The ichthyoplankton provides us with important information to determine the period and
spawning grounds of the fish, are fundamental for the knowledge of the taxonomy and
ecology of the species, however these studies are scarce in the middle Uruguay river. In this
sense, the objective of this work was to study the distribution and abundance of fish eggs and
larvae during an annual cycle in Porto Lucena / RS. The collections were carried out monthly
from October 2015 to September 2016 (an annual cycle), in the night period, from trawls
using plankton net of a conical-cylindrical shape of 500 ?m mesh. Four trawls were made
with two nets, 15 minutes each, totaling eight samples per month. In parallel to the samplings,
the following environmental variables were measured: water temperature, dissolved oxygen,
pH, electrical conductivity, water transparency and river level. The collected samples were
fixed in 4% formalin and taken to the laboratory, where the sorting (separation of eggs and
larvae) was carried out, the captured larvae were identified with the aid of a stereoscopic
microscope. To evaluate the temporal variation of the abundance of eggs, larvae, larval stages
and the six most abundant taxa, one-way ANOVA was applied and, when these were
significant, Tukey's a posteriori test was applied to to detect the differences. To verify the
association of the environmental variables in the abundance of eggs, larvae and the main taxa,
Pearson correlations were made. In order to reduce the dimensionality of the environmental
variables a Principal Components Analysis (PCA) was applied. During the study period,
5.648 larvae and 1.813 eggs were captured, 95.6% of which belong to the order Siluriformes.
By means of ANOVA, there were significant differences in the temporal distribution of eggs
(p <0.05) and larvae (p <0.05), both of the highest densities were observed from October to
December (p <0.05). The most abundant species were Pimelodus maculatus, Pimelodus
albicans, Pseudoplatystoma corruscans, Parapimelodus valenciennis, Iheringichthys labrosus
and Luciopimelodus pati. It is important to note the large number of larvae of migratory
species captured, corresponding to 84.6% of the total larvae. It is concluded that in Porto
Lucena there is a high reproduction rate, mainly of migratory fish, and their reproductive
activity occurs mainly in spring, coinciding with the increase of photoperiod, temperature and
water level of the river.O ictiopl?ncton nos fornece informa??es importantes para determinar o per?odo e locais de
desova dos peixes, que s?o fundamentais para o conhecimento da biologia e ecologia das esp?cies, no entanto esses estudos s?o escassos no m?dio rio Uruguai. Nesse sentido, este trabalho de conclus?o de curso teve como objetivo estudar a distribui??o e abund?ncia de ovos e
larvas de peixes, durante um ciclo anual no rio Uruguai, munic?pio de Porto Lucena/RS. As
coletas foram realizadas mensalmente entre outubro de 2015 a setembro de 2016 (um ciclo
anual), no per?odo noturno, a partir de arrastos utilizando rede de pl?ncton de formato c?nicocil?ndrico de malha de 500 ?m. Foram feitos quatro arrastos com duas redes, por 15 minutos
cada, totalizando oito amostras mensais. Paralelamente ?s amostragens, foram mensuradas as
seguintes vari?veis ambientais: temperatura da ?gua, oxig?nio dissolvido, pH, condutividade
el?trica, transpar?ncia da ?gua e n?vel do rio. As amostras coletadas foram fixadas em formol
4% e levadas ao laborat?rio, onde foi realizada a triagem (separa??o de ovos e larvas), as larvas capturadas foram identificadas com o aux?lio de um microsc?pio estereosc?pico. Para
avaliar a varia??o temporal da abund?ncia de ovos, larvas, est?gios larvais e os seis t?xons
mais abundantes foi aplicada An?lise de Vari?ncia unifatorial (one way, ANOVA) e, quando
estes foram significativos, aplicou-se o teste a posteriori de Tukey, a fim de detectar diferen-
?as nas m?dias. Para verificar a associa??o das vari?veis ambientais na abund?ncia de ovos,
larvas e dos principais t?xons, foram realizadas correla??es de Pearson. Com a finalidade de
reduzir a dimensionalidade das vari?veis ambientais foi aplicada uma An?lise de Componentes Principais (Principal Components Analysis; PCA). Durante o per?odo de estudo, foram
capturadas 5.648 larvas e 1.813 ovos, sendo 95,6% pertencem ? ordem Siluriformes. Atrav?s
da ANOVA, foi verificado que existem diferen?as significativas na distribui??o temporal de
ovos (p<0,05) e larvas (p<0,05). Para ambos as maiores densidades foram verificadas de outubro a dezembro (p<0,05). As esp?cies mais abundantes foram Pimelodus maculatus, Pimelodus albicans, Pseudoplatystoma corruscans, Parapimelodus valenciennis, Iheringichthys
labrosus e Luciopimelodus pati. Cabe destacar, o grande n?mero de larvas de esp?cies migradoras capturadas, correspondendo a 84,6% do total de larvas. Conclui-se que em Porto Lucena ocorre uma elevada taxa de reprodu??o, principalmente de peixes migradores e a atividade
reprodutiva desses ocorre principalmente na primavera, coincidindo com o aumento de fotoper?odo, temperatura e n?vel da ?gua do rio
