If I buy a new fish finder, can I still use my old transducer?

I have an old (late 80s-early 90s) Humminbird finder and was looking to upgrade. If I get a new Humminbird (looking at a 525 or Piranha), can I continue to use the same transducer, or do I need to us the one that comes with the new finder? Will I be able to use the same mount/bracket that’s already on my boat (at the bottom of the transom)? Also, if I decide to go with a brand besides Humminbird, will I need to remount another new bracket, or are all the brackets pretty much alike? I’m trying to save time, money, and holes in my boat. Thanks everybody!

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