The effect of certain antibiotics on bolti fish (Tilapia nilotica) preservation

The shelf life of bolti fish (Tilapia nilotica) caught in the river Nile, has been successfully prolonged for about 9 days by dipping in tetracycline (TC) or nisin solution followed by refrigeration, although the initial microbial contamination in the fresh fish was very high. The caught fish were gutted and treated with 10 and 20 ppm TC solutions for 10 and 15 min by dipping, and with 500 and 1000 R.U. nisin/g fish for 20 and 30 min. The treated and control fish samples, were stored and refrigerated at (4 +/- 1) degree C for 12 days. Total bacterial counts, the most probable number of coliform bacteria and lactic acid bacteria in the fish treated with TC or nisin, were lower than those of the control, especially at 20 ppm TC, 15 min dipping, and 1000 R.U. nisin/g, 30 min. Further more TC was more effective against yeasts and moulds. This result suggest that antibiotics would help in transporting chilled fish from the highdam lake in Aswan to Cairo (about 900 km). According to the present results it may be recommended to use the antibiotic TC, with the concentration of 20 ppm for 15 min dipping, for prolonging the shelflife of bolti fish. The presence and increase of coliform bacteria in fish, draw the attention to the necessity of hygienic measures when dealing with such fish until to the consumption.