Aspectos alimentares, reprodutivos e nutricionais de três espécies do gênero ( Hemiodus Müller,1842) em um lago de inundação - Pará.
Resumo
The objective of this study was to analyze the trophic ecology of Hemiodus unimaculatus,
Hemiodus argenteus and Hemiodus gracilis, through the determination of food content and
bromatological evaluation beyond the reproductive period if the H. argenteus e H. gracilis
according to seasonal variations in a floodplain lake located in Lower Tapajós, Pará, Brazil.
Samples were taken from October 2016 to June 2018, totaling 21 months of collection. For
the analysis of the diets the frequency of occurrence (FO%) and Relative Volume (V%) of
food items combined in the calculation of the Food Index (%IAi), were verified. Feed
intensity was represented by the Repletion Index (IR). The amplitude of the trophic niche was
calculated using the Levins measure and the diet overlap the Pianka Index. The food strategy
was defined using the Costello graphical method. The heat map was used to understand the
changes in the trophic structure and the patterns in the seasonal variation of the species
studied. The reproductive aspects were evaluated through RGS, weight-length and gonadal
condition factor, these were combined with the bromatological analyzes to verify possible
relationships between the parameters. The three species consumed a diverse number of food
items, composed of microalgae, microcrustaceans, insect eggs and larvae of Chironomidae
and which are found mainly adhered to the roots of macrophytes and detritus. The H. gracilis
was the one that presented the most heterogeneous diet, this species had greater amplitude of
niche, when compared to the other two species; however, the food items were consumed in
small quantities and therefore the niche amplitude showed a result whit the narrow niche. The
overlap of the diets was high in all periods analyzed. Costello’s graph showed that species are
generalists within the trophic category of detritus. The heat map showed the formation of the
groups of the species and the food items, and how the overlap of the diets adjusts according to
the seasonal variation. Quando aos aspectos reprodutivos para Hemiodus gracilis and
Hemiodus argenteus, females predominated in relation to males (2.5:1 and 1.7:1 respectively).
The weight-length relation indicated negative allometry for H. gracilis for sex together,
females and males and positive allometry for H. argenteus for clustered sex and females, and
negative for males. The analysis of the reproductive period of H. gracilis and H. argenteus
showed that the species used the environment mainly as an growth and development area,
highlighting the months from November to April for H. gracilis and September to December
for H. argenteus with mature gonads, indicating the reproductive period of the species. The
bromatological analyzes for H. argenteus did not present a strong correlation with the
reproductive parameters, whereas for H. gracilis it had a strong relation with the reproduction.
The composicion bromatological for H. argenteus the moisture analysis presented a mean of
79.0 ±2.5, ashes of 5.0% ±0.3, protein of 16.7% ±3.0 and lipids 4.7% ±1.4. In H. gracilis the
humidity averages 77.9% ±3.1, ashes of 4.5% ±0.6, protein of 17.4% ±2.5 and lipids of 3.7%
±0.4.
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