What's new since build 16
Superseded, and do not install it. Build 17 reached open testing on 19 August and was replaced the same day, because in it there was no way to sign in at all — see the 0.5 notes. The current build is 0.5.1 (build 19), on FishCoin's page on Google Play.
Build 16's Delete my account screen told you that catches stored on this phone are deleted from it. It cleared the app's own settings and catch history, and it left behind several files written by the Google libraries the app is built on — including the identifiers that tie an install to a person.
Nothing about that was visible: the screen said it had worked, and as far as anything you could see, it had. It is fixed. The wipe now clears everything the app has on the device rather than a list of files somebody wrote down.
If you deleted your account on build 16, your account and your catches were handled correctly on our side. This is about what stayed on the handset, and uninstalling the app clears it.
Nothing else changed.
Unchanged, and still first: tape-measure a fish and enter the number — with the tail pinched to a point, as the prompt asks.