State environmental and wildlife officials say it's not yet clear what killed the fish, which appear to exclusively small menhaden, also known as peanut bunker.
The wash-up, discovered Wednesday morning, encompassed a large stretch of the shoreline just north of Cape May. The heaviest amounts were in an area of Middle Township known as Pierce's Point.
New Jersey's Bureau of Marine Water Monitoring reviewed results of water samples taken Wednesday by federal environmental officials and found no indication of toxic phytoplankton species, such as red tide.
State officials also are analyzing oxygen levels in the water.