When it is said "fits in the mouth", it is meant girth-wise.
There is even such a thing as gradual swallowing and digestion, wherein the prey is swallowed partially length-wise, because it does not fit entirely in the stomach (but fits in the mouth and throat girth-wise), then digested, space in the stomach is freed, it is swallowed some more, and so on.
Watch out that the clarias' spines do not puncture paroon's stomach. It happens sometimes, though often it is inconsequential anyway.
If you feed now, the full paroon will hardly eat anything. Waiting is actually a better idea to lessen the bio-load on your filter.
There is even such a thing as gradual swallowing and digestion, wherein the prey is swallowed partially length-wise, because it does not fit entirely in the stomach (but fits in the mouth and throat girth-wise), then digested, space in the stomach is freed, it is swallowed some more, and so on.
Watch out that the clarias' spines do not puncture paroon's stomach. It happens sometimes, though often it is inconsequential anyway.
If you feed now, the full paroon will hardly eat anything. Waiting is actually a better idea to lessen the bio-load on your filter.