How do Fish know how big they are?

[Taegu]

A common consideration when adding a new fish is added to an aquarium
is the type, number and size of existing fish. I recently wanted to
add a Pacific blue Tang to my 150 gallon reef aquarium, and was
concerned since I had a medium sized yellow tang in the tank for about
2 years. I opted to try a Pacific blue larger than the yellow tang.
Since the blue tang was the newest fish, it tends to not be too
aggressive toward existing fish, and the yellow tang would be
intimidated and not be too aggressive toward a larger fish.

Bottom line is that after 12 hours both fish appear to have accepted
one another without so much as a single fin nip.

Still this episode brought a guestion to my mind. Can fish actually
see themselves without the aid of a relecting surface? Is their field
of vision wide enough to see themselves. If not, how do fish know how
large they are in comparison to other fish? It appears pretty evident
to me that fish do indeed have a concept for their size relative to
other fish since most fish of similar aggressiveness will not attack
larger fish.

[4G Mitsubishi]

hmm interesting.
not something id thought about b4.
is kinda related to how does a fish know what size hole can it swim through.
do they "get a feel"
as to what size they are and even if they do, do they have the mind to be
able to relate the size they feel
they are to another fish they see and know who is bigger?

kinda like if a human was to reach for an apple on a tree and not be able to
reach it so get one from a lower branch instead
then saw another person easily reach the apple from the high branch they
would then know a person that looked like that was bigger. (have a feel for
there size)

like a damsel of mine. whenever I stick a new plug with a frag glued to it
in a particular spot in my tank it likes to smash it out the way,
it knows it is big enough to do this, how? size them selves up against it?
maybe they can then c other fish swim past the same objects and know there
size?
I think maybe its just an inherent instinct that there brains subconsciously
calculate from simple things like that.


"Taegu" > wrote in message
m...
>A common consideration when adding a new fish is added to an aquarium
> is the type, number and size of existing fish. I recently wanted to
> add a Pacific blue Tang to my 150 gallon reef aquarium, and was
> concerned since I had a medium sized yellow tang in the tank for about
> 2 years. I opted to try a Pacific blue larger than the yellow tang.
> Since the blue tang was the newest fish, it tends to not be too
> aggressive toward existing fish, and the yellow tang would be
> intimidated and not be too aggressive toward a larger fish.
>
> Bottom line is that after 12 hours both fish appear to have accepted
> one another without so much as a single fin nip.
>
> Still this episode brought a guestion to my mind. Can fish actually
> see themselves without the aid of a relecting surface? Is their field
> of vision wide enough to see themselves. If not, how do fish know how
> large they are in comparison to other fish? It appears pretty evident
> to me that fish do indeed have a concept for their size relative to
> other fish since most fish of similar aggressiveness will not attack
> larger fish.