Q:

Built a shelf out of 2x4s but some braces do not meet, will they hold?

I paid someone else to build this basic shelf for me because i'm no carpenter, but i'm a little concerned about it's integrity because it will be holding aquariums. It's a frame of 2x4s with enough 2x4 braces running from front to back for the tanks to sit on, each brace is screwed in to the frame at the front and back with two screws. The problem is that half of the braces were short so there are 1/4th inch gaps instead of them fitting flush against the frame. Will they be able to hold 225 lb tanks like this? Or is there a way I could try to reinforce the braces?
The mending plates were added when I pointed out that I was concerned about the gaps. 

Edit: More pictures. One the top shelf all but the 2nd horizontal board from the left has the gap.

He also added this scrap piece on here when I told him I wasn't comfortable with the corner of this tank floating.

A:

I paid someone else to build this basic shelf for me because i'm no carpenter, 

Unfortunately, I am afraid the person that built this isn't either.  
There is a major weak point - the screws into the end grain of the cross pieces could just tear out of the wood.  The gaps are not really the problem.  
There are a lot of stronger options for the joint but most of them would involve starting from scratch, which would probably be best.  
If you want to salvage this, you might find a bracket that makes it strong enough.  I don't think it's ideal but the Simpson FBFZ for example might work:    

