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Responses to two generations of index selection in Atlantic salmon (Salmo salar)
Aquaculture 173 Ž1999. 143–147
Responses to two generations of index selection in Atlantic salmon žSalmo salar / Fiona M. O’Flynn
a,b,)
, John K. Bailey
b,c
, Gerard W. Friars
b
a School of Science, Institute of Technology Tralee, Clash, Tralee, Kerry, Ireland Salmon Genetics Research Program, Atlantic Salmon Federation, P.O. Box 429, St. Andrews, New Brunswick, Canada EOG 2XO c Applied Breeding Technologies, New Brunswick Salmon Growers Association, RRa4, St. George, New Brunswick, Canada EOG 2YO b
Accepted 14 October 1998
Abstract Linear indices were used to select broodstock for two generations of a Canadian Atlantic salmon strain. In 1988, a select line was formed on the basis of an index to increase fry length, percent S1 smolts and market and mature length. In 1992, the broodstock for the following generation of select families was chosen on the basis of an index to increase percent S1 smolts, percent non-grilse, market length and bacterial kidney disease resistance. There was an unselected control line for both generations. Progeny of selected parents compared to those of control parents for both generations showed positive direct and indirect responses to selection for various freshwater and seawater growth and development traits. The most significant response was found for harvest size, where a gain of 0.83 standard deviations was achieved after two generations. This represents on average an actual gain of 0.88 kg per fish. The mean harvest weight for select fish was 4.39 kg vs. 3.51 kg for control fish. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Broodstock selection; Genetic gains; Salmo salar
1. Introduction Farmed salmon production has increased substantially in the last decade. Genetic improvement has contributed significantly to this success. Reviews by Gjerde Ž1986.,
)
Corresponding author
0044-8486r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 9 8 . 0 0 4 8 2 - 7
144
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
Gjedrem et al. Ž1988. and Refstie Ž1990. indicate that controlled mating and selection practices can increase productivity in aquaculture species. Realised responses to mass selection for fork-length in Atlantic salmon were reported by Friars et al. Ž1990.. Similarly, progress through multiple objective selection in coho salmon has been observed by Hershberger et al. Ž1990.. Priorities for selection in aquaculture production of Atlantic salmon vary between freshwater and seawater growth stages. Although, S1 smolting rates are important during the freshwater stage, growth rate and age at maturity become important during grow-out in sea water. Several characteristics can be improved at once by using a form of multiple objective selection, the selection index. In this study, responses to two generations of index selection on an Atlantic salmon strain are reported in relation to both freshwater and seawater performance.
2. Materials and methods This selection study was carried out on Strain 84JC, a strain of Atlantic salmon, developed by the Salmon Genetics Research Program, at the Atlantic Salmon Federation, St. Andrews, New Brunswick, Canada. The base population for this strain was established in 1984 from 48 single-pair matings of two-sea-winter salmon returning to the Saint John river, New Brunswick. In all cases, single-pair matings were carried out. There were 33 control and 35 select full-sib families established in 1988 and 40 control and 52 select full-sib families established in 1992. 2.1. Index selection 1988 The control line was established by sampling at random a son and a daughter from each of the 48 full-sib families in the base population. Broodstock for the select line were chosen on the basis of an index to increase fry length, percent S1 smolts, harvest and mature length. The index was derived from both genetic and economic information. The genetic information included heritabilities and genetic and phenotypic correlations. Economic weights were calculated per phenotypic standard deviation for each trait included in the index. Seawater traits such as harvest and mature length received the highest economic weight. The formation of such an index is more fully described by Bailey Ž1988. and Friars et al. Ž1995.. The linear index equation used to select broodstock in 1988 was as follows: Index value s 1.0 p 1 q 0.5 p 2 q 6.9 p 3 q 3.1 p4 q 0.5 p5 where p 1 is the mean family fry length, p 2 is the percent S1 smolts per family, p 3 is the mean family harvest length, p4 is the individual mature length, p5 is the mean family mature length.
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
145
Table 1 Freshwater and seawater performance of control and select lines of the 1988 year-class of Strain 84JC after one generation of index selection Life-stage
Freshwater Fertilisation to eyed egg Fertilisation to fry Fry Ž0q. Parr Ž1q. Smolt Ž1q.
Seawater Harvest
Trait
Control
Select
Survival Ž%. Survival Ž%. Length Žcm. Weight Žg. Length Žcm. Length Žcm. S1 rate Ž%.
56.6 31.9 6.40 2.90 11.3 16.8 44.6
53.1 52.8 6.69 3.30 11.5 17.0 53.6
Length Žcm. Weight Žkg.
69.6 4.3
72.0 4.6
Gain s.d.
Actual unit
y0.09 0.09 0.43 0.38 0.24 0.16 0.40
y3.5 20.9 0.29 0.40 0.20 0.20 9.00
0.35 0.32
2.40 0.30
Gains are expressed in both standard deviations Žs.d.. and actual units.
2.2. Index selection 1992 In 1992, broodstock for the select line were selected using an index designed to increase S1 smolting, sea growth, resistance to bacterial kidney disease ŽBKD. and Table 2 Freshwater and seawater performance of control and select lines of the 1992 year-class of Strain 84JC after two generations of index selection Life-stage
Freshwater Fertilisation to eyed egg Fertilisation to fry Fry Ž0q.
Parr Ž1q.
Smolt Ž1q.
Seawater Post-smolt Harvest
Trait
Control
Select
Gain s.d.
Actual unit
Survival Ž%. Survival Ž%. Length Žcm. Weight Žg. Condition factor Length Žcm. Weight Žg. Condition factor Length Žcm. Weight Žg. Condition factor S1 rate Ž%.
78.5 47.3 7.69 5.13 1.10 11.74 16.36 1.00 17.79 58.69 1.03 87.8
74.8 48.9 7.91 5.69 1.12 11.77 16.58 1.00 18.09 61.46 1.03 89.8
y0.19 0.07 0.32 0.40 0.29 0.04 0.04 0.00 0.22 0.20 0.00 0.25
y3.7 1.6 0.22 0.56 0.02 0.03 0.22 0.00 0.30 2.77 0.00 2.00
Length Žcm. Length Žcm. Weight Žkg. Condition factor
37.53 66.13 3.51 1.18
38.94 70.61 4.39 1.21
0.50 0.80 0.83 0.23
1.41 4.48 0.88 0.03
Gains are expressed in both standard deviations Žs.d.. and actual units.
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
146
decrease grilsing. The formation of such an index is more fully described by O’Flynn et al. Ž1992.. The linear index equation was as follows: Index value s 7.5 p 1 q 9.2 p 2 q 8.9 p 3 q 1.2 p4 q 8.1 p5 where p 1 is the percent S1 smolts per family, p 2 is the percent non-grilse per family, p 3 is the mean family harvest length, p4 is the individual harvest length, p5 is the percent resistance to BKD per family. 2.3. Data collection Growth and developmental traits outlined in Tables 1 and 2 were monitored both in fresh and sea water for both the 1988 and 1992 year classes. The numbers of progeny measured per family varied from 25 to 30 for freshwater growth traits. The proportion of S1 smolts was based on 50 to 300 fish for the 1988 year class and 200 fish for the 1992 year class. For both year classes, approximately 60 S1 smolts from each family, identified by fin-clips and brands, were placed in the sea cages. 2.4. BKD data Samples from each family were challenged with Renibacterium salmoninarum, the causative agent of BKD. Diagnostic testing by Western Blot analyis confirmed BKD to be the cause of death ŽGriffiths and Lynch, 1991.. Resistance to BKD was measured as percent survival per family.
3. Results and discussion The responses to index selection can be termed direct or indirect. A direct response occurs in a trait that was used to derive the index, such as harvest length. Indirect or correlated responses result in changes in traits that were not used to index broodstock, such as parr weight. BKD survival was higher in the select line Ž57.2%. than in the control line Ž19.1%. for the 1988 year class. Mortality after the BKD challenge on the 1992 year class was extremely low Ž9.2%.. As a result, no further analysis was carried out and survival rates for the control and select lines were not compared. In most instances, responses to index selection in this study were positive. For both year classes, selected parents out-performed those of the controls for all traits measured except for early survival between fertilisation and first-feeding ŽTables 1 and 2.. Gains were estimated using the unselected control lines for both 1988 and 1992 year classes. As each generation had a control line, the gains reported here represent true genetic gains and do not include effects due to husbandry changes. For the 1988 year class, direct responses were larger than the correlated responses to index selection. Gains in fry length, percent S1 smolt and harvest length were higher than gains in correlated traits such as parr and smolt size ŽTable 1.. For the 1992 year class, fry size showed a large correlated response to index selection ŽTable 2..
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
147
In general, seawater growth traits showed a larger response to index selection than freshwater growth traits ŽTables 1 and 2.. This is attributed to seawater traits such as harvest size being assigned the highest economic weight. For both year classes, harvest length showed the largest genetic gain, 0.35 and 0.80 standard deviations for the 1988 and 1992 year classes, respectively. This represents on average a gain of 0.30 kg or 0.66 lb per select fish after one generation and a gain of 0.88 kg or 2 lb per select fish after two generations of index selection ŽTables 1 and 2.. The response to selection is greater in the 1992 year class than in the 1988 year class for harvest length, a trait included in both selection indices. This indicates that genetic gains are cumulative from one generation to the next. In conclusion, this study indicates that index selection can produce substantial genetic gains in both freshwater and seawater performance in farmed Atlantic salmon.
Acknowledgements Financial support for this research was provided by the Atlantic Salmon Federation, the Department of Fisheries and Oceans, the New Brunswick Department of Fisheries and Aquaculture and the New Brunswick Salmon Growers’ Association.
References Bailey, J.K., 1988. Selection criteria for sea ranched and cage reared Atlantic salmon Ž Salmo salar .. PhD Thesis, University of Guelph, Guelph, Ontario, Canada, 115 pp. Friars, G.W., Bailey, J.K., Coombs, K.A., 1990. Correlated responses to selection for grilse length in Atlantic salmon. Aquaculture 85, 171–176. Friars, G.W., Bailey, J.K., O’Flynn, F.M., 1995. Applications of selection for multiple traits in cage-reared Atlantic salmon Ž Salmo salar .. Aquaculture 137, 213–217. Gjerde, B., 1986. Growth and reproduction in fish and shellfish. Aquaculture 57, 37–55. Gjedrem, T., Gjerde, B., Refstie, T., 1988. A review of quantitative genetic research in salmonids at AKVAFORSK. In: Weir, B.S., Eisen, E.J., Goodman, M.M., Namkoong, G. ŽEds.., Proceedings of the 2nd International Conference on Quantitative Genetics. Sunderland, MA, USA, pp. 527–535. Griffiths, S.G., Lynch, W.H., 1991. Instability of the major soluble antigen produced by Renibacterium salmoninarium. Journal of Fish Diseases 14, 55–56. Hershberger, W.K., Myers, J.M., Iwamoto, R.N., Meauley, W.C., Saxton, A.M., 1990. Genetic changes in the growth of coho salmon Ž Oncorhynchus kisutch. in marine net-pens, produced by ten years of selection. Aquaculture 85, 187–197. O’Flynn, F.M., Friars, G.W., Bailey, J.K., Terhune, J.M., 1992. Development of a selection index to improve market value of cultured Atlantic salmon Ž Salmo salar .. Genome 35, 304–310. Refstie, T., 1990. Application of breeding schemes. Aquaculture 85, 163–169.
Responses to two generations of index selection in Atlantic salmon žSalmo salar / Fiona M. O’Flynn
a,b,)
, John K. Bailey
b,c
, Gerard W. Friars
b
a School of Science, Institute of Technology Tralee, Clash, Tralee, Kerry, Ireland Salmon Genetics Research Program, Atlantic Salmon Federation, P.O. Box 429, St. Andrews, New Brunswick, Canada EOG 2XO c Applied Breeding Technologies, New Brunswick Salmon Growers Association, RRa4, St. George, New Brunswick, Canada EOG 2YO b
Accepted 14 October 1998
Abstract Linear indices were used to select broodstock for two generations of a Canadian Atlantic salmon strain. In 1988, a select line was formed on the basis of an index to increase fry length, percent S1 smolts and market and mature length. In 1992, the broodstock for the following generation of select families was chosen on the basis of an index to increase percent S1 smolts, percent non-grilse, market length and bacterial kidney disease resistance. There was an unselected control line for both generations. Progeny of selected parents compared to those of control parents for both generations showed positive direct and indirect responses to selection for various freshwater and seawater growth and development traits. The most significant response was found for harvest size, where a gain of 0.83 standard deviations was achieved after two generations. This represents on average an actual gain of 0.88 kg per fish. The mean harvest weight for select fish was 4.39 kg vs. 3.51 kg for control fish. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Broodstock selection; Genetic gains; Salmo salar
1. Introduction Farmed salmon production has increased substantially in the last decade. Genetic improvement has contributed significantly to this success. Reviews by Gjerde Ž1986.,
)
Corresponding author
0044-8486r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 9 8 . 0 0 4 8 2 - 7
144
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
Gjedrem et al. Ž1988. and Refstie Ž1990. indicate that controlled mating and selection practices can increase productivity in aquaculture species. Realised responses to mass selection for fork-length in Atlantic salmon were reported by Friars et al. Ž1990.. Similarly, progress through multiple objective selection in coho salmon has been observed by Hershberger et al. Ž1990.. Priorities for selection in aquaculture production of Atlantic salmon vary between freshwater and seawater growth stages. Although, S1 smolting rates are important during the freshwater stage, growth rate and age at maturity become important during grow-out in sea water. Several characteristics can be improved at once by using a form of multiple objective selection, the selection index. In this study, responses to two generations of index selection on an Atlantic salmon strain are reported in relation to both freshwater and seawater performance.
2. Materials and methods This selection study was carried out on Strain 84JC, a strain of Atlantic salmon, developed by the Salmon Genetics Research Program, at the Atlantic Salmon Federation, St. Andrews, New Brunswick, Canada. The base population for this strain was established in 1984 from 48 single-pair matings of two-sea-winter salmon returning to the Saint John river, New Brunswick. In all cases, single-pair matings were carried out. There were 33 control and 35 select full-sib families established in 1988 and 40 control and 52 select full-sib families established in 1992. 2.1. Index selection 1988 The control line was established by sampling at random a son and a daughter from each of the 48 full-sib families in the base population. Broodstock for the select line were chosen on the basis of an index to increase fry length, percent S1 smolts, harvest and mature length. The index was derived from both genetic and economic information. The genetic information included heritabilities and genetic and phenotypic correlations. Economic weights were calculated per phenotypic standard deviation for each trait included in the index. Seawater traits such as harvest and mature length received the highest economic weight. The formation of such an index is more fully described by Bailey Ž1988. and Friars et al. Ž1995.. The linear index equation used to select broodstock in 1988 was as follows: Index value s 1.0 p 1 q 0.5 p 2 q 6.9 p 3 q 3.1 p4 q 0.5 p5 where p 1 is the mean family fry length, p 2 is the percent S1 smolts per family, p 3 is the mean family harvest length, p4 is the individual mature length, p5 is the mean family mature length.
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
145
Table 1 Freshwater and seawater performance of control and select lines of the 1988 year-class of Strain 84JC after one generation of index selection Life-stage
Freshwater Fertilisation to eyed egg Fertilisation to fry Fry Ž0q. Parr Ž1q. Smolt Ž1q.
Seawater Harvest
Trait
Control
Select
Survival Ž%. Survival Ž%. Length Žcm. Weight Žg. Length Žcm. Length Žcm. S1 rate Ž%.
56.6 31.9 6.40 2.90 11.3 16.8 44.6
53.1 52.8 6.69 3.30 11.5 17.0 53.6
Length Žcm. Weight Žkg.
69.6 4.3
72.0 4.6
Gain s.d.
Actual unit
y0.09 0.09 0.43 0.38 0.24 0.16 0.40
y3.5 20.9 0.29 0.40 0.20 0.20 9.00
0.35 0.32
2.40 0.30
Gains are expressed in both standard deviations Žs.d.. and actual units.
2.2. Index selection 1992 In 1992, broodstock for the select line were selected using an index designed to increase S1 smolting, sea growth, resistance to bacterial kidney disease ŽBKD. and Table 2 Freshwater and seawater performance of control and select lines of the 1992 year-class of Strain 84JC after two generations of index selection Life-stage
Freshwater Fertilisation to eyed egg Fertilisation to fry Fry Ž0q.
Parr Ž1q.
Smolt Ž1q.
Seawater Post-smolt Harvest
Trait
Control
Select
Gain s.d.
Actual unit
Survival Ž%. Survival Ž%. Length Žcm. Weight Žg. Condition factor Length Žcm. Weight Žg. Condition factor Length Žcm. Weight Žg. Condition factor S1 rate Ž%.
78.5 47.3 7.69 5.13 1.10 11.74 16.36 1.00 17.79 58.69 1.03 87.8
74.8 48.9 7.91 5.69 1.12 11.77 16.58 1.00 18.09 61.46 1.03 89.8
y0.19 0.07 0.32 0.40 0.29 0.04 0.04 0.00 0.22 0.20 0.00 0.25
y3.7 1.6 0.22 0.56 0.02 0.03 0.22 0.00 0.30 2.77 0.00 2.00
Length Žcm. Length Žcm. Weight Žkg. Condition factor
37.53 66.13 3.51 1.18
38.94 70.61 4.39 1.21
0.50 0.80 0.83 0.23
1.41 4.48 0.88 0.03
Gains are expressed in both standard deviations Žs.d.. and actual units.
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
146
decrease grilsing. The formation of such an index is more fully described by O’Flynn et al. Ž1992.. The linear index equation was as follows: Index value s 7.5 p 1 q 9.2 p 2 q 8.9 p 3 q 1.2 p4 q 8.1 p5 where p 1 is the percent S1 smolts per family, p 2 is the percent non-grilse per family, p 3 is the mean family harvest length, p4 is the individual harvest length, p5 is the percent resistance to BKD per family. 2.3. Data collection Growth and developmental traits outlined in Tables 1 and 2 were monitored both in fresh and sea water for both the 1988 and 1992 year classes. The numbers of progeny measured per family varied from 25 to 30 for freshwater growth traits. The proportion of S1 smolts was based on 50 to 300 fish for the 1988 year class and 200 fish for the 1992 year class. For both year classes, approximately 60 S1 smolts from each family, identified by fin-clips and brands, were placed in the sea cages. 2.4. BKD data Samples from each family were challenged with Renibacterium salmoninarum, the causative agent of BKD. Diagnostic testing by Western Blot analyis confirmed BKD to be the cause of death ŽGriffiths and Lynch, 1991.. Resistance to BKD was measured as percent survival per family.
3. Results and discussion The responses to index selection can be termed direct or indirect. A direct response occurs in a trait that was used to derive the index, such as harvest length. Indirect or correlated responses result in changes in traits that were not used to index broodstock, such as parr weight. BKD survival was higher in the select line Ž57.2%. than in the control line Ž19.1%. for the 1988 year class. Mortality after the BKD challenge on the 1992 year class was extremely low Ž9.2%.. As a result, no further analysis was carried out and survival rates for the control and select lines were not compared. In most instances, responses to index selection in this study were positive. For both year classes, selected parents out-performed those of the controls for all traits measured except for early survival between fertilisation and first-feeding ŽTables 1 and 2.. Gains were estimated using the unselected control lines for both 1988 and 1992 year classes. As each generation had a control line, the gains reported here represent true genetic gains and do not include effects due to husbandry changes. For the 1988 year class, direct responses were larger than the correlated responses to index selection. Gains in fry length, percent S1 smolt and harvest length were higher than gains in correlated traits such as parr and smolt size ŽTable 1.. For the 1992 year class, fry size showed a large correlated response to index selection ŽTable 2..
F.M. O’Flynn et al.r Aquaculture 173 (1999) 143–147
147
In general, seawater growth traits showed a larger response to index selection than freshwater growth traits ŽTables 1 and 2.. This is attributed to seawater traits such as harvest size being assigned the highest economic weight. For both year classes, harvest length showed the largest genetic gain, 0.35 and 0.80 standard deviations for the 1988 and 1992 year classes, respectively. This represents on average a gain of 0.30 kg or 0.66 lb per select fish after one generation and a gain of 0.88 kg or 2 lb per select fish after two generations of index selection ŽTables 1 and 2.. The response to selection is greater in the 1992 year class than in the 1988 year class for harvest length, a trait included in both selection indices. This indicates that genetic gains are cumulative from one generation to the next. In conclusion, this study indicates that index selection can produce substantial genetic gains in both freshwater and seawater performance in farmed Atlantic salmon.
Acknowledgements Financial support for this research was provided by the Atlantic Salmon Federation, the Department of Fisheries and Oceans, the New Brunswick Department of Fisheries and Aquaculture and the New Brunswick Salmon Growers’ Association.
References Bailey, J.K., 1988. Selection criteria for sea ranched and cage reared Atlantic salmon Ž Salmo salar .. PhD Thesis, University of Guelph, Guelph, Ontario, Canada, 115 pp. Friars, G.W., Bailey, J.K., Coombs, K.A., 1990. Correlated responses to selection for grilse length in Atlantic salmon. Aquaculture 85, 171–176. Friars, G.W., Bailey, J.K., O’Flynn, F.M., 1995. Applications of selection for multiple traits in cage-reared Atlantic salmon Ž Salmo salar .. Aquaculture 137, 213–217. Gjerde, B., 1986. Growth and reproduction in fish and shellfish. Aquaculture 57, 37–55. Gjedrem, T., Gjerde, B., Refstie, T., 1988. A review of quantitative genetic research in salmonids at AKVAFORSK. In: Weir, B.S., Eisen, E.J., Goodman, M.M., Namkoong, G. ŽEds.., Proceedings of the 2nd International Conference on Quantitative Genetics. Sunderland, MA, USA, pp. 527–535. Griffiths, S.G., Lynch, W.H., 1991. Instability of the major soluble antigen produced by Renibacterium salmoninarium. Journal of Fish Diseases 14, 55–56. Hershberger, W.K., Myers, J.M., Iwamoto, R.N., Meauley, W.C., Saxton, A.M., 1990. Genetic changes in the growth of coho salmon Ž Oncorhynchus kisutch. in marine net-pens, produced by ten years of selection. Aquaculture 85, 187–197. O’Flynn, F.M., Friars, G.W., Bailey, J.K., Terhune, J.M., 1992. Development of a selection index to improve market value of cultured Atlantic salmon Ž Salmo salar .. Genome 35, 304–310. Refstie, T., 1990. Application of breeding schemes. Aquaculture 85, 163–169.