during the rain, depending on how much rain and how big the body of water is, they fish may or may not eat if the water parameters are changing.
If the rain's pH, temp, etc are the same or close enough to the body of water's parameters, or if there isn't too much rain, fish are opportunistic and will eat stuff that gets washed in such as worms and bugs.
Fish will also eat more after the rains because things still get washed in.