Streptococcosis and motile Aeromonad septicemia (MAS) are the main bacterial diseases in tilapia culture worldwide, causing significant economic losses. Vaccination is an effective method of preventing diseases and contributes to economic sustainability. This study investigated the immuno-protective efficacy of a newly developed feed-based bivalent vaccine against streptococcosis and MAS in red hybrid tilapia. The feed-based bivalent vaccine pellet was developed by incorporating the formalin-killed S. agalactiae and A. hydrophila antigens into a commercial feed pellet with palm oil as the adjuvant. The bivalent vaccine was subjected to feed quality analyses. For immunological analyses, 900 fish (12.94 ± 0.46 g) were divided into two treatment groups in triplicate. Fish in Group 1 were unvaccinated (control), while those in Group 2 were vaccinated with the bivalent vaccine. The bivalent vaccine was delivered orally at 5% of the fish’s body weight for three consecutive days on week 0, followed by boosters on weeks 2 and 6. Lysozyme and enzyme-linked immunosorbent assays (ELISAs) on serum, gut lavage, and skin mucus were performed every week for 16 weeks. Lysozyme activity in vaccinated fish was significantly (p ≤ 0.05) higher than in unvaccinated fish following vaccination. Similarly, the IgM antibody levels of vaccinated fish were significantly (p ≤ 0.05) higher after vaccination. The bivalent vaccine provided high protective efficacy against S. agalactiae (80.00 ± 10.00%) and A. hydrophila (90.00 ± 10.00%) and partial cross-protective efficacy against S. iniae (63.33 ± 5.77%) and A. veronii (60.00 ± 10.00%). During the challenge test, fewer clinical and gross lesions were observed in vaccinated fish compared with unvaccinated fish. Histopathological assessment showed less severe pathological changes in selected organs than the unvaccinated fish. This study showed that vaccination with a feed-based bivalent vaccine improves immunological responses in red hybrid tilapia, and thus protects against streptococcosis and MAS.

Inconsistencies in the nutritional values of live food such as Artemia and Moina are well-known issues. The enrichment of live food is necessary to obtain the optimum nutrients needed for the growth, survival, and immune competence of fish and crustaceans' larvae. The enhanced growth and survival of fish and crustaceans' larvae are vital to continuous aquaculture production. However, enriched live food could be species-specific as various aquatic larval species may respond differently to the enrichment diets. The enrichment of Artemia and Moina as the "bags of nutrients" has been widely studied and involved various enrichment diets such as commercial diets containing essential fatty acids, highly unsaturated fatty acids, and vitamin C. The use of natural enrichment diets such as yeast, microalgae, and herbal extract, including the common name Chinese chaste tree leaf (Vitex negundo), is becoming popular in aquaculture nutritional development. These natural enrichment diets are more economical and environmentally friendly than commercial diets. The compositions of Artemia and Moina are both affected by the enrichment diets that they consumed, hence directly affecting the growth of the larvae that fed on them. Hence, this review highlights the development of enriched Artemia and Moina and their effects on the growth performance and the immune competence of fish and crustaceans' larvae.

Fisheries and Aquatic Sciences

Elucidating the Probiotic Potential of Malaysian Paenibacillus pabuli Against Vibrio alginolyticus in Artemia Culture