Choose the correct word to fill in the blanks.
PiranhasScientists in the UK have announced that the piranha fish's reputation 1) __________ a fearsome 2) __________ may well not be deserved. The fish, which is found in the Amazon in Brazil, have been portrayed as deadly 3) __________ that work in shoals to overwhelm their prey and strip it of its flesh in seconds.
However, 4) __________ from St Andrews University say that piranhas are omnivores that mainly eat fish, plants and insects. They form big groups not to hunt but to defend 5) __________ against other predators, according to the team.
"Previously it was thought piranhas shoaled as it 6) __________ them to form a cooperative hunting group," said Professor Anne Magurran. "However, we have found that it is primarily a defensive 7) __________."
Piranhas can be attacked by animals 8) __________ dolphins, caimans and large fish, so forming a shoal is a good way of 9) __________ being killed. Piranhas of 10) __________ age stay in the middle of the group for 11) __________ and the 12) __________ of the shoal 13) __________ according to the level of 14) __________. When the water level is high, the fish form small groups as there is space to escape, but when the water level drops, they form large groups as protection against 15) __________.