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Functional dorsoventral symmetry in relation to lift-based swimming in the ocean sunfish Mola mola.

Watanabe Y, Sato K - PLoS ONE (2008)

Bottom Line: We conclude that ocean sunfish have functional dorsoventral symmetry with regards to the non-homologous dorsal and anal fins that act as a pair of vertical hydrofoils.Although sunfish lack a swimbladder, we found that they are neutrally buoyant independent of depth because of their subcutaneous gelatinous tissue that has low density and is incompressible.Efficient lift-based swimming in conjunction with neutral buoyancy enables sunfish to travel long distances both horizontally and vertically.

View Article: PubMed Central - PubMed

Affiliation: International Coastal Research Center, Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate, Japan. watanabe.yuuki@nipr.ac.jp

ABSTRACT
The largest (up to 2 tons) and a globally distributed teleost--the ocean sunfish Mola mola--is commonly regarded as a planktonic fish because of its unusual shape including absence of caudal fin. This common view was recently questioned because the horizontal movements of the ocean sunfish tracked by acoustic telemetry were independent of ocean currents. However, direct information regarding their locomotor performance under natural conditions is still lacking. By using multi-sensor tags, we show that sunfish indeed swam continuously with frequent vertical movements at speeds of 0.4-0.7 m s(-1), which is similar to the records of other large fishes such as salmons, marlins, and pelagic sharks. The acceleration data revealed that they stroked their dorsal and anal fins synchronously (dominant frequency, 0.3-0.6 Hz) to generate a lift-based thrust, as penguins do using two symmetrical flippers. Morphological studies of sunfish (mass, 2-959 kg) showed that the dorsal and anal fins had similar external (symmetrical shape and identical area) and internal (identical locomotory muscle mass) features; however, the muscle shape differed markedly. We conclude that ocean sunfish have functional dorsoventral symmetry with regards to the non-homologous dorsal and anal fins that act as a pair of vertical hydrofoils. Although sunfish lack a swimbladder, we found that they are neutrally buoyant independent of depth because of their subcutaneous gelatinous tissue that has low density and is incompressible. Efficient lift-based swimming in conjunction with neutral buoyancy enables sunfish to travel long distances both horizontally and vertically.

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Depth, swimming speed, spectrogram of lateral acceleration (indicative of fin movements) where magnitude was expressed by color, pitch (red line), and roll (blue line) of an ocean sunfish (mass, 48 kg).Open circles on the spectrogram represent dominant stroke cycle frequencies calculated for each five-minute time bin. Positive pitch represents head-up attitude of the fish, while negative pitch indicates head-down attitude. Positive roll represents right-rotated position of the fish, while negative roll indicates left-rotated position.
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pone-0003446-g001: Depth, swimming speed, spectrogram of lateral acceleration (indicative of fin movements) where magnitude was expressed by color, pitch (red line), and roll (blue line) of an ocean sunfish (mass, 48 kg).Open circles on the spectrogram represent dominant stroke cycle frequencies calculated for each five-minute time bin. Positive pitch represents head-up attitude of the fish, while negative pitch indicates head-down attitude. Positive roll represents right-rotated position of the fish, while negative roll indicates left-rotated position.

Mentions: We recorded behavior of three ocean sunfish (mass, 48, 59, and 153 kg) for 14 h in total (Table 1). According to the recovery points of the loggers, all fish appeared to swim offshore from Otsuchi Bay, which opens to the east, in similar directions (80–89°) at horizontal speeds of 1.5–2.2 km h−1. All fish changed their swimming speeds widely during the first few minutes of the records, possibly due to handling. Then, the fish cruised with frequent vertical movements (Fig. 1). Fin movements were continuous throughout the records, and the frequency was constant within individuals regardless of swimming depth and whether the fish was ascending or descending. Pitch of the fish was close to horizontal when swimming horizontally, head-up (maximum, 65°) when ascending, and head-down (minimum, −55°) when descending. Absolute value of roll remained <30° over 80% of the tag records, and exceeded 30° most commonly during horizontal swimming. In one instance, a fish (mass, 59 kg) accelerated for 15 s up to 2.4 m s−1 horizontally near the surface with a right-rotated position (roll, 48°) and a high stroke cycle frequency (2.0 Hz). During the recordings, no fish drifted on its side at the surface.


Functional dorsoventral symmetry in relation to lift-based swimming in the ocean sunfish Mola mola.

Watanabe Y, Sato K - PLoS ONE (2008)

Depth, swimming speed, spectrogram of lateral acceleration (indicative of fin movements) where magnitude was expressed by color, pitch (red line), and roll (blue line) of an ocean sunfish (mass, 48 kg).Open circles on the spectrogram represent dominant stroke cycle frequencies calculated for each five-minute time bin. Positive pitch represents head-up attitude of the fish, while negative pitch indicates head-down attitude. Positive roll represents right-rotated position of the fish, while negative roll indicates left-rotated position.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2562982&req=5

pone-0003446-g001: Depth, swimming speed, spectrogram of lateral acceleration (indicative of fin movements) where magnitude was expressed by color, pitch (red line), and roll (blue line) of an ocean sunfish (mass, 48 kg).Open circles on the spectrogram represent dominant stroke cycle frequencies calculated for each five-minute time bin. Positive pitch represents head-up attitude of the fish, while negative pitch indicates head-down attitude. Positive roll represents right-rotated position of the fish, while negative roll indicates left-rotated position.
Mentions: We recorded behavior of three ocean sunfish (mass, 48, 59, and 153 kg) for 14 h in total (Table 1). According to the recovery points of the loggers, all fish appeared to swim offshore from Otsuchi Bay, which opens to the east, in similar directions (80–89°) at horizontal speeds of 1.5–2.2 km h−1. All fish changed their swimming speeds widely during the first few minutes of the records, possibly due to handling. Then, the fish cruised with frequent vertical movements (Fig. 1). Fin movements were continuous throughout the records, and the frequency was constant within individuals regardless of swimming depth and whether the fish was ascending or descending. Pitch of the fish was close to horizontal when swimming horizontally, head-up (maximum, 65°) when ascending, and head-down (minimum, −55°) when descending. Absolute value of roll remained <30° over 80% of the tag records, and exceeded 30° most commonly during horizontal swimming. In one instance, a fish (mass, 59 kg) accelerated for 15 s up to 2.4 m s−1 horizontally near the surface with a right-rotated position (roll, 48°) and a high stroke cycle frequency (2.0 Hz). During the recordings, no fish drifted on its side at the surface.

Bottom Line: We conclude that ocean sunfish have functional dorsoventral symmetry with regards to the non-homologous dorsal and anal fins that act as a pair of vertical hydrofoils.Although sunfish lack a swimbladder, we found that they are neutrally buoyant independent of depth because of their subcutaneous gelatinous tissue that has low density and is incompressible.Efficient lift-based swimming in conjunction with neutral buoyancy enables sunfish to travel long distances both horizontally and vertically.

View Article: PubMed Central - PubMed

Affiliation: International Coastal Research Center, Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate, Japan. watanabe.yuuki@nipr.ac.jp

ABSTRACT
The largest (up to 2 tons) and a globally distributed teleost--the ocean sunfish Mola mola--is commonly regarded as a planktonic fish because of its unusual shape including absence of caudal fin. This common view was recently questioned because the horizontal movements of the ocean sunfish tracked by acoustic telemetry were independent of ocean currents. However, direct information regarding their locomotor performance under natural conditions is still lacking. By using multi-sensor tags, we show that sunfish indeed swam continuously with frequent vertical movements at speeds of 0.4-0.7 m s(-1), which is similar to the records of other large fishes such as salmons, marlins, and pelagic sharks. The acceleration data revealed that they stroked their dorsal and anal fins synchronously (dominant frequency, 0.3-0.6 Hz) to generate a lift-based thrust, as penguins do using two symmetrical flippers. Morphological studies of sunfish (mass, 2-959 kg) showed that the dorsal and anal fins had similar external (symmetrical shape and identical area) and internal (identical locomotory muscle mass) features; however, the muscle shape differed markedly. We conclude that ocean sunfish have functional dorsoventral symmetry with regards to the non-homologous dorsal and anal fins that act as a pair of vertical hydrofoils. Although sunfish lack a swimbladder, we found that they are neutrally buoyant independent of depth because of their subcutaneous gelatinous tissue that has low density and is incompressible. Efficient lift-based swimming in conjunction with neutral buoyancy enables sunfish to travel long distances both horizontally and vertically.

Show MeSH
Related in: MedlinePlus