Snapper bumps.

[kingtin]

My re-awakened interest in fish keeping has reminded me of a long lost thread regarding the bump on snapper's heads and some of my observations from long ago being in the trade.

These thoughts have come to mind regarding cichlids that may well apply to snapper.

The bump is called a nuchal and although it can be very prominent in males, it is not necessarily devoid in (all) females, although somewhat smaller. The fact that females can have the nuchal, and based on my past observation of a couple of female mbuna who did, leads me to believe that the bump is somehow indicative of dominance as both these females were very dominant.

Also, the bump can diminish or grow in size in a relatively small period of time. I once had a red devil who was cock of the tank and he had a very large bump. I introduced a large Texas to the tank who almost immediately started to rule the roost. The RD was about 6 yr old and the texas only 3 and about half the size of the RD. Over a period of about 6 months the teaxas developed a hump (although not as pronounced as some cichlids) and the RD's hump diminished in size. as this process progressed, so too did aggression diminish.

My personal take on this is that the nuchal hump may in some way be an indicator of dominance and is used to give off signals to competitors, much as the red arse on a baboon does.........the smaller the hump, the less of a threat I am to you, so no need for aggression................the bigger the hump, the tougher Iam, so watch your step.

I'm guessing that this could be the case with snapper.

Just throwing a few thoughts out.

kev

[Lucky_Phill]

Very interesting observations Kev.

Dr Wayne Sumpton of Southern Fisheries based at Deception Bay, has been studying Snapper for many years and to this date has not come up with a definitive explanation as to the " Snapper Hump / Bump ".

Maybe you could contact this Department and pass on your observations. All info helps to maintain our fishery for the good of Rec and Com fishers.

SouthernFisheriesCentre@dpi.qld.gov.au


Cheers Phill
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[kingtin]

Very interesting observations Kev.

Dr Wayne Sumpton of Southern Fisheries based at Deception Bay, has been studying Snapper for many years and to this date has not come up with a definitive explanation as to the " Snapper Hump / Bump ".

Maybe you could contact this Department and pass on your observations. All info helps to maintain our fishery for the good of Rec and Com fishers.

SouthernFisheriesCentre@dpi.qld.gov.au


Cheers Phill
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Tis done Phil, thanks.

kev

[dazza]

hi kev,
this one always makes great conversation.
the bump comming and going is very interesting. it is made of bone, i don't see how it can re model itself.
if it is broken, then osteoblasts, osteoclasts etc go to work in remodeling the bone, pretty complex process that is in the back of my memory from my training::)::). this process lets us & all things with bones repair.

one typothesis may be: that it has something to do with hormones, these are pretty potent chemicals that the body produces and can do all sorts of things, they can be switched on or off by environmental factors.
the corticosteroids are one main group that respond to stressors (ie getting beaten up by a bigger more agressive looking fish) etc, i suppose fish have them in some fashion

have caught fairly small snapper with pretty big lumps
that is my 2 bob's worth
cheers
dazza

[DR]

Aren't the Kiwi snapper the same species as ours, yet they are mainly bumpless??
I always thought the bump had something to do with feeding in reefy areas..

[Noelm]

from personal observation, big bumps on Snapper can occur in certain areas, like as in Fish from around the Coffs Harbour to Port Macquarie area seem to have quite big bumps for their size, and then huge Fish from down arond SA have no bump at all! some say it is related to feeding patterns/habits, and in my own area (the Illawarra region) I have caught smallish Fish (say about 3KG) with a very pronounced bump, but my biggest (12.2KG) must have been on holidays from South Australia, because it had no bump. Who knows for sure huh?

[rando]

Gday kev
A reasonable hypothesis that.
Can you say whether the "nuchal" is a bony growth, or is it a fleshy/fatty thing.
It would be interesting to know the growth/recession mechanism if it proved to be a bony growth.
A lot of creatures use their profiles to display size & dominance, and a snapper with a bump always looks bigger IMO even if the scales say otherwise, so you might be onto something.

[kingtin]

hi kev,
this one always makes great conversation.
the bump comming and going is very interesting. it is made of bone, i don't see how it can re model itself.
if it is broken, then osteoblasts, osteoclasts etc go to work in remodeling the bone, pretty complex process that is in the back of my memory from my training::)::). this process lets us & all things with bones repair.


dazza

Hi dazza.

Mate, it's a documented fact that in some cichlids the nuchal hump enlarges during courtship and actually diminishes when rearing the fry. Form the first, one could assume that growing the hump would be logical, as mating fish compete physically when choosing a partner (survival of the fittest). Then a larger hump would be beneficial as it would indicate to potential partner and competitors, that one is indeed fit (and aggresive).

On 2nd thoughts though, if the hump is an indicator of physical prowess, why would it diminish when rearing the young as an indicator here would also be needed to ward off predators?

It is also documented that the humps in cichlids can diminish in size due to a change in water quality. Perhaps this could account for the differences in snapper from different parts of Oz?

kev

[Nic]

For years I have thought how interesting it would be to put some Kiwi snapper in southern Aussie waters and see whether they grew a bump. I guess it wouldn't be very responsible though to move fish around in that way!

[kingtin]

Gday kev
A reasonable hypothesis that.
Can you say whether the "nuchal" is a bony growth, or is it a fleshy/fatty thing.
It would be interesting to know the growth/recession mechanism if it proved to be a bony growth.
A lot of creatures use their profiles to display size & dominance, and a snapper with a bump always looks bigger IMO even if the scales say otherwise, so you might be onto something.

In the past I thought it was a fat storage mechanism as did many "experts" but it appears to be not so. I found this:

Sometimes mate choice is more subtle, the preference being for a particular aspect of the potential partner's morphology. In New World cichlids, the nuchal hump on the head of male cichlids seems an obvious possibility to explore. In aquaria, large male New World cichlids - and occasionally females - develop such a hump. In the wild, only males do so, and the humps are usually smaller than those seen in captive specimens. Nonetheless, the hump is a conspicuous character that demands explanation.

George Barlow and Paul Siri considered many possible functions for the hump. It could be an organ of fat storage, offer mechanical advantage in fights, improve hydrodynamics, serve as an anti-predation device, or be the object of mate choice. First the researchers marshalled the facts. The hump changes size over time. It gets larger during courtship and actually shrinks during the parental phase. Males and females fight during the parental phase so if the hump was a fighting weapon, females should develop humps equal to those in males. Similarly, if the hump serves in fat storage or as protection from predators, why don't females develop them? Furthermore, the hump doesn't actually contain large volumes of fat, it is for the most part filled with water. The hydrodynamic explanation may apply to other kinds of fishes with humps (e.g., salmon), but the bulbous shape of the cichlid's hump is likely a hydrodynamic deterrent, if anything.
By offering female Midas cichlids a choice of rubber dummies of male Midas cichlids molded with differently-sized humps, Barlow and Siri found that females prefer males with humps over those without, but only up to a certain point. Once the hump becomes enormous, female preference declines. Several possible explanations exist. Hump size may serve as a measure of a male's condition or quality. Or, the hump may merely serve as a way to distinguish males from females. Many of the species with humps are highly monomorphic - males and females look alike - and the fact that the hump peaks in size at the time of pair formation strongly suggests a role in sex recognition. Nonetheless, the story is not finished because, as the researchers point out, well-fed fish develop larger humps: if sex recognition were the sole factor, the hump would develop to a specific size, but no further. The enormous humps seen on some captive males - and shown to be unappealing to females in the experiments - may not occur in the wild because it may not be possible for large males to afford such elaborate displays. Future experiments and observations will be needed to sort out the explanations for this intriguing character.

[Dezzer]

G'day Kev

Very interesting thoughts.
I presumed it was a water pressure thing. Without starting a new "bay bump" debate, generally bay (shallow water) snapper don't while offshore (deeper water) do.

By the way, the water lilly started flowering and hasn't looked back.

Cheers
Derek

[kingtin]

G'day Kev


By the way, the water lilly started flowering and hasn't looked back.

Cheers
Derek

Had to take all mine out Derek...............they got that heavy rooted that they started floating upside down (even attached to the basket) and made a lovely perch for the bloody herons ;D

[PBass]

Hey guys i used to have a pair of Peacock Bass.. When it came breeding time the male which was smaller would grow a large hump on his head and become aggresive toward the female, then within days she would lay eggs.. This would happen every couple of months.. Not sure if this has anything to do with Snapper though.. Sean

[kingtin]

Hey guys i used to have a pair of Peacock Bass.

Sean

They're almost as nasty as my missus is at a certain time of the month ;D

kev

[StephenW]

Hi all, just to add a few thoughts to add to this thread.

Firstly the humps and bumps seen on snapper above the mouth and eyes are bony structures which don’t come and go, or reduce in size once present. Further more many fishers would also have seen bony structures/nodules along the backbone when they have filleted these same snapper.

I used to believe that these bony structures were associated with diet or possibly feeding behaviours (i.e. caused by rubbing against hard surface while searching for food) like many other people. However, more recently I have changed my opinion and now believe it is more likely due entirely to physiological/genetic reasons on an individual fish basis. I also think that it is more prominent in males than females but no substantiating data on this.

My change of opinion is due to a number of factors some of which I am sure many ausfish readers have witnessed for themselves.

Firstly, while searching the literature for information about otolith formation (ear bones) it appears that the primary uptake of calcium by fish is not through the diet but via the surrounding water through the gills.
The additional bony structures often seen along the backbone in fish with the lumps and bumps are internal and could not be the result of feeding behaviour.
There is no scaring or signs of physical trauma associated with the area around the bumps on the head like I would expect to see if it was caused by snapper bashing themselves against the rocks/reef while feeding.
It is possible to catch very large fish with no bony bumps, and it is possible to catch very small fish that have quite pronounced bumps.
It is possible to catch fish of the same size, feeding together in the same school and the same sex with very different appearances (big bumps or no bumps)
Fish can display these bumps regardless of where they are caught (inshore/ offshore).
The presence of these bony structures in snapper is quite different to those mentioned by others for cichlids. As mentioned by others, the structures on cichlids can come and go, or at least change in size most probably due to reproductive behaviour and doubt that they are made of bone (just guessing here because I have never personally dissected a cichlid) but are actually (as others have suggested) made of fluid filled sacs and fatty tissue.

Cheers Steve