A common mistake anglers make is thinking that a long arch means a big fish. A long arch only means that a fish was in your sonar cone for a longer period.
Individual Fish (A). The best indicator of fish size is the width of the fish arch. If an arch or line is thick and color intense, then you’re marking a bigger fish.
School of Fish (B). Depending on the type of school, they can appear as groups of small arches or dense clusters with intense coloring.