Abstract
The study evaluated the effects of two selected chemicals; methylene blue and saline on bacterial load in transport-water containing monosex tilapia (Oreochromis niloticus) fry. Fish fry was collected from a private hatchery located in Trishal upazilla, Mymensingh. A total of approximately 550 fry were added in each polyethylene bag containing water and transported to the Fish Disease Laboratory of the Department of Aquaculture, Bangladesh Agricultural University (BAU) for analysis. Two different concentrations of chemicals like 1 and 2 ppm methylene blue, 1 and 2 ppt saline and combination of the both were used. Samplings were done at 0, 4, 8 hours interval to determine the bacterial load in transport-water. Both methylene blue and saline were found effective in reducing bacterial load in water during transportation. The combined use of saline and methylene blue showed better result than the chemicals used individually in terms of final bacterial load. A gradual increase in bacterial load with time was found in control water having no chemicals (T0). In T1 (1 ppm methylene blue used) and T2 (2 ppm methylene blue used) the mean bacterial loads were 1.03±0.5×107 cfu/ml and 5.00±2×107 cfu/ml respectively. Similarly mean bacterial loads of 4.48±1.5×106 cfu/ml and 3.43±2.7×106 cfu/ml were obtained with 1 and 2 ppt saline (T3 and T4) respectively. Whereas combined use of 1 ppm methylene blue and 1 ppt saline (T5) end up with the mean bacterial load of 2.94±2.5×106 cfu/ml after 8 hours of exposure. It was 2.95±2.7×106 cfu/ml when the dose was doubled (T6). The highest percentage of mortality was found in control water in every sampling period. Water quality parameters like temperature, pH, and dissolved oxygen decreased after 8 hours of transportation. The experiment revealed that the combined low dose of methylene blue and saline can be recommended for transportation of tilapia fry.
 Asian J. Med. Biol. Res. March 2019, 5(1): 14-19
Highlights
Fish hatcheries have been playing an important role in the expansion of aquaculture of Bangladesh
The therapeutic action of methylene blue on bacteria and other parasites is probably due to its binding effect with cytoplasmic structures within the cell and its interference with oxidation-reduction processes
Methylene blue may be used for the treatment of Ichthyophthiriosis, skin and gill flukes, velvet disease, Costiasis, coral fish disease, Chilodonelliasis and as a palliative medicine in all cases of disease of the gills, where fishes suffer from difficulty in breathing (Van Duijn, 1973)
Summary
Fish hatcheries have been playing an important role in the expansion of aquaculture of Bangladesh. Monosex GIFT tilapia (Oreochromis niloticus) is the leading species in aquaculture of Bangladesh and its farming is growing day by day. The survival of fingerlings during transport from hatchery to grow-out farmers’ farm is very critical to both of them. To deal with the problem, hatchery owners use some chemicals to prevent the proliferation of bacteria during fish transport. Methylene blue (C16H18N3CIS.3H2O) and some commercially available saline are commonly used in different hatchery. Experience and research have shown that fish transport can be improved by the addition of certain chemicals such as sodium chloride and methylene blue (Fajardo, 2002). Common table salt or sodium chloride is one of the most commonly used drugs in aquaculture and it is sometimes referred to as the “aspirin of
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