| pubmed-article:1518982 | pubmed:abstractText | We have investigated structure and function of the external gill filaments, which occur transiently in the embryonic little skate, Raja erinacea. Approximately 25-30 days after spawning (body mass 0.03-0.05 g) external gill filaments appear as an outgrowth from the caudal side of the gill arches. These filaments are thread-like, each containing one afferent and one efferent blood vessel, and by day 70-75 (body mass 0.4-0.5 g) they reach their maximum size at a length of about 1 cm and a blood vessel diameter of 70-80 microns. Subsequent resorption of the filaments is characterized by a decrease in both length and diameter of the blood vessel. By day 90-95 (body mass 0.9-1.0 g) the external gill filaments are completely resorbed and replaced by internal gills. Blood velocity, measured in these external filaments, increased with development from 0.1 mm.sec-1 to about 0.7 min.sec-1, and decreased again during resorption. Blood flow, calculated therefrom with blood vessel diameter, showed a similar maximum curve. A model analysis supports the hypothesis that in a full grown filament respiratory gas exchange is mainly perfusion-limited and can contribute significantly to the total oxygen uptake of the embryo. Analysis of the results indicates, however, that the gill filaments are not adequate as a gas exchange organ for later developmental stages. | lld:pubmed |
