Wow now all is clear! Many thanks
I have in my enemy sprite some animations with large image png, 600x600 pixel
This animations increase that value.
But what is the best Way to save large images?
Png 8 bit can help me to keep memory usage low?
It does not matter what format you save it us, once in GPU memory, its a full texture.
Your 600 x 600 is slightly too large to fit into 512 x 512 texture so it has to go to the next one up (power of 2 size), so your image has to go into a 1024 x 1024 texture. As such, each animation frame would take up 4MB in memory.
You need to read the tutorial Ashley linked above. Consider it COMPULSORY reading before you starting designing your game, its incredibly important to have good practices from the start before you waste your time making a boat load of animations which are poorly optimized.
My advice is to not use any animated sprite above 256 x 256 in size. It's just too much of a memory hog to have 512 x 512 frames, if you have an enemy with 20 frames of that size, that single enemy is 20MB of memory once loaded into GPU.