They caught: 11/12 pounds of fish
First you need to change them to a same common denominator. Since 3 and 6 already go into 12, you just have to change 1/3 and 1/6 to a denominator with 12.
First you need to change 1/3 to 4/12. By doing that, you do: 1/3x4/4=4/12.
You then have to change 1/6 to 2/12. By doing that, you do: 1/6x2/2=2/12.
Then you just add up all the fractions and simplify: 4/12+2/12+5/12=11/12.
You can't simplify 11/12 any further so you're answer would be:
They caught 11/12 pounds of fish in total.
Hope this helps! :D