A food fight has been brewing over how the government should regulate animal tissue grown in labs. The prospect of lab-grown tissue has raised the hopes of animal welfare and environmental groups because it is created without slaughter and meant to substitute for traditional pork, beef, chicken, and fish. But divisions have emerged between the traditional meat industry, who are imploring the government to set rules out of concern for their own industry, and the companies creating the lab-grown foods, who fear that regulation could prevent their products from reaching consumers.Safety regulations have yet to be issued, but they are likely to include standards about how to grow the tissue, how to sign off on its safety, and how to label it in a way that consumers know what they're buying.