Phylogenetic tree for visual opsin gene sequences. The tree was generated by the neighbour-joining method , using amino acid sequences aligned by ClustalW . The degree of support for internal branching was assessed by bootstrapping with 1000 replicates using the MEGA2 computer package . The calibration bar is equivalent to 0.1 substitutions per site. GenBank accession numbers for the sequences (from top to bottom) are Eel rh1 "freshwater", L78007; Eel rh1 "deep sea", L78008; Goldfish rh1, L11863; Killifish rh1, AY296738; Salmon rh2, AF201470; Eel rh2, FJ515778; Goldfish rh2/1, L11866, Goldfish rh2/2, L11865; Ayu rh2/2, AB098704; Ayu rh2/1, AB098703; Salmon rh2, AY214132; Metriaclima zebra rh2B, DQ0088652; Killifish rh2, AY296739; Metriaclima zebra rh2Aβ, DQ088650; Metriaclima zebra rh2Aa, DQ088651; Eel sws2, FJ515779; Salmon sws2, AY214134; Metriaclima zebra sws2B, AF247118; Killifish sws2B, AY296736; Killifish sws2A, AY296737; Metriaclima zebra sws2A, AF247114; Goldfish sws2, L11864; Goldfish sws1, D85863; Killifish sws1, AY296735; Salmon sws1, AY214133; Goldfish lws, L11867; Killifish lws, AY296740; Salmon lws, AY214131; Drosophila rh4, NM_057353.