Oily Blackmouth
http://wow.allakhazam.com/images/icons/INV_Misc_MonsterHead_04.png
The Oily Blackmouth is used in Alchemy to make 
[Shadow Oil] and Blackmouth Oil .
It can be caught through Fishing, over about fishing skill-level 50, from, for example, Ratchet, Booty Bay, the Darkshore coast, and Zoram'gar.
Fished from... (full list)
Southshore, Menethil Harbor, Auberdine, The Long Wash, Ratchet, Fray Island, Booty Bay, Baradin Bay, The Zoram Strand, Sar'theris Strand, The Veiled Sea, The Great Sea, Theramore Isle, Mist's Edge, Moonglade, North Tide's Run, Verdantis River, The Hinterlands, Quel'Danil Lodge, Longshore, Westfall Lighthouse, Dreadmurk Shore, The Savage Coast, The Merchant Coast, Northwatch Hold, Nighthaven, Lake Elune'ara, Zoram'gar Outpost, Caer Darrow, The Tidus Stair, Southfury River, Menethil Bay, Stormwind City, Zul'Farrak, South Tide's Run, Purgation Isle, Western Strand, Wetlands, Bluegill Marsh, Eastern Strand, The Cape of Stranglethorn, Grom'gol Base Camp, Misty Reed Strand, Faldir's Cove, Tidefury Cove, Darrowmere Lake, South Seas, Hillsbrad Foothills, Sorrow Hill, Southern Savage Coast, The Vile Reef, The Marshlands, Valorwind Lake, Golakka Hot Springs, Dustwallow Bay, Wild Shore, The Twin Colossals, Camp Mojache, Earth Song Falls, Western Plaguelands, Thondroril River, Wildwind Lake, Felwood, The Forbidding Sea, Lower Wilds, The Broken Hall, Maraudon, Zaetar's Grave, Bloodsail Compound, The Temple of Atal'Hakkar, Talonbranch Glade, Azshara, The Drowned Reef, Desolace, The Writhing Deep, The Crystal Shore, Bloodvenom Falls, Ethel Rethor, Lakkari Tar Pits, Jaguero Isle, Janeiro's Point, Bloodvenom Post, Bloodvenom River, The Harborage, Agol'watha, Un'Goro Crater, Frayfeather Highlands, Jadefire Run, Lake Mennar, Beezil's Wreck, Poison Falls, Dustwallow Marsh, Cliffspring River, Skulk Rock, The Writhing Haunt, Wavestrider Beach, High Wilderness, Ruins of Andorhal, Felpaw Village, Fire Plume Ridge, The Pit of Refuse, Ruins of Isildien, Irontree Woods, Swamp of Sorrows, Vyletongue Seat, Fungal Rock, Ruins of Aboraz, Seradane, The Noxious Hollow, Jaedenar, Land's End Beach, Jintha'Alor, Black Channel Marsh, Foulspore Cavern, The Wicked Grotto, Ruins of Constellas, Twilight Shore, Shadow Hold, The Lost Fleet, Shadra'Alor, Darkshore, Rethress Sanctum, Pool of Tears, Shadowfang Keep, Shalzaru's Lair, Darkspear Strand, Temple of Zin-Malor, Stranglethorn Vale, Shadowprey Village, Emerald Sanctuary, Chillwind Point