Abstract
An investigation of sex-specific loci may provide important insights into fish sex determination strategies. This may be useful for biotechnological purposes, for example, to produce all-male or all-female fish for commercial breeding. The North African catfish species, Clarias gariepinus, has been widely adopted for aquaculture because its superior growth and disease resistance render the species suitable for hybridization with other catfish to improve the productivity and quality of fish meat. This species has either a ZZ/ZW or XX/XY sex determination system. Here, we investigate and characterize these systems using high-throughput genome complexity reduction sequencing as Diversity Arrays Technology. This approach was effective in identifying moderately sex-linked loci with both single-nucleotide polymorphisms (SNPs) and restriction fragment presence/absence (PA) markers in 30 perfectly sexed individuals of C. gariepinus. However, SNPs based markers were not found in this study. In total, 41 loci met the criteria for being moderately male-linked (with male vs. female ratios 80:20 and 70:30), while 25 loci were found to be moderately linked to female sex. No strictly male- or female-linked loci were detected. Seven moderately male-linked loci were partially homologous to some classes of transposable elements and three moderately male-linked loci were partially homologous to functional genes. Our data showed that the male heterogametic XX/XY sex determination system should co-exist with the ZZ/ZW system in C. gariepinus. Our finding of the co-existence of XX/XY and ZZ/ZW systems can be applied to benefit commercial breeding of this species in Thailand. This approach using moderately sex-linked loci provides a solid baseline for revealing sex determination mechanisms and identify potential sex determination regions in catfish, allowing further investigation of genetic improvements in breeding programs.
Highlights
Aquaculture plays an important role in global food production (Belton and Thilsted, 2014; Loring et al, 2019)
To determine whether XX/XY or ZZ/ZW sex chromosomes drive sex determination in C. gariepinus, we compared a number of SNP and PA after filtering with a gradually varying set of criteria
Our analysis reports the co-occurrence of male and female linked loci with a different proportion (70:30) across all the sampled specimens, suggesting that the XY and ZW systems can coexist inside the same fish individual
Summary
Aquaculture plays an important role in global food production (Belton and Thilsted, 2014; Loring et al, 2019). The availability of land and water resources for aquaculture is currently limited, while susceptibility to new diseases is increasing (Ayyam et al, 2019; Lebel et al, 2019) This has facilitated continuous improvements in breeding programs by cross-breeding between different species to generate new hybrid varieties that can tolerate high stocking densities (Dunham and Masser, 2012; Zhou et al, 2018). A hybrid was developed by crossing artificially male North African catfish and female bighead catfish (Senanan et al, 2004) This F1 hybrid catfish exhibits a rapid growth rate and has a high disease resistance, which has led to the propagation of these hybrids in the aquaculture market. The complexity of sex determination interaction between the two species might influence differences in fertility between F1 male and female hybrids (Ponjarat et al, 2019)
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