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 fro m 35 to 71 d of incubation is reported. A battery of 6 different horse radish peroxidase-labelled lectins, the PAS reaction and Alcian blue s taining were used to study the distribution of carbohydrate residues i n 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. WG A, DBA and SBA were good markers for the hatching gland cells (HGCs) a nd mucous cells. Other lectins, such as PNA and UEA I, reacted only fo r a short time at some sites during the considered period of incubatio n. 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.