If you read the post I attached you will see that your oil is breaking down and that is what is causing it to foam.
Oily fish (like mackerel) will impart some of it's oil and cause your frying oil to break down faster. If the food is dredged in flour, then the flour will cause the oil to break down faster too.
The smoke point is only important because above that point the oil will break down and taste burned and then rancid. This is why you shouldn't fry in olive oil. It has a low smoke point.
ALL oils are going to break down after being used for frying and depending on what is fried in them, they can break down after only a couple of uses.
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