SARF027a: Implementation of all female production in the UK halibut farming industry: progeny testing of neomales

Start Date: 15/02/2010
End Date: 15/04/2011
Main Contractor(s): University of Stirling

Other Sponsor(s):

Objectives

Collaboration: Otter Ferry Seafish Ltd. (OFS) and Machrihanish Environmental Research Laboratories (MERL)

To provide the guidance, practical and scientific help to a commercial hatchery to identify “neomale” halibut fish within a population which have been sex reversed in the project SARF 027. These fish will then be used as broodstocks to produce monosex female fish for the UK halibut farming industry.

Summary

The British marine aquaculture industry has identified that a delay or cessation of maturation during on-growing is crucial for profitable farming as maturation in marine fish species usually results in a loss of somatic growth rate, reduction in condition and changes in flesh composition. Despite extensive research it is currently generally accepted that the management of sexual maturation on farm remains unpredictable and limits profitability. In the case of halibut farming, evidence clearly shows that all female populations for ongrowing would dramatically increase the profitability of production and hence the competitiveness and sustainability of the industry. As part of the SARF027 project two methodologies were explored to help establish the ability to produce all female halibut stock in the UK. While research into “semen sexing” methodologies have proven to be ineffective in halibut, the project also researched direct hormone sex reversal in halibut and has successfully generated a population of phenotypic males which should be approximately 50% normal (XY) males and 50% XX “neomales”. The neomales within this population are central to the production of all female halibut stocks. To date, no sex specific genetic marker has been identified for halibut so sexing by genotype is not possible therefore, before all female halibut production can become a commercial reality, identification of neomales must be performed through progeny testing.  This methodology requires juveniles from selected crosses to be reared to a suitable size at which they can be sexed by histological examination, with the sex ratio of the progeny confirming the identity of the neomales. As access to numerous isolated rearing units is not possible it is necessary to rear crosses in a communal environment and then use genotyping for parental assignment. Progeny testing to identify neomales generated by SARF027 is a natural continuation of the ongoing work utilising resources, techniques and expertise already established in the field and is necessary to help realise the full commercial potential of the work. Identification of neomales will mean that the production of all female halibut will be a commercial reality returning UK halibut farming to the forefront of the European industry. Not only would it significantly improve the profitability of the UK ongrowing industry but the ability to produce all female stocks would also open up new markets for juvenile supply and potentially even milt sales. Clearly this work would improve the competitiveness of the UK industry and may help return investor confidence in the British marine finfish farming sector as a whole.