Gonadal morphology of hormonally and chromosomally manipulated rainbow trout (Oncorhynchus mykiss)

• Main Author: Krisfalusi, Michelle
• Format: Dissertation
• Language: English
• Subjects: agriculture, fisheries and aquaculture; biology, animal physiology; biology, genetics; biology, zoology
• ISBN: 9780599382237; 0599382236

The mechanisms governing sexual differentiation and subsequent gonadal development in salmonids are not completely understood. The development of the salmonid gonad appears to be influenced by multiple factors. Sex chromosomes undoubtedly play a fundamental role in sex determination and gonadal development in these fish; however, exposure to sex steroids as well as artificial chromosomal modifications have resulted in various gonadal phenotypes. The phenotypic sex of rainbow trout (RBT) can be reversed by the administration of exogenous androgens or estrogens during the period of sexual differentiation. Chromosomal manipulation has included the generation of triploid and gynogenetic fish. Triploidy alters gonadal development in a gender specific manner in RBT; basically males develop normal testes while females develop ovaries devoid of oocytes. Aberrant ovarian development has been reported to occur in gynogenetic fish and includes the appearance of intersex gonads. The overall objectives of the present investigation were to examine the gonadal morphology of hormonally and chromosomally manipulated RBT and to explore the mechanisms involved with the gender specific differences between the development of the triploid RBT ovary and testis.
The objective of the first experiment was to induce normal ovarian development in triploid female RBT. Results of this experiment did not support the hypothesis that the failure of ovarian development in triploid RBT is due to decreased endogenous estradiol. The objective of the second study was to sex reverse genotypic triploid female RBT into phenotypic males and genotypic triploid male RBT into phenotypic females. Results from this study indicate that triploid male and female RBT have the capacity for sex reversal and support the hypothesis that the gender specificity relative to gonadal development in triploid RBT occurs due to the timing of meiotic initiation. The objective of the third experiment was to determine whether the presence of chromosomal fragments in gynogenetic female RBT would result in abnormal ovarian development comparable to that observed in triploid females. Results from this study support the hypothesis that disruption of the diploid chromosomal complement alters germ cell development in gynogenetic RBT due to the unbalanced nature of the genome.