Giving that frame a closer look, I have to agree about the coral :) And yes the sense of depth is very well done.

I liked the orange fan coral too, but it blended in too much with the orange fish. It was easier to change the fan coral color than the fish color, so I bleached it out to light lavender. Purple contrasts with yellow nicely and I made it lighter in tone.  The tonal changes add depth to the picture. If you desaturate the image, you can see the lightest tones are in the foreground, midtones are in the middle and dark tones in the back.

Lol i swear i recognise that creepy yellow fish from somewhere..
Neat concept.

This is beutiful and one of the best challenge works in my opinion. Maybe less light colors. GJ. BG is lovely done.

pretty cool, might've looked better with some more texture on the fishes bodies? And I kinda liked the colors more (orange plant) in the second to last frame.

 Oh, I see what you mean.  I did use a gradient and a blur. It's just second nature to use shortcuts for basic backgrounds and things. I forgot I'd even done it since I was focusing on the foreground fish and reef.

I've fixed it with a rough hand drawn background and some squiggled dashes.

Yes, NPA. Should be fixed before entry, in spite of my public queue vote.

You should also try to make it pixel by pixel... ... ...the fish seem alright...but clearly the background is NPA