Cytogenetic identification of genomic elements of brook trout ( Salvelinus fontinalis ) in the karyotype of Arctic char ( Salvelinus alpinus ) from the aquaculture broodstock

Abstract

Summary Growing interest of Arctic char (Salvelinus alpinus) aquaculture in Europe, and the fact that it can easily hybridize with brook trout (Salvelinus fontinalis) resulting in fertile progeny, led us to investigate fish from the farmed stocks. Chromosomes of sampled Arctic char were examined using conventional and molecular cytogenetic (FISH) techniques in order to determine possible contamination of genomic elements of brook trout. Investigated fish possessed karyotypes composed of 80–82 chromosomes and up to three chromosome fragments. Using staining methods and FISH approach enabled identification of the brook trout chromosomes in the eight out of twenty‐two examined Arctic char. Specific location of AT‐, GC‐ positive and NOR sites observed on chromosomes as well as chromosome fragments in the karyotypes of several individuals points on past chromosomal rearrangements in fish from examined broodstock. Based on our results, it may be assumed that individuals with the brook trout genomic elements, although phenotypically identified as Arctic chars, were hybrids. Our results highlights that special care should be taken to protect gene pools of brook trout and Arctic char in farms where both species are cultured.

Cytogenetic investigation of Arctic char × brook trout F1, F2 and backcross hybrids revealed remnants of the chromosomal rearrangements

“…In one Sf × H individual, large a chromosome with interstitially, subtelomerically located CMA 3 -positive signal overlapped with active NOR. Similar chromosome was described in Arctic chars from aquaculture broodstock (Pomianowski et al 2019 ). It may have appeared in the course of pericentromeric inversion of st-a chromosome with NOR located on the short arm.…”

“…Here, in F 1 generation hybrids (Sa × Sf), we confirmed the presence of single ITS bearing chromosomes inherited after both Salvelinus parental species. Presence of the same ITS bearing chromosomes was previously described in one Arctic char individual from the aquaculture broodstock (Pomianowski et al 2019) what indicates past hybridization events during breeding practices. Identification of two brook trout chromosomes with ITS in Sf × H backcross, and one such chromosome in H × Sf fish, points on different type of chromosome selection during meiosis.…”

“…Described location was revealed in the majority of studied fish except H × Sa individuals, where pair of large acrocentrics with interstitially located DAPI band is observed and in H × Sf individuals possessing large uniarmed chromosome with DAPI signal reaching half of the arm. Both chromosomes were previously reported in the farmed Arctic chars (Pomianowski et al 2019) and taking into consideration their size, these chromosomes appeared in the course of the tandem fusion. Tandem fusions are rearrangements that affect number of chromosomes and chromosome arms and are responsible for differences in the chromosome number in European (2n = 54) and North American (2n = 58) populations of Atlantic salmon (Salmo salar) Horne 1984a, 1984b;Ueda and Kobayashi 1990).…”

“…Chromosome fragments were also visible in metaphase spreads obtained from inviable hybrids of rainbow trout and sea trout (Polonis et al 2018 ). Moreover, chromosome fragments were also observed in Arctic chars from the aquaculture broodstock (Pomianowski et al 2019 ).…”