The Formation of the Goldfish-Like Fish Derived From Hybridization of Female Koi Carp × Male Blunt Snout Bream

Abstract

Goldfish (Carassius auratus var., GF; 2n = 100) is the most popular ornamental fish in the world. It is assumed that GF evolved from red crucian carp (C. auratus red var., RCC; 2n = 100). However, this hypothesis lacks direct evidence. Furthermore, our knowledge of the role of hybridization in the formation of new species is sparse. In this study, goldfish-like fish with twin tails (GF-L; 2n = 100) was produced by self-mating red crucian carp-like fish (RCC-L; 2n = 100) derived from the distant crossing of koi carp (Cyprinus carpio haematopterus, KOC; 2n = 100; ♀) with blunt snout bream (Megalobrama amblycephala, BSB; 2n = 48; ♂). The phenotypes and genotypes of GF-L and RCC-L were very similar to those of GF and RCC, respectively. Microsatellite DNA and 5S rDNA analyses revealed that GF-L and RCC-L were closely related to GF and RCC, respectively. The presence of a twin tail of GF-L was related to a base mutation in chordinA from G in RCC-L to T in GF-L, indicating that the lineage of RCC-L and GF-L can be used to study gene variation and function. The sequences of 5S rDNA in GF-L and RCC-L were mapped to the genomes of CC and BSB, which revealed that the average similarities of both GF-L and RCC-L to CC were obviously higher than those to BSB, supporting that the genomes of both RCC-L and GF-L were mainly inherited from KOC. GF-L and RCC-L were homodiploids that were mainly derived from the genome of KOC with some DNA fragments from BSB. The reproductive traits of GF-L and RCC-L were quite different from those of their parents, but were the same as those of GF and RCC. RCC-L easily diversified into GF-L, suggesting that RCC and GF evolved within the same period in their evolutionary pathway. This study provided direct evidence of the KOC–RCC–GF evolutionary pathway that was triggered by distant hybridization, which had important significance in evolutionary biology and genetic breeding.

The Hybrid Genome of a New Goldfish-Like Fish Lineage Provides Insights Into the Origin of the Goldfish

“…In a long-term breeding experiment, we found that the GF originated from the distant hybridization of KOC (♀) and BSB (♂) (Wang et al, 2018). We believed that the GF was derived via the route KOC-RCC-GF.…”

“…Thus, hybrids could exhibit many advantageous traits, such as rapid growth, strong disease resistance, and strong environmental tolerance (Bartley et al, 2000;Liu et al, 2016). In previous research (Wang et al, 2018), the homodiploid hybrids (RCC-L and GF-L) originated from the distant hybridization of KOC (♀) × BSB (♂) exhibited significant changes in shape. These RCC-L and GF-L had bright black eyes and a white base colour covered with red and yellow patterns (Figure 1).…”

“…Some studies suggest that GF evolved from wild crucian carp (Chen et al, 2015). According to historical records, the GF derived from a wild silver-grey crucian carp that first mutated into a red-yellow gold crucian carp and was then domesticated during several periods (Watson et al, 1963;Fu and Shisan, 2016;Wang et al, 2018). However, this hypothesis lacks direct evidence.…”

“…However, few reports have focused on homoploid hybrids. Recently, we successfully obtained homodiploid hybrids of red crucian carp-like (RCC-L) homodiploid fish and goldfish-like (GF-L) homodiploid fish (Wang et al, 2018) (Figure 1). In terms of appearance, significant phenotypic differences were observed between GF-L, RCC-L, and their original parents (koi carp (KOC) and blunt snout bream (BSB)); for example, compared with KOC and BSB, RCC-L and GF-L have unique characteristics such as blue eyes, small heads and transparent bodies.…”

Variations in the Mitochondrial Genome of a Goldfish-Like Hybrid [Koi Carp (♀) × Blunt Snout Bream (♂)] Indicate Paternal Leakage

“…MtDNA recombination was also observed in the F 1 to F 3 generations of a crucian carp-like fish lineage that was derived via the distant cross of female common carp (COC, 2 n = 100) and male blunt snout bream (BSB, 2 n = 48) ( Wang et al, 2019 ). Koi carp, a variety of common carp that is characterized by red or colorful bodies, have the same age of sexual maturity as blunt snout bream ( Wang et al, 2018 ). Blunt snout bream and koi carp are in the same family (Cyprinidae) but different subfamilies (Cultrinae and Cyprinidae, respectively).…”