Scientists have found that a common pollutant, 4-nonylphenol (4-NP), is capable of disrupting the ability of fishes to school.
According the study by Practical Fishkeeping contributor Ashley Ward, Alison Duff, Jennifer Horsfall and Suzanne Currie published in the latest issue of the journal Proceedings of the Royal Society B: Biological Sciences, acute exposure to low dosages of 4-NP disrupted chemical communication in the banded killifish (Fundulus diaphanus), a shoaling species, and rendered them unable to school effectively.
The authors measured the relative times subject fishes spent in conspecific odour plumes and blank plumes in flow channels for various dosages of 4-NP (0.25"2 g per litre).
They also measured the mean distance between fish placed in an arena to assess shoal cohesion for fishes exposed to 1 g per litre of 4-NP.
The results of the study showed that at dosage levels of 1 and 2 g per litre of 4-NP (corresponding to levels recorded in aquatic habitats near sewage outflows worldwide), shoaling killifish avoided conspecifics in both flow channel and arena studies.
The authors write: Such effects on the fish s social behaviour are likely to have major fitness implications, even in the short term, as shoaling is an adaptive response to predation...and provides fish with an effective means of defence...
4-Nonylphenol is a common freshwater pollutant, and is commonly employed as a surfactant in industrial and sewage treatment processes.
Although it is subject to stringent regulations and freshwater concentrations of 4-NP are typically low, it is still present in concentrations ranging from 0.5 to 343 g per litre in sewage outflows.
The problem may not be confined to 4-NP. According to the authors: In the real world, aquatic environments may often be contaminated simultaneously by more than one, and often several, different chemicals.
The possibility exists therefore that different contaminants, each disrupting a separate element of the chemical communication pathway, may act in concert to seriously impair or to knock out the chemosensory abilities of fish at levels below those currently considered to be a problem based on single-chemical ecotoxicological studies...
For more information, see the paper: Ward, AJW, AJ Duff, JS Horsfall and S Currie (2008) Scents and scents-ability: pollution disrupts chemical social recognition and shoaling in fish. Proceedings of the Royal Society B: Biological Sciences 274, pp. 101"105.