Aquacultural effluents: Directive signals to the system downstream?

Animals continuously release biogenic substances that vary in composition with physiological state. In aquatic systems, animals can gain insight about conditions or events upstream and alter their physiology and behavior to exploit this information. Here, we review observations on aquatic animals as diverse as snails, shrimp, fish, and frog tadpoles to probe the possibility that high-density aquaculture might generate chemical messages that cause conspecific or related individuals to reduce productive processes (growth, metamorphosis, ecdysis, reproduction) or even to sicken and die (loss of immunocompetence, anaphylaxis). The potential for ecological disruption logically is maximized under conditions that uncouple the parts of the system generating and receiving such signals-as would be the case when aquacultural effluents enter natural aquatic systems.