Archerfish use their shooting technique to produce adaptive underwater jets

Abstract

Archerfish are renowned for dislodging aerial prey by well-aimed shots of water. Recently it has been shown that these fish can shape their aerial jets by adjusting the dynamics of their mouth opening and closing. This allows the fish to adjust their jet to target distance so that they can forcefully hit prey over considerable distances. Here we suggest that archerfish use the same technique to also actively control jets under water. Fired from close ranges the underwater jets are powerful enough to lift up buried food particles, which the fish then can pick up. We trained fish so that we could monitor the mouth opening and closing manoeuvers during underwater shooting and compare them with those employed in aerial shooting. Our analysis suggests that the fish use the same dynamic mechanism to produce aerial and underwater jets and that they employ the same basic technique to adjust their jets in both conditions. When food is buried in substrate that consists of larger particles the fish use a brief pulse but a longer one when the substrate is more fine-grained. These findings extend the notion that archerfish can flexibly shape their jets to be appropriate in different contexts and suggest that archerfish shooting might have been shaped both by constraints in aerial and underwater shooting.