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RFF - The Snapper's Knob?
I thought that, being winter at the time of writing this one, it's only appropriate to start off this week with a much sort after winter species the Australian snapper (Chrysophrys auratus).
The species, along with pearl perch are currently under a 1 month closure in QLD and thus a no take species (July 15, 12.01am - August 15, 11.59pm), so always remember to check the fisheries website in your region if you are unsure on current regulations.
We've also heard the term 'Old Man Snapper', normally used when referring to an older, larger specimen... almost wise looking with an abnormal, even deformed looking bony growth protruding from its head. Hence the other name they are sometimes given of knobbies I suppose. In saying that, it's amazing how different the same species can be in a different location. Look at some of the NZ snapper at up to 30lb and no sign of the bony growth, then it can be different again in SE Qld, SA, etc.
Some of you may have also heard that the protruding knob on the large fish is caused from the species banging their head on coral, shellfish and so forth when feeding, which is really an old wives tale as you never see them with any open wounds, abrasions or cuts and they always seem to be void of scare tissue.
So what is it?
Hyperostosis, basically a bone or bones that grow faster than usual and a surprising large amount of species have it. One of the other most common would the king threadfin salmon (Polydactylus macrochir) with its enlarged bony nodes on its backbone. The cause is unknown and only occurs in wild fish of all species.
Scientists have a few varying opinions and one that makes the most sense is genetics, with predominate species being predictable in their attributes, i.e. the snapper's knob on its head and the threadfins backbone nodes. This seems especially the case with snapper, male or female and seems more location genetics then environment or food source.
Another opinion is that, being predominantly bottom feeders, the increased bone growth and density helps them by providing negative buoyancy, in turn keeping them close to the bottom when feeding.
Interested to hear what your thoughts and experiences are.
How Good's Australia,
Robbie Wells