M. B. R. Chowdhury
Department of Aquaculture, Bangladesh Agricultural UniversityMymensingh 2202Bangladesh
T. Rahman
Department of Aquaculture, Bangladesh Agricultural UniversityMymensingh 2202Bangladesh
Health management, Pathogens, Chemotherapeutics, Medicinal plants
Animal Health and Management
Aquatic animal
The experiment was conducted to select and apply the effective low-cost chemotherapeutic and medicinal plants against diseased fish under laboratory and field condition at the Department of Aquaculture, Bangladesh Agricultural University during the period 2010-20111. Pathogens: Laboratory stocked highly virulent bacterial isolate Aeromonas hydrophila (TL-2) and fungal isolate Aphanonomyces invadans (TK-1) were used in this study. The pathogenicity of the isolates were checked before use in the experiment. For bacterial culture, tryptone soya agar (TSA) and for fungal culture glucose peptone (GP) broth and agar were used. Experimental fish: Healthy young Thai silver barb (Barbonymus gonionotus) weighing 20-25 gm were used in all the experiments performed. The fish were cultured in the Departmental experimental pond, acclimatized in aquarium and checked for disease signs before use in the challenge test. Chemotherapeutics: Chemotherapeutics were selected based on our previous studies (Chowdhury,et al. 2004; 2005 a & b ). Low-cost and effective chemotherapeutics such as, salt and lime, alum (fitkari, i.e., potash alum) and two mild antibiotics, viz., doxycycline and oxytetracycline were screened out primarily and used in the present study. Eco-friendly and effective dosage of these chemotherapeutics were standardized and applied to the experimental infection of fish both under laboratory condition and field trial. Medicinal plants: Effective and usable medicinal plants were screened out based on our previous studies (Chowdhury and Rahman, 2007; 2008) and a preliminary study. The selected medicinal plants were neem (Azadirachta indica), akand (crown flower, Calotropis gigantea), garlic (Allium sativum), turmeric (Curcuma longa), shoti (arrowroot, Curcuma zedoaria), Indian sorrel (Oxalis corniculata), guava (Psidum guajava) and kalijira (black cumin, Nigella sativa). Crude extracts were prepared individually from neem (leaves), akand (leaves), garlic (bulb), turmeric (rhizome) and shoti (rhizome) and applied to the experimental fish under laboratory condition. For field trial, paste of the leaves of Indian sorrel, guava, rhizome of shoti and seeds of black cumin were fed to the experimental fish adding with normal feed before infection challenge. Therapeutic effects of chemotherapeutics: Experimental fish were artificially infected each with the virulent bacterial and fungal pathogens and kept in separate aquaria for bath treatment under laboratory condition for 10 days. Freshly cultured bacterial pathogens were injected to 10 fish (5 fish/ aquarium with 20L water) smoothly and carefully at a dose of 2x107 CFU/ fish. For fungal infection, 10 fish were externally abraded and contacted with suspension of fungal zoospore at a density of 3x105 CFU/ml. Chemotherapeutics were applied for each set of experiment at their particular doses, viz., salt + lime (10 gm + 10 gm/20L), alum (40 ppm), doxycycline (35 ppm), and oxytetracycline (50 ppm). Aeration was done and water temperature was maintained at 26-28ºC. No chemotherapeutic was applied to the control fish. Everyday 50% water from the individual aquarium was exchanged. In the case of field trial, fish with experimentally infection by both bacterial and fungal pathogens were kept separately in two 1 decimal (approximately) tanks at a stocking density of 50 fish/ decimal and treated with each chemotherapeutic for 2 weeks. Another tank was used for controlled treatment without using chemotherapeutic. In the field case dose of salt + lime was 500 gm + 500 gm/ decimal and the doses of other chemotherapeutics were same as used in the laboratory experiments. The water of each tank was exchanged after each treatment and 2 weeks of withdrawal period was maintained. In another field trial at small-scale farmers’ ponds, alum and salt + lime were applied to check the prevalence of the out-break of epizootic ulcerative syndrome or similar disease. Keeping one control pond (6-8 decimal size) having no chemotherapy, four similar ponds were used to apply alum and salt + lime at their pre-selected dose (two ponds for each treatment) in Boyra village area adjacent to the BAU campus. This was a sort of preventive treatment during the onset of winter season (in December) and was repeated twice at weekly interval to obtain better result. Observation on the prevalence of disease occurrence was recorded accordingly. Therapeutic effects of medicinal plants: In the case of laboratory trial, the experimental fish were challenged with the bacterial and fungal pathogens and then exposed to the extracts of the selected medicinal plants for an hour at the selected standard dose. The exposed fish were then transferred to the (5 fish/ aquarium of 20L of water) aquaria at room temperature (25-26ºC). In all cases aeration was maintained. Neem and akand (1 gm + 1 gm/L) were used together to have better performance against bacterial and fungal infection whereas garlic (0.5 gm/L), turmeric (0.5 gm/L) and arrowroot (1 gm/L) were applied individually. All treatments were continued for a week with 50% exchange of the aquarium water. Control fish were maintained in the same way having no treatment with medicinal plants. Occurrence of disease was observed for two weeks. In the field trial, parts of medicinal plants were selected as food ingredient depending on food intake by the fish before two weeks of challenge with bacterial and fungal pathogens based on preliminary trial and laboratory experiments. The fish were first treated with medicinal plants by feeding paste of the leaves of Indian sorrel and guava (10%) everyday with normal feed (20% mastered oil-cake + 20% fish meal + 40% rice bran + 10% wheat flour) in mini nursery ponds of BFRI, Freshwater Station, Mymensingh. The size of pond was 8m x 5m x 1.5m with water level 0.8m. Every pond was used for individual treatment and 30-40 fish were maintained in each pond. After 2 weeks of such culture treatment, randomly sampled fish were challenged with the bacterial pathogen under laboratory condition as described before and observed their prevalence of disease occurrence. Similarly, for fungal infection experiments paste of the rhizome of arrowroot and seeds of black cumin were fed to the experimental fish mixed with the normal feed and maintained in the BFRI nursery ponds as above. The treated fish were challenged with fungal pathogens under laboratory condition as described before. Prevalence of the disease occurrence was recorded for two weeks. In every case, control fish were maintained only with normal feed.
J. Bangladesh Agril. Univ. 10(2): 385–390, 2012
Journal