Ovarian development and sex ratio of gynogenetic Atlantic cod (Gadus morhua)

Pre-harvest sexual maturation is common in farmed Atlantic cod. This redirection of energy investment from muscle tissue to gonadal development results in reduced flesh quality prior to harvest. A potential solution to this challenge is to use female triploid stocks, as their ovarian development is suppressed. However, an understanding of the genetic basis of sex determination is necessary to produce all-female stocks. The objective of this research was to determine the genetic basis of sex for Atlantic cod, by means of gynogenesis. This process results in uniparental maternal inheritance following exposure of spermatozoa to UV radiation and subsequent duplication of the maternal genome. Small-scale experiments showed that gynogenetic diploids could be produced by activating development in eggs with UV-treated spermatozoa (pre-dilution of milt to 15% spermatocrit followed by further 1:10 dilution and then exposure to 113.4 mJ/cm(2) UV) and then applying hydrostatic pressure (5 min at 58,600 kPa, beginning 180 degrees C-min post-activation). Diploid control and gynogen populations (as confirmed by genotyping and flow cytometry) were raised until large enough to be sexed. The sex ratio of controls was not significantly different from the anticipated 1:1. Gynogens, on the other hand, were all female, demonstrating female homogamety for sex determination. Although they showed normal ovarian development, gynogens were delayed compared to controls in terms of numbers of cells progressing through early stages of oogenesis. (C) 2011 Elsevier B.V. All rights reserved.