Mystery bone identified

Our story begins with the finding of a strange bone on a bank of the Tweed River. A photo was sent to the Museum for identification...

I recognised it as one of the head bones of a large fish - the preopercular bone to be precise. This boomerang-shaped bone lies between the cheek and the gill cover.

Ordinarily I would have said “It’s a fish preopercle.” and left it at that, but the spines and serrations on this bone are very distinctive.  My curiosity was piqued.

I had a quick cruise on the web (as you do!) searching on keywords such as 'fish', 'bone', 'serrated', 'spines' etc.,  without luck.

The next step was to consult a classic book on fish skulls (see below). After making some educated guesses (that were way off!) I found an illustration of the skull of a Nile Perch, Lates niloticus, which looked very similar but lacked the long row of serrations.

My next thought was “Aha! What about Lates calcarifer”. This species, better known to most people as the Barramundi, is in the same genus ‘Lates’, as the Nile Perch. I checked the museum’s database to see if the collection contained any skulls. It did!  

After a jog up the stairs to the skeleton area (I was pretty excited by this stage), I opened the relevant cupboard to reveal a large box inside which was the skeleton of a Barramundi. Even more exciting was the fact that its preopercular bone had a distinctly serrated posterior margin (see top photo on the right).

Ok, one mystery solved.  The other mystery is why would the preopercle from a pretty good sized Barramundi be found on the banks of the Tweed River? Despite finding released Barramundi well south of the Tweed River, the 'official distribution' of the species records it only as far south as the Fitzroy River, about 600 km to the north. So, why was the bone on the bank of a river in northern New South Wales? I can’t answer that!

Reference:

Gregory, W.K.1959. Fish skulls; a study of the evolution of natural mechanisms. Laurel, Florida, E. Lundberg. Pp. 481.