Monkfish

The monkfish is a deepwater fish weighing up to 70 lbs., with skin instead of scales and a toothy mouth that can be more than a foot wide.

In the mid-19th century, an ichthyologist named Heinrick Brockmann described marble-sized protrusions inside the monkfish's abdominal cavity, which he named "Brockmann's bodies."  Decades later, physiologists recognized them as hormone-secreting cells which, unfortunately for Heinrich Brockmann, had already been named for someone else:  Paul Langerhans.

The islets of Langerhans are the source of a variety of hormones, including insulin. The most famous example of their malfunction is diabetes, in which a lack of insulin causes a build-up of sugar in the blood that can slowly damage the blood vessels, eyes, kidneys and other organs.  In other vertebrates, the islets are just tiny clusters of cells scattered throughout the tissues of the pancreas; but in the monkfish, they come in accessible globs attached to the abdominal tissues.

One monkfish yields 20 to 40 times more islet tissue than can be obtained through other methods.

Diabetes research with monkfish could have implications for many hormones other than insulin. No enzyme normally involved in processing hormones has yet been characterized in any vertebrate. The monkfish model may provide one of the first full descriptions of this phenomenon.