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A feeding trial was conducted to investigate the effects of administration of microencapsulated probiotic Bacillus sp. NP5 and prebiotic mannan oligosaccharide (MOS) for the prevention of Aeromonas hydrophila infection on Pangasianodon hypophthalmus. Pangasius with initial body weight of 6.54±0.17 g were stocked into 40 L aquariums with a stocking density of 10 fish per aquarium. Control (C) diet (no addition of Bacillus sp. NP5 and MOS), probiotic Bacillus sp. NP5 1% (10 g kgG 1), prebiotic MOS 0.2% (2 g kgG 1) and synbiotic (probiotic Bacillus sp. NP5 1%+prebiotic MOS 0.2%). Then 10 fish of each aquarium were challenged by Aeromonas hydrophila. The results showed that fish with synbiotic supplementation resulted the highest Specific Growth Rate (SGR), Food Conversion Ratio (FCR) and those were significantly different (p<0.05) from the other treatment. The immune responses showed that fish fed with the control diet resulted the lowest hematocrit, hemoglobin and red blood cell count and those were significantly different from the probiotic and prebiotic group (p<0.05). White blood cell count, phagocytic activity and respiratory burst activity of the fish fed with probiotic 1% and MOS 0.2% were not significantly different from control. Moreover, fish fed with diet supplemented with probiotic, prebiotic and synbiotic had notably lower mortality after 10 days infected with A. hydrophila (p<0.05). Dietary Bacillus sp. NP5 and MOS had a significant interaction on enhancing immune responses and growth performances of Pangasianodon hypophthalmus (p<0.05).

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This study evaluated the effects on viral immune responses and bacterial co-infection, of different feeding frequencies of a synbiotic supplemented diet given to Pacific white shrimp (L. vannamei). A synbiotic-supplemented diet was formulated from probiotic Vibrio alginolitycus SKT-b R and prebiotics from sweet potato (Ipomoea batatas L.) oligosaccharide. Pacific white shrimp were fed with synbiotic diet at different frequencies, i.e. daily (P1), twice a week (P2), and once a week (P3) for a 30 day pre-challenge test. After the 30 day feeding period, the shrimps were challenged by intramuscular injection of Infectious Myonecrosis Virus (IMNV) and Vibrio harveyi. The results showed that shrimp treated with a synbiotic-supplemented diet showed significantly higher growth performance than control groups (P<0.05). Shrimp treated under regime P1 showed the highest values for phenoloxidase (PO) and respiratory burst (RB) parameters compared to shrimp given with other treatments. Following the challenge test, higher survival rate were seen in the P1 treatment group, in comparison to the positive control, and the P1 treatment group showed the highest values in total haemocyte count (THC), PO, and RB.

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<p class="Default">Koi herpesvirus (KHV) is a herpesvirus that particularly infects and causes mass mortality to koi and common carp. Therefore, the protection of common carp from KHV infection is urgently needed. In this study, we developed an application of DNA vaccine encoding KHV glycoprotein-25 by immersion method to increase survival of common carp against KHV infection. A total of 400 common carp juveniles at 30-day-old were immersed in 1-L water containing 1.3×10⁸CFU/mL of the killed <em>Escherichia coli</em> cells carrying DNA vaccine. Three frequencies and three duration of fish immersion were tested, namely: 1×30 minutes, 1×60 minutes, 1× 90 minutes, 2×90 minutes and 3×90 minutes by interval of 24 hours. Reversetranscription polymerase chain reaction analysis showed that DNA vaccine was successfully expressed in the vaccinated fish. Fish at twenty eight days post vaccination were challenged by injecting 10^-4 mL of KHV per fish. The result showed that vaccination by 1×30 minutes immersion allowed 61% of fish survived, and this was significantly higher (p&lt;0.05) compared to control (without vaccination), but it was similar among vaccination treatments (p&gt;0.05). The relative percent survival of vaccinated fish were also similar among treatments (p&gt;0.05). DNA vaccination has increased fish survival about two fold higher compared to unvaccinated fish control (26.67%). Thus, DNA vaccination was effectively delivered by immersion for 1×30 minutes, and this technique can be useful to level up the resistance of common carp juveniles against KHV infection.</p> <p class="Default">Keywords: DNA vaccine, KHV, glycoprotein, immersion, common carp</p>