Abstract
ABSTRACT Pygocentrus nattereri is a carnivorous fish widely distributed in the Brazilian wetland and occupies different river strata. Based on the sexual maturity, the standard length (SL) has been used to categorize age and physiological attributes. However, hematological parameters and their relationship with age and growth features are unknow. Here, the aim was to evaluate the hematological profile and leukocyte data of juvenile and adult specimens, associating it with SL. Specimens of both sexes were weighted, and SL were measured for classify as juveniles (SL ≤16.0 cm) and adults (SL ≥16.1 cm). Blood was collected to perform the hemogram, for leukocyte quantification and ultrastructural descriptions. In general, hemogram values and leukocyte, lymphocyte, and monocyte counts were high in juveniles. Hemogram variables were negatively correlated with SL. Thrombocyte and neutrophil counts were higher in adults than in juveniles. SL was correlated with leukogram variables. Ultrastructural analysis showed that granular leukocyte count in P. nattereri was similar another fishes. PAS-positive granular leukocytes are slightly smaller than neutrophils and are characterized by dense elongated and semi-lunar shapes in the cytoplasm. Our results suggest that age-based SL may be useful for the analysis of the relationship between P. nattereri health status and wetland aquatic environments.
Highlights
The Brazilian Pantanal is a wetland region that is mainly formed by tributaries from the left margin of the Paraguay River and represents approximately 74% of the total drainage area (Alho, 2005)
We aimed to evaluate the association between standard length (SL) and the hematological profile of juvenile and adult P. nattereri specimens and provide a morphological description of leukocytes in this species
Potential factors that modulate the hematological response in fish such as sex, age, season, feeding habitat, reproductive patterns, parasites, and microbiota homeostasis interactions have been widely studied (Barber, Wright, 2005; Ahmed et al, 2020)
Summary
The Brazilian Pantanal is a wetland region that is mainly formed by tributaries from the left margin of the Paraguay River and represents approximately 74% of the total drainage area (Alho, 2005). The seasonal mean temperature is usually constant and ranges between 20 °C in July and 27 °C in December; the rainfall is seasonally well defined (Krepper et al, 2006; Assine et al, 2015) Within this wetland region, there are 11 hydrographic sub-basins, including the Miranda River basin (Paranhos Filhos et al, 2017). Pygocentrus nattereri are highly abundant and widely distributed in different river strata They have known feeding strategies, are recognizable, occupy a clear trophic position, and have a well-defined reproductive season. They are ideal for use as an ecological bioindicator in lotic or lentic environments (Chovanec et al, 2003; Burger, 2006). Their phylogeny, endoparasites, environmental life-history features, and breeding behavior have all been studied; their hematological profiles are unknown (Uetanabaro et al, 1993; Vicentin et al, 2013; Ferreira et al, 2014)
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