Test feed no. 11 was fish feed supplemented with oxytetracycline in the ratio of 1:149 (w/w). Distilled, deionized water was added to each test feed mixture (1 mL/g) and mixed until homogenous. The mixture was passed through a meat mincer producing extruded strings, which were
dried at 30 °C for 24 h and then broken to ∼2 mm long pellets. A control test feed (no.
12) was prepared using the same process as the other test feeds except no supplements were added.