Use of parental individuals from allochthonous lineages to produce stocking specimens resulted in genetic contamination of many local European grayling (Thymallus thymallus) populations. Stocking programs including triploid individuals that are not able to reproduce with stocks located in natural habitats due to being reproductively sterile could contribute to populations of the European grayling and prevent regional lineages from the genetic pollution. The main goal of the present research, therefore, was to provide conditions for triploidization of the European grayling and examine gonads of triploid individuals. High Hydrostatic Pressure (HHP) shock (9000 psi/5 min.) applied to activated and incubated grayling eggs at 10 °C between the 17 min. 30 sec. and 20 minute timepoints subsequent to the time of insemination resulted in inhibition of the second polar body release and triploidization. Histological analysis confirmed that all 1-yr-old cytogenetically confirmed triploids had gonadal tissues indicative of sterility with the gonads being composed of connective tissue including fibroblasts, adipocytes and degenerated epithelial structures without there being any differentiated germ cells detected. There were no differences in the body length and Fulton's condition factor between 1 year old diploid and triploid grayling, however, the average body weight was markedly less in triploid than diploid specimens. Although, 1-yr-old triploid European female and male graylings did not have fully developed gonads, before these triploid specimens are deemed safe, as a result of being reproductively sterile for stocking in natural grayling habitats, there needs to be further examination of the 2- and 3-year-old triploid specimens.
Keywords: Chromosome set manipulations; Fish; Gonads; Histology; Sterility; Triploidization.
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