In the Amazon near Manaus, larvae of Characiformes, Clupeiformes, Tetraodontiformes, Pleuronectiformes, Gymnotiformes, Belonidae and Sciaenidae were sampled in the river during most of the year, except in June and July, when the water level was at its maximum. Characiformes, Tetraodontiformes and Siluriformes were found in the ichthyoplankton mostly during the rising waters, but Clupeiformes and Sciaenidae drifted in the river almost all year around. Egg abundance was extremely low, suggesting that they do not drift or have a very short residence time. Two types of larval drift seemed to occur: a rising water drift and a lowering water drift. Characiformes, Tetraodontiformes and some Clupeiformes drifted mostly during the rising waters and were more abundant near the banks. Their strategy seemed to be a passive dispersion towards the floodplain with the flood pulse. The high densities near the banks optimized their chances of reaching a floodplain inlet. The groups that drifted during the lowering waters showed an alternative strategy. They were flushed from the floodplain lakes and may have stayed in the main river channel for a few months before returning to the floodplain. Predation in the lakes during the period when water level decline was probably the force behind this drift.

Many streams and large rivers present higher ichthyoplankton densities at night. However, in some rivers this does not occur and larvae are equally abundant during the day. Larval drift diel variation is an important information for planning sampling programs for evaluating larval distribution and production. The aim of this study was to test whether the abundance of larval fish was different at either period. We tested it by comparing day and night densities of characiform, clupeiform and siluriform larvae during five years in the Amazon and one year in Rio Negro. We found that larvae of three species of characiform and larvae of siluriform were equally abundant during day and night in the Amazon. Conversely, the catch of Pellona spp. larvae was significantly higher during the day. In Rio Negro, however, larval abundance was higher during the night. These results imply that day samplings estimate adequately the abundance of these characiform and siluriform larvae in the Amazon, but not Pellona larvae. Evaluations of larved densities of Rio Negro will have to consider night sampling.

The abundance and distribution of ichthyoplankton and their relationships to current velocity, temperature, dissolved oxygen, pH and electrical conductivity of the water in the Anavilhanas Ecological Station, Negro River, Amazonas State, Brazil, were analyzed. Preferred microhabitats for spawning, dispersion and nursery were also verified. Sampling was undertaken during the falling water period of 2001 and the rising water period of 2002, in a section of 100 km subdivided into 5 subsections, with a total of 20 stations (5 beaches, 5 ravines, 5 channels, and 5 lake channels) at night and during the day at the surface and at the bottom. 647 eggs and 4,187 larvae were captured, belonging to 10 families and four orders: Characiformes (6), Siluriformes (2), Perciformes (1), and Clupeiformes (1). Engraulidae (55.39%), Pimelodidae (30.45%), Auchenipteridae (5.23%) and Sciaenidae (5.13%) were the dominant families. The hierarchical statistical model (ANOVA) with three factors (microhabitat, depth and period) was applied to the environmental variables and the larval abundance, showing greater abundances of sciaenids in the ravines and lower abundances of engraulids in the channels. The highest captures were obtained at lower temperature values, at the bottom during the day and at the surface at night, suggesting an active larval behavior. The presence of the four larval development stages in all subsection for pimelodids and sciaenids, and in three subsections for engraulids, indicates that the Anavilhanas Ecological Station is an important spawning and nursery area for species of these groups in the Negro River. Larvae abundance of all characiform families was extremely low (from 0.1 to 1.17%), suggesting that they do not spawn in this system.A abundância e distribuição do ictioplâncton e suas relações com a velocidade da corrente, temperatura, oxigênio dissolvido, pH e condutividade elétrica da água na Estação Ecológica Anavilhanas, rio Negro, Amazonas, Brasil, foram investigadas, bem como o uso de áreas e microhabitats preferenciais para desova, dispersão e criação. As coletas foram realizadas em dois perío-dos: vazante de 2001 e enchente de 2002, em um trecho de 100 km dividido em cinco subseções, e em cada um delas foram amostrados os microhabitats praia, barranco, canal e canal de lago, com um total de 20 pontos de coletas (cinco praias, cinco barrancos, cinco canais e cinco canais de lago). As coletas foram realizadas durante o dia e à noite na superfície e no fundo. 647 ovos e 4.187 larvas de peixes foram capturados, pertencentes a quatro ordens e dez famílias: Characiformes (6), Siluriformes (2), Perciformes (1) e Clupeiformes (1). As famílias dominantes foram Engraulidae (55,39%), Pimelodidae (30,45%), Auchenipteridae (5,23%) e Sciaenidae (5,13%). O modelo de estatística hierárquica (ANOVA) com três fatores (microhabitat, profundidade e período) foi aplicado às variáveis ambientais e às abundâncias de larvas, mostrando maior abundância de Sciaenidae nos barrancos e menor de Engraulidae nos canais. As maiores ca...

The larvae distribution of Mylossoma aureum and M. duriventre were analyzed on the Solimões river comprising 60 km long, during two years (1995)(1996). Distributions between habitats and in the vertical strata were considered. The main habitats considered were cutting banks, filling banks, mouth lake channels and lake channels. The distribution was not homogeneous between habitats. The lowest densities were found in the filling banks and the highest in the cutting banks and mouth of lake channels. Lake channels present higher larval abundance than filling banks. This pattern seems to be related to hydrodynamics processes associated with the spawning and larval behavior of the two species. In the most habitats M. aureum was more abundant at the surface samples than the bottom samples, but M. duriventre showed the opposite vertical distribution. The vertical stratification seems to be due to swimming abilities of the larvae.

RESUMO -A distribuição sazonal das larvas de Mylossoma aureum e M. duriventre (Osteichthyes: Serrasalmidae), foi estudada na costa do Catalão, rio Amazonas durante três anos. As larvas de ambas espécies de Mylossoma foram mais abundantes na estação marginal do que na estação localizada no centro do rio. O período de ocorrência das duas espécies foi semelhante e durou em média 109 dias, variando de novembro-janeiro a abril-maio. A variação na abundância de larvas durante o período de ocorrência não se relacionou com a luminosidade da lua, nem com a pluviosidade local. Porém, a enchente apresentou efeito na variação da densidade de Palavras-chave: Amazônia, peixe, larva, distribuição sazonal, Characiformes.Seazonal Larval Distribution of the Mylossoma aureum and M. duriventre (Osteichthyes: Serrasalmidae) on the Coast of Catalão in the Amazon River, Amazonas State, Brazil ABSTRACT -The seazonal variation of larval distribution of Mylossoma aureum and M. duriventre (Osteichthyes: Serrasalmidae), were studied in the coast of Catalão, Amazon River during three years. Only the first feeding stage larvae were found drifting on the river. Larvae were more abundant near the banks than in the middle river channel. The average larval drift lasted 109 days, varying from November-January to April-May. The variation of larval abundance was not related to the rain or the moon phases, but only to an increase of water level for M. aureum in year of 1994-1995.