The effect of certain antibiotics on the keeping quality of bolti fish (Tilapia nilotica).

Fresh bolti fish (Tilapia nilotica), caught in the river Nile was immersed in 10 and 20 ppm tetracycline (TC) solutions for 10 and 15 min respectively and in 500 and 1000 R.U. nisin/g fish for 20 and 30 min respectively. Total volatile bases (TVN) showed in both fish treated with TC and nisin a slow increase at the first stage and after that a fast increase. There was an increase in trimethylamine (TMA) during the storage period, but the fish treated with TC and nisin contained less TMA than the control. Starting from 6 h the residual TC decreased gradually till the third day, when it disappeared completely. There is no change in pH values in both control and treated fish. Optical density (OD) of gills extract increased gradually as the storage period progresses. The treated fish showed lower OD values than the controls. The refractive index of muscle fluids and the OD of muscle extract showed no significant differences between the control and treated fish.