The antifungal activity of two Bornean medicinal wild gingers Plagiostachys megacarpa and Zingiber phillippsiae were examined against Lagenidium thermophilum. The most active extract was P. megacarpa at concentration of 320 µg/mL inhibiting both hyphal growth and zoospore production of L. thermophilum in 24 h. Toxicity tests were conducted using mud crab (Scylla tranquebarica) larva. Bath treatment of P. megacarpa at concentrations of 320 and 640 µg/mL for 24 h were highly effective against hyphae and zoospores of the strain and it is non-toxic to mud crab larva. Therefore, crude extracts P. megacarpa may be used as alternative treatment for marine Oomycete infection of mud crab.
The prevalence of antibiotic resistant bacteria in aquaculture has reached alarming proportions and intensified the search for microbe derived antimicrobial compounds. This study isolated bacteria from the intestine of Sagor catfish (Hexanematichthys sagor) and screened it for antagonistic properties. Five out of 334 bacterial isolates inhibited growth of fish pathogens. The 5 bacterial strains included relatives of Shewanella haliotis, Myroides odoratimimus, Vibrio harveyi, Vibrio alginolyticus and Alcaligenes faecalis. The growth profiles and probiotic properties of these bacteria were examined. The results showed that the isolate 9 (3) 7.5.2.1, whose closest relative was S. haliotis exhibited growth and probiotic advantage compared to the other bacterial strains, such as highest doubling time and the ability to survive at all experimental temperatures (18 to 60℃) , and bile concentrations (0.01 to 1.00%) and pH (pH2 to 9) . While the bacteria with probiotic properties were successfully isolated. Further study is necessary to examine the efficiency of the probiotic candidate bacteria in boosting fish immunity against pathogens.
Aquaculture is developing so fast that infectious disease outbreak happens regularly. Antibiotic treatment results in development of antibiotic resistance pathogens, thus cause urgent action in searching of other alternative treatment method. Postbiotic was one of the explored strategies among various proposed alternatives. Due to its benefits in agriculture industry, it may be useful in aquaculture industry. Although many reviews were reported on other alternative strategies, the review on postbiotic in aquaculture is limited. This mini review provides an overview of different postbiotics as aquaculture disease control agents. Peptides and exopolysaccharides have antimicrobial properties against bacterial pathogens. Then, short chain fatty acids have both antimicrobial activities against bacterial pathogens and immunostimulating effects to aquatic organism. Vitamins, peptidoglycan and lipopolysaccharide are reported as immunostimulants. Finally, cell surface proteins and teichoic acid can act as vaccine.
Fungal infection mostly caused by marine oomycetes had hindered crustacean production thus searching for natural and safe treatment is currently needed. Thus, this study was conducted to investigate the antimycotic effect of different seaweed extract against marine oomycetes (Lagenidium spp. and Haliphthoros spp) . Two seaweeds species (Eucheuma cottonii and Caulerpa lentillifera) were extracted using ethanol, methanol and water. Each extracts was tested on four fungi strains of marine oomycetes species for minimum inhibitory concentration (MIC) and fungicidal activities. C. lentillifera ethanol extract showed the highest antifungal effect where it can inhibit three from four fungal strains. Meanwhile, E. cottonii ethanol extract has lowest MIC (500 ppm) and inhibit L. thermophilum IPMB 1401 and H. sabahensis IPMB 1402 hyphal growths. Antimycotic effect on zoospores production shows reduction in production after 12 h immersion for three marine oomycetes species. Seaweed extracts toxicity on Artemia sp. showed approximately 5% mortality at 12 h immersion. It is suggested that 12 h immersion of seaweed extract is a suitable treatment for marine oomycetes in aquaculture. This study does not only show potential alternative control method for crab larvae health management, it may also contribute to the sustainable development and food security of aquaculture industry.
Pathogenic marine fungi, Lagenidium thermophilum is known causative agent in the crustacean industry. Current disinfection practice in hatchery has risks and negative impacts which prompts suitable substitute to synthetic antifungal agents. Thus, this study was conducted to evaluate the antifungal potential of postbiotic from four potential probiotics towards marine oomycetes, L. thermophilum IPMB 1401. The screening test showed that the Lactobacillus plantarum GS12 and Bacillus cereus GS15 postbiotics were positive for antifungal activity on L. thermophilum IPMB 1401. These two bacterial extracts have minimum inhibitory concentration （MIC） at 50%. The toxicity assay on MIC level of the postbiotic revealed that the cumulative mortality of brine shrimp nauplii exposed to B. cereus postbiotic was significantly lower compared to L. plantarum GS12 postbiotic and formalin. This indicates a high potential of B. cereus GS15 as a prospect for alternative control method for fungal infections in the crustacean culture industry.