With the version 1.5.10 Joomla changed some the structure of install packages. The bug report explains some of the changes in which it became clear that the understanding of having files in a sub-directory of your package was somehow wrong. It is explained nicely by others that the <installfile> attribute is already very old and that the understanding of what is the correct behavior shifted over the time.

The Joom!Fish project released today an updated version 2.0.3 which we had already prepared for the new release of Joomla. The fix for this installation topic is also included in the package and this allows you to use the latest version with your new Joomla 1.5.10 installation.

If you use an existing 1.5.9 installation and perform an upgrade to the latest version using one of the existing patch files you will have no problems at all, as this topic refers only to new installations. For upgrading the latest version of Joom!Fish you can just perform an upgrade process within your Joomla extension installer. We will provide suitable patch files shortly.