Characterization of Andrenocortical Tissue Morphology, Histology, and Steroid Synthesis Among Finetooth (\u3ci\u3eCarcharhinus isodon\u3c/i\u3e), Blacktip (\u3ci\u3eCarcharhinus limbatus\u3c/i\u3e), Atlantic Sharpnose (\u3ci\u3eRhizoprionodon terraenovae\u3c/i\u3e), and Bonnethead (\u3ci\u3eSphyrna tiburo\u3c/i\u3e) Sharks

Adrenocortical (interrenal) tissue is composed of steroidogenic cells that produce corticosteroids involved in the stress response and hydromineral balance. Previous research characterizing the elasmobranch interrenal suggests that the number of interrenal bodies that produce the single primary corticosteroid, 1a-hydroxycorticosterone (1a-OHB), varies among species. However, potential species-specific differences in the amount of interrenal tissue and major steroid products produced have been understudied. To address this critical gap in our understanding of elasmobranch biology, this study examined interrenal morphology, cell structure, steroidogenic enzyme distribution (3bHSD), and steroid production in four shark species: Finetooth Carcharhinus isodon, Blacktip Carcharhinus limbatus, Atlantic Sharpnose Rhizoprionodon terraenovae, and Bonnethead Sphyrna tiburo. Morphological analysis revealed differences in interrenal structures among species. Finetooth and Blacktip Sharks have numerous discrete white interrenal bodies along the dorsal midline of the kidney. The Atlantic Sharpnose Shark interrenal is a single yellow-white to dark green body along the kidney midline. Bonnethead sharks possess one thin strip of white tissue extending from the anterior potion of the kidney ending past the division of the kidney lobes. Histological assessment of cell type and 3bHSD expression confirmed putative interrenal cytology and steroidogenic potential among all species. Ex vivo tissue incubations confirmed steroidogenesis and validated 1a-OHB as the dominant steroid product; however, corticosterone (B) and deoxycorticosterone (DOC) were also produced. This study is the first to describe interrenal morphology in Atlantic Sharpnose and Bonnethead sharks. These results advance our understanding of elasmobranch corticosteroid production as well as potential mechanisms for species-specific responses to acute and chronic stress