COMPARISON OF GROWTH AND MORPHOLOGICAL CHARACTERISTICS OF KOI CARP AND HYBRIDS WITH GOLDFISH OR SILVER CARP MALES

In the most comprehensive review on distant hybridization in cyprinid fishes, Wang et al. (2019, Sci.China 62:22-45) provides evidence of multiple crosses of species with 100 maternal chromosomes and 48 paternal chromosomes (reciprocal hybrids are not viable) where progeny is composed of diploids (2n=100), triploids (2n=124) and tetraploids (2n=148). The unique feature of F1 hybrids is the formation of unreduced, diploid eggs and sperm (Gomelsky et al. 1988. Dokl.Akad.Nauk.SSSR 301:1210). However, survival, growth potential, and fertility of polyploids was not sufficiently scrutinized. We propagated maternal half-siblings of koi carp (Cyprinus carpio; 100 chromosomes, Cc) with goldfish (Carassius auratus; 100 chromosomes; Ca), silver carp (Hypophthalmichthys molitrix; 48 chromosomes, Hm) and koi males. Larval-juvenile rearing stage (21 days) involved replicated small static containers with live feeds (rotifers and Artemia), algal turbidity, salinity and constant light adopted from the zebrafish protocol (Dabrowski, Miller, 2018.Zebrafish 15: 295).

Fish were then moved to formulated feed (Otohime B1 and 2) and larger tanks with continuous water flow. Survival during larval-juvenile stage (at 26 dpf) amounted to 94.5 ± 10.7 (Ca), 66  ± 21 (Hm), and 87.5 ± 6.3% (Cc). Red blood cells fluorocytometric analysis of each offspring cross (n=5-18) revealed c-values (pg) of 1.74 ± 0.01, 1.36 ± 0.02, and 1.69 ± 0.05 for Ca, Hm and Cc, respectively.