Last year my wife and I rented a couple of SOT kayaks and used them to paddle around our local lake. We enjoyed it so much we have decided to purchase our own this year.
We are looking at some entry level kayaks to use at the lakes and rivers here in Illinois. 
I am also an avid fisherman and I would like to get a fishing kayak but I don't know if there is a difference, performance wise, between a fishing kayak and a touring/recreational kayak. I don't want to struggle to keep up with my wife if we decide to kayak for 4 to 5 hours on a river or lake.
Would I be able to use a fishing kayak like a regular touring/recreation kayak?

Thanks
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I have used a touring kayak for fishing, and it works out ok. You can rig up a rod holder in your cockpit, but paddling is a bit awkward, though this is probably also a problem with any kayak used for fishing.

It might be somewhat difficult to use a fishing kayak on overnight trips given that most fishing kayaks are sit on top (SOT) and have no internal storage.
I have been considering just the same. I have come up with two kayacks that I like. The first is a fishing kayak by kudo. It tracks well and speed is good. I have a strong upper body so it makes it easier for me but its all in the core. Try different techniques as you will get tired just doing one.

The other kayak is a 14 foot looksha by Necky. I have been eyeing that one for 3 years now. It is a sit in oh the kudo is a sit on top which I stood up in and tried paddle boarding on it. Great stability. The looksha tracks and maneuvers great.

Not stable enough for fishing, what are you going to do when you land the mother of all fishes? How you bring that into the boat? Consider what you do more spending time with the wife or fishing in a kayak?