5.8 SAMPLING OF FISH LARVAE
The larvae were submerged in ice-cold saline under a stereomicroscope during measurement of the length and dissection of the liver. In the first and second experiment eight livers were pooled and homogenized at 0°C in 800 ^L 0.25 M sucrose using a 0.5mL Potter-Elvehjem homogenizer (size 18) with six up and down strokes at 400 r.p.m. Because of the limited size of the Potter-Elvehjem homogenizer, four livers at a time were homogenized in 400 ^L 0.25 M sucrose, whereupon the two homogenates were pooled. The homogenates were immediately portioned into ice-cold cryo-tubes and submerged in liquid nitrogen. In the third experiment the same procedure was used, but three livers were pooled and homogenized in 300 ^L 0.25 M sucrose. Hence, eight or three larvae corresponded to n = 1 for the calculation of enzyme activities. In the first and second experiments 40 livers were dissected from each exposure group and control group. In the third experiment 15 livers were dissected from each group. Hence n = 5 for the calculation of enzyme activities in all three experiments. Directly after liver dissection the muscles of the larvae were put into cryo-tubes and submerged in liquid nitrogen for determination of acetylcholinesterase (AChE) activity. Length, as a measure of growth, was expressed as percent above non-injected and carrier control, with negative values denoting retarded growth compared with control.