Hydrodynamic function of dorsal and anal fins in brook trout(Salvelinus fontinalis)

Abstract

SUMMARY Recent kinematic and hydrodynamic studies on fish median fins have shown that dorsal fins actively produce jets with large lateral forces. Because of the location of dorsal fins above the fish's rolling axis, these lateral forces, if unchecked, would cause fish to roll. In this paper we examine the hydrodynamics of trout anal fin function and hypothesize that anal fins,located below the fish's rolling axis, produce similar jets to the dorsal fin and help balance rolling torques during swimming. We simultaneously quantify the wake generated by dorsal and anal fins in brook trout by swimming fish in two horizontal light sheets filmed by two synchronized high speed cameras during steady swimming and manoeuvring. Six major conclusions emerge from these experiments. First, anal fins produce lateral jets to the same side as dorsal fins,confirming the hypothesis that anal fins produce fluid jets that balance those produced by dorsal fins. Second, in contrast to previous work on sunfish,neither dorsal nor anal fins produce significant thrust during steady swimming; flow leaves the dorsal and anal fins in the form of a shear layer that rolls up into vortices similar to those seen in steady swimming of eels. Third, dorsal and anal fin lateral jets are more coincident in time than would be predicted from simple kinematic expectations; shape, heave and pitch differences between fins, and incident flow conditions may account for the differences in timing of jet shedding. Fourth, relative force and torque magnitudes of the anal fin are larger than those of the dorsal fin; force differences may be due primarily to a larger span and a more squarely shaped trailing edge of the anal fin compared to the dorsal fin; torque differences are also strongly influenced by the location of each fin relative to the fish's centre of mass. Fifth, flow is actively modified by dorsal and anal fins resulting in complex flow patterns surrounding the caudal fin. The caudal fin does not encounter free-stream flow, but rather moves through incident flow greatly altered by the action of dorsal and anal fins. Sixth, trout anal fin function differs from dorsal fin function; although dorsal and anal fins appear to cooperate functionally, there are complex interactions between other fins and free stream perturbations that require independent dorsal and anal fin motion and torque production to maintain control of body position.

Hydrodynamic function of dorsal fins in spiny dogfish and bamboo sharks during steady swimming

“…However, a stabilizing function may incur locomotor costs as drag is increased and reduces downstream flow. A similar function of the dorsal fin for stabilization coupled to a slightly different behavior has been demonstrated in brook trout (Standen and Lauder, 2007).…”

“…The first dorsal fin is relatively stiff (Maia and Wilga, 2013a) and the lack of fin bending during propulsion results in a different lateral velocity pattern and the lack of jet formation. In teleost fishes, fins functioning as active stabilizers beat laterally, producing large lateral forces, as shown by flow visualization data from the dorsal fin of brook trout (Standen and Lauder, 2007). In spiny dogfish, for the first dorsal fin, x (mm)…”

“…Longitudinal and lateral components are indicators of forces contributing to thrust and stabilization, respectively (e.g. Drucker and Lauder, 2001;Standen and Lauder, 2007).…”

“…Studies of flow visualization have been applied to pectoral fins Lauder, 2000, 2001;Lauder et al, 2006), caudal fins (Lauder, 2000;Drucker and Lauder, 2000;Wilga and Lauder, 2004a;Tytell and Lauder, 2004), dorsal fins Lauder, 2001, 2005;Tytell, 2006;Standen and Lauder, 2007) and pelvic fins (Standen, 2010) in a diversity of fishes, but the hydrodynamic function of dual shark dorsal fins has not yet been analyzed.…”

Experimental hydrodynamics imaging and undulatory movement equation of steady swimming fish (Pangasius sanitwongsei)

“…In 2007, Standen and Lauder presented that the dorsal fins produce vortices that are encountered by the caudal fin. These vortices can increase the thrust produced by caudal fins [7].…”