Oily fish
<p ><b>Oily fish</b> have <a href="http://en.wikipedia.org/wiki/Fish_oil" title="Fish oil" >oil</a> in their tissues and in the belly cavity around the <a href="http://en.wikipedia.org/wiki/Gut_(zoology)" title="Gut (zoology)" class="mw-redirect" >gut</a>. </p>
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Their <a href="http://en.wikipedia.org/wiki/Fillet_(cut)" title="Fillet (cut)" >fillets</a> contain up to 30 percent oil, although this figure varies both within and between species. </p>
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Examples include small <a href="http://en.wikipedia.org/wiki/Forage_fish" title="Forage fish" >forage fish</a>, such as <a href="http://en.wikipedia.org/wiki/Sardine" title="Sardine" >sardines</a>, <a href="http://en.wikipedia.org/wiki/Herring" title="Herring" >herring</a> and <a href="http://en.wikipedia.org/wiki/Anchovy" title="Anchovy" >anchovies</a>, and other larger <a href="http://en.wikipedia.org/wiki/Pelagic_fish" title="Pelagic fish" >pelagic fish</a>, such as <a href="http://en.wikipedia.org/wiki/Salmon" title="Salmon" >salmon</a>, <a href="http://en.wikipedia.org/wiki/Trout" title="Trout" >trout</a>, <a href="http://en.wikipedia.org/wiki/Ilish" title="Ilish" >ilish</a> and <a href="http://en.wikipedia.org/wiki/Mackerel" title="Mackerel" >mackerel</a>.</p>
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Oily fish can be contrasted with <a href="http://en.wikipedia.org/wiki/Whitefish_(fisheries_term)" title="Whitefish (fisheries term)" >whitefish</a>, which contain oil only in the <a href="http://en.wikipedia.org/wiki/Liver" title="Liver" >liver</a>, and much less overall than oily fish. </p>
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Examples of whitefish are <a href="http://en.wikipedia.org/wiki/Cod" title="Cod" >cod</a>, <a href="http://en.wikipedia.org/wiki/Haddock" title="Haddock" >haddock</a> and <a href="http://en.wikipedia.org/wiki/Flatfish" title="Flatfish" >flatfish</a>. Whitefish are usually <a href="http://en.wikipedia.org/wiki/Demersal_fish" title="Demersal fish" >demersal fish</a> which live
on or near the seafloor, whereas oily fish are <a href="http://en.wikipedia.org/wiki/Pelagic_fish" title="Pelagic fish" >pelagic</a>, living in the <a href="http://en.wikipedia.org/wiki/Water_column" title="Water column" >water column</a> away from the bottom. </p>
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Oily fish are a good source of <a href="http://en.wikipedia.org/wiki/Vitamin" title="Vitamin" >vitamins</a> <a href="http://en.wikipedia.org/wiki/Vitamin_A" title="Vitamin A" >A</a> and <a href="http://en.wikipedia.org/wiki/Vitamin_D" title="Vitamin D" >D</a>, and are rich in <a href="http://en.wikipedia.org/wiki/Omega-3_fatty_acid" title="Omega-3 fatty acid" >omega-3 fatty acids</a> (whitefish contain the same nutrients but at a much lower level).<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Oily_fish#cite_note-0" >[1]</a></sup> </p>
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For this reason the consumption of oily fish rather than whitefish can be more beneficial to humans, particularly concerning <a href="http://en.wikipedia.org/wiki/Cardiovascular_disease" title="Cardiovascular disease" >cardiovascular diseases</a>,<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Oily_fish#cite_note-1" >[2]</a></sup> but oily fish are known to carry higher levels of <a href="http://en.wikipedia.org/wiki/Contaminant" title="Contaminant" class="mw-redirect" >contaminants</a> (such as <a href="http://en.wikipedia.org/wiki/Mercury_(element)" title="Mercury (element)" >mercury</a> or <a href="http://en.wikipedia.org/wiki/Dioxins_and_dioxin-like_compounds" title="Dioxins and dioxin-like compounds" >dioxin</a>) than whitefish.<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Oily_fish#cite_note-2" >[3]</a></sup> </p>
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Amongst other benefits, studies suggest that the Omega 3 fatty acids in oily fish may help improve inflammatory conditions such as <a href="http://en.wikipedia.org/wiki/Arthritis" title="Arthritis" >arthritis</a>.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Oily_fish#cite_note-3" >[4]</a></sup></p>