A Study of Behavioral Patterns and Biomechanics of Head-Tail Display in Paradise Fishes (Macropodus opercular L.)

• Main Authors: Yi-Ping Tszng, 曾億萍
• Other Authors: 紀凱容
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/31207855851040552641

碩士 === 國立中興大學 === 生物物理學研究所 === 99 === Male paradise fishes Macropodus opercularis L. fight for territory during breeding season. During fighting a distinctive behavior, so-called “Head-Tail Display” (HTD), can be observed and characterized by the opponents following the other’s tail leading to swimming in a rotational fashion, with bodies oriented in parallel and bended in J-shape. After several rounds of HTD, the dominant fish might be determined; but previous studies never investigated the role of HTD during fighting. It is also unclear how flapping of pectoral fins might affect the motion of two fishes during HTD. In this study, I examined the behavioral patterns and kinematics of pectoral fin flapping during HTD, and assessed the physical factors that might determine the results of fighting. To this end, the fighting behaviors were recorded from the top using a regular speed DV (30 fps) and a high-speed video camera (500 fps), from which the flapping frequency and amplitude of pectoral fins were analyzed. The period of HTD could be determined quantitatively as the time between maximum and minimum angular velocity of the pectoral fins. My results show that: (1) Despite lower moving speed (0.73±0.26 BLs-1, N=20) than that of swimming (1.37±0.37 BLs-1, N=17), during HTD the flapping frequency, position, and amplitude of pectoral fins are significantly greater. During swimming, the pectoral fins flapped at 4.11±1.51 Hz, with amplitude of 30.38±3.68° from the position of 32.56±3.52°. But during HTD, the pectoral fins flapped at 8.52±1.34 Hz, with amplitude of 48.91±6.05° from 84.23±13.45°, a position farther away from the body. (2) During HTD, the flapping frequency and amplitude were not significantly different between two fishes. However, whether it started HTD earlier (the attacker, A) or later (the defender, D), the pectoral fin of the inner side (near the opponent) flapped at an angle (A: 92.06±10.94°; D: 94.45±8.73°) significantly greater than that of the outer side (far from opponent; A: 75.83±8.78°; D: 74.58±11.84°). Therefore, the inner fins flapped at an angle close to 90° would have greater opportunity to touch its opponent’s body, while the outer fins provided the force (and moment) to maintain rotational motion. (3) The dominances and submissions had similar flapping frequency and amplitude, but the dominances spent more power (0.89±0.55 x 10-4 J/s) flapping the inner fins than the submission do (0.70±0.36 x 10-4 J/s). The dominances flapped their inner fin from a position of 93.60±6.90°, making them easier to transmit mechanical signals to the opponents than the submissions do (119.04±7.40°). Furthermore, the dominances had different flapping angles between two sides allowing it to rotate; while the submissions had similar angles, both greater than 90°, for backward retreat from the HTD pairing. (4) Observations of the whole fighting periods show that in some cases, the dominance could be determined in less than three HTD events and no fish was injured; however, when HTD events were greater than eight times fishes would begin more aggressive behaviors like biting or mouthlocking, increasing the risk of injury. In conclusion, during HTD, the male paradise fishes could control flapping of their pectoral fins to adjust their motion and relative position to each other, and could also affect the transmission efficiency of mechanical signals. Hence HTD provides both functions in display and mechanical rivalry that can reduce injury from aggressive fighting.