Exposure to mercury in the environment continues to be a significant worldwide concern, especially for developing embryos and fetuses. While extensive research effort has focused on the effects of mercury on the developing nervous system, much less is known concerning adverse effects of mercury on other organ systems, including the development of skeletal muscle. We exposed developing zebrafish embryos to a range of concentrations of mercuric chloride (100 to 400 μg/liter or ppb) and compared them to control embryos (0 μg/L mercuric chloride). Embryos were examined at 48 hours post fertilization (hpf) for morphometry and morphological deformities of skeletal muscle fibers in the trunk and tail. Embryos exposed to 400 ppb mercuric chloride showed decreased trunk and tail areas compared to control embryos. A dose-dependent reduction in muscle fiber length was observed, and exposure to all concentrations of mercuric chloride used in this study resulted in decreased muscle fiber immunohistochemical staining with anti-myosin antibodies. Irregular muscle fiber diameters, twisted muscle fibers, and degenerated muscle fibers were observed in sections of embryos stained with eosin at the higher exposure concentrations. Evidence presented in this study suggests that exposure to even low concentrations of mercuric chloride adversely affects skeletal muscle fiber development or muscle fiber integrity, or both.
KEY WORDS: Zebrafish; Muscle fiber development; Striated muscle; Myosin; Embryonic Development.