are jumbo crabs just older crabs?

[ladybug15057]

The larger the hermie normally the older they are. But 2 hermies the same age can be different sizes. Exercise, food, and shell availability can be factors in size too.

[emmac350]

Don't worry - I had a PP (he's living with my sister until 2013) who wore the same shell for a year and still fit it at the end of that year. Meanwhile, the other crab I got at the same time moved up several shell sizes and was a small on the edge of medium during the same time frame.

[kgbenson]

Crabs grow at different rates as stated above. This is based on feed quality, quantity and genetics, both at the species level and at the individual level. Just like people, elephants, snakes etc. So you can have a younger animal that is larger than an older animal. There is a paper that states that the coconut crabs from islands with lots of coconuts are larger than coconut crabs from islands without many nuts.

The question of aging has always interested me, especially the claims of looking at otoliths and so forth. I cannot seem to find information about using otoliths in crustaceans. The term otolith is really best used with fin fish, but because crustaceans are not supposed to retain the structures in their balance apparatus:

From: http://www.unbsj.ca/sase/biology/rochet ... ograms.htm “
Whereas the age of wild animals can often be determined by examining calcified structures (e.g., bones, scales, otoliths, shells), this method has not been used in decapod crustaceans, due to the loss of integumental structures at each moult.”

From The Journal of comparative neurology, Volume 8: “At each moulting these animals, like the crayfish and many other crustaceans, cast off the otoliths together with inner lining of the otocyst. Afterwards, by means of their chelse, they place fine grains of sand or other hard particles ...”

From: http://www.cbl.umces.edu/~harvey/MOGEL/crab.htm Biochemical Approaches for Age Determination in Crustaceans “Age determination of crustaceans, however, is difficult because they lack permanent hard structures. “

Perhaps the author that refers to otoliths is thinking of some other structure?

Rings on antennae is another interesting idea, but I cannot find anything on whether or not crabs do indeed add a segment to their antennae when they molt. Many have shorter than normal antennae due to loss so I am not sure where that comes in. I am sure someone will correct me if I am on the wrong track here.

As far as I can tell, the only method that has proven thus far reliable in crustaceans is to look at lipofuscin deposition in the brain and that in many instances this correlated well with age (not every instance though) regardless of growth - meaning it could pick out the small crabs that are older. The problem is though that while this is a great tool for populations biologists, I certainly would not want people to take my pets brain tissue. Google up lipofuscin and crustaceans - there is a lot of work being done in this area.

Age determination is an area of active research within the decapoda because it will help to assess fisheries by better understanding the age ratios of the animals in a given population and control for differences in size due to differences in resource availability - I wonder if there might be a spin off technology we can use in the future that is less invasive.

I cannot find anything on using DNA to age crabs, any insight people have would be appreciated (I looked into the telomere thing but came up with nothing in crabs, it sounds promising though.

Keith