Microscopic Analysis of Two Glands Involved in Osmoregulation in Elasmobranchs: The Rectal Salt and Interrenal Glands of Dasyatis sabina

Date of Award

7-2014

Degree Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Brian M Matayoshi, PhD

Second Advisor

H Keith Brown, PhD

Third Advisor

Mary P Owen, PhD, JD

Abstract

To date there is limited imaging research and anatomical analysis on stingrays reported in the literature. One of the most cosmopolitan groups of fish, stingrays are unique in morphology and can be found from arctic to sub-tropical climates, thriving in oceans, marine coastal environments and freshwater. This environmental flexibility is the result of the active osmotic mechanism, osmoregulation. While some species reside solely in salt water or freshwater, a few other ray species (euryhaline) are able to migrate between brackish, marine and freshwater environments, making them an ideal model for the study of the anatomical adaptations involved in adapting to different osmotic conditions. The purpose of the project was to describe the ultrastructure associated with osmotic accommodations examining the distinctive two zonal and little known osmotic and infrastructure role of the interrenal gland and the known osmotic and salt secreting role of the rectal gland of the euryhaline stingray, Dasyatis sabina. One male and one female Dasyatis sabina were caught from the brackish estuaries of the St. Johns River in Jacksonville, Florida and then perfused through the conus arteriosus with Elasmobranch Ringer Solution, followed by 2.5% glutaraldehyde/2% paraformaldehyde fixative in 0.133M Sorenson's buffer. A blood sample was taken prior to perfusion to analyze hematocrit, key electrolytes, and other solutes that aid towards internal fluid retention. The interrenal and rectal tissues were excised, fixed and sectioned for microscopic examination using a high resolution JEM 1210 transmission electron microscope. Imaging revealed that both tissues exhibited extensive interdigitation of basolateral membrane folding with occasional cell-cell protein complex junction of the zonula adherens type. The tissues also displayed a large number of columnar and cuboidal epithelial cells with occasional largely opaque nucleus, abundant cellular granules and lysosome clusters, and densely packed and abundant round and rod shaped mitochondria. These findings are consistent with the structural expectations for cellular membrane mechanisms involved with osmoregulation of fluid compartments in larger organisms and suggest that further description of the cellular function of both of these tissues is important to the understanding of how this species is able to adapt to large osmotic changes in its environment.

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