Nile tilapia belongs to the second most cultivated group of fish in the world, mainly because of its favorable characteristics for production. Genetic improvement programs and domestication process of Nile tilapia may have modified the genome through selective pressure, leaving signals that can be detected at the molecular level. In this work, signatures of selection were identified using genomewide SNP data, by two haplotype-based (iHS and Rsb) and one F ST based method. Whole-genome re-sequencing of 326 individuals from three strains (A, B and C) of farmed tilapia maintained in Brazil and Costa Rica was carried out using Illumina HiSeq 2500 technology. After applying conventional SNP-calling and quality-control filters, ~ 1.3 M high-quality SNPs were inferred and used as input for the iHS, Rsb and F ST based methods. We detected several candidate genes putatively subjected to selection in each strain. A considerable number of these genes are associated with growth (e.g. NCAPG, KLF3, TBC1D1, TTN), early development (e.g. FGFR3, PFKFB3), and immunity traits (e.g. NLRC3, PIGR, MAP1S). These candidate genes represent putative genomic landmarks that could be associated to traits of biological and commercial interest in farmed nile tilapia. Nile tilapia (Oreochromis niloticus) is a teleost fish of the Cichlidae family native to Africa and the Middle East. The geographic range of the species extends from 8°N to 32°N 1. The first record of domestication is dated around 3,500 years ago as evidenced in paintings at the Theban tombs in Egypt 2. Nowadays, this species is the second most cultivated group of fish in the world 3. Favorable characteristics for production include rapid growth, adaptability to different culture conditions, tolerance to high densities, disease resistance, easy reproduction, and tolerance to low concentrations of oxygen 4. Genetic improvement programs (GIPs) for Nile tilapia began in 1988 as an approach to counteract the production decrease generated by introgressions with Mozambique tilapia (Oreochromis mossambicus) 5,6. Since then, nearly twenty GIPs have been established for Nile tilapia around the world 7,8. GIPs aim to improve traits of commercial interest, such as growth rate, disease resistance, cold and salinity tolerance 7. The GIFT (Genetic Improvement of Farmed Tilapia) 9 Nile tilapia strain was developed by the ICLARM (International Centre for Living Aquatic Resources Management, now the WorldFish Center), in collaboration with the Norwegian Institute of Aquaculture Research (AKVAFORSK, now NOFIMA Marin) 1. The implementation of GIPs for the GIFT population has been successful, because growth rate in Nile tilapia has doubled in five generations, showing that this species had a positive response to selection 1 .

26Nile tilapia (Oreochromis niloticus) is one of the most cultivated and economically important species in 27 world aquaculture. Faster male development during grow-out phase is considered a major problem that 28 generate heterogeneous sizes of fish at harvest. Identifying genomic regions associated with sex 29 determination in Nile tilapia is a research topic of great interest. The objective of this study was to 30 identify genomic variants associated with sex determination in three commercial populations of Nile 31 tilapia. Whole-genome sequencing of 326 individuals was performed, and a total of 2.4 million high-32quality bi-allelic single nucleotide polymorphisms (SNPs) were identified. A genome-wide association 33 study (GWAS) was conducted to identify markers associated with the binary sexual trait (males = 0; 34 females = 1). A mixed logistic regression GWAS model was fitted and a genome-wide significant signal 35 comprising 36 SNPs, located on chromosome 23 spanning a genomic region of 536 kb, was identified. 36Ten out of these 36 genetic variants, intercept the anti-Müllerian hormone gene. Other significant SNPs 37 were located in the neighboring Amh gene region. This gene has been strongly associated with sex 38 determination in several vertebrate species, playing an essential role in the differentiation of male and 39 female reproductive tissue in early stages of development. This finding provides useful information to 40 better understand the genetic mechanisms underlying sex determination in Nile tilapia. 41 42 Keywords: SNP, sex control, quantitative trait loci, WGS, GWAS 43 44 45

Nile Tilapia (Oreochromis niloticus) is the second most important farmed fish in the world and a sustainable source of protein for human consumption. Several genetic improvement programs have been established for this species in the world and so far, they are mainly based on conventional selection using genealogical and phenotypic information to estimate the genetic merit of breeders and make selection decisions. Genome-wide information can be exploited to efficiently incorporate traits that are difficult to measure in the breeding goal. Thus, SNPs are required to investigate phenotype-genotype associations and determine the genomic basis of economically important traits. We performed de novo SNP discovery in three different populations of farmed tilapias. A total of 29.9 million non-redundant SNPs were identified through Illumina (HiSeq 2500) whole-genome resequencing of 326 individual samples. After applying several filtering steps including removing SNP based on genotype and site quality, presence of Mendelian errors, and non unique position in the genome, a total of high quality 50,000 SNP were selected for validation purposes. These SNPs were highly informative in the three populations analyzed showing between 43,869 (94%) and 46,139 (99%) SNP in HWE; 37,843 (76%) and 45,171(90%) SNP with a MAF higher than 0.05 and; 43,450 (87%) and 46,570 (93%) SNPs with a MAF higher than 0.01. The final list of 50K SNPs will be very useful for the dissection of economically relevant traits, enhancing breeding programs through genomic selection as well as supporting genetic studies in farmed populations Nile tilapia using dense genome-wide information.

Nile tilapia (Oreochromis niloticus) is one of the most produced farmed fish in the world and represents an important source of protein for human consumption. Farmed Nile tilapia populations are increasingly based on genetically improved stocks, which have been established from admixed populations. To date, there is scarce information about the population genomics of farmed Nile tilapia, assessed by dense single nucleotide polymorphism (SNP) panels. The patterns of linkage disequilibrium (LD) may affect the success of genome-wide association studies (GWAS) and genomic selection (GS), and also provide key information about demographic history of farmed Nile tilapia populations. The objectives of this study were to provide further knowledge about the population structure and LD patterns, as well as, estimate the effective population size (N e) for three farmed Nile tilapia populations, one from Brazil (POP A) and two from Costa Rica (POP B and POP C). A total of 55 individuals from each population, were genotyped using a 50K SNP panel selected from a whole-genome sequencing (WGS) experiment. The first two principal components explained about 20% of the total variation and clearly differentiated between the three populations. Population genetic structure analysis showed evidence of admixture, especially for POP C. The contemporary N e estimated, based on LD values, ranged from 78 to 159. No differences were observed in the LD decay among populations, with a rapid decrease of r 2 with increasing inter-marker distance. Average r 2 between adjacent SNP pairs ranged from 0.19 to 0.03 for both POP A and C, and 0.20 to 0.03 f or POP B. Based on the number of independent chromosome segments in the Nile tilapia genome, at least 9.4, 7.6, and 4.6K SNPs for POP A, POP B, and POP C respectively, are required for the implementation of GS in the present farmed Nile tilapia populations.

No abstract

Nile tilapia (Oreochromis niloticus) is one of the most cultivated and economically important species in world aquaculture. Intensive production promotes the use of monosex animals, due to an important dimorphism that favors male growth. Currently, the main mechanism to obtain all-male populations is the use of hormones in feeding during larval and fry phases. Identifying genomic regions associated with sex determination in Nile tilapia is a research topic of great interest. The objective of this study was to identify genomic variants associated with sex determination in three commercial populations of Nile tilapia. Whole-genome sequencing of 326 individuals was performed, and a total of 2.4 million high-quality bi-allelic single nucleotide polymorphisms (SNPs) were identified after quality control. A genome-wide association study (GWAS) was conducted to identify markers associated with the binary sex trait (males = 1; females = 0). A mixed logistic regression GWAS model was fitted and a genome-wide significant signal comprising 36 SNPs, spanning a genomic region of 536 kb in chromosome 23 was identified. Ten out of these 36 genetic variants intercept the anti-Müllerian (Amh) hormone gene. Other significant SNPs were located in the neighboring Amh gene region. This gene has been strongly associated with sex determination in several vertebrate species, playing an essential role in the differentiation of male and female reproductive tissue in early stages of development. This finding provides useful information to better understand the genetic mechanisms underlying sex determination in Nile tilapia.

From a physiological-behavioral perspective, it has been shown that fish with a higher density of black eumelanin spots are more dominant, less sensitive to stress, have higher feed intake, better feed efficiency and therefore are larger in size. Thus, we hypothesized that genetic (co)variation between skin pigmentation patterns and growth exists and it is advantageous in rainbow trout. The objective of this study was to determine the genetic relationships between skin pigmentation patterns and BW in a breeding population of rainbow trout. We performed a genetic analysis of pigmentation traits including dorsal color (DC), lateral band (LB) intensity, amount of spotting above (SA) and below (SB) the lateral line, and BW at harvest (HW). Variance components were estimated using a multi-trait linear animal model fitted by restricted maximum likelihood. Estimated heritabilities were 0.08±0.02, 0.17±0.03, 0.44±0.04, 0.17±0.04 and 0.23±0.04 for DC, LB, SA, SB and HW, respectively. Genetic correlations between HW and skin color traits were 0.42±0.13, 0.32±0.14 and 0.25±0.11 for LB, SA and SB, respectively. These results indicate positive, but low to moderate genetic relationships between the amount of spotting and BW in rainbow trout. Thus, higher levels of spotting are genetically associated with better growth performance in this population.

25Nile Tilapia (Oreochromis niloticus) is the second most important farmed fish in the world and a 26 sustainable source of protein for human consumption. Several genetic improvement programs have been 27 established for this species in the world and so far, they are mainly based on conventional selection using 28 genealogical and phenotypic information to estimate the genetic merit of breeders and make selection 29 decisions. Genome-wide information can be exploited to efficiently incorporate traits that are difficult to 30 measure in the breeding goal. Thus, SNPs are required to investigate phenotype-genotype associations 31 and determine the genomic basis of economically important traits. We performed de novo SNP discovery 32 in three different populations of farmed tilapias. A total of 29.9 million non-redundant SNPs were 33 identified through Illumina (HiSeq 2500) whole-genome resequencing of 326 individual samples. After 34 applying several filtering steps including removing SNP based on genotype and site quality, presence of 35Mendelian errors, and non unique position in the genome, a total of high quality 50,000 SNP were selected 36 for validation purposes. These SNPs were highly informative in the three populations analyzed showing 37 between 43,869 (94%) and 46,139 (99%) SNP in HWE; 37,843 (76%) and 45,171(90%) SNP with a MAF 38 higher than 0.05 and; 43,450 (87%) and 46,570 (93%) SNPs with a MAF higher than 0.01. The final list 39 of 50K SNPs will be very useful for the dissection of economically relevant traits, enhancing breeding 40 programs through genomic selection as well as supporting genetic studies in farmed populations Nile 41 tilapia using dense genome-wide information. 42 43