Laboratory and Field Assessments of Oral Vibrio Vaccine Indicate the Potential for Protection against Vibriosis in Cultured Marine Fishes

Vibriosis is one of the most common threats to farmed grouper; thus, substantial efforts are underway to control the disease. This study presents an oral vaccination against multiple Vibrio spp. in a marine fish with double booster immunisation. The Vibrio harveyi strain VH1 vaccine candidate was selected from infected groupers Epinephelus sp. in a local farm and was formalin inactivated and combined with commercial feed at a 10% ratio (v/w). A laboratory vaccination trial was conducted for seventy days. The induction of IgM antibody responses in the serum of Asian seabass Lates calcarifer immunised with the oral Vibrio harveyi strain VH1 was significantly (p < 0.05) increased as early as week one post-primary vaccination. Subsequent administration of the first and second booster for 5 consecutive days, starting on days 14 and 42, respectively, improved the specific antibody level and reached a highly significant (p < 0.05) value at days 35 and 49 before slightly decreasing from day 56 onwards. Antibody titres of the control unvaccinated group remained relatively stable and low throughout the experimental period. At the end of the 70-day vaccination trial, 23 days post final boost, an intraperitoneal challenge with a field strain of Vibrio harveyi, V. alginolyticus, and V. parahaemolyticus was carried out. Our challenge study showed that oral Vibrio harveyi strain VH1 vaccine candidate could induce significant protection, with an RPS of 70–80% against different Vibrio species. Thereafter, a field trial was conducted in a mariculture farm to study the effect of field vaccination using the oral Vibrio harveyi strain VH1 vaccine candidate. A total of 3000 hybrid grouper juveniles were divided into two groups in triplicate. Fish of Group 1 were not vaccinated, while Group 2 were vaccinated with the feed-based vaccine. Vaccinations were carried out on days 0, 14, and 42 via feeding the fish with the vaccine at 4% body weight for 5 consecutive days. At the end of the study period, the fish survival rate was 80% for the vaccinated group, significantly (p < 0.05) higher than the 65% seen in the control unvaccinated group. Furthermore, the vaccinated fish showed significantly (p < 0.05) better growth performances. Therefore, the oral Vibrio vaccine from the inactivated Vibrio harveyi strain VH1 is a potential versatile vaccine candidate that could stimulate good immune responses and confer high protection in both Asian seabass, Lates calcarifer, and farm hybrid grouper Epinephelus fuscoguttatus × Epinephelus lanceolatus.

Draft Genome Sequences of Aeromonas schubertii Strains Isolated from Asian Seabass from Thailand

Aeromonas schubertii is a Gram-negative, rod-shaped bacterium. It is a rare species that has been reported in humans and aquatic animals. Here, we report the genome sequences of A. schubertii strains isolated from two mass mortality events in central Thailand that were associated with aquaculture of Asian seabass.

Estimating the Economic Loss Due to Vibriosis in Net-Cage Cultured Asian Seabass (Lates calcarifer): Evidence From the East Coast of Peninsular Malaysia

This study aims to estimate the economic loss due to vibriosis in the production of Asian seabass in floating net-cages on the east coast of Peninsular Malaysia. Asian seabass has contributed significantly to Malaysia's economic activities and food security. However, its production can be hindered by the occurrence of diseases, such as vibriosis, causing severe economic losses to farmers. A questionnaire-based survey was conducted on 14 small-scale monoculture Asian seabass net-cage farms. Using a stochastic bioeconomic model and inputs from the survey, existing literature, and expert opinion, the economic losses were determined. Moreover, this model considered the prevalence of Vibrio spp. at a farm on the east coast and the risk posed by its infection from hatcheries. The results showed that 71.09% of Asian seabass simulated in the stochastic model survived. The mortality rate due to vibriosis and other causes was at 16.23 and 12.68%, respectively. The risk posed by Vibrio spp. infection from hatcheries contributed to 2.77% of the increase in Asian seabass mortality. The stochastic model estimated that the total cost of producing a tail of Asian seabass was €2.69 per kilogram. The economic loss of vibriosis was estimated at €0.19 per tail per kilogram, which represents 7.06% of the total production cost of Asian seabass per kilogram. An increase in the prevalence of clinical vibriosis and vibriosis case fatality rate at 42 and 100%, respectively, will lead to an increase in the cost of grow-out Asian seabass by €0.29 per tail from the default value. An increase in pellet price per kilogram by €1.38 and feed conversion ratio pellet by 0.96 will consequently increase the cost of grow-out Asian seabass by €2.29 per tail and €0.82 per tail, respectively. We find that the occurrence of Vibrio spp. infection at the hatchery level can contribute to an increased risk in the mortality of Asian seabass during the grow-out phase. Hence, we also need to focus on the control and prevention of vibriosis infection from hatcheries.

Fish disease study of Asian seabass (Lates calcarifer) in a floating marine cage: Endoparasite and blood profile

Hidayati D, Nurindra AR, Abdulgani N, Setiawan E, Maulidina N, Syahroni N, Mulyadi Y. 2021. Fish disease study of Asian seabass (Lates calcarifer) in a floating marine cage: Endoparasite and blood profile. Biodiversitas 22: 4505-4511. The Indonesian government has multiple targets and priority programs to increase aquaculture productivity in 2021. Hence, the development of mariculture commodities such as Asian seabass (Lates calcarifer) in one of the potential coastal areas, Sendang Biru, is strategic. However, sustainable productivity needs good management, including the health monitoring of fish. This study aimed to determine the condition of seabass under mariculture in a floating cage in Sendang Biru, Malang, Indonesia. Thirty seabass (Lates calcarifer) from 0 to 60 days after stocking age (ASE) were taken from a Sendang Biru floating cage. Blood and intestine samples were taken five times from day 0 to day 60 ASE. Blood samples were carried out through the caudal vein and observed using a hemocytometer. Endoparasite analysis was performed by fish intestine examination from the anterior intestine to the posterior rectum. Pseudoterranova and Diphyllobothrium were found with 10% and 3.33% prevalence, respectively. The intensity of Pseudoterranova was one individual/fish, and that of Diphyllobothrium was 2.33 individuals/fish. The highest mean of total erythrocyte count (TEC) found in 0 day ASE was at the level of 0.82±0.55×106 cells/mm3, and the lowest was found in 60 days ASE (0.51±0.24×106 cells/mm3). The highest mean of total leucocyte count (TLC) was 9.20±3.69x104 cells/mm3, at day 0, and leukocyte levels tended to decrease until day 60 ASE (7.74±3.43×104 cells/mm3). Overall, despite the TEC and TLC tending to decrease from 0 to 60 days ASE, in statistically indicated no significant differences in TLC at different ASEs (p > 0.05). The hematological profile indicated the health statuses of the cultured Asian seabass in the current study were in a condition of anemic and infected.