Besides the small space, it could theoretically be safe for fish with adequate filtration and cleaning systems and coatings that protect from excess UV light and infrared heat from the sun.
The entire existence of femboys is a fetish. "Femboy" had always been a sexualized exonym from the internet. Its fetishized trans-lite. It is the pure fetishized form of female transgenderhood. Femboy doesn't just mean feminine gay boy.