Conservation between O. niloticus opsin-containing BAC regions and four fish genomes. A) SWS1 opsin-containing region. B) SWS2-LWS opsin-containing region. C) RH2 opsin-containing region. Top line represents O. niloticus BAC sequence. Conserved non-coding elements (CNEs) are numbered and highlighted in red; repetitive sequences are highlighted in green; promoter sequences later examined for interspecific polymorphism are highlighted in blue.