greatest densities in November 1991. The specimens occured in every timetable, however, larvae in pretlexion and flexion were captured during day time and, posflexion and juvenile, at night. According to series of morphological development, high body proportions variation were verifyed mainly in the head lenght, eye diameter and in height body. Moreover, the individuais showed little pigmentation and myomeres number changing between 39 to 42. The majority of morphometric characteristics have negative allometry with the cxception of head lenght with regard to standart lenght that have positive allometry.

The ontogenetic aspects of larvae of Hypophthalmus edentatus (Spix, 1829) from the ichthyoplankton samples collected in the Itaipu reservoir between March 1988 and April 1990 were analysed. Sample were caught by 0.5 mm mesh conic-cylindrical plankton net. Larvae of H. edentatus were identified and described as Siluriforms from the morphological and morphometric development series. They have a small to medium-sized head, long body, small eyes, little pigmentation, mandibular barbules and 53 to 56 myomeres. High values obtained with correlation coefficient (r > 0.97; p < 0.001) show that growth was proportional in different parts of the body.

The spatial and temporal distribution and nychthemeral variation of fish larvae in six stations (Ivinhema, Patos, Paraná, Cortado, Baía and Guaraná) in the floodplain of the high Paraná river are provided. The paper also provides the relationship of this distribution to some environmental factors. From March 1992 to February 1993 ichthyoplanktonic samples were collected by conic cylindrical nets, with 0.5mm of mesh size and fluxometer attached, in 10-minute hauls at the surface and bottom during nychthemeral cycles. At the same time water samples were taken to determine environmental factors. During the above period 5,672 larvae were collected: 57,6% from Cortado station and 13,2% from Ivinhema and Paraná stations. The greatest densities were recorded between October and February, chiefly at night at the surface and by day at the bottom.

The aim of the present study was to characterize the larval development of Plagioscion squamosissimus (Heckel, 1840) morphometrically, collected at Itaipu reservoir from March 1988 to April 1990. It was obtained the samples monthly, with a conic-cylindrical plankton net with 0.5mm mesh. The morphological description of the larvae of P. squamosissimus was based on different stages of development. The specimens less than 6mm long present a moderate sized head and those that are larger than this length, present a large head. The pectoral fins are in an elevated position, near the operculum bones, and the ventral fins are in thoracic positions, the body has a moderate height, the eyes are small to moderate and the mouth is large with caniniform teeth. This species presents a proportional growth among the different parts of the body, as can be seen by the high correlation coefficient values (r>0.98; p<0.001).

Studies on the occurrence, temporal distribution and nychthemeral variation of Macrobrachium amazonicum (Heller, 1862) were undertaken in Leopoldo's Inlet, upper Paraná River, Porto Rico, Paraná, Brazil. Seventeen thousand and sixty specimens (11,786 larvae and 5,274 juveniles) were captured with a conicalcylindrical plankton net of mesh 0.5mm in monthly samples between February 1991 and February 1992. Results show that the greatest densities of larvae (301.83 larvae/10m³) and juveniles (168.8/10m³) of this species were caught in December 1991. Largest captures were made during the night. With regard to abiotic factors water temperature ranged from 20º to 30ºC, pH ranged from 5.66 to 7.37 and electric conductivity ranged from 51.83 to 65.33µS/cm. Relationship between the density of larvae and juveniles and abiotic factors was calculated by the Principal Components Analysis (PCA) which revealed the influence of some limnological variables especially on the distribution of larvae.

Abundances of Zooplankton volumes, fish eggs and larvae were determined for 812 oceanographic stations on six survey cruises to the southern Brazilian continental shelf. Contour charts of Zooplankton volumes are presented. A marked seasonality on Zooplankton volumes and number of fish eggs and larvae was observed. The highest values were obtained during late spring and summer seasons and the lowest in the autumn. The mean values of Zooplankton volumes, eggs and larvae for different depth zones and subareas were presented. Major part of fish larvae were classified into 55 families. The most abundant group were those of family Engraulidae, Myctophidae and Gonostomatidae. The larvae of Clupeidae were abundant in the late-spring and summer cruises.

Eggs and larvae of the cutlassfish, Trichiurus lepturus, were collected during the survey cruises of the project FINEP to determinate spawning areas and season. Six cruises were made from 1975 to 1977 in southern Brazil (23º S -29º S). Spawning occurred throughout the year, but intensively in the cruise, May 1976 (autumn). The heavy spawning area was offshore region of Ilha Grande and of Ilha de Sta. Catarina. Mean temperature of the spawning area was 24.09 ºC, ranging from 21.15 to 26.29 ºC and mean salinity was 35.31 ‰, ranging from 35.04 to 35.52 ‰. Catch data of cutlassfish fishery showed a gradual increase last several years in the two states: São Paulo and Santa Catarina.

Relaciona-se neste trabalho a ocorrência de 11 famílias e 26 gêneros de diferentes espécies de larvas e jovens de peixes coletados na Ilha Anchieta, Ubatuba (Lat. 23º32'S - Long. 45º05'W), durante os anos de 1973 e 1974. Foram analisados todos os peixes coletados, procurando-se estabelecer o período das desovas através da ocorrência dos diferentes estágios de desenvolvimento em que se encontravam, relacionando-os com as condições ambientais. A espécie mais abundante foi Eucinostomus sp., que ocorreu principalmente no verão. Umbrina coroides apareceu quase que durante o ano todo, Menticirrhus littoralis durante o inverno, enquanto que M. americanus ocorreu durante o verão. No outono, houve a ocorrência de Coleotropis sp. e a espécie mais abundante durante o inverno foi Anchoa lyolepis. Outras espécies que ocorreram em abundância durante o verão foram Albula vulpes, Sardinella brasiliensis, Harengula jaguana, Trachinotus carolinus e T. falcatus. Apresenta-se também a descrição morfológica de larvas e jovens de castanha (Umbrina coroides).

Occurrences of fish larvae and juveniles taken by beach seine at the Ilha Anchieta (Lat. 23º32'S; Long. 45º05'W) during the period from August 1973 to July 1974, were studied. The predominant species was Eucinostomus sp. (Gerreidae) which occurred more abundantly during summer season. Other species which occurred during hot summer season were: Albula vulpes (Linnaeus, 1758) (Albulidae), Sardinella brasiliensis (Steindachner, 1879), Harengula Jaguana Poey, 1865 (Clupeidae), Trachinotus carolinus (Linnaeus, 1766), Trachinotus falcatus (Linnaeus, 1758) (Carangidae), and Menticirrhus americanus (Linnaeus, 1758) (Sciaenidae). Menticirrhus littoralis (Holbrook, 1856), occurred all the year-round. Anchoa lyolepis (Evermann & Marsh, 1902) (Engraulidae) occurred more abundantly during winter and Coleotropis sp. (Atherinidae) during autumn. Morphological description of larvae and juveniles of Umbrina coroides Cuvier, 1830 was given.