Meeting Abstract

54.2  Thursday, Jan. 6  Dorsal Fin Muscle Activity During Steady Swimming in Two Shark Species MAIA, Anabela*; WILGA, Cheryl D.; Univ. of Rhode Island; Univ. of Rhode Island amaia@my.uri.edu

Elasmobranch dorsal fins have simpler muscoskeletal systems than teleost fishes. This has not deterred elasmobranchs from occupying most available ecological niches. The goal of this study was to examine dorsal muscle activity during steady swimming in two shark species that occupy different niches. Spiny dogfish, Squalus acanthias, cruises open waters, occasionally inhabiting coastal areas. While white spotted bamboo sharks, Chiloscyllium plagiosum, is a reef dwelling species with strong benthos reliance. To look at fin function, we swam three sharks of each species in a flow tank at two different speeds, 0.50 and 0.75BL/s, and bilaterally recorded muscle activity in three locations along each dorsal fin muscle. We also implanted the epaxial musculature to relate activity to tail beat cycle. Activity was present in all the muscles tested during each tail beat. Dorsal fin muscle burst duration was longer at the 0.5BL/s than at 0.75BL/s for spiny dogfish but not for bamboo sharks. Each dorsal fin muscle appears to be working as a unit. However, left and right asynchrony was evident in both dorsal fins in bamboo sharks at both speeds, while asynchrony was only present in spiny dogfish second dorsal. Fin activity is consistent with previous kinematic data indicating thrust function of bamboo shark dorsal fins at both speeds. Lack of differences in burst duration with increasing speed in bamboo sharks suggests that increased speed is achieved by higher tail beat frequency, while dorsal fin activity is already maximized. Dogfish first dorsal fin appears to function as a stabilizer, as left and right muscles are activated at the same time likely stiffening the fin. In contrast, second dorsal fin is actively moving sideways acting potentially as a thruster.