Genetic and reproductive mode analyses of a golden-back mutant of crucian carp from a rice-fish integrated farming system

Traditional agricultural systems demonstrated farmers' wisdom in farming, while extending many new agricultural ecosystems and breeding a lot of new and interesting organisms. This study introduced the discovery of an indigenous golden-back crucian carp (GBCrC; Carassius gibelio) from the Dong's Rice-Fish-Duck System, one of the Globally Important Agricultural Heritage Systems in the world, by exploring and analyzing its external morphological characteristics, distribution, paddy field selection, reproductive mode, genetic diversity and origin. It was found that about 27.33% of 150 surveyed paddy fields in 6 villages, characterized by exchange of continuous culture water, inclusion of local paddy field common carp and feed provision, contained GBCrC. In the breeding season, inclusion of local paddy field common carp was the major factor in selection of paddy field by GBCrC. No male individual was observed in all detected GBCrC, female individuals could mate with the local male paddy field common carps to produce fries, and all the fries represented the characteristics of the GBCrC. Genetic diversity analysis showed that the crucian carp had evolved into an independent population, while phylogenetic analysis demonstrated that GBCrC was clustered with several local crucian carp (LCrC) individuals, and other LCrC ones clustered with other geographical strains. Compared with other distribution areas of GBCrC, Pingzheng village (PZ) presented special temperatures, altitudes, sizes of GBCrC, fish reproduction and sales. The chromosome slide observation showed there were 150 chromosomes in GBCrC. Based on these findings, this study maintained that GBCrC, deriving from LCrC and originating from PZ, might adopt the reproductive mode of gynogenesis. The results of this study enrich the understanding of the traditional agricultural system.