Definitely some type of schooling fish in that snapshot but no way to tell what they are. There is one larger fish that looks like it took off. On the left side there is a line that starts at about 30 feet and runs out to about 70 feet – this could be a larger fish that was swimming away from the boat but managed to stay in the thin Si beam or it could be some kind of a cable. Sonar can only show you that some type of fish is present; you will still have to use your own knowledge of what species of fish are in that water, where they would be for the time of year and weather as well as how they will respond to each other (schooling type fish?) or the presence of a boat.