The sensitivity of certain local medicinal herbs was evaluated against pathogenic Aeromonas hydrophila, Pseudomonas fluorescens and Edwardsiella tarda bacteria of fish during the period from April 2001 to March 2002. A suspension of freshly cultured experimental bacteria (2 x 107 CFU / ml) was prepared and 0.1 ml of this suspension was spread over the tryptic soya agar (TSA) plates. Then crude extract (0.1ml / plate) of each herb was inoculated in the middle of the cultured plate to detect the response. The herbal extract was categorized as high, medium and low inhibitory responded by observing the clear zone of inhibition. Fine extract of the high inhibitory responded herbs was applied under in vitro conditions against the bacteria tested. Twenty-one (80.76%), twenty-four (92.30%) and twelve (46.15%) species of the herbs tested showed antibacterial effect against A. hydrophila, P. fluorescens and E. tarda, respectively. Among them, high inhibitory responded herbs were 38.09% for inhibition of A. hydrophila and P.  fluorescens and 38.33% for E. tarda. However, the extract collected from bulb of Allium sativum for inhibition of A. hydrophila and P.  fluorescens and the decoction obtained from leaves of Calotropis gigantea for E. tarda were detected to be the most promising herbs considering effectiveness with  minimal inhibitory concentration (MIC) among all of the herbs tested. Key words: Sensitivity; pathogenic bacteria; herbal extract; minimal inhibitory concentration doi: 10.3329/bjvm.v2i1.1941 Bangl. J. Vet. Med. (2004). 2 (1) : 75-82

An experiment was conducted to compare the efficacies of some selected antibiotics and medicinal plants against common bacterial fish pathogens viz., Aeromonas hydrophila, Pseudomonas fluorescens and Edwardsiella tarda. Four different antibiotics viz., CFCIN (ciprofloxacin), Renamycin (oxytetracycline), and Sulfatrim (sulphadiazine + trimethoprim) were exposed in different doses (100, 75, 50 and 25 ppm) to the culture of freshly isolated bacteria under the in vitro condition for sensitivity test and minimum inhibitory dose (MID) was determined. Based on in vitro results, antibiotics were applied to the experimental infection of Thai silver barb, Barbonymus gonionotus. CFCIN showed the best result with 100% recoveries of challenged fish in prolonged bath treatment. Medicinal plants were selected on the basis of previous studies. Crude extracts were prepared from various parts (leaves and bulb) of garlic, turmeric, akand and neem and four different doses were applied to the fresh culture of pathogenic isolates under the in-vitro condition to determine minimum inhibitory dose (MID). However, garlic offered the best result with 90.00 ± 2.89% recoveries of challenged fish in aquarium trial. Akand + neem, turmeric and akand showed moderate to weak recovery rates with the same dose. The present study thus showed that medicinal plants would be an effective control measure along with antibiotics against bacterial fish diseases.

Infectivity of Flexibacter columnaris to loach, Misgurnus anguillicaudatus (Bleeker, Gijnther),, was studied with variation in water conditions and the presence of other bacteria in the water medium. Invasion offish by the pathogen varied with different water conditions. containing 0-03% NaCl. 0-01% KCl, 0-002% CaCl2-2H2O and 0-004% MgCl2-6H2O. The percentage of infection in tap water was similar to that of the formulated water. The infeetion rate was low in the individual salt solutions, and no infection occurred in distilled water. Even in the formulated water, the pathogen failed to infect the fish when Citrobacter freundii, Aeromonas hydrophila or Pseudomonas fluorescens were present at densities 100 times that of F. columnaris. However, in such eases, the numbers of F. columnaris in the mucus of the fish body surfaee did not increase mueh throughout the experimental period. In contrast, F. columnaris suceessfully invaded the fish in the presence of cither Streptococcus sp., Flavobacterium flavescens or Flavobacterium fuscum. even when the numbers of these bacteria were 1000 times that of F. columnaris. In this ease, F. columnaris gradually inereascd its numbers on the fish body surfaee.Correspondenec and present address: M, B. R. Chowdhury,

Experiments were conducted maintaining under aquarium and pond conditions using feed containing medicinal plants/extracts was evaluated on artificially and naturally infected fish with bacterial pathogens. When the fish were exposed to high bacterial pathogens Aeromonas hydrophila Ah-11, Pseudomonas fluorescens Pf-13 and Edwardsiella tarda Et-70, recovery of the infected fish varied with the pathogens challenged and feed treatments. Fish feed containing bulb extract of Allium sativum (3% feeding) showed significantly (p<0.01) high therapeutic effect recovering the infected fish (Thai silver barb, Barbodes gonionotus) with A. hydrophila (100 ± 0% recovery) and P. fluorescens (90±0% recovery). A similar result was observed in the case of pangas fish feed containing decoction of leaves of Calotropis gigantea where 100 ± 0% E. tarda infected Thai pangas (Pangasius hypophthalmus) were found to be cured. These two types of herbal feed offered similar result when applied to the naturally ulcer-affected Thai silver barb and Thai pangas fingerling under aquarium condition. In pond condition, the herbal feed containing bulb extract of A. sativum was applied experimentally to A. hydrophila infected different fish species maintained in different individual ponds where, 91.67 ± 2.35% Thai silver barb, 84.99 ± 2.35% Rui (Labeo rohita) and 74.99 ± 2.35% Mrigal (Cirrhinus cirrhosus) were found to be recovered. In contrast, plants mixed pangas feed containing decoction of leaves of C. gigantea was cured 94.44 ± 3.84% E. tarda infected Thai pangas. The other medicinal plants used in this study showed medium to weak effect recovering the bacterial infected fish.

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