The genetic architecture of phenotypic diversity in the betta fish (Betta splendens)

Abstract

The Betta fish displays a remarkable variety of phenotypes selected during domestication. However, the genetic basis underlying these traits remain largely unexplored. Here, we report a high-quality genome assembly and re-sequencing of 727 individuals representing diverse morphologies of the betta fish. We show that current breeds have a complex domestication history with extensive introgression with wild species. Using GWAS, we identify the genetic basis of multiple traits, including several coloration phenotypes, sex-determination which we map to DMRT1, and the long-fin phenotype which maps to KCNJ15. We identify a polygenic signal related to aggression with many similarities to human psychiatric traits, involving genes such as CACNB2 and DISC1. Our study provides a resource for developing the Betta fish as a genetic model for morphology and behavior in vertebrates.

Sex Reversal in Siamese Fighting Fish Larvae by Thermal Management

“…However, even when XX vs XX cross was performed, 10% of offspring were male, confirming an incomplete genotypic sex determination in betta (Kwon et al, 2021). Zhang et al (2021) also find in minor proportions homogametic males in their study, which, according with authors, suggest the influence of environmental factors in sex determination in this species.…”

“…As regards the influence of temperature, there are several factors that affect the sex ratio in fish, such genetic, epigenic and environmental, as reviewed by Budd et al (2015). Zhang et al (2021) find evidence that betta is a heterogametic specie (male XY and female XX), which indicate the existence of genotype sex determination (GSD) mechanism, even finding in less proportion (~8,8%) males with homogametic female genotype between the fish analyzed in their study. According with authors, this may suggest also the influence of environmental factors in sex determination in this specie.…”

“…In bettas, recently, two papers (Kwon et al, 2021;Zhang et al, 2021) showed that the most of heterozygous individuals are male, which supports that in such specie, the male phenotype could be formed by heterogametic sexual chromosomes (XY/XX). However, even when XX vs XX cross was performed, 10% of offspring were male, confirming an incomplete genotypic sex determination in betta (Kwon et al, 2021).…”

Something Fishy about Siamese Fighting Fish (Betta splendens) Sex: Polygenic Sex Determination or a Newly Emerged Sex-Determining Region?

“…Siamese fighting fish are indigenous to central Thailand and the lower Mekong. They are mostly known as domesticated ornamentals, originally bred for use in gambling matches [ 37 ]. Thais have bred and sold Siamese fighting fish for centuries (primarily the males) for their beauty and fighting abilities.…”

The ornamental fighting fish is the next model organism for genetic studies

“…This review highlights the complementarity of fighting fish to other animal models (e.g., mice, zebrafish and medaka) in the study of the genetic bases of phenotypic variation and aggression, as well as domestication and evolution of fishes. In comparison to mice, zebrafish and medaka, fighting fish has more diverse phenotypes, 2 a longer history of domestication and more obvious aggressive behaviour 3,12,20 . Therefore, studies on fighting fish will complement those of other existing model animals, and contribute to the understanding of phenotypic variation, domestication and aggressive behaviour, which in turn, will facilitate the understanding of many biological questions related to aquaculture and aggressive behaviour in humans and other animal species.…”