mackerel
... that mackerel have vertical stripes on their sides which may help them stay in formation when they are schooling ?
... that <b id="mwDEg"><a href="./Mackerel" id="mwDEk" rel="mw:WikiLink" title="Mackerel">mackerel</a></b> have vertical stripes on their sides which may help them stay in formation when they are <a href="./Shoaling_and_schooling" id="mwDEo" rel="mw:WikiLink" title="Shoaling and schooling">schooling</a> <i id="mwDEs">(pictured)</i>?