A histochemical study of the distribution of lectin binding sites in the developing branchial area of the trout Salmo trutta.

A histochemical study of the branchial area of brown trout embryos from 35 to 71 d of incubation is reported. A battery of 6 different horseradish peroxidase-labelled lectins, the PAS reaction and Alcian blue staining were used to study the distribution of carbohydrate residues in glycoconjugates along the pharyngeal and branchial epithelia. Con A and WGA reacted at every site of the branchial region thus showing the ubiquitous presence of alpha-D-mannose and N-acetyl-D-glucosamine. WGA, DBA and SBA were good markers for the hatching gland cells (HGCs) and mucous cells. Other lectins, such as PNA and UEA I, reacted only for a short time at some sites during the considered period of incubation. From 35 d until posthatching stages, a manifest strong reaction was noted both in the dorsal epithelium of branchial arches and the HGCs as shown by SBA reactivity. This may be significant with regard to the controversial origin of HGCs, which is thought to be endodermal.