Production and verification of the first Atlantic salmon (Salmo salar L.) clonal lines.

BACKGROUND: In several fish species homozygous and heterozygous clonal lines have been produced using gynogenetic and androgenetic techniques. These lines are standardized and can be reproduced over generations. In rainbow trout such lines have existed for decades and has become important research tools in genome studies as well as in studies of commercially important traits. The Atlantic salmon is one of the best studied fish species globally, but all experiments are done on fish of wild or domesticated origin and access to standardized immortal fish lines would be of great benefit. Here, we describe the protocols developed to produce mitotic gynogenes, and from these the first clonal lines in Atlantic salmon. RESULTS: Atlantic salmon eggs fertilized with UV irradiated sperm combined with a pressure shock applied at 4700-4800 minC at 8 °C gave all homozygous (doubled haploid) gynogenetic progeny with high survival. From the six first maturing females, five all homozygous clonal lines were produced by meiotic gynogenesis and were verified as clonal and identical to their mother with microsatellite markers. CONCLUSIONS: We have now produced the first documented cloned Atlantic salmon lines. This work demonstrates the potential for production of further Atlantic salmon clonal lines, potentially with distinct characteristics. Such lines will provide an important resource for further elucidation of phenotypic and genetic traits in this globally important species.

A genetic method to infer ploidy and aberrant inheritance in triploid organisms.

Polyploidy occurs naturally across eukaryotic lineages and has been harnessed in the domestication of many crops and vertebrates. In aquaculture, triploidy can be induced as a biocontainment strategy, as it creates a reproductive barrier preventing farm-to-wild introgression, which is currently a major conservation issue for the industry. However, recent work suggests that triploidisation protocols may, on occasion, produce 'failed triploids' displaying diploidy, aneuploidy and aberrant inheritance. The potentially negative consequences for conservation and animal welfare motivate the need for methods to evaluate the success of ploidy-manipulation protocols early in the production process. We developed a semi-automated version of the MAC-PR (microsatellite DNA allele counting - peak ratios) method to resolve the allelic configuration of large numbers of individuals across a panel of microsatellite markers that can be used to infer ploidy, pedigree and inheritance aberrations. We demonstrate an application of the approach using material from a series of Atlantic salmon (Salmo salar) breeding experiments where ploidy was manipulated using a hydrostatic pressure treatment. We validated the approach to infer ploidy against blood smears, finding a > 99% agreement between these methods, and demonstrate its potential utility to infer ploidy as early as the embryonic stage. Furthermore, we present tools to assign diploid and triploid progeny to families and to detect aberrant inheritance, which may be useful for breeding programmes that utilise ploidy manipulation techniques. The approach adds to the ploidy verification toolbox. The increased precision in detecting ploidy and inheritance aberrations will facilitate the ability of triploidisation programmes to prevent farm-to-wild introgression.

Molecular genetic analysis of stomach contents reveals wild Atlantic cod feeding on piscine reovirus (PRV) infected Atlantic salmon originating from a commercial fish farm.

In March 2012, fishermen operating in a fjord in Northern Norway reported catching Atlantic cod, a native fish forming an economically important marine fishery in this region, with unusual prey in their stomachs. It was speculated that these could be Atlantic salmon, which is not typical prey for cod at this time of the year in the coastal zone. These observations were therefore reported to the Norwegian Directorate of Fisheries as a suspected interaction between a local fish farm and this commercial fishery. Statistical analyses of genetic data from 17 microsatellite markers genotyped on 36 partially-degraded prey, samples of salmon from a local fish farm, and samples from the nearest wild population permitted the following conclusions: 1. The prey were Atlantic salmon, 2. These salmon did not originate from the local wild population, and 3. The local farm was the most probable source of these prey. Additional tests demonstrated that 21 of the 36 prey were infected with piscine reovirus. While the potential link between piscine reovirus and the disease heart and skeletal muscle inflammation is still under scientific debate, this disease had caused mortality of large numbers of salmon in the farm in the month prior to the fishermen's observations. These analyses provide new insights into interactions between domesticated and wild fish.