To solve problems that an organotin is readily dissolved and dispersed in culture seawater to easily toxify and pollute the seawater though the organotin is effective in preventing adhesion of seaweeds or burnacles to culture nets when culturing is carried out by using the culture nets coated and dyed with a conventional algicidal agent having the organotin.

A method for vacuum dyeing is to dip a fiber material in the algicidal agent and dye the fiber material under decompression. A net or a rope or constituent fiber materials, etc., thereof are dipped and dyed in the algicidal agent liquid in a vacuum chamber maintained in a vacuum state by decompression. Since the algicidal agent is deeply and rapidly penetrated into the fiber material under the decompression to strengthen the dyeing power, the degree of dyeing can be increased and uniformized. The dyed algicidal agent becomes a state of scarcely peeling from the fiber material, high degree of dyeing and algicidal actions can be maintained over a long period.