Norway’s $890 billion wealth fund is taking the rare step of publicly criticizing the proliferation of dark pools, arguing the world’s biggest investors only need one such platform. The fund says institutional investors, and the savers they represent, are wasting money paying multiple fees amid a fragmentation of anonymous trading venues over the past decade. The dark pools have become associated with the phenomenon of front-running, in which bid and offer information is used by high-frequency traders to pre-empt transactions and make a profit at the expense of investors.