The frequency of spontaneous triploidy in farmed Atlantic salmon produced in Norway during the period 2007-2014.

Kevin A Glover,Vidar Wennevik,Tom J Hansen,H Craig Morton,Øystein Skaala,Abdullah S Madhun,Per G Fjelldal,Anne G E Sørvik,Geir Dahle

doi:10.1186/s12863-015-0193-0

Abstract

BackgroundSpontaneous triploidy has been reported in a number of fish species, and is often linked with in vivo or in vitro ageing of eggs post ovulation. Here, we provide the first investigation into the frequency of spontaneous triploidy in farmed Atlantic salmon by analysing more than 4000 fish from 55 farms, and approximately 1000 recaptured escapees, all sampled in the period 2007–2014. In addition, we compare microsatellite genotyping against flow cytometry and red blood cell diameter in a set of 45 putatively diploid and 45 putatively triploid Atlantic salmon.ResultsThe three methods implemented for ploidy determination gave consistent results, thus validating the methods used here. Overall, 2.0% spontaneous triploids were observed in salmon sampled on farms. The frequency of spontaneous triploids varied greatly among sea cages (0-28%), but they were observed in similar frequencies among the three primary breeding companies (1.8-2.4%). Spontaneous triploids were observed in all farming regions in Norway, and in all years sampled. Spontaneous triploids were also observed among the escapees recaptured in both the marine environment and in rivers.ConclusionsSpontaneous triploidy in commercially produced Atlantic salmon is likely to be a result of the practices employed by the industry. For logistical reasons, there is sometimes a pause of hours, and in some cases overnight, between killing the female broodfish, removal of her eggs, and fertilization. This gives the eggs time to age post ovulation, and increases the probability of duplication of the maternal chromosome set by inhibition of the second polar body release after normal meiosis II in the oocyte.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0193-0) contains supplementary material, which is available to authorized users.

Highlights

Spontaneous triploidy has been reported in a number of fish species, and is often linked with in vivo or in vitro ageing of eggs post ovulation
Spontaneous triploidy originates from the duplication of the maternal chromosome set by inhibition of the second polar body release after normal meiosis II in the oocyte
Based upon the analysis of microsatellite DNA profiles of more than 4000 salmon collected from 55 fish farms, and a group of nearly 1000 farmed escapees recaptured in the wild, all sampled in the period 2007–2014, we were able to document that spontaneous triploidy occurred at 2.0% in the samples taken on farms, and 1.8% in the total material

Summary

Introduction

Spontaneous triploidy has been reported in a number of fish species, and is often linked with in vivo or in vitro ageing of eggs post ovulation. We provide the first investigation into the frequency of spontaneous triploidy in farmed Atlantic salmon by analysing more than 4000 fish from 55 farms, and approximately 1000 recaptured escapees, all sampled in the period 2007–2014. Norwegian breeders (Aqua Gen AS, Marine Harvest and Salmobreed AS) has been distributed to fish farms in other regions of the globe (e.g., [9]), farmed salmon originating from Norwegian breeding programs dominate global production. Thousands or hundreds of thousands of farmed fish escape from their net pens into the wild. While many of these escapees disappear never to be seen again, some return to freshwater and can interbreed with wild salmon [10,11]. In response to requests from the Norwegian Directorate of Fisheries (NDF), who are responsible for production and implementation of aquaculture regulations in Glover et al BMC Genetics (2015) 16:37

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