What is the modern technology for fishing devices used to monitor fish presence in the ocean?

I’ve heard it called a fish finder by some who use them.

Fortuna
Raytheon

Make the best electronic devices for locating fish. Those who sold you the boat know which one is right for you.

When you said ya’ wanted to make some money to payoff your boat, etc., I’m assumin’ you be referrin’ ta’ commercial fishing?? Lowrance has high quality instrumentation and in my opinion are one of the best fish finders on the market (only my opinion). Be a good idea when ya’ do decide on brand, is make sure one has GPS (Global Positioning System) here is a link that will give pretty much in depth, what the GPS system does.

Good luck and hope this helped ya’ out somewhat!?