we are frying fish and just realized we don't have a thermometer for the oil. it needs to be at 375. any suggestions for how to measure temp.?

I don't often bother with a frying thermometer. As someone has suggested, it's not necessary to be too precise. Think "in the range of" 360 to 375, and that's the temp at which a small (1 inch, no more) cube of bread will crisp and turn golden in a minute or less.

You can also stick a bamboo chop stick into the oil. The hotter the oil, the more bubbles will come out. 350 is a steady stream of bubbles, 375 will be more.

Hopefully you have a good frying rig that won't spill over when you add the fish. All you really need is a pinch of bread crumbs to test. They will sizzle and brown in seconds. For good frying quality you need oil that is at least 375F but don't fret about precise measurements. What's important is that the oil is hot enough to fry the fish (or donut or whatever you are doing).

A one inch cube of bread should brown in about 60 seconds at 365 according to "Joy of Cooking". So add a few seconds for 375.