My experience is that Paul Ysart fish facing left are not common but I have no idea what the proportion would be compared to the right-facing ones. Pretty small, I'd imagine, though. My two examples, one likely 1950s and the other a 1970s "H" version, both face to the right, but I would not be surprised to find a few left-swimmers from any of Paul's fish weight periods.
I think I've seen a few that do face left, but the brain cells aren't up to revealing where I may have seen them - except for ... ... page 199 of Bob Hall's
Scottish Paperweights book and it has a PY cane so the image must the right way round [see below for comment on this]
But ... ... I have a personal photo of that actual weight and although I can comfirm 100% that the fish is a "lefty", the cane is not a "PY" one. In the book image, it appears as a rather fuzzy washed out white core with a green outer, and any initials are all but invisible. In my own photo, the inner white core also dominates the cane but is has a feint "H" - not a "PY".
Some of you might take issue with me about a cane being an "H" when it has a green sleeve, not a pink one. That would be well noted if you did spot it. But greensleeves do exist for H canes - and now I'll come clean. Willie Manson told me (and probably a few other folk, too) that the "H" canes with a green coating were produced in the first year of the Harland period, but very soon after they all became pink-coated ones. So, a green-outer "H" is much rarer than the usual pink ones! And now I probably have very little chance of locating a green-outer "H" cane weight, having been hoping for one for several years

And with my "have you thought about this" hat on ...
If any of us see an image of a left-facing Ysart fish without a signature cane or with an "H" cane, then we must bear in mind that the image could be the wrong way around (flipped horizontally) and we'd never know! That could apply to photos in books when publishers decide that speed of production takes precedence over thorough review; although it's less likely than having a simple upside down image which is an easy slip to make with some weights.
Another case of "lefters" and "righters" is Paul Ysart 3D parrot weights.
(And while I'm in "precision" mode [nicer word than "pedantic"], if anyone does take a look at the fish weights in the
Scottish Paperweights book, please also note that the one on page 118 has a false "py" cane, but at the time of preparing the book, I am sure that point was not realised in respect of that weight.)