Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment

Immunization against Vibriosis in Maricultured Yellow Grouper Epinephelus awoara in China

Qiwei Qin, Zaohe Wu, Jinpei Pan


Grouper Epinephelus spp. is highly priced and popular for seafood fishes among the major maricultured fish species in China and Southeast Asia. However, with the rapid development of aquaculture in recent years, the aquaculture environment is becoming more and more stressful. The grouper aquaculture industry has been severely affected by infectious diseases, especially by vibriosis in China. Vibrio vulnificus has been isolated and identified as the pathogen of vibriosis in grouper in southern China (Liu et al. 1994). This pathogen can cause more than 70% mortality in maricultured grouper in the disease season, from July to September, and result in heavy economic losses.

Vibriosis is one of the most serious bacterial diseases affecting the marine culture industry worldwide. At least eight members of the genus Vibrio have been implicated in marine fish diseases: V. anguillarum, V. ordalii, V. salmonicida, V. vulnificus, V. damsela, V. cholerae, and V. carchariae. Among them, vaccines have been developed and tested for V. anguillarum, V. ordalii, and V. salmonicida. However, no commercial vaccines are yet available to prevent the vibriosis caused by V. vulnificus (Newman 1993; Toranzo et al. 1997). In this paper, we present our recent studies on protective immunity of grouper using killed V. vulnificus.

Vaccines FV and HV were developed from a virulent strain of V. vulnificus using formalin-killed and heat-inactivated whole bacterial cells, respectively (Qin and Pan 1996). As shown in Table 1, V. vulnificus could be killed by formalin at the minimum concentration of 0.25% and could be inactivated by heating at 50°C. A formalin concentration of 0.4% and a temperature of 80°C were chosen to kill V vulnificus. Both FV and HV were safe to grouper after injection (Table 2). Vaccination against V. vulnificus was investigated in grouper Epinephelus awoara (Qin et al. 1996). Fish were vaccinated once with FV or HV by various routes. The fish serum antibody was quickly produced against V. vulnificus after intramuscular or intraperitoneal injection, and the highest titer was obtained by injection with FV after 4 weeks (Table 3).

Fish were administered the lethal dosage of V. vulnificus at 35 d and 56 d after vaccination. The highest level of protection was obtained in fish by intraperitoneal injection of FV. Good protection was also obtained by immersing the fish into the vaccine solution pretreated with hypertonic solution or by spraying the vaccine onto the fish (Table 4). However, serum antibody titers were not detected in fish vaccinated by these routes.

The results of field trial showed that significant immune protection was obtained in marine fish-farming (Table 5). Grouper cultured in marine net cage farming were vaccinated by single intraperitoneal injection of FV. Survival of vaccinated fish was 72.82% compared with 52.60% in the unvaccinated control after 1 year of farming. The survival rate of vaccinated fish increased by 20.22%.