Aquaculture Europe 2023

September 18 - 21, 2023


Add To Calendar 21/09/2023 10:00:0021/09/2023 10:15:00Europe/ViennaAquaculture Europe 2023GENETICS OF EARLY SEXUAL MATURITY IN RAINBOW TROUT Oncorhynchus mykissSchubert 5The European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982


M. L. Aslam *a ,  A. A. Berge b ,  T. Solberg b,  T. Bue b ,  and B. Gjerde a


a Nofima, AS, Ås, Norway; b Osland Genetics AS , 5962 Bjordal

E-mail addresses:



 When  rainbow trout and  the  other salmonids become sexually mature, they experience reduced growth , poor  carcass quality ( external sex characters,  reduced body fat and filet color) , and high mortality if reared in seawater .  Thus, early sexual maturity  before the desired market  size  is  a serious  economic  drawback for the producers .  Limited number of estimates are available for genetic variation of this trait in rainbow trout, but evidence suggests the presence of significant genetic variation



T he aim of this study was to obtain reliable estimates of  genetic variation for  early  sexual maturity at two years of age in rainbow trout,  and to search for possible quantitative trait loci (QTL) for the trait  that can be used for  genomic ( GS)  and/or marker assisted selection (MAS).

Material and Methods

 The population used in the current study originated from the breeding nucleus (year-class 2020) of Osland Genetics AS, comprising  a total of 2054 fish, i.e., the offspring of 92 sires and 144 dams, with  a median full- sib  family size of 12 (ranging from 3-43).  The fish  were slaughtered  at a mean body weight of 4.9 kg at about two years of age . The s exual maturity  status (1 =maturing; 0 =immature)  and  the  gender  of each fish were recorded through the visual observation and palpation of gonads after the fish were killed and gutted .  All the recorded individuals were genotyped using Illumina Infinium  SNPs genotyping array carrying around ~22K SNPs. 

Analyses:  Estimates  of genetic parameters were obtained using a linear mixed model(s) implemented in “ASREML, v4.2”  with  genomic and pedigree information. T he  GWAS analysis was performed with “GCTA, v1.94” program using  the “--mlma-loco” function


 The  fixed and  the  random effects in the  applied  statistical  model are as follows:

w here  is the vector of  the observed  binary  sexual maturity trait  (0 immature and 1 maturing );  is the overall mean; and are design matrices to relate the  animal  records to  appropriate level of the  fixed and  the  random  genetic effects, respectively;  is a  vector of  the  fixed effect of gender ,  is  the  random  animal genetic effect with  , where  is the genetic variance,   is the  genetic  relationship matrix obtained using pedigree information,   is a genomic relationship matrix computed using VanRaden’s method 1 ; and  is the vector of random residuals with . Additionally, estimates of genetic variation for early sexual maturity trait  were also obtained on  the  underlying liability scales using  a threshold model(s).

Results and Discussion

 The incidence of  early  sexual maturing fish at two years of age was very low (2% );  with males showing significantly higher incidence (2.3%) than females (1.7%).

 The  estimated genetic parameters revealed low but significant genetic variation for early sexual maturity with estimates of heritability ranging from ~0.06 to ~0.16 (Table 1) which varied across model (LM vs. TM) and source of information (pedigree vs. genomic).

The g enome-wide association  analysis revealed  a strong signal of  a quantitative trait loci (QTL) at chromosome 28 with 27 SNPs surpassing chromosome and/or genome-wide Bonferroni corrected significant threshold (Figure 1).  In spite of the low frequency of early sexually maturing fish in the current data, the highly significant SNP at chrom osome 28 explained ~31% of the  total genetic variance  computed using  (Falconer and Mackay, 1996

).  The  display  of  a  single clear QTL  at  chromosome 28 together with some minor indications from the SNPs located at other chromosomes (18 and 30) directs that  the  trait  may be affected by a few gene(s) with large  effect  and multiple other genes with smaller effect size.  The results show that  the selection through GS and/or MAS can be used to  further reduce incidences of undesired  early sexual maturity in this population of rainbow trout.

Similar parameter estimates  will  also  be obtained  based on data  from a  more recent year-class (2021). In addition, we will present  estimates of  accuracy of prediction using cross validation scheme(s) with different models (PBLUP, GBLUP, Bayesian, and MAS) to assess and compare the potential of genomic and/or marker assisted selection over classical pedigree information.


 The results of the current study are a part of the R& D agreement between NOFIMA AS and OSLAND GENETICS AS .


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