Let's consider a few things here; 1-By 'on plane' I am assuming you mean over 25 mph, so when you consider the size and species of the fish, the diameter of the cone angle at the depth of the fish, and the speed of the boat traveling over the fish, you are likely already marking fish, but, they would be very small specks or dots on your screen. And it doesn't really matter which transducer you are using. There's just not much you can do about it! If you really want a different transducer you can check Airmar's fine line-up. You can spend from about $135 to about $800 and you will get marked improvement in your target seperation and identification, but I doubt you will be able to see fish arches while on plane. If you do pull the plug on a new ducer, remember to change the transducer selection to the proper model in the 'Installation' part of your Sonar/Sonar menu.
Edd