Mermaid BL??

http://www.mangago.zone/read-manga/mermaid_s_egg/

(๑•ㅂ•)و✧+
http://www.mangago.zone/read-manga/gone_with_the_bubbles/ New!

Also, this is highly recommend http://www.mangago.zone/read-manga/wadatsumi_no_yometori/

http://www.mangago.zone/read-manga/seashell_boy_pearl_cum_boy/ More man than merman

Got an amazing chapter right here (⌒▽⌒)
http://www.mangago.zone/read-manga/tell_me_your_wish/mpn/ibx_chapter-17/pg-1/

And this is the most beautiful merman BL anime ever!!!
https://www.anime-planet.com/anime/this-boy-caught-a-merman

http://www.mangago.zone/read-manga/deep/

Thank you!!