Bold, bullish and packed with bucket loads of bite, the bull shark is the most menacing shark out there. Steve Backshall comes face to face with these apex predators off the coast of Mexico, and reveals it's not just the ocean that they hunt in - they can also move into freshwater rivers and lakes, and have been found thousands of kilometres up the Amazon river. Back in Steve's Shark Lab, he reveals how the bull shark adapts to the varying salt levels using its very clever kidneys.