Survival and immune responses of two populations of Babylonia areolata and their hybrids under pathogenic Vibrio challenge

Disease outbreaks among cultured ivory shells (Babylonia areolata) have occurred frequently in recent years, causing mass mortality and seriously hindering the development of the B. areolata industry. Hybridization is an effective way of improving germplasm in aquaculture, as it often generates desirable traits in the hybrids, including increased disease resistance. This study analyzed the dynamic changes in several immune indexes, including the survival rate, total hemocyte count (THC), hemocyte mortality, reactive oxygen species (ROS) level, and hemolymphatic pathogenic bacteria content, in two parental populations, Thailand B. areolata (TT) and Hainan B. areolata (HH), and their reciprocal hybrids, Thailand B. areolata ♀ × Hainan B. areolata ♂ (TH) and Hainan B. areolata ♀ × Thailand B. areolata ♂ (HT), challenged with Vibrio harveyi, the main pathogenic bacterial species affecting B. areolata. The results showed that the median lethal concentrations (LC50) of the four populations were in the order HH-LC50 > TT-LC50 and TH-LC50, and HT-LC50 > TT-LC50 at 48 and 72 h post challenge. The changes in non-specific immune parameters showed that under control conditions, HT had a higher THC than the other three populations and that it maintained this level throughout the infection process, while HH and HT showed significantly lower hemocyte mortality rates and higher ROS levels than TT and TH. In addition, the pathogenic Vibrio (V. harveyi) count in the hemolymph of the four populations increased sharply to a peak value and then slowly decreased after infection. Compared with the control groups, the change rates of the cumulative total pathogen content in the hemolymph were in the order TT > TH > HH > HT at 72 h after infection, indicating that HT suppressed and eliminated pathogenic microorganisms most effectively. HT may have inherited the more efficient non-specific immune function from HH. Overall, the results suggest that TT may be more susceptible to V. harveyi infection than HH, and hybridization could be a useful way to improve the disease resistance of the ivory shell, thereby benefiting the aquaculture industry. •The disease resistance of two populations of ivory shell and their hybrids was compared.•The Thailand ivory shell population was more susceptible than the Hainan ivory shell population to pathogenic Vibrio infection.•Hybridization increased the disease resistance of hybrids, especially the HT, which showed a higher ROS level, more efficient p