but plenty of snapper have them!!i only seen a few of them years back but they are getting more common these days

But nearly every (if not all) snapper I've filleted has them, and the bigger snapper have the bigger ones.

Could be where they've had a broken bone and the callus forms around the break before it heals.

Have seen it in most other fish as well, not just pinkies.

In fish they are similar. Googling Exostosis snapper I found this:

"fish hyperostoses. They are not uncommon in older specimens of the snapper Sparus auratus and are also reported in 92 other species of marine bony fish in 22 families. Hyperostoses take the form of regular, cellular swellings in otherwise thin, acellular bone, such as vertebral spines or the thin bones of the skull. In each species they generally occur in the same specific places.The Australian old-man snapper that the questioner enjoyed so much is characterised by a bony knob or casque on the back of the skull, which is another example of hyperostosis. Fish hyperostoses also occur as fossils (sometimes called fossil brains by collectors), and have been the subject of research for a long time. They are often known as "Tilly bones" by palaeontologists, after the palaeoneurologist Tilly Edinger (1897-1967), who made them a special interest.Hyperostoses do not seem to inconvenience the fish and are apparently not pathological, but their purpose is uncertain. However, because they occur only in tropical and subtropical marine fish (plus a few temperate species such as the snapper), and a couple of species of freshwater fish in hypersaline environments, it is thought that they may play some part in calcium regulation.Neville Pledge, South Australian Museum, Adelaide, Australia"

Breaking some scientific words down: Hyper = over or bigger, -ostosis = pertaining to bone, a problem or pathology.

Hope that helps. Out of interest surfers or swimmers in cold water get a similar problem in their ears called surfers ear.

Neels

Intresting , wondering what they where last i caught a decent snapper .

Of all the snapper I have caught in SA over the past 3 years almost all over about 4kg have the same thing. Some 1 some 2 or 3.Makes no difference to the quality of the fish. Some of the fish over 10kg have them the size of golf balls.