The effect of hybridization on fish physiology, immunity and blood biochemistry: A case study in hybridizing Cyprinus carpio and Carassius gibelio (Cyprinidae)

The majority of biochemical, physiological and immune parameters were primarily affected by sampling period. For these parameters, hybrids achieved an intermediate character between parental species, but for biochemical and immune parameters they were still more similar to common carp, i.e. the species in the paternal position. The intermediate glucose and cholesterol levels together with the intermediate intestine-body size index in hybrids suggest the role of genetic introgression in determining the range of food utilizable for C. carpio × C. gibelio hybrids as well as their nutritional status, metabolic activity, and energy intake. In spring, females of gibel carp and hybrids reached higher GSI when compared to common carp; however, no spring increase in calcium (important for egg development) was found in hybrid females. Leukocyte count and complement activity in hybrids were intermediate between parental species. IgM level was significantly higher in females in both sampling periods, probably reflecting the different costs of reproductive investment between genders. We propose that the intermediality of traits associated with health and condition status in hybrids resulting from genetic introgression may potentially represent some advantage for hybrid vigor. Our results also highlight the good condition status of C. gibelio and may indicate a potential risk of competition between this invasive species and the economically important C. carpio in breeding ponds.