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Pat is a trusted home cook.
It's probably just me but the only time I save oil for frying is when we fry turkeys on Thanksgiving day and then fry a few more the next day....I rarely deep fry however, instead opt for shallow pan frying so not that much oil is used.
Depends on the method of frying. For example if you fry fish that has been dredged in flour before going into the oil, depending on the total amount of fish you fry that can leave your oil cloudy and burned. If you use a batter, the oil will remain clearer overall, and can be reused again, following a straining.
I would go by the color. Golden brown oil makes golden brown food. The darker it gets the more burnt flavor and the darker the food becomes.
Sam is a trusted home cook.
I think if you're frying fish..it's once thing. Unless the oil is specifically purposed for frying fish and only fish.
Canolia oil is a special beast, as even when it doesn't touch fish---it can impart a 'fishy' smell to other things.
Canolia isn't really a good oil to use IMHO...it's "Rapeseed Oil" renamed as "Canada Oil/ CANOila" for marketing, as rape is bad press. It's also one of the major Genetically Modified Oils to first hit the market as 'round up ready' in the crops. (I don't think that gets imported into the US tho). Okay, I'm not a fan of canolia oil. I'd rather have peanut, duck fat, or for fish Clarified Butter---easy to make and store. Canolia does have a 'fishy taste' when heated to frying temp all on it's own, even without fish.
To me fish is so delicate in flavor--a oil, like canolia which brings it's own fishy taste to the dish really doesn't work for me. Butter/clarified butter really pares well with fish.