Meeting Abstract

P1-142   -   Cell and tissue composition of paddlefish gill rakers Robertson, JC; Westminster College PA robertjc@westminster.edu

As filter-feeding planktivores, juvenile and adult paddlefish (Polyodon spathula) rely on their gill rakers for nutrient acquisition. Paddlefish have single rows of hundreds of long, fine, bristle-like rakers that extend from the sides of the gill arch cartilage bars. In feeding, separation of the gill arches and elevation of the rakers creates a sieve-like trap for water and food particles exiting the oropharynx. In cross section, individual rakers are diamond to pyramid shaped, depending on age of the fish; rakers increase in length and width with body growth. Biochemical (SDS PAGE) and histochemical (Von Kossa staining) evidence suggests that the largely acellular core of the rakers is calcified keratin. Histological observations indicate that the rakers are vascularized. One to several layers of epithelium overlie the rakers. Staining with PAS reveals large numbers of superficial mucus cells, restricted to the arch-facing raker surfaces. Rakers anchor at their gill arch origins by a hairpin loop. Given their central role in obtaining food, results are discussed in terms of the functional morphology of paddlefish rakers. In addition, models for the morphogenesis and mechanism of growth of paddlefish rakers are proposed. Paddlefish gill raker structure is compared with that of other acipenseriformes and other species of fish. This work contributes to understanding of the feeding ecology and basic biology of this remarkable and vulnerable species.