G'day ashprog,

Please put your code in <code>...</code> tags. "Writeup Formatting Tips" explains about this.

The code you've posted does not declare a subroutine: it may be invalid syntax; it certainly doesn't do what you appear to think it does. Take a look at "perlintro: Writing subroutines".

I expect the answer you're looking for is:

print $_->{GENOME_SIZE} for @genome_data;
[download]

[Disclaimer: I've had to make assumptions about what your real code might look like. If you correct the code you've posted, my answer may change.]