Project number: 2000-206
Project Status:
Completed
Budget expenditure: $737,531.00
Principal Investigator: Bob Ward
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 29 Dec 2000 - 4 Jan 2006
Contact:
FRDC

Need

We have demonstrated that oyster characteristics deemed valuable by industry can be improved by selective breeding. We and industry are convinced that substantial performance increases for commercial lines are achievable.
Thus far we have concentrated our efforts on a single trait (growth), but we have a number of family lines which permit the improvement of several traits simultaneously. We plan to continue selecting for increased growth rate and combine these advances with other desirable traits such as high meat yield and irradication of the deleterious curl-back trait. This will yield a much improved commercial product.
Modifications to our existing protocols need to be trialed to see whether substantial gains in time and savings of funds are possible in the development of a long-term breeding strategy for broodstock improvement. We need to:

1. continue the breeding program through at least three more generations, in both the mass selection and family lines, by producing, where possible, improved lines every year rather than every two years as currently. Performance assessment will continue through to the second year.
2. develop a selection index which uses all information about genetic merit over several commercial traits. This is the sum of the commercial gains an individual can transmit weighted by commercial value.
3. monitor grow-out performance at one year of age and two years of age, to determine if crosses can be made at one year of age rather than two years. This would speed selective improvement. We need to assess whether performance at one year is a good indicator of performance at market size (currently ~2.5 years).

If the Joint Venture company (JVC) proposed to commercialise our work is not established, then we will need to:

4. work with industry to conduct trials of particular lines in both Tasmania and South Australia under full commercial conditions.
5. develop sophisticated long-term breeding plans which yield on-going performance improvements while avoiding the deleterious effects of inbreeding. These plans will be based on analysis of data collected during the project, and require a major commitment from both technical staff and geneticists.
FRDC funding is thus required to complete the development program and, if the JVC is not established, to conduct the commercialisation trials and development of breeding plans. If the JVC is established, then we would provide it with broodstock for the trials but would expect it to develop its own long-term breeding strategy with input from and collaboration with our technical staff and geneticists.

Objectives

1. Continued production of mass selection lines for growth rate and family lines for other industry-desired traits.
2. Creation of crossbred family lines to assess the feasibility of combining desirable traits from different families into a single line.
3. Development of a multi-trait selection index.
4. If the Joint Venture Company is not established by November 2000, we have the following additional objective: Assessment of the performance of chosen lines in full-scale commercial trials.
5. If the Joint Venture Company is not established by November 2000, we have the following additional objective: Development of a breeding plan for sustainable genetic improvement.
6. Development of a commercilisation strategy within 12 months of start.

Final report

ISBN: 1-921061-07-3
Author: Robert Ward
Final Report • 2005-12-15 • 1.68 MB
2000-206-DLD.pdf

Summary

The Pacific oyster breeding project initiated in FRDC 97/321 was continued. Both mass selection and family selection procedures were employed. The main trait of interest was growth rate, although shell shape and condition index were also recorded.

Families were monitored on five farms. Two were intertidal Tasmanian farms, one was a subtidal Tasmanian farm, and two were intertidal South Australian farms.

Growth rates among farms varied considerably, with the two South Australian farms generally producing higher growth rates than the three Tasmanian farms. However, rank performance of farms also varied from year to year, presumably due to environmental factors. Environmental variability from year to year makes inter-generational comparisons difficult, as any genetic gains may be confounded by environmental fluctuations. However, within any one generation, families generally performed with similar rank orders among farms, meaning that genotype by environment interactions were limited. That is, a good performing family at one farm usually also performed well at other farms.

There was a negative correlation between progeny numbers produced per family and weights at the end of nursery phase. This density dependent effect disappeared by the time oysters had reached two years of age.

Growth rates responded well to selection. The final generation of the project for which we have full data to the end of grow-out is generation four. In generation four, the mean of the mass selection lines and the mean of the family selection lines were both about 1.6x greater than the unselected commercial control line; while the three mass selection lines performed similarly, the fastest and slowest growing of the family selection lines had about 2.2x and 1.2x, respectively, the growth rate of the control line.

There was evidence in some but not all years of a negative correlation between growth rate and condition index. That is, the fastest growing families tended to have a lower condition index. However, condition index was estimated before animals reached market size, and there was some evidence that, at market size, differences in condition index might disappear. This needs further attention.

Attention was also paid to shape when selecting parents. In the fourth generation, virtually all oysters when individually measured showed acceptable shape. Indeed, using the ASI Shape Index, the mean shape scores of all selected families were lower than that of the control line, indicating superior shape for the selected families. There was some evidence that the heavier oysters were somewhat more elongate than lighter oysters, but the effect was very small.

There was also evidence from the fourth generation that the selected families showed less inter-individual variability for weight and condition index than the Control line; for shape variability there was little difference. Generally the selected lines gave more uniform product than the control line.

Full-scale commercial trials of some lines were undertaken. These were carried out to collect data from a much larger number of farms and also to expose these lines (and the project) to the wider community. Collecting reliable quantitative data from these lines proved impossible, but anecdotally these lines generally performed as well or better than control lines. These were necessarily early-generation lines and later lines would perform still better. Several lines have also been recently produced as standard commercial runs.

Heritability estimates indicated that additive genetic variance is present for most traits and that these could be exploited in any ongoing selective breeding program. Weight and length at both farms assessed (both Tasmanian) had high heritabilities, and at the better-sampled of these farms width and depth heritabilities were moderate to high. Overall there was no evidence for sire or dam (maternal) effects particularly in the parameter estimates from both farms. We observed very little evidence of genotype x environment interactions. 

Genetic gains for the multi-traits identified as economically important (weight, width index and depth index) were estimated under different market scenarios and different genetic selection strategies. High weight gains, predicted to be 28%, were still possible when applying sufficient selection pressure on width index and depth index to maintain current shape. The strategy that produced the best gain was family/within family selection.

Molecular genetic research included developing new microsatellite DNA loci and comparing levels of genetic variation in mass selection lines with those in natural populations. The later generations of mass selection lines were shown to have reduced numbers of microsatellite alleles while allozyme alleles had been maintained. It was considered that because the allozyme diversity had been maintained, the microsatellite allele loss was not a great concern at this time. Census broodstock numbers in the mass selection lines examined were greater than the biologically effective broodstock numbers. Broodstock numbers in mass selection lines need to be maintained at reasonable numbers (ideally around 40-50 per generation and with equal numbers of males and females). It was shown that microsatellite DNA genotyping of individual larvae was achievable.

The project and its predecessor FRDC 97/321 produced five generations of selectively bred oysters before the program was handed over to Australian Seafood Industries Pty Ltd (ASI). ASI was established by the Tasmanian and South Australian industries during the course of the project to ensure the continuation of the breeding program at the end of the project and to facilitate technological transfer to industry. 

Keywords: Pacific oyster, Crassostrea gigas,  growth rate, heritability, genetic selection,  selection index, microsatellites.

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