Try
boxplot(fishjump$Time ~ fishjump$Treatment, xlab="Treatment",ylab="Time",names=c("Control","Air")
I think the categorical variable needs to follow the numeric.
A slightly tidier way to write this would be:
boxplot(Time ~ Treatment, data = fishjump, xlab="Treatment",ylab="Time",names=c("Control","Air")
It makes it a bit easier to see what you are doing. In any case I like @ BLukomski' suggestion to use ggplot2