The effects of synbiotics and various herbs during the Photobacterium damselae challenge test on the histopathology of seabass (Lates calcarifer) internal organs

Seabass (Lates calcarifer) is a widely distributed species with high economic potential in fish culture. However, death in the cultivation of seabass is often caused by Photobacterium damselae bacteria. Fish can be protected from disease by providing the feed with synbiotics and natural herbal substances. The study examines the internal histological organs of seabass exposed to P. damselae to determine the impact of administering synbiotics and various herbs. The study was carried out at the Lampung Marine Aquaculture and Fishery Center with a completely randomized design method, consisting of 5 treatments and 4 replications. The treatments included commercial feed (- control), commercial feed + synbiotics (+ control), synbiotics, commercial feed + some herbs (herbs), and commercial feed + herbs + synbiotics (mixed), which was given to seabass fry with a mean length of 7.7±0.8 cm. The challenge test was conducted by infecting the fish with P. damselae bacteria through intra-peritoneal injection. The results indicated that the mixed treatment maintained the lowest mortality rate during the challenge test with P. damselae. Meanwhile, internal organ histopathology observations in each treatment showed no differences. According to histological findings, all treatments resulted in organ necrosis, congestion, hemorrhaging, melanomacrophage centers (MMCs), inclusion bodies, and fat degradation. Clinical symptoms appear in fish, such as flaking on the caudal and anal fin, body, and abdomen necrosis with red spots, loose scales, and distended head and abdomen.