Saltwater performance of all-female triploid Atlantic salmon

Abstract

Survival and growth in a saltwater net-pen was compared between sexually immature all-female diploid and triploid Atlantic salmon ( Salmo salar). All-female fish were produced using sperm from sex-reversed gynogenetic males and triploidy was induced by heat shock. At 17 months post-initiation of feeding, fish larger than 60 g were individually tagged and transferred to a saltwater net-pen where they were reared communally for 376 days. Survival from transfer to harvest was 65% for diploids and 40% for triploids, the difference between ploidy groups having occurred primarily during the 3.5 month period following transfer. Initial average weights of diploids and triploids at stocking were 112 and 103 g per fish, respectively; these values were not significantly different (α = 0.05). Average final weights were 766 and 679 g per fish for diploids and triploids, respectively; these values were significantly different between ploidy groups ( P < 0.01). However, specific growth rates calculated for individual fish identified at harvest and averaged within ploidy groups did not differ significantly (0.52% per day and 0.49% per day, respectively). Average condition factor of fish at stocking was significantly lower for diploids than for triploids (0.98 and 1.02, respectively; P < 0.001), and was significantly greater for diploids at harvest (0.90 and 0.83, respectively; P < 0.001). In summary, triploid all-female Atlantic salmon appeared to require a larger size to complete smoltification, and to grow comparably to or slightly slower than diploids.