Robson heads to the town of Itatí in the northeastern province of Corrientes in Argentina. On the southern shores of the second biggest river in south America, the Paraná, Robson lays some baited-lines to catch the largest freshwater fish in world – the short-tailed river stingray. Further down river he searches for the pacu, a close cousin of the piranha. Using a curried-fruit lure, the boys mix up the bizarre fish food, then cast towards the reeds and wait for the normally timid fish to feed. But Robson’s first real bite is not at all timid! Leaving the river behind, Robson’s next stop is the Iberá marshes, to a traditional working cattle ranch. Robson is here for the lagoons which are home to packs of piranha. But before getting near the water, Robson earns his Gaucho spurs fishing for cattle with a lasso. Robson gets a chance to catch both yellow and river piranhas, the hook just has to be in the water for a second or two before there is a tug. Robson’s last visit is to a place renowned for producing record breakers, the Salto Grande Dam on the river Uruguay.

• Robson Green