Osaka, Japan) and injections of 5 l PBS/6·7% luciferin (Sigma-Aldrich, Tokyo, Japan)
into the right lateral muscle. The emission of light resulting from luciferase activity on
the luciferin substrate was measured for 10 min with a low light video image analyser
(Argus 50, Hammatsu Photonics, Hammatsu, Japan), during which the immobilised fish
were kept wet in anaesthetic solution. The system was semi-quantitative and was
deemed su$ciently sensitive to distinguish between weak and strong expression.
Di#erences in light emission 1 week after DNA administration were observed between
groups of fish injected with 0·1, 1 or 10 g pCEP4-luc (data not shown), there being
a dose-dependent correlation with light emission. The detection system appeared
sensitive since light emission from fish injected with only 0·1 g DNA was easily
observed (data not shown). Control fish that were not previously injected with
pCEP4-luc DNA showed no expression (Fig. 1b). Although the fish usually recovered
after analysis, some mortalities occurred, probably due to stress caused by the
detection method.