Mariana Rojas; Mario Pellón; Claudio Cerda; Roberto Ulloa; Rudy Suarez; Marcos Godoy & Mariano del Sol

This study analyzes the deformity of Atlantic salmon fry (Salmo salar) caudal fin, which gives it a "pointed tail" appearance. Although at hatching specimens were normal, the deformities were detected later. The objective of this work is to des- cribe the anatomical and histological changes of the deformed cau- dal fin of the Atlantic salmon fry (Salmo salar). In this analysis we used 60 specimens for laboratory analyses, to rule out the presence of viral or bacterial pathogens. Another 60 fry, developmental stage between 600 and 700 Accumulated Thermal Units (UTAs) were anesthetized with 5 % Benzocaine, fixed in 10 % formalin, weighed and measured. Of these, a group of 30 fry (15 normal and 15 deformed) underwent the Hanken and Wassersug technique to evaluate lepidotrychia or dermal rays. The remaining 30 fry (15 normal and 15 deformed) were processed using H & E / Alcián blue histochemical techniques to evaluate general histological characteristics. Additionally, immunohistochemical techniques were used to deter- mine the location and presence of Sonic hedgehog (Shh) signal centers for lepidotrychia development. The values obtained for the quantitative variables body weight, length and width of the tail fin were described using the arithmetic mean and standard deviation. The deformity was observed from 600 UTA. Weight of deformed fry was less than normal fish, length of the fin was similar in normal and deformed fish. In contrast, width of the deformed fin was significantly reduced. The sharp fin phenotype presented a change in the conformity of the edges, lepidotrychia fractures. The epidermis presented active Shh signaling centers, but the interray blastema showed vasodilation, congestion and hemorrhages. The presentation of this case was related to sudden increases in perieclosional temperature.

KEY WORDS: Atlantic salmon, Salmo salar; Caudal fin; Deformity.

ROJAS, M.; PELLÓN, M.; CERDA, C.; ULLOA, R.; SUAREZ, R.; GODOY, M. & DEL SOL, M. Deformation of the caudal fin in Atlantic salmon fry (Salmo salar), in the yolk sac stage. Int. J. Morphol., 38(6):1631-1638, 2020.