P2.75 Thursday, Jan. 5 Structure and Growth of the Paddlefish Rostrum: Investigating Vertebrate Postembryonic Morphogenesis ROBERTSON, J.C.; Westminster College, PA email@example.com
Paddlefish (Polyodon spathula) are native to North American river systems and are known for the prominent rostrum that extends from their head. As chondrosteans, paddlefish exhibit other interesting adaptations - including a derived cartilaginous skeleton. Interestingly, paddlefish hatch with no rostrum; under good growth conditions, the rostrum is first evident at about 30 days post-hatching and quickly grows to represent a third of the total body length of the fish. As such, the paddlefish rostrum offers a remarkable case of postembryonic morphogenesis in a vertebrate. This report describes studies of the structure and growth of the rostrum of juvenile paddlefish. Internally, the rostrum is characterized by a medial hyaline cartilage element that is continuous with the skull and features a lipid-filled medullary cavity. Extending laterally from the cartilage core are fibrous connective tissue wings rich in randomly oriented collagen-like fibers. The shape and relative areas of these three major compositional elements (cartilage, cavity and wings) changes along the length of the rostrum. Superficially, the lateral wings are sites of high concentrations of the well-described ampullary electroreceptors that are involved in prey detection. A single “U”-shaped lateral line canal running the length of the rostrum is located in the medial wing in a ventral position. This water-vibration sensing structure is continuous with the head lateral line canal system and makes a turn near the rostrum tip. Neuromasts, a “C”-shaped surrounding support structure, and accessory canals open to the external environment are significant features of the rostrum lateral line. Results of this work contribute to our understanding of the anatomy of this species and reaffirm that the paddlefish rostrum may be a subject of interest in studies of chondrogenesis and developmental sensory neurobiology.