Aquacultural effluents: Directive signals to the system downstream?

Animals continuously release biogenic substances that vary in composition w ith physiological state. In aquatic systems, animals can gain insight about conditions or events upstream and alter their physiology and behavior to e xploit this information. Here, we review observations on aquatic animals as diverse as snails, shrimp, fish, and frog tadpoles to probe the possibilit y 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 i mmunocompetence, anaphylaxis). The potential for ecological disruption logi cally is maximized under conditions that uncouple the parts of the system g enerating and receiving such signals-as would be the case when aquacultural effluents enter natural aquatic systems.