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Elasmobranch endocrinology is complex, but the organs, stimuli, and targets of action are similar to other vertebrates.

The pituitary is similar to teleosts, with slight anatomical variations. It produces growth, thyroid, reproductive, and vasopressin‐like hormones (Anderson 2015). The hypothalamus (within the diencephalon) is a well‐developed organ. It is important for feeding, reproduction, aggression, and likely migration (Hofman 1999).

The interrenal gland (equivalent of the mammalian adrenal cortex) is grossly visible as a section of yellow tissue between each kidney. It is long, thin strip in sharks and a smaller oval in skates and rays (Figure A1.20). The chromaffin cells of the suprarenal bodies are separate and located on the dorsal kidneys near the dorsal aorta (Anderson 2015). The hypothalamo‐pituitary‐interrenal axis is considered the endocrine stress axis, although this has not been fully characterized in elasmobranchs (Shuttleworth 2012).

The single thyroid gland is encapsulated and varies in size and shape across species. In batoids, the thyroid is usually located ventral to the pharynx near the bifurcation of the ventral aorta. In sharks, it is under the commissure of the mandible. The ultimobranchial bodies produce calcitonin, similar to the mammalian parathyroid system although the actions of calcitonin in cartilaginous fish are less well‐understood (Anderson 2015). In batoids, the ultimobranchial bodies are paired and found in the caudal wall of the pericardial cavity. In sharks, they are only on the left side of the body on the dorsal wall of the pericardial cavity (Stoskopf 1993).

Figure A1.20 Interrenal gland (arrow) between the kidneys removed from a southern stingray (Hypanus americanus).

Source: Image courtesy of Catharine Wheaton, Disney’s Animals, Science and Environment.

The bilobed pancreas and gastrointestinal tract produce the expected hormones, though detail on their function and activity are limited. The heart and kidney can also be considered endocrine glands as they produce several natriuretic peptides and have a renin–angiotensin system which regulates the renal and cardiovascular systems (Anderson 2015).

The pineal organ and gonads also have endocrine functions.