Some info emailed to me on the above mentioned topic on snapper.

In this case some light shed on the 'Bump on the Head' seen on some of the large snapper we see photographed often in magazines or here on this forum.

* Bumps do increase with size and/or age. It's not clear which of these factors is more important.

* Bumps do not inevitably form with increasing size or age.

* Bumps occur on both male and female fish.

* Bump-headed (often called "old-man") snapper seem to be more common in some localities than others. The Nelson Bays (Sounds to Golden Bay) snapper, which seem not to mix freely with Cook Strait and West Coast North Island snapper, were one such place, at least in the past when big fish were commoner. West Auckland/Northland, and parts of the Hauraki Gulf, were others.

* Such fish are not common, and presumably will become less
common as commercial and recreational fishing pressure reduces the number of old fish (snapper can live to 60+ yrs).

* Bump-headed snapper are possibly relatively more common, or at least are written about and pictured more frequently, in Australia.

* The bumps result from the enlargement of particular skull bones.
Some enlargement can also occur in the lower vertebral spines just behind the vent - not visible until the fish is filleted. Similar bone enlargement occurs in other marine fish species, as the following abstracts of papers will show. You may have noticed that some large New Zealand trevally (Family Carangidae) also have "enlarged foreheads". The condition is called hyperostosis, which really just means excessive bone growth. Its cause is unknown. One explanation I've seen is that it's simply a way for the fish to store excess calcium. In any species of fish, it always occurs in the same bones - often at the front of the skull, and in lower vertebral spines. Thus the snapper is a typical example.

* I have not heard the theory that it is used to open shellfish and kina, but think it very unlikely. The powerful jaws of the large snapper with such head bumps would be much more capable of doing this.

Some references:

Meunier, FJ; Bearez, P; Francillon-Viellot, H (1999). Some
morphological and histological aspects of hyperostosis in the eastern Pacific marine fish Prionotus stephanophrys Lockington, 1880 (Triglidae). Proceedings of the 5th Indo-Pacific Fish conference, Noumea - New Caledonia, 3-8 November 1997. pp. 125-133.
Abstract
All the fish studied show the same hyperostotic bones: both frontals,
the ethmoid complex, both operculars and one or two caudal
vertebrae. Hyperostosis was always found in the 21st vertebra and
sometimes in the 20th and 22nd. The cranial bones show a typical and
regular thickening. On the contrary, in the case of the vertebrae, this
thickenning concerns each side of the centrum only. The swelling of all
these bones is the result of an active osteogenesis associated with
resorbing processes resulting in the deposition of spongy acellular
bone. This cancellous bone is surrounded by a thin cortical primary
bone. Thus, the histological characteristics of the swollen bones of
Prionotus stephanophrys are the same as those already described in
the majority of other hyperostotic species, regardless of the bones
involved. The causality and the biological signification of the
hyperostotic phenomenon in P. stephanophrys seem unclear in the
current state of knowledge but, given the particularly specific vertebral
swelling of this species, this fish could represent an interesting model
to study the etiology of hyperostosis.

Smith-Vaniz, WF; Kaufman, LS; Glowacki, J (1995). Species-specific
patterns of hyperostosis in marine teleost fishes. Marine biology
121(4): 573-580.
Abstract
The occurrence of swollen or hyperostotic bones in skeletal
preparations, preserved museum material or whole fresh specimens of
marine teleost fishes was identified in 92 species belonging to 22
families. Patterns of hyperostotic skeletal growth were typically
consistent and often species-specific in all individuals larger than a
certain size. The taxonomic distribution of hyperostosis in diverse
phylogenetic groups suggests that it has arisen independently many
times. Selected bones from two species of the family Carangidae,
horse-eye jack Caranx latus and crevalle jack Caranx hippos, were
examined in detail by light and electron microscopy. Nonhyperostotic
bone was acellular (anosteocytic), while the hyperostotic bone
contained osteoid-producing osteoblasts, resorbing osteoclasts,
occasional osteocytes, and a rich vascular network, all characteristics
of cellular bone. Thus, these fishes have a spatial juxtaposition of
cellular and acellular bone tissues in adjacent and often serially
homologous bone sites. The functional significance of hyperostosis is
unknown, but it is a predictable manifestation of bone growth and
development for the many taxa in which it occurs.

Gauldie, RW; Czochanska, Z (1990). Hyperostosic bones from the
New Zealand snapper Chrysophrys auratus (Sparidae).Fishery Bulletin
88(1): 201-206.
Abstract
General hyperostoses are well known in fossil fish bone literature
(Tiffany et al. 1980). Hyperostosic bones have been described as
occurring as nodules on the ventral pterygiophores as well as other
bones of Recent fishes. Consistent occurrence of hyperostosic bones
in many species has been taken to indicate that they are not
pathological. Various roles have been suggested for hyperostosic
bones ranging from aids in fin erection to hydrostatic correction.

Meunier, FJ; Desse, G (1986). Hyperostosis in the Teleostei:
Description, histology and etiological considerations. Ichtyophysiologica
acta (Lyon) no. 10: 130-141.
Abstract
Hyperostosis are hypertrophied bones that can affect different levels of
the skeleton in Teleostei. Generally, the hypertrophy is the result of an
abundant osteogenesis with remodeling giving spongy bony tissue.
Hyperostosis have been described only in fishes with acellular bone
and living in sea water. The etiology of this phenomenon in fishes is
unknown. Mechanical factors during swimming and with aging seems
to be the predominant cause for hyperostosis.

I trust this information will be of some interest.

Courtesy of:
L J Paul, Fisheries Scientist, National Institute of Water and Atmospheric Research, Wellington.

cheers eric

Leave those big kingies alone will ya. Might have to plan a trip up there with Mr Matthews.

good luck

eric

funny as duck!!!...certainly amussing!

Thanks for the heads up Eric.....do you think (Dr??) L J Paul would be interested in helping us out from time to time with sticky ichthyological questions from the forum?

perhaps we in turn could help him out with specimens and first hand experiences etc etc?

Let me know...happy to approach him!

This is from a book called Fish Might Fly by Australian marine biologist Julian Pepperell. It's a good book, goes into a lot of the fishy things that we fishos puzzle over.

continued...

If I gave a snapper head like those ugly bastards to my oldman to eat He'd have a heart attack! they are seriously deformed.