However I have begun subscribing to a science related newsletter or two because I have the feeling that there is so much out there on the Net I'm not finding in relation to guppies and other aquarium topics.

There are different search engines for different purposes. Some of these aren't even listed in this tutorial and I'm sure there are lots more.

Science Direct, the provider of that page, wants to sell you all sorts of reprints for pretty good money. It may be reasonable for them to ask those fees considering what it cost to print and research that info, but a lot can be gleaned from the entries and article summaries. If you really want one of their articles in full, copy down or print the citation and drop by a local college library & photocopy it. (Easier said than done sometimes, I realize.)

That first tutorial is one of 10. Notice the list in the box on the left side of the page.

In the first tutorial, rather than use their topic with the search engine, use "guppy mate selection" . With the image search use "delta guppy" or "fancy guppy".

I think you will be as pleased as I was. I still am impressed by the usefulness of google.com but there are evidentally far more useful engines for the fish head. :)