No abstract

SUMMARYElasmobranch fishes are thought to possess greater olfactory sensitivities than teleost fishes due in part to the large amount of epithelial surface area that comprises their olfactory organs; however, direct evidence correlating the size of the olfactory organ to olfactory sensitivity is lacking. This study examined the olfactory morphology and physiology of five distantly related elasmobranch species. Specifically, we quantified the number of lamellae and lamellar surface area (as if it were a flat sheet, not considering secondary lamellae) that comprise their olfactory organs. We also calculated the olfactory thresholds and relative effectiveness of amino acid odorants for each species. The olfactory organs varied in both the number of lamellae and lamellar surface area, which may be related to their general habitat, but neither correlated with olfactory threshold. Thresholds to amino acid odorants, major olfactory stimuli of all fishes, ranged from 10 -9.0 to 10 -6.9moll -1 , which indicates that these elasmobranch species demonstrate comparable thresholds with teleosts. In addition, the relative effectiveness of amino acid stimuli to the olfactory organ of elasmobranchs is similar to that previously described in teleosts with neutral amino acids eliciting significantly greater responses than others. Collectively, these results indicate parallels in olfactory physiology between these two groups of fishes.

The distribution and density of the ampullary electroreceptors in the skin of elasmobranchs are influenced by the phylogeny and ecology of a species. Sensory maps were created for 4 species of pristid sawfish. Their ampullary pores were separated into pore fields based on their innervation and cluster formation. Ventrally, ampullary pores are located in 6 areas (5 in Pristis microdon), covering the rostrum and head to the gills. Dorsally, pores are located in 4 areas (3 in P. microdon), which cover the rostrum, head and may extend slightly onto the pectoral fins. In all species, the highest number of pores is found on the dorsal and ventral sides of the rostrum. The high densities of pores along the rostrum combined with the low densities around the mouth could indicate that sawfish use their rostrum to stun their prey before ingesting it, but this hypothesis remains to be tested. The directions of ampullary canals on the ventral side of the rostrum are species specific. P. microdon possesses the highest number of ampullary pores, which indicates that amongst the study species this species is an electroreception specialist. As such, juvenile P. microdon inhabit low-visibility freshwater habitats.

openAccessArticle: TruePage Range: R150-R150doi: 10.1016/j.cub.2012.01.055Harvest Date: 2016-01-12 15:12:37issueName:cover date: 2012-03-06pubType: Correspondenc

Although the majority of batoid elasmobranchs, skates and rays, are benthically associated, benthic locomotion has been largely overlooked in this group. Only skates have been previously described to perform a form of benthic locomotion termed "punting." While keeping the rest of the body motionless, the skate's pelvic fins are planted into the substrate and then retracted caudally, which thrusts the body forward. In this study, we demonstrate that this form of locomotion is not confined to the skates, but is found across a range of phylogenetically and morphologically diverse batoid species. However, only the clearnose skate, Raja eglanteria, and the lesser electric ray, Narcine brasiliensis, performed "true punting," in which only the pelvic fins were engaged. The yellow stingray, Urobatis jamaicensis, and the Atlantic stingray, Dasyatis sabina, performed "augmented punting," in which pectoral fin movement was also used to generate thrust. Despite this supplemental use of pectoral fins, the augmented punters failed to exceed the punting capabilities of the true punters. The urobatid and the true punters all punted approximately half their disc length per punt, whereas the dasyatid punted a significantly shorter distance. The skate punted significantly faster than the other species. Examination of the pelvic fin musculature revealed more specialized muscles in the true punters than in the augmented punters. This concordance of musculature with punting ability provides predictive power regarding the punting kinematics of other elasmobranchs based upon gross muscular examinations. In contrast to previous assumptions, our results suggest that benthic locomotion is widespread among batoids.