Mammals are known to reduce in size in response to environmental risks. It has been studied in great detail.

The icecap may not be the only thing shrinking in the Arctic. The genitals of polar bears in east Greenland are apparently dwindling in size due to industrial pollutants.

That might not be the best example; it has been known for some time that polar bears are losing weight overall.

A new ecology study now says mammals are not the only species. It turns out even fish can shrink under harsh living conditions

In examining how juvenile salmonid fish responded to harsh environmental conditions, we were faced with unexpected and previously undocumented observations in terms of growth performance, indicating that fish do shrink in harsh winter conditions. Young salmonids showed significant shrinking of individual body length, up to 10% of the body length, over the course of winter. The dynamics of the growth in length of these fish can be explained by a combination of anorectic stress and environmental conditions. Under stable, sheltered underwater conditions fish were best able to maintain positive growth in length.