1.4 Maple Syrup Density Measurement. 1.4.1 Background; 1.4.2 Hydrometers; 1.4.3 Hydrotherms; 1.4.4 Refractometers . 1.4.4.1 Optical Refractometers; 1.4.4.2 Digital Refractometers; 1.4.5 Temperature Correction; 1.4.6 Instrument Calibration . 1.4.6.1 Hydrometers; 1.4.6.2 Thermometers; 1.4.6.3 Refractometers; 1.4.7 Collecting a Representative Sample
Because of this distinction, you may safely use fish even after the sell by date has lapsed. If there is a use-buy date on fresh fish, then it is recommended to either cook or freeze the fish by that date. Commercially frozen fish, if kept frozen, can be safely stored for 10-12 months.
The folks over at Brooklyn's Fish Tales say that fish will keep for three days maximum. Of course, they buy fresh fish every morning and urge anyone to buy fish the same day they're going to cook it. If that's impossible, you should keep it on ice in the refrigerator. Never keep it in the freezer, they say.