Pretty close between silurus glanis/euro wels and the mekong giant cat for length. Both have been caught and recorded over 9’… mekong wins for weight tho around 650lbs recorded where as wels are around 300lb at the same length.
#1 is definitely the Mekong cat, but #2 is somewhat disputed. In terms of recorded weights, it would go to the piraiba at ~340 lbs. There are claims that both wels cats and piraiba get much larger than their official record sizes.