Understanding flesh colour variation in Atlantic salmon: molecular mechanisms and genetic effect
Flesh colour in Atlantic salmon is considered a fundamental, if not the most important, quality parameter, and affects acceptance and price of the product. The dietary pigments responsible for flesh colour (i.e. astaxanthin and canthaxanthin) are expensive and represent 6-8% of the total production cost. Therefore, reduced flesh colour in the stock results in considerable economic losses. Several factors have been shown to impact flesh colour (e.g. environment, diet formulation, size, genetics) highlighting the complexity underlying the variation. As variable/reduced flesh colour was identified in a portion of the Petuna stock following periods of high summer temperatures, the project focused on the possible genetic effect on the trait. Furthermore, due to a general lack of knowledge of the molecular mechanisms responsible for flesh colour and its metabolism in general, which involves multiple organs and tissues, and given the opportunity to compare good and affected individuals, such investigations were also undertaken. In light of climate change and increasing seawater temperature, understanding the genetic component of the differential response manifested as variable/reduce flesh colour following thermal stress, would pave the way for improving genetic selection and producing fish with increased thermal tolerance. Finally, detection and understanding of the variation affecting flesh colour in Atlantic salmon are fundamental in order to improve marketability of the product.
Final report
This report describes critical findings and new knowledge on flesh colour variation, from both a genetic and a molecular perspective, in Atlantic salmon in Tasmania. The investigation on flesh colour variation, due to its strong correlation with high seawater temperature, led to new important insights into thermal tolerance in Atlantic salmon and their performance in a context of climate change and global warming.
The project was carried out between June 2016 and June 2020 and was the result of a collaboration between the University of the Sunshine Coast (USC) and Petuna Aquaculture (Petuna), initiated by Dr Mark Porter and Prof Abigail Elizur. The principal investigator of the project was Prof. Abigail Elizur (USC) and she was supported by two co-investigator, Dr. Tomer Ventura (USC) and Dr. Gianluca Amoroso (Petuna). Two additional co-investigators from USC, Dr. Chan D.H. Nguyen and Ms Thu T.M. Vo, were included at a later stage in order to carry out part of the research required for the project completion and formed part of their PhD projects. The investigation of the fish took place in northern Tasmania where Petuna owns both freshwater and marine sites and all the laboratory work was undertaken at both USC Genecology Research Centre and at Xelect, a genetic services provider based in Scotland (UK).
This project was originally designed to study an issue which is impacting commercial production in Petuna. Flesh colour variation post-summer (at times extending to harvest), had been identified during 2015-16 by Petuna to affect commercial value. As this issue is not impacting Petuna only, this project was expected to generate important knowledge on the factors which contribute to reduced flesh colour in Atlantic salmon stocks and result in significant ‘spill-over’ of information that will assist the wider Tasmanian salmon industry.
Seafood CRC: optimisation of viral clearance from broodstock prawns using targeted RNA interference
Outbreaks of viral disease accompanied by morbidity and mortalities occur sporadically in Australian prawn farms and are generally worst when environmental conditions are less favourable, as in the recent 2010/2011 grow-out season. Poor survival and poor market quality caused by viral disease can impact significantly on farm productivity and even the larger and more sophisticated operations are vulnerable. As the Australian industry moves towards the use of domesticated lines of genetically improved prawn species, there is an increasing need for a method capable of clearing or markedly reducing viral infection loads from valuable broodstock, thus minimizing the risks of infection being passed to progeny, either as part of breeding programs or for commercial production. Similarly, as the infection prevalence of viruses can be high amongst wild-caught broodstock still used in most hatcheries, an easy and commercially-applicable method for clearing or reducing viral infection loads would have broad industry value. In the case of Australian farmed P. monodon, GAV has the highest economic impact of known viral pathogens whilst for Australian farmed Banana prawns (Penaeus merguiensis), it is Hepatopancreatic-parvovirus (HPV). This project will therefore optimise RNAi methods to clear GAV from P. monodon whilst also producing putative RNAi reagents suitable for accomplishing the same with the Australian strain of HPV for future use in P. merguiensis. The HPV-specific dsRNAs generated will be used in this project as non-GAV non-specific controls during optimisation of dsRNAs targeted specifically at GAV.As mentioned earlier, the industry value of this project is demonstrated by the strong letter of support from the APFA attached to this application.
Final report
Economic losses due to diseases mostly caused by viruses remain a major obstacle to realizing the production potential of prawn aquaculture industries in many parts of the world. Broodstock used in prawn hatcheries in Australia are generally managed quite intensively and numbers used are generally low. Opportunities thus exist to inject broodstock with virus-specific dsRNAs to induce RNAi responses that reduce viral infection loads prior to them being mated and/or spawned to generate seedstock.
In Australia, disease caused by Gill-Associated Virus (GAV) infection results in the most substantial economic impacts to Banana Prawn farmers. Hepatopancreatic-parvovirus (HPV) or more recently named Penaeus merguiensis densovirus (PmergDNV) are the most problematic virus. This project aimed to optimise RNAi methods for clearing or reducing GAV infection loads in P. monodon broodstock and to produce RNAi reagents targeted to PmergDNV.
Juvenile P. monodon with subclinical GAV infections were collected from a farm in North Queensland and injected with different dsRNAs and infection loads in individuals were tracked. Reproductive assessment of egg and nauplii numbers and hatch rates showed that spawning performance of the females was not impaired by dsRNA injection.
This study demonstrated that the targeted injection of a cocktail of 5 GAV dsRNAs or a single dsRNA can reduce pre-existing infection loads in juvenile P. monodon. Similarly, the injection of a cocktail of 5 GAV dsRNAs in broodstock prawns appeared to reduce pre-existing infection loads without any adverse impacts on the ability of females to produce viable nauplii. This experiment provided the first evidence that an RNAi approach applied in hatcheries might be able to contribute to mitigation viral disease impacts in prawn aquaculture that are vertically transmitted to improve farm productivity.
SCRC: Seafood CRC: ‘WERA’ Industry Bursary 2008
This subject was suggested as an education and training priority at the Oyster Consortium meeting in Sydney March’07, was reaffirmed at the Oyster Consortium planning meeting in Hobart in September 07, and was broached again at the Shellfish Futures Conference in Hobart, Nov 07. Whilst Roy Palmer was in Rhode Island (on other business) he had a meeting with the Chair of WERA and obtained information which he put into a report that was circulated to the Oyster Consortium.
WERA objectives are
1. Provide a forum for geneticists, physiologists, nutritionists, biotechnologists and others interested in the aquaculture of molluscan shellfish to exchange ideas and information on molluscan genetics, reproduction, pathology, brood-stock management, breeding programs, hatcheries, husbandry techniques, and restoration strategies.
2. Develop protocols for the preservation of valuable genetic material for future use by researchers.
3. Maximise and co-ordinate research efforts among scientists on the Pacific, Atlantic and Gulf coasts, USA, as well as international researchers.
4. Identify research needs for enhancement of commercial molluscan production through genetic improvement while maintaining environmental quality.
5. Evaluate different approaches for restoration of depleted stocks of native oysters.
6. Provide industry members with up-to-date research information that will lead to optimal brood-stock management and breeding programs to enhance commercial production.
7. Publish committee reports and documents.
Final report
Judd Evans and I attended the WERA 099 Broodstock Management, Genetics and Breeding Programs for Molluscan Shellfish meeting on Sunday the 6th of April and the National Shellfish Association Annual Conference, 6th to 10th of April, held in Providence, Rhode Island. We then travelled, via New York, to Newport, Oregon (the Hatfield marine Research Centre) and up to Shelton, Washington (Taylors’ Shellfish) visiting an oyster farm and a hatchery along the way. We returned home on the 18th of April. The following is a report, in diary form, of this trip.