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Add To Calendar 23/02/2016 14:15:0023/02/2016 14:35:00America/ChicagoAquaculture 2016MONOSEX PRODUCTION AND INSIGHT INTO MECHANISMS OF SEX DETERMINATION AND DIFFERENTIATION IN SABLEFISH Anoplopoma fimbria   Versailles 2The World Aquaculture Societyjohnc@was.orgfalseanrl65yqlzh3g1q0dme13067DD/MM/YYYY


J. Adam Luckenbach*, William T. Fairgrieve, and Edward S. Hayman
Northwest Fisheries Science Center
National Marine Fisheries Service, NOAA
Seattle, WA 98112

Fish exhibit a variety of sex determination systems that may be under strict genetic control or influenced by exogenous factors. Sex is often strongly associated with differences in growth performance and therefore monosex production of the faster-growing sex is an objective for aquaculture of many species. Sablefish (or black cod) is an emerging marine aquaculture species that, like numerous marine species, exhibits superior growth of females relative to males. A method for monosex sablefish production has therefore been a key objective.

A series of experiments was conducted to develop an effective method for feminization of sablefish and gain a better understanding of mechanisms of sex determination and differentiation in marine teleosts generally. Morphological sex differentiation was first characterized to establish its timing in sablefish. Subsequently an experiment was conducted in which juveniles were treated with dietary methyltestosterone or 17β-estradiol prior to and during gonadal sex differentiation to induce sex reversal. Histological and genetic sex (PCR) analyses demonstrated that our protocol achieved complete sex reversal of both male and female sablefish. Remaining fish were reared until sexual maturity and sex-reversed females (i.e., neomales) and normal males were reciprocally crossed with the same female broodstock (n=16 total crosses). Resultant embryos from neomale/female crosses were 100% genotypic females, while those from normal male/female crosses were 55% female/45% male on average. Six months later, fish were sampled for gonadal histology, demonstrating that all-female stocks developed ovaries indistinguishable from those of controls. This demonstrated that sablefish utilize an XX/XY sex determination system and provided the first monosex populations of sablefish for aquaculture.

In parallel with this work, experiments were conducted focusing on molecular events associated with the processes of sex determination and differentiation in sablefish. Next-generation sequencing (454 pyrosequencing) was used to sequence expressed transcripts in differentiating ovaries and testes. Selected genes associated with these processes, including transcription factors, steroidogenic enzymes and growth factors were ontogenetically analyzed during gonadal differentiation and development via quantitative PCR. Increases in early markers of sex differentiation (e.g., dmrt1, amh, cyp19a1a) preceded morphological differentiation of the gonads as anticipated, whereas other genes (e.g., cldn29a, zpc) were delayed in onset of expression suggesting involvement in gametogenesis, not sex differentiation. Analysis of embryonic sablefish around time of hatching revealed that a transforming growth factor known as gonadal soma-derived factor (gsdf) was sexually dimorphic when other sex differentiation-associated genes were not. This together with genomic analyses strongly suggests gsdf is the major sex determinant in sablefish. We are now interested in tying the sex determination event to ovarian and testicular differentiation.

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