Figure 2. Loss of collective behaviors in cavefish. The visual sense is depicted by dotted lines. The lateral line, neuromast-mediated sense is depicted by thunderstorm arrows. (A) Surface fish shoal or school. This collective behavior is dependent on the lateral line system.⁸ The dominant fish in the school has low raphe 5HT levels (gray fish). Prey detection and escape from predators also depend on the lateral line, but relies heavily as well on the visual sense in a lighted environment. (B) Blind cavefish do not shoal or school, they perform isolated swim. Their increased lateral line helps them navigate in the dark and finding food through the VAB (vibration attraction behavior),² in the absence of visual sense. Their motivation to search and find food is high, probably governed by hypothalamic circuits, including a large 5HT neuronal group.