To provide an additional liquid which is used for preventing the adhesion of shellfishes, has high safety, and solves a problem wherein the shellfishes such as corn barnacles and algae adhere to ships to increase seawater resistance and fuel consumption costs, and a problem wherein the adhesion of shellfishes to various apparatuses used in oceans, fishing nets, and the like cause the deterioration of their functions.

This shellfish adhesion-inhibiting additional liquid prepared by compounding a combination of several kinds of liquids (pine oil, tall oil, olive oil, neem oil, castor oil, and the like) extracted from natural plants having sterilizing forces. When the additional liquid is mixed with a ship bottom coating or the like and then used, the adhesion of the shellfishes such as corn barnacles and algae are prevented, and the additional liquid has high safety and does cause marine pollution and the like.