AquaBreeding Project title: “Towards enhanced and sustainable use of genetics and breeding in the European aquaculture industry”




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2. Genetic variability of the species

Wild genetic resources available

The natural geographic area of the turbot extends from the northeast Atlantic, throughout the Mediterranean and along the European coasts to the Arctic Circle. It is also found in most of the Baltic Sea. A subspecies, Psetta maxima maeotica, has been described in the Black Sea.

Turbot migrates locally from the coast to its spawning grounds. However, its eggs are dispersed over a large area by the currents.

Only a few publications describe the genetic variability of wild populations. Using allozymes, no differences were observed from the Aegean Sea to the North Sea [5]. A similar result was later found other authors [6, 7] between two Atlantic populations from the Spanish coast (Cantabria and Galicia). The same conclusions were also drawn using microsatellites to compare populations from the Irish Sea with those from the west coast of Norway [8], and compare French turbot from the Bay of Biscay with those from the North Sea or Baltic Sea [9]. These last authors observed a hybrid zone between the North Sea and the Baltic Sea that confirms the existence of at least two distinct populations in the Atlantic. Recently, using mtDNA, [10] identified two distinct mitochondrial lineages within the turbot: the Atlantic or ‘Western Mediterranean’ (French Atlantic coast and Spanish Mediterranean) and ‘Eastern Mediterranean’ lineages (Aegean Sea, Black Sea, Azov Sea, and Sea of Marmara). All these elements confirm previous phenotypic observations suggesting the existence of 3 turbot populations: one in the Baltic Sea, a second from the west Atlantic coast to the west Mediterranean coast and finally one in the eastern Mediterranean basin.


Differences between wild and/or domesticated populations

Several authors report lower genetic variability of samples collected from fish farms [6, 8, 7]. The relevance of some of this analysis is questionable, as it was not performed on the breeding nucleus. Borrell et al [11] observed differences in genetic variability between 5 different broodstock populations from 2 Spanish hatcheries. Some rare alleles were lost but the mean genetic variability was equivalent to the variability of wild populations. Recently, [12] have evaluated genetic variability of the breeding nucleus of one of the leading fry producers from Spain. This broodstock presents a high level of genetic variability, comparable with that observed in one French broodstock population [13] and some wild populations [8].


Interaction between wild and domesticated stocks

No data on interactions are reported in the scientific literature, though a review lists the potential impacts of escapees [14]. Escapes are thought to be rare, as production is limited and mainly performed in land-based facilities, or in recirculation systems for the hatcheries. Risk analysis has not been documented, but the farming of sterile triploids to ensure genetic containment should be explored if such problems arise.


Inbreeding effects

Not documented.



3. Reproduction

Fecundity and main reproductive features

Females are multiple spawners and spawn either every day, or every 2-3 days, according to individuals. Ovulated females swim at the surface and display an increase in belly volume when they are ready to spawn. Collection of gametes is routinely practiced using gentle hand stripping by massage of the flank. Oocytes show a high rate of over-maturation, making management of artificial reproduction highly complex [15]. The turbot, as with most marine fish species, presents a high female fecundity (400,000 eggs / kg body weight per stripping) [16]

Males are oligospermic and only a limited volume of sperm can be collected by hand stripping (0.5-1 ml/ kg).

Appropriate egg to sperm ratio has been defined [17] and ovulation can be induced by GnRH analogues [16].

The natural reproductive season is in summer but can be manipulated to occur throughout the year by photoperiod and temperature regimes [18]. Application of extended light during the 6 first months increases the growth of males and females and decreases the rate of male sexual maturation [19]. Application of extended photoperiods after 6 months of age increases the final size reached at 18 months, in both maturing and immature fish, and decreases the percentage of mature males at 24 months of age [20]. Application of long day length or continuous photoperiod regimes after sexual maturation at 6 years old reduces female maturation and their investment in reproduction [21].
Cryopreservation

Sperm freezing technology has been described using the DMSO as a cryoprotectant, saline extenders and freezing in French straws (IMV) in the liquid nitrogen vapour [22]. Extenders for cryopreservation are available on the market from companies such as IMV-Technology.



Genetic and environmental sex determination, sexual dimorphism

As in many flatfish, turbot females grow faster than males [23, 24, 25], mainly when the water temperature is higher than 16°C [2]. However, triploid females present a better productivity [26] and the production of all-female populations is recommended in order to optimise production.

Sex reversed males and females were induced using 17α-methyltestosterone and 17β-ostradiol respectively, at 3 or 5 mg / kg of food over 500 or 700 degree days after weaning [27].

Based on sex ratios of two gynogenetic families and one triploid family [28, 26] suggested a female homogamety genetic sex determination (XX/XY). However, a male homogamety sex determination (ZZ/ZY) has also been inferred, based on the sex ratios of 33 families obtained by crosses using sex reversed male or females [27]. A limited temperature interaction was also observed, dependent on family and rearing temperature after weaning (14°C, 17°C and 20°C tested). This temperature effect provides some explanation for the curious results observed by previous authors. Further work is necessary to confirm the basis of genetic sex determination in this species.


Cryobanks and reproductive biotechnologies (cloning, cell transfer, germ cell transfer)

No cryobank has been reported.


4. Selection

Genetic variability per trait

In the single publication available that reports heritability for growth in turbot, fish of Norwegian wild origin [29] produced estimates of 0.45 ± 0.28 for h2d and 0.70 ± 0.19 for h2s. However, the large errors of these estimates indicate their poor reliability and high non genetic maternal effects are also suspected. Moreover,, a long period of family rearing in separate tanks (140-220 days) before the fish were tagged (one third of the rearing time) may also have introduced environmental effects common to fullsibs (tank effect) as indicated by the higher heritability estimated from dam component than sire component.

Differences in juvenile growth and feed efficiency were assessed between hatchery populations originating from Norway, Iceland, Scotland and France [30]. The northern populations generally showed better growth, feed intake and feed efficiency. Different hypotheses were proposed, suggesting that there could have been differences in selection or genetic drift between samples from the different hatcheries.

Genetic bases for most of the important traits remain undefined in turbot. However, as female reproduction is difficult and larval rearing associated with high mortality 70-90 %, family selection is expensive, introduces additional sources of environmental variation and increases the possibility of errors. The use of fingerprinting to trace genealogy in the broodstock is already adopted by some breeders. Their application to estimate genetic parameters and breeding value need to be evaluated to obtain unbiased genetic parameters (Estoup et al., 1998).


Genetic correlations and undesirable side effects

Not documented.


G*E interactions

Not documented.


Genetic responses, progresses and control lines

Not documented.


Dominance and intraspecific crossing

Not documented.



5. Polyploidisation and monosexing and hybrids

Triploid induction and performances

Sterilisation has been recommended as a means of limiting the reproductive investment associated with the multiple spawning of turbot, and to avoid the growth losses observed during sexual maturation. Altered photoperiod regimes have not succeeded in preventing sexual maturation. Sterilisation through triploidisation appears to be a potential alternative technical solution. Normal diploid turbot has 44 chromosomes [31], triploids would have 66. Triploids were produced by cold shock [32], and conditions for production in large volumes have been assessed [33]. Triploids are sterile [26] and have equivalent survival to diploids up to 24 months old. Above this age, triploids survive better than diploids, as diploids initiate their sexual maturation and can suffer post-spawning-associated mortality. Triploids show 11 % less growth than diploids (4.3 to 23.0%) at 48 months old. Productivity however, that combines survival and weight, is 10 % better in triploids. Since triploid females grow better than triploid males, development of all-female stocks is recommended to support the farming of triploid turbot. As in the other fish species, triploids have a lower number of red blood cells associated with a lower haematocrit, though the red blood cells are larger in size [34]. However, activities of the humoral components of the innate immune system are similar in diploid and triploid fish, indicating that the lower leucocyte number observed in triploids is compensated by a higher cell activity [35].


Tetraploid induction and performances

Not documented.


Gynogenesis, androgenesis and mitotic clone performances

Gynogenetic turbot were produced by cold shock [36], and grow less well than diploids [28]. Gynogenetic males mature like normal males but gynogenetic females show a delay of one year in their sexual maturation. Although 100 % females were observed in one gynogenetic family, an abnormal sex ratio skewed towards females (1 M : 3 F ) was observed in another. Such results suggest a non homogametic sex genetic determination.


Interspecific hybridisation

Hybrids between the female brill Scophthalmus rhombus and male turbot are nearly all-male and the reciprocal hybrids, with female turbot and male brill, are nearly all-female (all hybrids having rudimentary gonads). These results suggest a complex situation within the genus [37]. However, the larval rearing and weaning of the female brill * turbot male hybrid appears to be very difficult and no evidence of hybrid vigour for growth was observed at 120 days old [38].



6. Genomics

Tools to evaluate population genetic variability

Allozymes and microsatellites markers are the main polymorphic genetic markers available for turbot. More than 300 microsatellites markers have been published [39, 13, 40, 41, 42, 43]. Castro et al [44] report important sources of genotyping error with some markers (null alleles, mutation). Population variation of mitochondrial DNA sequences (control region) has also been described [10]. Recently, AFLP markers have been developed for analysing genetic variability [45].


Genetic markers for genealogical traceability

Microsatellites developed by [13] were used to evaluate the power of different numbers of markers for parentage assignment by simulation. More than 98 % unique assignment could be provided by 6 to 8 markers in different kinds of mating design. Castro et al. [44] designed a tool to identify the exclusive maternal inheritance in gynogenetics. Borrell et al. [11] identified different sources of discrepancy among expected levels of correct assignment using simulation procedures and those obtained with real descendants. Like [44], they identified several factors that could reduce the efficiency of parentage assignment, such as mutation and null alleles. Under commercial conditions, they achieved a high rate of assignment (> 99 %) using 12 markers on a limited number of progeny (498) from 109 families: thus confirming the earlier simulations [13]. The average exclusion probability was above 99.9%, and average mutation rate was estimated as 6.7 *10-4.



QTL and Marker Assisted Selection

Not documented.


Other genomic tools

Much effort has been made in the last three years to develop structural and functional genomic tools as an additional support in breeding programs. A microsatellite genetic map with 250 microsatellites has been recently published [46]. This map comprises 26 linkage groups, around 1500 cM length and shows sex recombination differences when common stretches are compared between males and females. The turbot map is presently being used to identify QTLs for disease resistance and growth. In addition, cDNA libraries have been constructed to obtain an EST database of mostly immunity-related genes. An oligo-microarray has been designed and is presently being used to identify genes and pathways related to resistance to pathogens.


Transgenesis

Not documented.


References

  1. FEAP, 2007. http://www.feap.info

  2. A. K. Imsland, A. Folkvord, G. L. Grung, S. O. Stefansson and G. L. Taranger, “Sexual dimorphism in growth and maturation of turbot, Scophtalmus maximus (Raffinesque, 1810),” Aquaculture, vol. 28, pp. 101-114, 1997.

  3. A. E. Toranzo, B. Magariňos, and J. L. Romalde, “A review of the main bacterial fish diseases in mariculture systems,” Aquaculture, vol. 246, pp. 37-61, 2005.

  4. J. Castric, F. Baudin-Laurencin, M. F. Coustans and M. Auffret, “Isolation of infectious pancreatic necrosis virus, Ab serotype, from an epizootic in farmed turbot, Scophthalmus maximus,” Aquaculture, vol. 67, pp. 117-126, 1987.

  5. A. Blanquer, J. P. Alayse, O. Berrada-Rkhami and R. Berrebi, “Allozyme variation in turbot (Psetta maxima) and brill (Scophthalmus rhombus) (Osteichthyes, Pleuronectiformes, Scophthalmidae) throughout their range in Europe,” J. Fish Biol., vol. 41, pp. 725-736, 1992.

  6. C. Bouza, L. Sanchez and P. Martinez, "Gene diversity analysis in natural populations and cultured stocks of turbot (Scophthalmus maximus L.),” Anim. Genet., vol. 28, pp. 28-36, 1997.

  7. C. Bouza, P. Presa, J. Castro, L. Sanchez and P. Martinez, “Allozyme and microsatellite diversity in natural and domestic populations of turbot (Scophthalmus maximus) in comparison with other Pleuronectiformes,” Can. J. Fish. Aqua. Sci., vol. 59, pp. 1460-1473, 2002.

  8. J. P. Coughlan, A. K. Imsland, P. T. Galvin, R. D. Fitzgerald, G. Naevdal and T. F. Cross, “Microsatellite DNA variation in wild populations and farmed strains of turbot from Ireland and Norway: a preliminary study,” J. Fish Biol., vol. 52, pp. 916-922, 1998.

  9. E. E. Nielsen, P. H. Nielsen, D. Meldrup and M. M. Hansen, “Genetic population structure of turbot (Scophthalmus maximus L.) supports the presence of multiple hybrid zones for marine fish in the transition zone between the Baltic Sea and the North Sea,” Mol. Ecol., vol. 13, pp. 585-595, 2004

  10. N. Suzuki, M. Nishida, K. Yoseda, C. UstUndag, T. Sahin and K. Amaoka, “Phylogeographic relationships within the Mediterranean turbot inferred by mitochondrial DNA haplotype variation,” J. Fish Biol., vol. 65, pp. 580-585, 2004.

  11. Y. J. Borrell, J., Ălvarez, E. Văsquez, C. F. Pato, C. M. Tapia, J. A. Sănchez and G. Blanco, “Applying microsatellites to the management of farmed turbot stocks (Scophthalmus maximus L.) in hatcheries,” Aquaculture, vol. 241, pp. 133-150, 2004.

  12. J. Castro, C. Bouza, P. Presa, A. Pino-Querido, A. Riaza, I. Ferreiro, L. Sănchez, and P. Martiňez, "Potential sources of error in parentage assessment of turbot (Scophthalmus maximus) using microsatellite loci,” Aquaculture, vol. 242, pp. 119–135, 2004.

  13. Estoup, K. Gharbi, M. SanCristobal, C. Chevalet, P. Haffray. and R. Guyomard, “Parentage assignment using microsatellites in turbot (Scophtalmus maximus) and rainbow trout (Oncorhynchus mykiss) hatchery populations,” Can. J. Fish. Aquat. Sci., vol. 55, pp. 715-725, 1998.

  14. A. Danancher D. and García-Vázquez E. (2007). Genetic effects of domestication, culture and breeding of fish and shellfish, and their impacts on wild populations. Turbot – Scophthalmus maximus. p 55-61, In: Svåsand T., Crosetti D., García- Vázquez E., Verspoor E. (eds). Genetic impact of aquaculture activities on native populations. Genimpact fi nal scientifi c report (EU contract n° RICA-CT-2005-022802). http://genimpact.imr.no/

  15. C. Fauvel, M. H. Omnes, M. Suquet, and Y. Normant, “Enhancement of the production of turbot, Scophthalmus maximus (L.), larvae by controlling overripening in mature females,” Aquat. Fish. Manage., vol. 23, pp. 209–216, 1992.

  16. C. Mugnier, M. Guennoc, E. Lebegue, A. Fostier and B. Breton, “Induction and synchronisation of spawning in cultivated turbot (Scophthalmus maximus L.) broodstock by implantation of a sustained-release GnRH-a pellet,” Aquaculture, vol. 181, pp. 241–255, 2000.

  17. M. Suquet, R. Billard, J. Cosson, Y. Normant, and C. Fauvel, “Artificial insemination in turbot, Scophthalmus maximus.: determination of the optimal sperm to egg ratio and time of gamete contact,” Aquaculture, vol. 133, 83–90, 1995.

  18. M. Girin, and N. Devauchelle, "Décalage de la période de reproduction par raccourcissement des cycles photopériodique et thermique chez des poissons marins,” Ann. Biol. Anim., Biochim., Biophys., vol. 18, pp. 1059–1065, 1988.

  19. A. K. Imsland and T. M. Jonassen, “Growth and age at first maturity in turbot and halibut reared under different photoperiods,” Aquaculture International, vol. 11, pp. 463-475, 2003.

  20. A. K. Imsland, A. Folkvord, O. Jónsdóttir and S. O. Stefansson, “Effect of exposure to extended phoyoperiods during the first winter on long-term growth and age at first maturity in turbot (Scophthalmus maximus),” Aquaculture, pp. 125-141, 1997.

  21. A. K. Imsland, M. Dragsnes and S. O. Stefansson, “Exposure to continuous light inhibits maturation in turbot (Scophthalmus maximus),” Aquaculture, vol. 219, pp. 911-919, 2003

  22. O. Chereguini, R. M. Cal, C. Dréanno, B. Ogier de Baulny., M. Suquet and M. Maisse, "Short-term storage and cryopreservation of turbot sperm,” Aquat. Living Resour., vol. 10, no. 4, 251-255, 1997.

  23. C. E. Purdom, A. Jones, and R. F. Lincoln, “Cultivation trials with turbot (Scophthalmus maximus),” Aquaculture, vol. 1, pp. 213-230, 1972.

  24. V. J. Bye, and A. Jones, “Sex control – A method for improving productivity in turbot farming ?,” Fish Farming International, pp. 31-32, 1981.

  25. N. Devauchelle, J. C. Alexandre, N. Le Corre and Y. Letty, “Spawning of turbot (Scophthalmus maximus) in captivity,” Aquaculture, vol. 69, pp. 159-184, 1988.

  26. R. M. Cal, S. Vidal, C. Gomez, B. Alvarez-Blazquez, P. Martinez and F. Piferrer, “Growth and gonadal development in diploid and triploid turbot (Scophthalmus maximus),” Aquaculture, vol. 251, pp. 99-108, 2006.

  27. P. Haffray, E. Lebègue, S. Jeu, M. Guennoc, Y. Guiguen, J.F. Baroiller and A. Fostier, “Genetic and temperature sex determination in the turbot Scophthalmus maximus”,
    Aquaculture (accepted), 2007.

  28. R. M. Cal, C. Gomez, C. Castro, C. Bouza, P. Martinez and F. Piferrer, “Growth and gonadal development of gynogenetic diploid turbot (Scophthalmus maximus),” J. Fish Biol., vol. 68, pp. 401-413, 2006.

  29. B. Gjerde, J. E. Røer, J. Stoss, and T. Refstie, “Heritability for body weight in farmed turbot,” Aquaculture International, vol. 5, pp. 175-178, 1997.

  30. A. K. Imsland, A. Foss, and S. O. Stefansson, “Variation in food intake, food conversion efficiency and growth of juvenile turbot from different geographic strains,” Journal of Fish Biology, vol. 59, pp. 449–454, 2001.

  31. C. Bouza, L. Sánchez and P. Martinez, “Karyotypic characterisation of turbot (Scophthalmus maximus) with conventional fluorochrome and restriction endonuclease-banding techniques,” Mar. Biol., vol. 120, pp. 609-613, 1994.

  32. F. Piferrer, R. M. Cal, B. Álvarez-Blázquez, L. Sánchez and P. Martinez, “Induction of triploidy in the turbot (Scophthalmus maximus). I. Ploidy determination and the effects of cold shocks,” Aquaculture, vol. 188, pp. 79-90, 2000.

  33. F. Piferrer, R. M. Cal, C. Gómez, C. Bouza and P. Martínez, “Induction of triploidy in the turbot (Scophthalmus maximus): II. Effects of cold shock timing and induction of triploidy in a large volume of eggs,” Aquaculture, vol. 220, pp. 821-831, 2003.

  34. R.M. Cal, S. Vidal, T. Camacho, F. Piferrer and F.J. Guitian, “Effect of triploidy on turbot haematology,” Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology, vol. 141, pp. 35-41, 2005.

  35. B. Budiño, R. M. Cal, M. C. Piazzon and J. Lamas, “The activity of several components of the innate immune system in diploid and triploid turbot,” Comparative Biochemistry and Physiology - Part A, vol. 145, pp. 108-113, 2006.

  36. F. Piferrer, R.M. Cal, C. Gómez, B. Alvarez-Blázquez, J. Castro, and P. Martínez, “Induction of gynogenesis in the turbot (Scophthalmus maximus): Effects of UV irradiation on sperm motility, the Hertwig effect and viability during the first 6 months of age,” Aquaculture, vol. 238, pp. 403-419, 2004.

  37. C. E. Purdom and G. Thacker, “Hybrid fish could have farm potential,” Fish Farmer, vol. 3, no. 5, pp. 34-35, 1980.

  38. S. P. Heap and J. P. Thorpe, “A preliminary study of comparative growth rate in 0-group malpigmented and normally pigmented turbot, Scophthalmus maximus (L.), and turbot-brill hybrids S. maximus * S. rhombus (L.), at two temperatures,” Aquaculture, vol. 60, pp. 251-264.

  39. J. Coughlan, R. McCarthy, D. McGregor et al., “Four polymorphic microsatellites in turbot Scophthalmus maximus,” Animal Genetics, vol. 27, pp. 441, 1996.

  40. A. Iyengar, S. Piyapattanakorn, D. A. Heipel, D. M. Stone, B. R. Howell, A. R. Child and N. MacLean, “A suite of highly polymorphic microsatellite markers in turbot (Scophthalmus maximus L.) with potential for use across several flat fish species,” Mol. Ecol., vol. 9, pp. 368-371, 2000.

  41. B.G. Pardo, L. Casas, G.G. Fortes, C. Bouza, P. Martínez, M.S. Clark, and L. Sánchez, “New microsatellite markers in turbot (Scophthalmus maximus) derived from an enriched genomic library and sequence databases,” Molecular Ecology Notes, vol. 5, pp. 62-64, 2005.

  42. B. G. Pardo, M. Hermida, C. Fernandez, C. Bouza, M. Perez, A. Llavona, L. Sanchez, and P. Martinez, “A set of highly polymorphic microsatellites useful for kinship and population analysis in turbot (Scophthalmus maximus L.),” Aquaculture Research, vol. 37, pp. 1578-1582, 2006.

  43. B.G. Pardo, C. Fernández, M. Hermida, A. Vázquez, M. Pérez, P. Presa, M. Calaza, J.A. Alvarez-Dios, A.S. Comesaña, J. Raposo-Guillán, C. Bouza, and P. Martínez, “Development and characterization of 248 novel microsatellite markers in turbot (Scophthalmus maximus),” Genome, vol. 50, pp. 329-332, 2007.

  44. J. Castro, C. Bouza, L. Sánchez, R.M. Cal, F. Piferrer, and P. Martínez, “Gynogenesis assessment by using microsatellite genetic markers in turbot (Scophthalmus maximus),” Marine Biotechnology, vol. 5, pp. 584-592, 2003.

  45. G.G. Fortes, F. Nonnis Marzano, C. Bouza, P. Martínez, P. Ajmone-Marsan, and G. Gandolfi, “Applicatiion of AFLP markers to assess molecular polymorphims in gynogenetic haploid embryos of turbot (Scophthalmus maximus)” Aquaculture Research (in press), 2007.

  46. C. Bouza, M. Hermida, B.G. Pardo, C. Fernández, J. Castro, G. Fortes, L. Sánchez, P. Presa, M. Pérez, A. Sanjuán, S. Comesaña, J.A. Álvarez, M. Calaza, R. Cal, F. Piferrer, and P. Martínez, “A microsatellite genetic map in the turbot (Scopthalmus maximus),” Genetics, vol. 177, pp. 2457-2467, 2007.




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