Morfometria cutânea e branquial de juvenis de jundiá (Rhamdia quelen)

Abstract

The interest in native fish species has increased exponentially in recent years. The silver catfish (Rhamdia quelen) is a species that has stood out and received attention from several researchers and fish farmers, due to its easy cultivation, rusticity and good productive performances, however, there is still a lack of morphological and structural information for the maximum use of the potential of the species. Therefore, this study aimed to evaluate the morphological profile of the epithelial and branchial structure of juvenile silver catfish, and how each stage of development can manifest the expression of mucous cells, making it possible to recognize the most representative area for future analyzes. The fish used in the study were purchased from a local fish farm and acclimated in boxes with a capacity of 30L in a recirculation system with water parameters monitored according to the optimum range for the species. During the experimental period, two groups of fish were fed with fish food (37% protein) daily - three times a day until their satiety. The groups, composed of juvenile fish, were evaluated according to their stage of sequential cutaneous and gill development. The group of juveniles I was composed of 9 fish with an average weight of 7.65g and a length of 9.18cm. The group of juvenile animals II, also composed of 9 fish, had an average weight of 28.09g, and a length of 16.69cm. At the end of the experimental period, all the animals were anesthetized and euthanized by spinal cord sectioning. Afterwards, 6 sections of skin were collected from the left side of the fish, three sections in the dorsal region and three in the ventral region, in addition to the second branchial arch, also on the left side. The samples were fixed in 10% formaldehyde and subjected to routine histological procedures with PAS + Alcian Blue pH 2.5 staining and Masson-Goldner Trichomium. The results indicated that due to the species' benthic habit, the ventral region is the most representative point for skin collection due to the higher concentration of mucous cells found. In the gills, the distribution of mucous cells allows for health assessment based on the excessive or scarce production of mucus that covers the lamellae. Silver catfish (R. quelen) have greater sensitivity in terms of immunological protection arising from the viscoelastic properties of the mucous layer and the epithelial barrier.