Project number: 2018-121
Project Status:
Completed
Budget expenditure: $99,326.00
Principal Investigator: Luis O. Afonso
Organisation: Deakin University Warrnambool Campus
Project start/end date: 16 Sep 2018 - 30 Aug 2020
Contact:
FRDC
TAGS
Reproduction
Physiology
Nutrition
Life History
Biology
SPECIES
Atlantic Salmon

Need

Based on the National Fishing and Aquaculture RDE strategy 2016, our project relates to Strategic Goal 3: Benefits and value from fisheries and aquaculture resources (productivity and profitability) are maximised, and aquaculture production increased.

Priority area: Develop new technologies and systems to improve the efficiency of production methods.

This project is needed because the Australian Atlantic Salmon Industry is lacking basic and applied knowledge that could lead to the development of a reliable, non-steroidal method to produce all-female populations of Atlantic salmon. One of the drivers of this project is the fact that eliminating males from the production cycle (grow-out period), will reduce the effects of precocious sexual maturation, including reduced growth, reduced flesh quality, and susceptibility to diseases. As a consequence of eliminating males from the production cycle is a concomitant increase in overall productivity (biomass produced) and profitability

We will use genetic and morphological techniques to improve our understanding of sex differentiation in Atlantic salmon. This knowledge is needed to inform the exact period that sex reversal treatments with exogenous substances are more effective to produce neo-males. This exact timing can then be used in the trial of next generation non-steroidal substances, ensuring that they have the greatest chance of success. This will be the first time that detailed gene expression and morphological information will be collected throughout the entire period of sexual differentiation.

Objectives

1. Investigate morphological sex differentiation processes in male and female Atlantic salmon larvae
2. Quantify the expression of several key genes involved in sex differentiation in male and female Atlantic salmon embryo’s and male and female Atlantic salmon larvae (gonadal and estrogenic non-gonadal tissues)
3. Investigate the effects of MDHT treatment on expression of several key genes involved in sex differentiation in female Atlantic salmon larvae (gonadal and estrogenic non-gonadal tissues)
4. Investigate the effects of DMSO on the masculinizing potential of a single MDHT immersion treatment in female Atlantic salmon.
5. Investigate the effects of the aromatase inhibitor letrozole on expression of several key genes involved in sex differentiation in female Atlantic salmon larvae (gonadal and estrogenic non-gonadal tissues)

Final report

ISBN: 978-0-7300-0340-3
Authors: Luis O.B. Afonso Morgan S. Brown Brad S. Evans
Final Report • 2021-06-01 • 3.14 MB
2018-121-DLD.pdf

Summary

The Tasmanian Atlantic Salmon (Salmo salar) aquaculture industry strives to produce all-female fish, as male Atlantic Salmon are subject to precocious maturation and consequently reduced flesh quality and increased disease susceptibility when reared in high water temperatures. Several fish species, including Atlantic Salmon, can have their natural sex ratio changed by sex reversal, which involves the application of steroid (androgens and estrogens) and non-steroid (aromatase inhibitors) substances (by immersion or inclusion in the diet) during early stages of development, most of the time prior to phenotypic (morphological) sex differentiation. The timing of application of these substances is instrumental for achieving high rates of sex change. All-female populations can be produced by crossing a masculinized female (XX male or neomale) with a normal female (XX female). Therefore, it is important to test the potential of different substances in producing neomales, which then can be crossed with normal females to consistently produce all-female fish. This indirect method leads to the production of individuals that were never exposed to exogenous steroids.
Our studies are indicating that:
1. Based on histology and morphology, sex differentiation in Atlantic Salmon seems to occur by 79 dph.
2. Based on gene expression, three male specific genes are upregulated prior to morphological sex differentiation, whereas in females only one gene is differentially upregulated prior to morphological sex differentiation.
3. Immersion treatment with MDHT and MDHT+DMSO led to masculinization of genetic females to rates between 81 and 87%.
4. Immersion in MDHT led to the upregulation of male specific genes, which occurred 15 days after (dph) the date observed in normal males (34-66 dph) in the sex differentiation study.
The implications of these findings are relevant to the industry and academic/research communities as they demonstrate that is possible to obtain higher rates of masculinization using androgens but not aromatase inhibitors. The higher rates of masculinization will provide more neomales that can be grown to maturity and crossed with normal females to produce all-female populations of Atlantic Salmon. The combination of MDHT + DMSO increased the rate of masculinization (although not significantly different from MDHT alone), and further studies in this area could lead to the optimization of a sex reversal protocol to further increase the rates of masculinization. The sex differentiation and gene expression studies are showing that Atlantic Salmon is a unique species regarding these aspects, and this information needs to be taken into consideration when developing sex reversal protocols.

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