An anonymous reader quotes a report from CBC News: It's rare that cancerous tumors can spread from one individual to another. But a genetic study suggests that's what's happening with melanoma tumors among catfish in Quebec and the northeastern U.S. The discovery represents the first known transmissible cancer in fish and one of very few transmissible cancers ever found, reported the study published in the journal Nature on Wednesday. Julie Dragon, co-leader of the new study, noted that only three other transmissible cancers have ever been identified so far -- in Tasmanian devils, dogs and shellfish. "These conditions are incredibly rare in nature," she said. "So something has to be happening to allow this to happen." Anglers in Lake Memphremagog, which spans the border between Quebec and Vermont, first reported catching brown bullhead catfish with strange black spots and lumps in 2012. They turned out to be melanoma skin cancer tumors. (Humans can also get this kind of cancer.) Now, about a third of the brown bullheads living in the lake have them. It's not clear how sick the fish become. In some cases, the cancer spreads to other organs, such as the brain or liver. But many fish with lesions seem relatively healthy and some older fish even have them, suggesting they can live with the disease for a time. Because of the sudden appearance of the black lesions in Lake Memphremagog the year after a huge flood caused by post-tropical storm Irene, locals worried they were caused by carcinogens washed into the lake by floodwaters. Tests for carcinogens haven't been conclusive, although a study published in May found higher concentrations of seven metals, including zinc and the carcinogen arsenic, in the skin of fish with the tumors. Researchers suspect the tumors may spread among adult fish during spawning, when crowded fish rub against one another and may be punctured by their spines. "They... swim all over each other and we think it's possible that they poke each other and cells can get into other fish that way," Dragon said, though transmission has not yet been demonstrated.

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A new study by researchers at the University of California at San Francisco "adds to growing research linking increased social media use to detrimental effects on attention, memory and cognition," reports the Washington Post: The study followed more than 11,000 U.S. adolescents over a period of five years, with participants first asked about their own social media use at the average age of 12, and surveyed annually through the average age of 16. Researchers found that increases in addictive social media use were followed by rising ADHD one year later — particularly among boys who reported rising addictive social media use at ages 14 and 15. This association was not found consistently in reverse, meaning that ADHD symptoms did not appear to precede higher levels of addictive social media use... "When an individual adolescent's addictive social media use score increased from one year to the next, that same adolescent tended to show an increase in ADHD symptoms in the following year...." [said Jason Nagata, lead author of the study and an associate professor of pediatrics at the University of California at San Francisco]. He urged parents to consider: "Can their kids stop if they want to? Is social media interfering with their schoolwork? Is it impairing their social relationships? Are there addiction-like symptoms, like withdrawal and relapse?" Approximately 7 million American children between the ages of 3 and 17 have received an ADHD diagnosis, according to the Centers for Disease Control and Prevention, and boys are diagnosed with ADHD at about twice the rate of girls. The study did not find a clear link between addictive social media use and ADHD among girls, Nagata said. "Some studies do suggest that teenage boys in particular may be more sensitive to immediate reward and sensation-seeking in adolescence," he said. And social media platforms are designed to provide exactly that: "It encourages frequent task-switching, and there's this constant stream of stimulation that might make it harder for adolescents to maintain and sustain attention that is needed for schoolwork and daily life," he said. "The design features of social media offer the constant reinforcement of impulsivity — it offers immediate gratification and novelty and it encourages multitasking, which can then override working memory and executive control." Experts have long noted that this kind of digital exposure is particularly significant during critical stages of mental, social-emotional and cognitive development... [I]t's especially important for parents themselves to demonstrate a healthier relationship with screens and social media. "One of our previous findings was that parental screen use is a very strong predictor of kids' screen use," Nagata said.

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