The ichthyoplankton studies develops an extreme important role on rivers? ecosystem,
consisting an essential relation between species in organisms? trophic web, and at its
primary production in food chain. The various reproductive strategies of fish present an
important study area, increasing many researchers curiosity during the last years in order to
search and understand the association between full moon period, water temperature,
strategies used for each species, spawning locations and horizontal, vertical and nictemeral
distribution. Concerning to the research, it aims to evaluate the vertical and nictemeral
variation of ichthyoplankton organisms? density at Uruguay River channel, on the months
of December 2016 to January 2017, on three sample stations located at Porto Lucena,
Roque Gonzales and S?o Nicolau cities, all situated at Rio Grande do Sul state. To reach
the objective of study, daytime and nocturnal collect were made, on surface and bottom of
the river, materializing the collect of 24 samples on surface and 24 samples of the bottom
for each research station, totalizing 288 samples during the two months of study. Along
with the collect the following variables were measured: water speed, transparency,
temperature, dissolved oxygen, electric conductivity, pH and river level. Samplings were
accomplished with taper-cylindrical nets of 0.5 mm mesh. The collection instruments were
fixed with 4% formalin. Eggs and larvae were triad on labs; afterwards the larvae were
identified with the aid of specialized bibliographic references. It was utilized Analysis of
Variance (ANOVA), Tukey?s post-hoc test and Pearson?s correlation to observed the
organisms? correlations with environmental variables. On the present study 2.856 larvae
and 2.494 eggs were captured. Most of the captured larvae correspond to the
Characiformes and Siluriformes orders. Among the most abundant species, the
prominence is the Bryconamericus stramineus lambari and the Schizodon altoparanae
vogue. During the study it was possible to conclude that exists a periodicity on the fishes?
eggs and larvae?s drift. These organisms are found mostly on surface during nocturnal
period. The interaction of daytime with the water column position was significant in all
larvae development stages, moreover, it was verified that the larvae prefers to stay on the
bottom during daytime and migrate to the surface at night on the after-flexion stage. At this
study, it was also registered the presence of migratory species of great size, such as:
Megaleporinus obtusidens, Prochilodus lineatus, Rhaphiodon vulpinus, Pterodoras
granulosus, Luciopimelodus pati, Pseudopimelodus mangurus, Sorubim lima and
Pseudoplatystoma corruscans. It is conclude that ichthyoplankton organisms perform
vertical migration, emerging mostly to the surface during night period. On the other hand,
the research region is essential for many life cycles of various migratory large species,
since many species were reported on this work.O ictiopl?ncton desempenha um papel de extrema import?ncia nos ecossistemas
dos rios, constituindo uma importante liga??o entre esp?cies na teia tr?fica dos organismos,
e na produ??o primaria das mesmas na cadeia alimentar. As variadas estrat?gias
reprodutivas dos peixes se apresentam uma importante ?rea de estudo, que nos ?ltimos
anos alavancou a curiosidade de muitos estudiosos a fim de buscar entender a rela??o entre
o per?odo das cheias, temperatura da ?gua, estrat?gias usadas por cada esp?cie, locais de
desova e distribui??o na coluna da ?gua. O presente trabalho teve como objetivo avaliar a
varia??o vertical e nictemeral da densidade de organismos ictioplanct?nicos na calha
principal do rio Uruguai. O estudo foi desenvolvido nos meses de dezembro de 2016 e
janeiro de 2017, em tr?s esta??es amostrais situados nos munic?pios de Porto Lucena,
Roque Gonzales e S?o Nicolau, todos situados no estado do Rio Grande Sul. Para a
realiza??o da pesquisa foram feitas coletas diurnas, noturnas, de superf?cie e fundo,
concretizando a coleta de 24 amostras de superf?cie e 24 amostras de fundo por cada
esta??o amostral, totalizando 288 amostras nos dois meses de estudo. Juntamente com as
coletas foram mensuradas as seguintes vari?veis de qualidade da ?gua: velocidade da ?gua,
transpar?ncia, temperatura, oxig?nio dissolvido, condutividade el?trica, pH e o n?vel do rio.
As amostragens foram realizadas com redes c?nico-cil?ndricas com malha de 0,5mmm. O
material de coleta foi fixado com formol 4%. No laborat?rio da Universidade Federal da
Fronteira Sul ? Cerro Largo, ovos e larvas foram triados, e posteriormente as larvas foram
identificadas com ajuda de refer?ncias bibliogr?ficas especializadas. Foram utilizados a
An?lise de Vari?ncia (ANOVA), o teste posteriori de Tukey e a correla??o de Pearson para
ver a varia??o dos organismos e a sua correla??o com as vari?veis ambientais. No presente
estudo foram capturadas 2.856 larvas e 2.494 ovos de peixes. A maior parte de larvas
capturadas corresponderam a ordem Characiformes e Siluriformes. Dentre as esp?cies mais
abundantes destaca-se o lambari Bryconamericus stramineus e a voga Schizodon
altoparanae. Durante o estudo foi poss?vel constatar que existe uma periodicidade na
deriva dos ovos e larvas dos peixes. Estes organismos s?o encontrados principalmente na
superf?cie no per?odo noturno. A intera??o do turno do dia com a posi??o na coluna da
?gua foi significativa para todos os est?gios de desenvolvimento larval, inclusive no
est?gio de Pos-flex?o foi verificado que a larva prefere estar no fundo durante o dia e
migrar para a superf?cie ? noite. No estudo tamb?m foi registrado a presen?a de esp?cies
migradoras de grande porte tais como: Megaleporinus obtusidens, Prochilodus lineatus,
Rhaphiodon vulpinus, Pterodoras granulosus, Luciopimelodus pati, Pseudopimelodus
mangurus, Sorubim lima e Pseudoplatystoma corruscans. Conclui-se que os organismos
do ictiopl?ncton realizam migra??es verticais sendo que ? durante a noite quando eles se
encontram principalmente na superf?cie. Por outro lado, a regi?o estudada ? importante
para o ciclo de vida de muitas esp?cies migradoras de grande porte, visto que larvas de
muitas destas esp?cies foram registradas neste trabalho
