What is a large fish ?

[Herbert Lorenzo]

I was looking over the instruction booklet that came with some of my old and some of my newer fish finders and noticed for those that opt for fish Id  mode ...you have small , medium  and large fish symbols. What does that mean ? A small Great White or a large Bass ? Just random thought .

[813basstard]

My graph shows their blood pressure and cholesterol level. If they seem high or smoke heaters, I go for those. The jerks swimming around for exercise and such I leave them be. 

 

Hope this helps

[papajoe222]

Seriously, all those fish symbols represent is how strong the return signal is. The stronger/longer the signal is returning to the unit, the larger the symbol. You could have@1lb. bass suspending directly under your transducer and get a big fish symbol, or an 8lb. bass swim past the outer edge of the transducers cone show up as a small symbol. 
Turn off the fish ID and check out how to read the sonar screen either on simulator mode, or check out some YouTube videos. 

[WRB]

Understand what the 2D sonar signal is and what it isn't.

What it isn't is a sonar return of a fish body mass. 

What it is a sonar return of the fish airbladder. Air/gas is far more dense to sonar then tissue or bones.

Air bubble coming out of the lake bottom is shown the same as a fish.

Tom