It must be something in the water

Israelis' fondness for hikes in the country appears to be exacting a high price from rare fish populations in the Jordan River basin. Researchers at Tel Aviv University believe that the bodily excretions of women hiking in Hakibbutzim Stream, in the Beit She'an Valley, are causing sexual changes in the Acanthobrama Lissneri, a species that is unique to the area. Another interesting discovery from the same area is that the Astatotilapia Flaviijosephi, which is also found only in Israel, eats mainly stones from the riverbed.

As part of a comprehensive survey of the state of the fishes in the Jordan River basin that was supervised by Dr. Menachem Goren of the TAU Zoology Department, Yaron Krotman examined the fish population in various locations, including the Astatotilapia Flaviijosephi, which lives in an area filled with springs and pools that are popular with day-trippers.

In one of the sites examined by Krotman, he found a disproportionately high number of females - more than twice the number of males. In other sites, the numbers were nearly equal. Tests of the water at the sites revealed high levels of the female hormone ethinylestriadol, which is used in contraceptive pills and is excreted with the urine into the environment.

International studies have shown that exposure to this hormone causes significant changes in fish populations, expressed in an increase in the number of females. Exposure can cause changes in sexual characteristics in all developmental stages, from the larval to the adult.

According to a comprehensive Danish study on the feminization of fish, such hormonally-caused changes in fish have been found in several European countries. In some cases the fish had been exposed to urban sewage containing synthetic hormones excreted by humans.

Hormonally-introduced sexual changes in male fish have also been found in breeding pools in the north of the country, apparently due to exposure to treated sewage.

"Since there is no sewage contamination in Hakibbutzim Stream or any other external source [of the hormone], we are assuming that the fish were exposed to the hormone when they were in the larval stage on the stream bed, which caused them to develop as females," Goren explains. "The most likely source of the hormone is from the excretions of women hiking in the stream. However, it should be stressed that this is only a theory."

You've heard of rock lobsters

Yifat Gueta, another TAU researcher, discovered in the course of examining the digestive system of the Astatotilapia Flaviijosephi that stones make up the vast majority of the contents of this system.

"Many animals eat stones. For birds, it helps then to grind seeds and nuts," Goren explains, "but the quantity found in the Astatotilapia was extremely high and clearly not merely coincidental." Additional study led to the conclusion that this species eats stones for the plant and animal material that clings to them. "For every two grams of stones, the fish gets the same amount of organic material it would get from eating one gram of snails," Goren explains. The stones are eventually excreted, he noted.