That was clever! The mixture of block-fitting and residency management was engaging and stimulating, and the quick difficulty curve is perfect for an arcade-style game. The fish are also charming!
I couldn't figure out why certain builds had larger residencies than others (like how to tell the 1x1 that holds 3 anchovies versus the 1x1 that only holds 1 anchovy). That might just be me.
I'm not sure why, but by the end, my view zoomed out much larger than I could actually build/destroy. It was a little awkward.
All-in-all, great work!