Hybridization with Percocypris pingi male can improve the cultivation characteristics of snow trout (Schizothorax wangchiachii), especially the resistance to white spot disease (Ichthyophthirius multifiliis)

Abstract

Snow trout (Schizothorax) is an important cold-water economic fish in Asian aquaculture, but it has some disadvantages, such as slow growth rate, weak resistance to white spot disease (Ichthyophthirius multifiliis) and high temperature, etc. In contrast, their sister genus, Percocypris, has stronger resistance to white spot disease and high temperature. Distant hybridization can integrate the advantages of both parents, so we attempted to cross S. wangchiachii with P. pingi to obtain F1 hybrids combining the advantages of both parents. Hybridization between P. pingi males and S. wangchiachii females was successful, but backcrossing failed. To explore the cultivation characteristics of hybrid fish, the growth performance, digestive enzyme activity, nutrient composition, gonad development, high temperature tolerance, and white spot disease resistance of hybrid fish and their parents were compared. In growth, a total of 18-week culture experiment (20 °C) were carried out, and the body weight of hybrid fish at 18 weeks (26.13 ± 7.34 g) was significantly higher than that of P. pingi (16.65 ± 6.82 g) and S. wangchiachii (16.05 ± 5.93 g). In digestive enzyme activity, the hybrid fish showed hybrid weakness, but there was no correlation between the digestive enzyme activity and body weight of the hybrid fish and its parents, indicating that the digestive enzyme activity could not reflect the growth differences. In nutritional composition, P. pingi had a higher crude protein content, S. wangchiachii had a higher crude lipid content, and both contents of hybrid fish were closer to those of P. ping. The relative contents of amino acids of the three fishes were similar, while the relative contents of polyunsaturated fatty acids were higher in hybrid fish and P. ping, and their relative content of fishy substances was lower than that of S. wangchiachii. In high temperature tolerance, the mortality temperature of P. ping (33.48 ± 0.39 °C) and hybrid fish (33.00 ± 0.92 °C) was significantly higher than that of S. wangchiachii (31.24 ± 1.07 °C). In tolerance to white spot disease, the hybrid fish showed a significant increase in resistance compared to S. wangchiachii and was almost free of I. multifiliis. In gonad development, the spermatic cells of the pentaploid hybrid fish remained in the spermatocyte stage without spermatozoa, their ovarian cells were lowly differentiated, and these characteristics were sterile phenotypes. In conclusion, hybridization with male P. ping can improve the cultivation characteristics of S. wangchiachi through preliminary research, providing a new perspective and reference for snow trout breeding.