It means that Pluto is the sub-ruler of your Pisces Sun.So when it comes to you, you have the added staying power of Pluto's influence to your Sun. Perhaps mitigating some of the Pisces naïveté and more gullible nature to one of suspicion and intense commitment to a goal.
Your attraction may be towards a Cancer-Scorpio and Scorpio- Scorpio decanate-due to the shared intense natures
I also think that physically, this decanate may give you a more square,solid physique that looks like it conserves spontaneous reactions and has much energy reserves for long-term or physically taxing undertakings.