BEIJING--A chemical applied to ship hulls is robbing Chinese sturgeon of their eyes and causing other deformities, according to a new study. The toxicant may deal a death blow to the already-endangered fish, a living fossil that the Chinese government considers a "national treasure."
The Chinese sturgeon (Acipenser sinensis) has lived in the Yangtze River for 140 million years, making it one of the world's oldest fish. Although the 450-kilogram sturgeon once thrived in these waters, overfishing and the loss of spawning areas to dams has cut its numbers by roughly 85% over the past 30 years. As of 2007, there were only about 500 spawning sturgeon left in the Yangtze.
Now Chinese scientists have identified a new threat: triphenyltin (TPT), a biocide applied to ship hulls and fishing nets that prevents the buildup of algae and other aquatic hitchhikers. The compound has slowly washed from ships and accumulated in Yangtze sediments. In this week's issue of the Proceedings of the National Academy of Sciences, Hu Jianying, a professor at the College of Urban and Environmental Sciences at Peking University in Beijing, and colleagues report a direct correlation between TPT levels in water and sturgeon deformities. The team captured more than 1000 Chinese sturgeon larvae from the Yangtze and recorded the incidence of mutations: 6.3% exhibited morphological deformities such as gnarled spinal cords, and 1.2% had only one eye or no eyes at all. In addition, four adult sturgeon were captured for artificial propagation in a TPT-free environment. Their offspring maintained a high concentration of TPT and showed comparable rates of deformities to sturgeon in the wild, suggesting that the chemical accumulates in the fish and is passed to its eggs.
Hu's group also exposed a close relative of the Chinese species, the Siberian sturgeon (Acipenser baerii), to TPT and found similar rates of deformities in a dose-dependent relationship. When raised in a TPT-free environment in land-based breeding facilities, these sturgeon showed only a 0.66% rate of morphological deformities and no ocular deformities. Other biocides that are present in the Yangtze and similar to TPT--dibutyltin, monobutyltin, and tributyltin--resulted in fewer deformities and did not show a dose-dependent response.
TPT appears to harm reproduction as well. In a separate study conducted by Zhang Zhaobin of the College of Urban and Environmental Sciences at Peking University, exposure to TPT reduced the ability of the Japanese Medaka fish (Oryzias latipes) to produce viable offspring by as much as 75% in a controlled facility. Because both the Chinese sturgeon and the Medaka showed similar deformities when exposed to the same levels of TPT, Hu's team believes that TPT is likely reducing the sturgeon's fertility in the wild.
The findings may have come too late. Hu argues that although the sturgeon's population can be sustained by captive breeding and restocking the Yangtze, banning TPT at this stage would do little to undo the damage in the wild. TPT is a "legacy contaminant," says Hu, meaning that it has a very slow rate of breakdown. Even if a ban on the chemical were introduced, TPT already present in sediment could continue to cause damage for years to come. Those sturgeon still plying the Yangtze today might end up being the last of their kind: "the living dead," says aquatic ecologist David Dudgeon of the University of Hong Kong.
In the original version of this article, it was stated that Chinese sturgeon raised in a TPT-free environment had a 0.66% rate of morphological deformities. This rate actually refers to the Siberian sturgeon. Chinese sturgeon raised in a TPT-free setting still showed high rates of deformities due to the chemical being passed on from parent to offspring.
A reader pointed out that the original article erroneously referred to TPT as a toxin; this has also been corrected.