Chromosome aberrations in pressure-induced triploid Atlantic salmon

Abstract

Background: Triploid organisms have three sets of chromosomes. In Atlantic salmon, hydrostatic pressure treatment of newly fertilized eggs has been extensively used to produce triploids which are functionally sterile due to their unpaired chromosomes. These fish often perform poorly on commercial farms, sometimes without explanation. Inheritance patterns in individuals subjected to pressure treatment have not been investigated in Atlantic salmon thus far. However, work on other species suggests that this treatment can result in aberrant inheritance. We therefore studied this in Atlantic salmon by genotyping 16 polymorphic microsatellites in eyed eggs and juveniles which had been subjected to pressure-induction of triploidy. Communally reared juveniles including fish subjected to pressure-induction of triploidy and their diploid siblings were included as a control. Results: No diploid offspring were detected in any of the eggs or juveniles which were subjected to hydrostatic pressure; therefore, the induction of triploidy was highly successful. Aberrant inheritance was nevertheless observed in 0.9% of the eggs and 0.9% of the juveniles that had been subjected to pressure treatment. In the communally reared fish, 0.3% of the fish subjected to pressure treatment displayed aberrant inheritance, while their diploid controls displayed 0% aberrant inheritance. Inheritance errors included two eyed eggs lacking maternal DNA across all microsatellites, and, examples in both eggs and juveniles of either the maternal or paternal allele lacking in one of the microsatellites. All individuals displaying chromosome aberrations were otherwise triploid. Conclusions: This is the first study to document aberrant inheritance in Atlantic salmon that have been subjected to pressure-induction of triploidy. Our experiments unequivocally demonstrate that even when induction of triploidy is highly successful, this treatment can cause chromosome aberrations in this species. Based upon our novel data, and earlier studies in other organisms, we hypothesize that in batches of Atlantic salmon where low to modest triploid induction rates have been reported, aberrant inheritance is likely to be higher than the rates observed here. Therefore, we tentatively suggest that this could contribute to the unexplained poor performance of triploid salmon that is occasionally reported in commercial aquaculture. These hypotheses require further investigation.

Autosomal sdY Pseudogenes Explain Discordances Between Phenotypic Sex and DNA Marker for Sex Identification in Atlantic Salmon

“…Over the past decade, we have conducted a number of pedigree-controlled studies on a multiple-generation experimental population of domesticated and wild Atlantic salmon and their crosses at the aquaculture facility owned by the Institute of Marine Research located in Matre, western Norway ( Solberg et al, 2013 , 2014 ; Ayllon et al, 2015 ; Harvey et al, 2016 , 2018 ; Glover et al, 2018 , 2020 ; Perry et al, 2019 ; Besnier et al, 2020 ). The reader is directed to these publications for full details regarding the standard rearing conditions experienced in this fish farm.…”

A comparison of triploid and diploid Atlantic salmon (Salmo salar) performance and welfare under commercial farming conditions in Norway

“…In diploid Atlantic salmon, reduced hypo-osmoregulatory ability during transfer to seawater creates loser fish, but these individuals survive up to harvest size, often retaining normal growth rates and condition factors after a period in seawater (unpublished personal results). Recently, Glover et al (2020) reported that triploid salmon display chromosomal aberrations. If the triploid loser fish phenomenon is related to osmoregulatory dysfunction, infections and/or genetic aberrations need to be further investigated to fully understand the suitability of triploid salmon in commercial aquaculture…”

Early, nonlethal ploidy and genome size quantification using confocal microscopy in zebrafish embryos

“…While triploid embryos do produce a peak nuclear volume approximately 50% larger than that of diploids (as expected), the values are not normally distributed, extending into and below the modal volume of diploid embryos. This may reflect some degree of aneuploidy; indeed, recent work has demonstrated a high frequency of chromosomal aberrations in pressure‐induced triploid Atlantic salmon especially in cases when the rate of triploid induction is low (Glover et al, 2020).…”