The uptake of macromolecular materials in the hindgut of viviparous rockfish embryos

Regions of the gut of near-term embryos and new-born larvae of the viviparous rockfish Sebastes taczanowskii were examined histologically and immunohistochemically in order to ascertain whether they possessed the potential to absorb intact macromolecules. Compared with the hindgut of larvae 24 h after parturition, that of near-term embryos (stage 31) was found to be markedly hypertrophied and to react positively when tested for the presence of eosinophilic materials and with antibodies raised against extracts of the rockfish yolk (ab.a-E). In addition, near-term embryos incubated in Ringer solution containing 1% bovine serum albumin appeared to accumulate the protein within the epithelium of the hindgut. Furthermore, as confirmed by immunodiffusion analysis, the ovarian fluid contained materials which reacted positively to ab.a-E. These results suggest that ingestion of intact macromolecules occurs during the late embryonic stages and that the yolk-like substances detected within the hindgut epithelium of such embryos may be derived from the bathing ovarian fluid.