The man, carrying two shotguns and a knife, was detained just days after separate incidents of random street attacks in Nantes and Dijon.
Terrorism was rule out for two attacks in which vehicles were driven at city-centre crowds, but PM Valls said he understood public 'worry'.
Total of 529 anti-Semitic actions or threats were registered up to the end of July, against 276 for the same period last year.
Paris manhunt launched after a photographer was seriously wounded in attacks on daily Libération and the Societe Generale bank HQ.
Fishermen will kill some 20 sharks off Indian Ocean island of La Réunion in an official operation to discover what prompted recent attacks on surfers.