Loss of basihyal element in catfishes. Catfishes (Siluriformes) are characterized by the loss of the basihyal element in contrast to relatives, including zebrafish. (A) Zebrafish, Danio rerio (purchased from an aquarium fish store by P. Mabee). (B) Spotted Bullhead Catfish, Ameiurus serracanthus (ANSP 185358; provided by K. Luckenbill). Images show lower branchial elements in ventral view. bb, basibranchial; bh, basihyal; cb, ceratobranchial; ch, ceratohyal. Scale bars = 100 µm.

Pharyngeal arches develop later in catfish than in zebrafish. Chondrification of jaw (mandibular arch), hyoid arch, and branchial arches as detected by Alcian Blue staining. Images show lower branchial elements in ventral view. (A) Ictalurus punctatus, 96 hpf; (B) Ancistrus cf. triradiatus, 96 hpf; (C) Corydoras aeneus, 102 hpf; (D) Danio rerio, 72 hpf. m, Meckel’s cartilage; bh, basihyal; ch, ceratohyal cartilage; cb, ceratobranchial cartilages. Scale bars = 100 µm.

Catfishes lack brpf1 expression in the region where the basihyal forms in zebrafish. Expression of brpf1 during pharyngeal arch skeletal development in Danio rerio and Ictalurus punctatus, as detected by whole-mount in situ hybridization. Staining of pharyngeal arch cartilages using (A) Alcian Blue in D. rerio (72 hpf) and (B) Alcian Green in I. punctatus (86 hpf). Endogenous brpf1 expression in (C) D. rerio (72 hpf) and (D) I. punctatus (86 hpf). Arrows indicate location of basihyal element in D. rerio (cypriniform) and lack of basihyal element in I. punctatus (siluriform). Images are representative of e30 embryos. No labeling was detected in negative controls (data not shown). m, Meckel’s cartilage; ch, ceratohyal cartilage; cb, ceratobranchial cartilages. Scale bars = 100 µm.