fish schools
... that Atlantic herrings form immense fish schools containing up to three billion fish?
... that <a href="./Atlantic_herring" id="mwCYI" rel="mw:WikiLink" title="Atlantic herring">Atlantic herrings</a> form immense <b id="mwCYM"><a href="./Shoaling_and_schooling" id="mwCYQ" rel="mw:WikiLink" title="Shoaling and schooling">fish schools</a></b> <i id="mwCYU">(pictured)</i> containing up to three<span id="mwCYY" typeof="mw:Entity"> </span>billion fish?