A silhouette of the world’s largest fish in crystal clear tropical waters. The Whale shark. These guys can grow up to 18m long and 20 tonnes. Whale sharks are negatively buoyant so as soon as they get tired and stop moving their tail, they will sink. It is due to this that humans have never recorded whale sharks mating or giving birth. The theory being, they sink to great depths somewhere remote in the ocean for such practices. Deeper than where any tracking tags can reach and cameras can find them, the Humble Whalesharks have done a good job at keeping their private business 'private'.