Advances in disease diagnosis, vaccine development and other emerging methods to control pathogens in aquaculture. New Technologies in Aquaculture. Elsevier; 2009. pp. 197-214. [DOI: 10.1533/9781845696474.2.197]

Review of current perspectives and future outlook on bacterial disease prevention through vaccination in Asian seabass (Lates calcarifer)

Asian seabass, Lates calcarifer, is an important aquatic species in mariculture. Intensive farming of this species has faced episodes of bacterial diseases, including those due to vibriosis, scale drop, and muscle necrosis disease, big belly disease, photobacteriosis, columnaris, streptococcosis, aeromoniasis, and tenacibaculosis. Vaccination is one of the most efficient, non-antibiotic, and eco-friendly strategies for protecting fish against bacterial diseases, contributing to aquaculture expansion and ensuring food security. As of now, although numerous vaccines have undergone laboratory research, only one commercially available inactivated vaccine, suitable for both immersion and injection administration, is accessible for preventing Streptococcus iniae. Several key challenges in developing vaccines for Asian seabass must be addressed, such as the current limited understanding of immunological responses to vaccines, the costs associated with vaccine production, forms, and routes of vaccine application, and how to increase the adoption of vaccines by farmers. The future of vaccine development for the Asian seabass industry, therefore, is discussed with these key critical issues in mind. The focus is on improving our understanding of Asian seabass immunity, including maternal immunity, immunocompetence, and immune responses post-vaccination, as well as developing tools to assess vaccine effectiveness. The need for an alignment of fish vaccines with state-of-the-art vaccine technologies employed in human and terrestrial animal healthcare is also discussed. This review also discusses the necessity of providing locally-produced autogenous vaccines, especially for immersion and oral vaccines, to benefit small-scale fish farmers, and the potential benefits that might be extended through changes to current husbandry practices such as the vaccination of broodstock and earlier life stages of their off-spring.

Evaluation of Flathead Grey Mullets (Mugil cephalus) Immunization and Long-Term Protection against Vibrio harveyi Infection Using Three Different Vaccine Preparations

In recent years, flathead grey mullets (Mugil cephalus) cultured in Eilat (Israel) have been highly affected by Vibrio harveyi, showing neurological signs such as uncoordinated circular swimming followed by high mortality rates. Despite the advances in and different approaches to control vibriosis associated with Vibrio harveyi, including commercial vaccines, most of them have not succeeded in long-term protection. In this study, we evaluated the effectiveness, long-term protection, and antibody production of three vaccine preparations: heat-killed bacteria (HKB), membrane proteins denaturation (BME PROT), and internal proteins (INT PROT) developed specifically against Vibrio harveyi for grey mullets. Our results show that fish immunized with heat-killed bacteria emulsified with adjuvant presented the most effective and long-lasting protection against the bacterium, and a cross-protection against other bacteria from the harveyi clade. The effectiveness of each immunization treatment correlated with the levels of specific antibody production against Vibrio harveyi in the serum of the immunized fish.

First description of Vibrio harveyi as the causative agent of morbidity and mortality in farmed flathead grey mullet Mugil cephalus

Flathead grey mullet Mugil cephalus is an important species in the aquaculture industry in the Mediterranean basin and throughout the world. During the last 10 yr, M. cephalus breeding stocks, larvae, and juveniles cultured in Eilat (Israel) have shown neurological signs such as uncoordinated circular swimming, while also presenting oral hemorrhages. Death follows days after the onset of the clinical signs, and mortality rates may reach 80% in some cases, causing high economical losses. Bacteriology isolations from different organs, including the brain, and a Koch's postulate experiment, confirmed Vibrio harveyi as the causative agent. Histological analyses showed the presence of the bacterium in different organs. However, in the brain, the bacterium was observed only within blood vessels and meninges. In some samples, mild to severe brain tissue damage was seen. In order to understand the virulence and lethality of V. harveyi, a median lethal dose was calculated, and the result was 106 colony-forming units fish-1. To the best of our knowledge, this is the first report that describes V. harveyi isolated from the brain of M. cephalus and validates it as an etiological agent causing neurological signs in this fish species.