This study describes anatomical, histological and histochemical features of the digestive tract mucosal layer of the matrinxã Brycon amazonicus, an omnivorous freshwater fish endemic from the Amazon basin. This species presents short thick oesophagus with longitudinal folds, that allow the passage of large food items. The mucosa is lined with a stratified secretory epithelium rich in goblet cells that secrete neutral and acid mucins. The two mucin types provide different viscosity in anterior and posterior oesophagus related to the protective and lubricant functions, respectively. The stomach is a highly distensible Y‐shaped saccular organ. Here, it is proposed that this anatomical shape plays an essential role in food storage when food availability is abundant. The stomach mucosa is composed of epithelial cells with intense neutral mucin secretion to protects against gastric juice. The intestine is slightly coiled and presents internally a complex pattern of transversal folds that increases the absorption surface and the retention time of food. Goblet cells in the intestine secrete acid and neutral mucins that lubricate the epithelium and aid in the digestive processes. In the rectum, an increase in goblet cells population occurs that may be related to better lubrication.
The purpose of this study was to describe the structure of the midgut (hepatopancreas and intestine) in the endemic species, Macrobrachium carcinus. Thirty specimens were collected, and the midgut was fixed in Bouin's solution for histological and histochemical analyzes by light microscopy. The hepatopancreas consists of two lobes that connect to the end of the stomach by primary ducts, which originate secondary tubules or hepatopancreatic ducts, that branch into hepatopancreatic tubules. The hepatopancreatic duct presents a columnar epithelium composed of R-and F-cells with evident brush borders for absorption and storage. The hepatopancreatic tubule is lined by epithelium with five cell types (E, F, R, B, and M). The distal region presents all cell types, with a predominance of E-cells that correspond to epithelial renewal. The middle region presents F-and B-cells, characteristic of extracellular and intracellular digestion. The proximal region, with B-and R-cells, performs the final digestion, storage, and extrusion of the cells with
B chromosomes are non-essential additional genomic elements present in several
animal and plant species. In fishes, species of the genus
Psalidodon
(Characiformes, Characidae) harbor great
karyotype diversity, and multiple populations carry different types of
non-essential B chromosomes. This study analyzed how the dispensable
supernumerary B chromosome of
Psalidodon paranae
behaves during
meiosis to overcome checkpoints and express its own meiosis-specific genes. We
visualized the synaptonemal complexes of
P. paranae
individuals
with zero, one, or two B chromosomes using immunodetection with anti-medaka
SYCP3 antibody and fluorescence
in situ
hybridization with a
(CA)
15
microsatellite probe. Our results showed that B
chromosomes self-pair in cells containing only one B chromosome. In cells with
two identical B chromosomes, these elements remain as separate synaptonemal
complexes or close self-paired elements in the nucleus territory. Overall, we
reveal that B chromosomes can escape meiotic silencing of unsynapsed chromatin
through a self-pairing process, allowing expression of their own genes to
facilitate regular meiosis resulting in fertile individuals. This behavior, also
seen in other congeneric species, might be related to their maintenance
throughout the evolutionary history of
Psalidodon
.
Testes and vasa deferentia are parts of the male reproductive system of decapod crustaceans. Both organs show morphological differences among decapod species in terms of anatomical and histological patterns reflecting the diversity of this group.Describing these features may assist in systematics, phylogenetics, and studies of reproductive behavior, especially for species of commercial interest, such as Macrobrachium carcinus, a native American species that, unusually for this genus, has no precopulation courting behavior. This study aims to describe the reproductive morphology and spermatogenesis of the male freshwater prawn M. carcinus. The male reproductive system of this species consisted of lobed testes connected to the vasa deferentia. The testis of M. carcinus was divided into several lobules. Each lobule was formed by a cluster of germ cells surrounded by connective tissue and nurse cells.This microscopic anatomy and histology of the testicular histoarchitecture has been described for many species of Decapoda and may represent a derived design of the testes. Unlike that in other decapod species, spermatogenesis proceeds in short transitory phases that produce spermatozoa at high concentrations and frequencies, corroborating the uncommon male reproductive behavior of this species. In the spermatic pathway, the lobules develop and fuse before releasing spermatozoa from the testes; however, this process has not been observed in decapods, yet. The neutral compounds secreted by the vas deferens are important for sperm nutrition as females secrete a substance for spermatophore adhesion during reproduction. This study presents different features and dynamics of the spermatogenic process in the male reproductive system of M. carcinus that have not yet been presented in the literature for decapods.
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