Gambit,
Ordinarily I'd say that this zuchinni is over ripe but the size does not indicate that. Try harvesting the next zuchinni when it is closer to 6-8 inches and see what it looks and tastes like.
Sometimes, the plant is just not good and it will yield a bitter veggie. I'd toss it out if it tastes bitter at all, otherwise you may risk some gastro-intestinal discomfort...and nobody wants to be shitting and farting all night!