Dobrzemetal;145171 said:
As AM points out, size is not a good indicator of age. Octos in the Abdopus comoplex also vary greatly in size but they have identified lots of species in this group and size would have a bit more reliability if only we could determine WHICH of the species the animal belongs to (not something the hobbiest can do with a live animal). There is one exception for us in US. Briareus caught in the FL keys have been pretty reliable for aging if the mantle is under 2". This is most likely because the food is still plentiful in the area so growth rates vary less. We have not seen briareus from other places so the species may vary widely but not the ones we are seeing.
Interestingly, size is not a good indicator of age for a lot of things it is just not as obvious because of the short ceph lifespan. Clown fish stay small juveniles if there is a male and female pair in the troup. The juveniles will remain small until one of the the mated pair dies and then only the largest (much smaller than the mated pair) will grow rapidly and become the male. If the female died, the original male becomes the female. I set up an experimental tank to see if I could observe this and have been delighted with the results. I started with 5, lost both the male and female after about 8 months. We think they tried to brood in an area of the tank that was oxygen poor - since corrected with circulation - and were removed from the family when they had difficulty swimming but they never recovered. This left us with three unsexed juveniles and we have seen one become female (easily recognized by size), one became male and the other still looks like a baby even though all are likely the same aged sibblings.
I have seen flower anemones and star fish shrink from lack of appropriate food. One of my flower anemones disappeared in the reef (it was the only one I have had that continually wandered). After almost a week (usually I could find it anywhere in the tank) I was very puzzled and it occured to me to look in the filter sock. It was totally white and the size of a half dollar. I move it to the above mentioned anemone/clown tank, it climbed up to the surface near the best lighting and is now larger than it was in the other tank and has regrown all of its algae, returning the green and red normal coloration.
I also have a very tiny star that I was sure was a baby. I have had it three years and it has never grown. I have two other common stars that have shrunk (still trying to remedy their nutrional needs and have moved them to another tank) but have survived over 5 years.
These are all common occurances where size fools the observer about age but these animals have a much longer natural lifespan and it goes unnoticed.
