Successful electromagneitc pulses radiate outward also disabling any nearby Servofish.
The Stunna Fishing Spear can be bought for 5,000 Standing 5,000 from The Business while at the rank of Doer, given that one has already purchased the Shockprod Fishing Spear beforehand.
Characteristics
On a successful catch, Stunna emits an electromagnetic pulse that temporarily prevents other servofish from scurrying away when the water is disturbed, similar to the effects of Pharoma, and also widens the catch zone on the fishing gauge. The coursing electricity can be clearly seen, making servofish easier to spot.
Successfully performing a "catch" on a fish in the Plains of Eidolon will also create the electromagnetic pulse, stunning fish within the radius. This will not retrieve the fish, however; they must be struck with a Cetus-bought spear.