Many people are interested in the question: does the echo sounder scare the fish? It is very difficult to give a definite answer, since everything depends on each specific case, namely: fishfinder echo sounder
what specific fish are you interested in;
“character” of the fish: is it active or passive;
what is the depth?
fish on the open bottom or in snags;
what boat does the fisherman use;
geographical location (whether the fish is familiar with humans).
On a wild reservoir somewhere in the north, the pulses of the Lucky echo sounder are more likely to attract fish with their novelty. But at the same time, the same fish in similar conditions, but only in a densely populated fishing area, can perceive the sound of an echo sounder quite warily, since it will be associated with recent life-threatening events. But, nevertheless, having communicated with many fishermen and listening to different stories, plus everything, comparing my own experience, I will say that the echo sounder does not scare the fish at all, so you don’t have to turn it off, except to save the battery.
Another question that I often heard: Is it possible to detect fish if you “shine” the sensor from the boat, and what will happen?
Nothing will happen. For such purposes, a classic boat echo sounder will not be suitable, since the echo sounder will stop perceiving space when the bottom disappears, and the impulse will have nothing to reflect from. There are echo sounders for side viewing, but I have never heard good reviews about budget echo sounders, and industrial ones are too expensive.