// cas_fishusespear.nss
#include "cas_fishinc"

void main()
{
    object oPC    = OBJECT_SELF;              // per your system: self = user
    object oItem  = GetEventParamObject(0);   // item used (spear)
    object oTarg  = GetEventParamObject(1);   // target object (fish)

    CasFish_OnUseSpear(oPC, oItem, oTarg);
}