attack and defence

Hi,
Can anyone tell me please, why Angels give each other a reminder who is boss by attacking in the normal upright position, yet when getting really angry, say when defending eggs they go into the attack laying horizontally.
Is it to do with the ability to bite?
Cheers

Thats a good question French & i have offen wonderd this myself so hopefully someone will be able to give the answer.

I always thought that the change in posture, laying horizontally, was just a ploy to look bigger.

The upright attack, to show who is boss, is probably not a real attack, most sparring of this nature does not result in any injury it just puts the subordinate fish in its place.

The horizontal attack is a real attack intended to inflict injury.

Mind you....

Regardless of any theory, will we ever know what is going on in the mind of an angelfish?

Indeed, a very good question, and one to which I don't know the answer.

I've always assumed that the reason angels are laterally compressed serves two functions, but this is just my theory, so it might well be wide of the mark...

Firstly it enables them to hide in amongst plants and tangled roots, but I suspect more importantly it makes life difficult for predators. Think of the mouth of a typical predator, red tail cat fish, giant otter, etc. In most cases the mouth is wider than it is high. Any such predator wishing to eat an angel would need to turn on it's side, or open it's mouth very wide indeed. If it takes the latter approach, the angel's dorsal and anal fin spines are perfectly positioned to stick in the predator's mouth. However, if the predator takes the former approach, it will be much less manoeverable as the angel darts in and out of the twisted roots.

If I'm correct, when conducting territorial disputes it makes sense for the angels to maintain a vertical posture, in case they are so distracted seeing off the interloper, that they fail to notice the predator sneaking up on them.
However, when defending young or eggs, then shooing off any predator is paramount. I've noticed that when swimming horizontally, in some situations the fish appear to flash and I would imagine the effect is quite dramatic and startling for any potential fry stealer. But to maintain the surprise element, it's important not to over use it, and save it for special occasions!