Enables histone H3-methyl-lysine-9 demethylase activity. Acts upstream of or within histone H3-K36 demethylation; histone H3-K9 demethylation; and negative regulation of histone H3-K9 trimethylation. Located in pericentric heterochromatin. Is expressed in several structures, including early conceptus; genitourinary system; heart; nervous system; and sensory organ. Human ortholog(s) of this gene implicated in autosomal dominant non-syndromic intellectual disability; breast cancer; colorectal cancer; malignant peripheral nerve sheath tumor; and stomach cancer. Orthologous to human KDM4B (lysine demethylase 4B). [provided by Alliance of Genome Resources, Apr 2022]