i'm not a professional but since you asked for a critique, here is my opinion - your colors seem to be on the poor side, makes it a bit bleak but based on the composition some of your pictures would greatly benefit if you bring more color. below is what i think about some of them.
#6 - the fish is out of focus. actually 2/3 of the left part is somewhat out of focus. it's hard to see what exactly you want to convey. also, the fish reflected too much light, so it's hard to concentrate on it. the background on itsown does not hold too much attention.
#5 - i like the colors a lot but the "out of focusness" and very slight bleaching of the middle blue object makes it hard to concentrate. i'd love to see the intricate design of that blue thing. was it your goal to make is a bit blurry?
#4 - what's your main subject: the fish or the "tubes"? tome, the tubes are awesome by themself, the fish only distract; however, if you want us to watch the fish, then the tubes compete with it way to much. the very top of the middle tube is a bit bleached, i would photoshop it.
#1 - i really like the whole thing. almost perfect. i think had you changed the angle it would improve it.
#3 - ok. the lighting is not even.
#2 - nice shot, but uneven focus of the background shifts my attention away from the middle foldy thing
