Evolution of Terrestrial Behaviors in Aquatic and Amphibious Fishes

Fishes are generally thought to be fully aquatic organisms, but many fishes have evolved mechanisms that facilitate terrestrial excursions. When stranded on land, fishes can respond with a variety of behaviors to bring them back to water. Because mostly aquatic fishes are not frequently observed on land, not much is known about their behaviors once stranded. This begs the question as to whether these fishes evolved mechanisms to facilitate adequate terrestrial locomotion when compared to amphibious fishes. Hypothesis: fishes that rarely leave the water will jump quickly and often as a means to return to the water quickly as they may not have evolved mechanisms to survive for long periods on land. For this experiment, a variety of teleost fishes with disparate terrestrial inclinations were used to investigate their response to being stranded. We used amphibious fishes (mummichog, mosquito fish, and guppies) that have all been observed to voluntarily leave the water and move on land and compared these to fishes considered to be fully aquatic (longfin and wildtype zebrafish) that are not known to voluntarily leave the water. Fishes were stranded in a plastic arena and their voluntary response to being stranded was recorded for 2 minutes. Using these videos, we measured how many times the fishes flopped and jumped, measured the distance of each jump, the total distance moved, and how quickly it took the fish to start moving. We found that longfin and wildtype zebrafish took less time to begin moving, moved more often, spent more time moving, and traveled a greater distance than the amphibious fishes. Interestingly, the amphibious fishes barely made any movements over the two-minute stranding period. These results indicate that fishes that rarely leave the water are still capable of producing effective and coordinated overland movements although, their frequent behaviors indicate that these fishes have not evolved mechanisms to remain out of water for extended periods and must quickly return to water if stranded