Alaska Department of Fish and Game
333 Raspberry Road, Anchorage, AK 99518
EXTENDED ABSTRACT The use of triploid fish has been promoted for many management applications (Ihssen et al. 1990, Thorgaard 1992). Stocking of triploid salmonids instead of diploids may promote long-term conservation of biodiversity. Stocking diploids can result in unwanted hybridization, predation, or competition with native species (Taggart and Ferguson 1986, Garcia de Leániz et l. 1989, Mork 1991). Triploids are reproductively sterile, thereby eliminating the potential for hybridization (Allen et al. 1986). In many salmonids, sterility also means that fish will live longer, resulting in some trophy individuals (Lincoln and Scott 1984, Donaldson et al. 1993). If competition or predation problems arise between stocked triploids and native species, then halting stocking would eliminate these interactions within one life cycle. Interestingly, proposed uses in aquaculture include gene conservation as well as enhanced meat production (Seeb et al. 1993). Several nations have considered requiring that farmed salmonids be sterilized in order to protect wild stocks from introgression due to large-scale escapes (Gausen and Moen 1991, Lura and Saegrov 1991). Triploidy has also been suggested by some workers as a prerequisite to the use of transgenic fish (Kapuscinski and Hallerman 1990, Seeb and Miller 1990).
Problems with triploid production and performance occasionally have been reported, but these problems are not consistent and depend on the species examined and on the production environment. For example, achieving 100% triploids in production lots can be an elusive goal with some species, limiting conservation applications. Additionally, triploids have exhibited growth superior to (Scheerer et al. 1987), equal to (Habicht et al. 1994), or inferior to (Solar et al. 1984) the corresponding diploid controls depending on the species tested and rearing environment. Finally, there is a risk that triploid males may try to spawn with diploid females in wild-stock areas, disrupting wild-stock production (Masaru et al. 1993).
These factors make it difficult to form generalizations concerning usage of triploids. Successful applications will depend on project goals, and managers must balance the needs of gene conservation against the possibility of reduced performance of triploids. Thought must be given to standardizing certification of triploid salmonids for stocking and to the consequences of false spawning of triploid males.
Finally, managers must be aware that the risks of stocking diploids are seldom evaluated as thoroughly as are the risks of stocking triploids. Clearly, in some cases, use of diploids will have more dire consequences than the use of triploids. We believe that, given the information available now, use of triploids should be required for some types of stocking programs and most net-pen farming.
ACKNOWLEDGMENTS Our sterile-fish research is supported by funds from the U.S. Department of Agriculture Cooperative State Research Service under Grant 9104215 "Improved Performance of Salmonids Through Production of Triploid Hybrids" and from the Alaska Department of Fish and Game general funds project 11000013-41100-11005253. This manuscript is contribution PP-096 of the Alaska Department of Fish and Game, Commercial Fisheries Management and Development Division, Juneau. LITERATURE CITED
Allen, S.K., Jr., R.G. Thiery, and N.T. Hagstrom, 1986. Cytological evaluation of the likelihood that triploid grass carp will reproduce. Trans. Amer. Fish. Soc. 115: 841-848.
Donaldson, E.M., R.H. Devlin, I.I. Solar, and F. Piferrer, 1993. The reproductive containment of genetically altered salmonids. In: J.G. Cloud and G.H. Thorgaard (eds.), Genetic conservation of fishes, pp. 113-129. NATO ASI Series A., New York, NY, Plenum Press.
Garcia de Leániz, C., E. Verspoor, and A.D. Hawkins, 1989. Genetic determination of the contribution of stocked and wild Atlantic salmon, Salmo salar L., to the angling fisheries in two Spanish rivers. J. Fish. Biol. 35 (Suppl. A): 261-270.
Gausen, D., and V. Moen, 1991. Large-scale escapes of farmed Atlantic salmon (Salmo salar) into Norwegian rivers threaten natural populations. Can. J. Fish. Aquat. Sci. 48: 426-428.
Habicht, C., J.E. Seeb, R.B. Gates, I.R. Brock, and C.A. Olito, 1994. Conspecific triploid coho salmon outperform triploid hybrids between coho salmon and chinook salmon during their first year. Can. J. Fish. Aquat. Sci. (Accepted and in press).
Ihssen, P.E., L.R. Mckay, I. Mcmillan, and R.B. Phillips, 1990. Ploidy manipulation and gynogenesis in fishes - cytogenetic and fisheries applications. Trans. Amer. Fish. Soc. 119: 698-717.
Kapuscinski, A.R., and E.M. Hallerman, 1990. American Fisheries Society position statement on transgenic fishes. Fisheries 15(4): 2-4.
Lincoln, R.F., and A.P. Scott, 1984. Sexual maturation in triploid rainbow trout, Salmo gairdneri Richardson. J. Fish. Biol. 25: 385-392.
Lura, H., and H. Saegrov, 1991. Documentation of successful spawning of escaped farmed female Atlantic salmon, Salmo salar, in Norwegian rivers. Aquaculture 98: 151-159.
Masaru, N., F. Tsuchiya, M. Iwahashi, and Y. Nagahama, 1993. Reproductive characteristics of precociously mature triploid male masu salmon, Oncorhynchus masou. Zool. Sci. 10: 117-125.
Mork, J., 1991. One-generation effects of farmed fish immigration on the genetic differentiation of wild Atlantic salmon in Norway. Aquaculture 98: 267-276.
Scheerer, P.D., G.H. Thorgaard, and J.E. Seeb, 1987. Performance and developmental stability of triploid tiger trout (brown trout female x brook trout male). Trans. Amer. Fish. Soc. 116: 92-97.
Seeb, J.E., and G.D. Miller, 1990. The integration of allozyme analyses and genomic manipulations for fish culture and management. In: D. Whitmore (ed.), Electrophoretic and isolectric focusing techniques in fisheries management, pp. 265-280. Boca Raton, FL, CRC Press, Inc.
Seeb, J.E., G.H. Thorgaard, and T. Tynan, 1993. Triploid hybrids between chum salmon female X chinook salmon male have early sea-water tolerance. Aquaculture 117: 37-45.
Solar, I.I., E.M. Donaldson, and G.A. Hunter, 1984. Induction of triploidy in rainbow trout (Salmo gairdneri Richardson) by heat shock, and investigation of early growth. Aquaculture 42: 57-68.
Taggart J.B., and A. Ferguson, 1986. Electrophoretic evaluation of a supplemental stocking programme for brown trout, Salmo trutta L. Aquacult. Fish. Man. 17: 155-62.
Thorgaard, G.H., 1992. Application of genetic technologies to rainbow trout. Aquaculture 100: 85-97.