We isolated a marine bacterium strain S2V2 which inhibited the growth of pathogenic marine Vibrio spp. The aims of this research were to identify a new antibioticproducing marine bacterium strain S2V2, and evaluate its spectrum activity and pathogenic property. Analysis of 16S rDNA sequence placed strain S2V2 in the genus Pseudoalteromonas, but the sequence similarity was low (95.46%) implying the strain might be a new species in this genus. Strain S2V2 inhibited the growth of 67.9% of 28 Vibrio strains tested. This strain inhibited V. alginolyticus, V. anguillarum, V. fluvialis, V. harveyi, V. metschnikovii, V. splendidus, V. ordalii, V. parahaemolyticus, and V. vulnificus, but inactive against V. campbellii, Aeromonas hydrophyla and Staphylococcus aureus. Strain S2V2 produced extracellular non proteinaceous antibacterial substances. The highest antibacterial activity was found when strain S2V2 was cultured for 96 h in ZoBell broth medium. An artificial infection to post larvae of Lithopenaeus vanname indicated that strain S2V2 was a non pathogenic bacterium. Non pathogenic property and specific antibacterial activity against a broad range of fish pathogenic marine Vibrio of strain S2V2 suggest that this strain is a prospective source of unique antibiotic and a potential biocontrol agent in marine aquaculture.

Vibriosis is a bacterial disease that has been reported in Indonesian marine fish culture since the 1990s. The disease was reported mostly in grouper and shrimp (monodon and vanname) farming, although the infections in snapper (Lates calcarifer) and abalone (Haliotis squamata) aquaculture were also occurred. Causative agents of vibriosis in Indonesia marine fish is involving 14 species of vibrio namely Vibrio harveyi, V. anguillarum, V. alginoluticus, V. parahaemolyticus, V. fluvialis, V. furnisii, V. methcnikovii, V. vulnificus, V. ordalii, V. cincinnatiensis, V. carchariae, V. azureus, V. mimicus and V. damsela. Control of vibriosis is conducted with water quality management, applications of vaccines, antibiotics, probiotics and immunostimulants. Most vaccines developed and commercially available in Indonesia are in the form of inactive-whole cell types. The vaccine product is effective enough to protect fish from vibriosis. Probiotics have been widely studied since the 2000s and have been shown to increase fish and shrimp growth and resistances against vibriosis. Immunostimulants began to be developed since 2010 based on the extracts of terrestrial plants, seaweeds and chitosan. It is therefore concluded that the continuous existence of pathogenic strains in aquaculture farm requires further development of the control methods, including periodic updating of the vaccines, probiotics and immunostimulant formulas for more potent efficacies.

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Fish farming has always involved a risk of microbial infections, especially those caused by pathogenic viruses, for which chemotherapeutics are generally ineffective. Viral nervous necrosis (VNN), otherwise known as viral encephalopathy and retinopathy (VER), caused

Southeast Maluku Regency, Maluku. Freshlycollected specimen of sponges and part of coastal plants including barks, leaves, fruits, and twigs were immediately transported to the laboratory. A total of 32 samples were washed with water to remove ABSTRACT Objective: The objective of this study was to investigate the antibacterial activity of coastal plants and marine sponges extracts against fish bacterial pathogens. Methods: Samples were extracted by maceration and the extracts were examined for their antibacterial activities against Streptococcus sp. BJ0509, Staphylococcus aureus ATCC 6538, Aeromonas hydrophila BA03 and Vibrio parahaemolyticus 29S by means of paper disc diffusion method. Active extracts were partitioned and purified by column chromatography. The purified substance was tested for minimum inhibitory concentration (MIC) against seven bacterial fish pathogens namely Streptococcus sp., Vibrio parahaemolyticus, V. alginolyticus, V. harveyi, Photobacterium damselae, Aeromonas hydrophila and A. dhakensis. Results: The highest antibacterial activity against all bacteria used in the assay was demonstrated by OKA 6, a bark extract sample of a coastal plant, Diospyros maritima. It showed a diameter of inhibition zones against Streptococcus sp. BJ0509, S. aureus ATCC 6538, A. hydrophila BA03 and V. parahaemolyticus 29S of 19, 33, 18, and 18 mm, respectively. The column chromatography fraction of OKA 6 inhibited the growth of S. aureus ATCC 6538 with MIC of 3.125 µg/mL. The MIC of this fraction against seven bacterial fish pathogens ranged < 0.098 to 3.125 µg/mL. The antibacterial activity of partially purified substance obtained from column chromatography fractionation of OKA 6 was higher than those of oxytetracycline and kanamycin. Conclusions: This result indicates that antibacterial activity of the partially purified substance is potentially higher than those of the commercial antibiotics tested. It further indicates that OKA 6 extract from D. maritima can serve as a promising resource for the development of therapeutic agents against bacterial infections in aquaculture.

This research was conducted to isolate, identify, and characterize pathogenic Vibrio spp., causative agents of vibriosis in grouper at Brackishwater Aquaculture Development Center (BADC), Situbondo. Twenty-nine isolates were isolated from wound, gills, eyes, liver, and ren of grouper with vibriosis on Thiosulphate Citrate Bile Sucrose Agar (TCBSA) medium. Koch Postulate Test was conducted to determine pathogenic Vibrio spp., by intraperitoneal injection to humpback grouper (Cromileptes altivelis) (9-10 cm of total length) at 106 cells/fish in triplicates. Results indicated that the pathogenic Vibrio spp., causative agents of vibriosis in grouper at BADC, Situbondo were identified to be V. alginolyticus, V. anguillarum, V. metchnikovii, V. vulnificus, V. fluvialis, V. furnisii, and V. parahaemolyticus. Infection of the pathogenic Vibrio spp. caused acute mortality within 17-46 hours with specific disease signs like haemorhagic on fins (pinnae pectorales, pinnae abdominales, pinna analis) and also on the body. These results suggested that vibriosis should be monitored and controlled properly and quickly.

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Vibriosis is a prevalent disease in almost all mariculture species worldwide. The pathogens causing this disease can survive freely in water regardless of the host and can very easily infect marine organisms in warm water (Klesius & Pridgeon, 2011). They cause the death of shrimp and marine fish (Istiqomah et al., 2020), which in turn leads to severe economic losses and becomes a major public health problem. These causative bacteria are classified as Gram-negative and opportunistic pathogens that infect the marine organisms when the host is under stress. Clinical signs of infected fish include anorexia, eyes opacity, pigmentation of the fish skin, skin ulcers, lesions in the muscle, exophthalmia, ulcers in the eye, fin rot, and swollen intestines (Mohamad et al., 2019;Zhang et al., 2014).Vibriosis is controlled by administering quinolone, tetracycline and erythromycin. However, the application of antibiotics strengthens the antibiotic-resistant Vibrio. Vibrio spp. have become resistant to antibiotics commonly used for treatment (Isnansetyo et al., 2009). Vibrio campbellii is resistant to oxytetracycline, ampicillin and carbenicillin (Nakayama et al., 2006). It has also been reported that some strains of V. harveyi have become resistant to more than three types of antibi-