In recent years, aqua-farmers have faced increasing problems with jellyfish and algae blooms. A so-called “bubble curtain” system has been found to be a simple, yet effective, method of preventing jellyfish and algae from adversely affecting the fish within the cages. When a threat is reported, a compressor is activated which produces a ring of air bubbles. The rising bubbles and water turbulence create a ‘curtain’, thus preventing algae or jellyfish from entering the cage. The ocean current drives the threat alongside the bubble curtain until it has passed the farm.