'There's nothing like' means that what follows is a very good example of something: 'There's nothing like being in a near-fatal car crash to make you focus on what's important in your life'. Often the resulting good thing isn't mentioned: 'There's nothing like a walk in the fresh air'. This syntactic trick leaves room for quite a few jokes along the lines of 'There's nothing like a good X; and that was nothing like a good X!'
an interest in common' = 'a shared interest'. What this has to do with fish-bowls only the author can tell us.
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