activity was found in eight of the ten fish, and after 4 days all fish were positive.
Expression reached its maximum after 1–2 weeks (Fig. 1a) and was then relatively
stable in most fish for at least 1 month. At day 28 one of five surviving fish no longer
showed expression and after 6 months only one of the two surviving fish still showed
expression. Analysis of this fish at 1, 6, 12 and 24 months (Fig. 1c–e; 12 months not
shown) indicated that the luciferase expression decreased only very gradually.