Across 683 ranked games on patch 16.21 in Master and above, Fiddlesticks mains win 50.7% of their games in the jungle.
Their most common build appears in 37.0% of those games and wins 54.2% of its 253 games.
It starts 
Gustwalker Hatchling, completes 
Hextech Rocketbelt, 
Shadowflame, 
Zhonya's Hourglass and 
Void Staff in that order, and takes 
Sorcerer's Shoes.
Three other builds are played often enough in the jungle to be measured on their own.
In the jungle, Fiddlesticks mains fare best against 
Nidalee (won 65.0% of 20 games), 
Wukong (won 66.7% of 12 games) and 
Qiyana (won 52.2% of 23 games).
Their hardest matchups, the champions that counter Fiddlesticks, are 
Lee Sin (won 30.8% of 26 games), 
Graves (won 30.8% of 13 games) and 
Viego (won 35.7% of 14 games).