Merlino daggers are blades are made from fish bones, specifically the merlino fish found around the Bellezzan lagoon island of Merlino. The daggers are highly valuable and very sharp. However, the daggers are rarely seen outside of Bellezza and most Talians prefer blades from Fortezza as their weapons of choice.
Many fishermen from Merlino actually gain their livelihood from producing and selling merlino daggers rather than fishing. Because merlino fish have not been seen in many years, the fish bones have become increasingly difficult to obtain, which drives up the price of existing daggers. The Gasparini brothers catch and release a live merlino fish at the end of City of Masks, foreseeing that the merlino fish are not extinct and the possibility that they will gradually regain their population..
As fisherman living on Merlino, both Angelo and Tommaso Gasparini have merlino blades; as promised, they give their adoptive younger sister, the Duchessa of Bellezza, a merlino blade on her sixteenth birthday. She carries the blade with her at all times in order to protect herself, which she winds up using to kill an assailant who attacks her decoy during the massacre at the Church of Annunciation. After foiling the first assassination attempt on Silvia Bellini, Luciano Crinamorte was permitted to keep the assassin's merlino blade; Guido Parola and the Duchessa's bodyguard, Marco, are also believed to carry merlino blades.