We conducted a dietary feeding study with juvenile chinook salmon (Oncorhynchus tshawytscha) to assess
the potential for tributyltin (TBT) to elicit the obesogen response that has been described for mammals.
The results show increases in whole-body lipid content, which is consistent with the obesogen response;
however, we also observed associated parameters that were dissimilar. We found increases in body
mass and alterations to several physiological parameters at doses between 0.4 and 3.5 ng/g fish/day
(1.4 to 12 pmol/g fish/day) and reduced body mass at the highest dose after 55 days of exposure. Lipid
related plasma parameters (plasma triacylglycerols, cholesterol, and lipase) exhibited monotonic
increases over all doses while other values (glucose and insulin-like growth factor (IGF)) exhibited
increases only for the low-dose treatments. The increases noted for several parameters in fish were
opposite to those reported for the obesogen metabolic syndrome, which is characterized by a reduction in
serum glucose, free fatty acids, and triglycerides. This is the first report of growth stimulation resulting
from low-dose exposure to this pesticide, which is an unusual response for any animal exposed to an
organic or organometallic xenobiotic. Because a number of environmental contaminants act as metabolic
disruptors at very low doses, these results are noteworthy for a variety of species. Intuitively, enhanced
growth and lipid storage may appear beneficial; however, for salmonids there are numerous potentially
negative consequences for populations.