Table 2.

Acetylcholinesterase activity in pesticide-exposed juvenile Chinook salmona

Pesticide (tissue)	Concentration (μg/l)b	Average ± S.D.c	Ranged
Chlorpyrifos (brain)	Controle	206 ± 12	2.1
	Solventf	183 ± 18	2.0
	1.2	168 ± 23	1.7
	7.3	27 ± 6*	2.1
Chlorpyrifos (muscle)	Control	158 ± 34	1.2
	Solvent	162 ± 29	1.4
	1.2	180 ± 32	1.7
	7.3	13 ± 4*	2.0
Esfenvalerate (brain)	Control	206 ± 12	2.1
	Solvent	183 ± 18	2.0
	0.01	197 ± 21	2.2
	0.1	195 ± 8	1.4
Esfenvalerate (muscle)	Control	158 ± 34	1.2
	Solvent	162 ± 29	1.4
	0.01	151 ± 33	1.5
	0.1	145 ± 20	1.1

^aJuvenile Chinook salmon were exposed to the indicated concentration of pesticide for 96 h as described in Section 2. Only the salmon exposed to 7.3 μg/l chlorpyrifos had significantly inhibited acetylcholinesterase activity.

^bAll reported water concentrations are nominal values. Chlorpyrifos concentrations were measured to be 1.2 and 7.3 μg/l (as opposed to 1.0 and 10.0 μg/l nominal). Esfenvalerate concentrations were observed to deviate by ∼20% from nominal concentrations (unpublished results).

^cActivity values are in units of nmol/min/mg and are the average ± the standard deviation (S.D.) for 10 fish (n = 10), except for the 7.3 μg/l chlorpyrifos exposure (n = 8). Assays were performed in triplicate and variability was less than 10%.

^dRange values are given as the fold difference in activity between the lowest and highest individuals.

^eControl fish were not exposed to either pesticides or vehicle and did not go through the experimental testing regimen.

^fSolvent fish were exposed to the highest concentration of vehicle (0.005% MeOH) and went through the full 96 h testing regimen.

^*Statistically different from the control, solvent-exposed, and the 1.2 μg/l chlorpyrifos-exposed salmon (P < 0.001).