In contrast, zebrafish larvae with abnormal muscle structure, such as the dystroglycan (dag1)-deficient zebrafish that model congenital myopathy, have generally reduced birefringence, and zebrafish larvae with dystrophic or damaged muscle often display darkened patches or holes (Smith et al., 2013; Berger et al., 2012). This evidence concerns the gene DAG1 and congenital myopathy with cores.