Tiny fins drive them leisurely forward – but seahorses impressively offset their modest swimming abilities, according to a study. Lightning-like head movements turn the bizarre fish into high-speed hunters of the seas: They can make their “horse’s head” snap upwards in up to 0.002 seconds, so that a powerful stream of water carries the prey into their muzzle. The suction is about eight times stronger than in “normal” fish of comparable size, the researchers report.
Their head shape reminds us of a horse, they are upright in the water and their abdomen functions as a gripping arm: Due to their strange characteristics, the seahorses are prominent among the inhabitants of the seas. Although they hardly look like other fish, they are representatives of the pipefish-like (Syngnathiformes), which in turn belong to the large group of ray-fins. The unusual characteristics of the seahorses are the result of adaptations to a life as a lurking predator: Seahorses usually hold onto corals or seaweed with their prey tails and wait until small prey animals come within their reach. For locomotion they have a hem-like dorsal fin, which can only provide modest propulsion.
Seahorse snouts in sight
In addition, the seahorses lack the strong muscles that other predatory fish quickly open their mouths to suck in food. Nevertheless, they successfully prey on crustaceans that are capable of extremely nimble evasive maneuvers. They are already known to use a mechanism associated with the equine appearance of their head to do this. Instead of a muscle contraction, the discharge of tension energy ensures the movement: In the downward tilted position of the head, energy is stored in two elastic tendons, which can be suddenly relaxed like a crossbow. When catching prey, the seahorse’s head jerks upwards. This creates a suction in the snout, which carries the victim into the throat.
Details of this mechanism have so far remained unclear, however, and also how effective the process is in comparison to the usual, muscle-strength-based suction process for fish. Corrine Avidan and Roi Holzman from Tel Aviv University have dedicated themselves to this research topic. As part of their study, they examined the prey catching behavior of three seahorse species from the Red Sea. High-speed cameras and laser technology were used to record head movements and the effects of currents in the seahorses’ hunting behavior. At the same time, the scientists carried out the experiments with “normal” fish species of similar body size, which snap with their mouths through muscle power.
Powerful natural patent
The results of the investigation made it clear that the spring mechanism enables the seahorses to have outstanding hunting capabilities. According to this, they can make their head spin up within around two milliseconds. The comparison fish, however, took 41 milliseconds to open their mouths. This difference was also reflected in the suction power, the analyzes showed: The seahorses were therefore able to provide an approximately eight times stronger water flow in order to transport the prey into their throats. “The ability of the seahorses to create a quick suction through their alternative mechanism is really amazing,” sums up Avidan.
As the scientists finally emphasize, the spring mechanism remains an exciting research topic. Because other representatives of the pipefish also use charged tension energy in the hunt – although not as highly developed as with the seahorses. “An open question now remains as to how and when this concept came about in the course of evolution. I hope that our study will lead to further research that will help uncover more of the secrets of this unusual group of fish, ”says Holzman.
Source: Tel Aviv University, Article: Experimental biology, doi: 10.1242 / jeb.243282