Whisk together first 8 ingredients; gradually whisk in olive oil until well blended. Remove half of juice mixture, and set aside.
Place catfish in a shallow dish or heavy-duty zip-top plastic bag; pour remaining marinade over catfish. Cover or seal bag, and chill 15 minutes, turning catfish once.
Remove catfish from marinade, discarding marinade.
Coat grill rack with cooking spray; place on grill over medium-high heat (350° to 400°). Place catfish on rack, and grill 5 minutes on each side or until done. Remove to a serving platter; drizzle with reserved marinade. Garnish, if desired.
NOTE: To broil catfish, follow recipe up to removing fish from marinade. Place fish on a rack coated with cooking spray; place rack in a broiler pan. Broil, 3 inches from heat, 7 to 8 minutes or until golden brown. Remove to a serving platter; drizzle with reserved marinade. Garnish, if desired.
Most of the fat calories come from omega-3 fatty acids (in catfish) and monounsaturated fat (in olive oil), both of which are associated with lowering LDL (bad) cholesterol and increasing HDL (good) cholesterol.