Preparing　nitrogen-doped　(N-doped)　photoluminescent　carbonaceous　nanodots　(C-dots)　from　the　recycling/utilisation　of　nitrogen-rich　carbonaceous　waste　has　received　considerable　research　interest.　In　this　work,　by　using　fish　scales,　an　abundant　food　industry　waste,　as　a　starting　material,　we　have　developed　a　green,　cheap　and　convenient　approach　for　the　preparation　of　N-doped　photoluminescent　C-dots,　which　represents　a　great　potential　for　large-scale　production.　The　as-synthesized　C-dots　are　highly　soluble,　regularly　sphere　shaped　and　homogeneously　sized　with　an　average　diameter　of　2　nm.　X-ray　photoelectron　spectroscopy　results　demonstrate　that　the　nitrogen　content　can　reach　14.6%,　which　is　higher　than　that　of　most　N-doped　C-dots　reported　previously.　The　C-dots　present　a　narrow　photoluminescence　emission　band　(400-490　nm)　with　a　high　quantum　yield　up　to　17%,　owing　to　the　fluorescence　enhancement　effect　of　nitrogen　doping.　Besides,　their　fluorescence　can　be　sensitively　quenched　by　the　addition　of　hypochlorite　(ClO-),　making　them　a　promising　sensing　platform　for　ClO-.　©　The　Royal　Society　of　Chemistry　2015.