I dont believe the statement on skinless haddock is at all accurate.
Most of the haddock sold is dresssed, skinned, deboned and the skin is removed. Maybe you refer to something local?

Fish can spoil more quoickly than many meats. While bacteria is an issue, oxidization of oils, in oily fish like mackerel, herring and salmon, is more of a problem. Once oxidized, it gives off a rancid taste. Mackerel is especially oily and spoils rapidly. Outside of salt and drying, freezing at very low temperatures hampers this oxidization. Glazing with water decreases the oxidization even farther. Smoking does little to preserve fish, its mostly the salt that does this job.


One has to watch out for mercury levels in river and lake fish, like trout, (because of pollution and land and rain based sources).

With ocean fish, mercury is mostly accumulated with age and size. Larger and older fish, like tuna, and swordfish (large pelagics) accumulate much mercury. (the larger the tuna,like bluefin and albacore have higher levels). There is very low levels in most smaller, short lived fish like cod, haddock (groundfish), mackerel and herring (small pelagics)). Generally, these fish are very safe and low in mercury.

Fish caught near industrial sources can accumulate mercury and heavy metals in the oils and organs. Unfortunately, one does not know where fish is caught, if bought in a big market.

Some folks are alergic to all fish and shellfish (including marine mullucs like clams, oysters, scallops mussels). Some are only alergic to some. Mackerel has a lot of histimine,which causes difficulty for many.

As for marine filter feeding marine mulluscs, care must be taken to know they come from a clean water source, as you are eating the whole species. With scallops, not much worry, you are just eating the meat from the shell hinge.