Minireview: The modes of egg attachment in teleost fishes

Abstract

Oocytes and eggs from teleost fishes are always surrounded by an egg envelope of variable dimensions. This envelope (zona radiata) in teleosts normally consists of two layers, a zona radiata interna and a zona radiata externa. The chemical composition of the interna is proteinaceous. Neutral and acid mucopolysaccha‐rides are the main components of the externa. The zona radiata interna is largely responsible for a protective function, whereas the zona radiata externa is used to attach the eggs to the substrate where they are deposited. For the latter it is equipped with variable mechanisms such as special sticky layers (e.g., in Phoxinus pboxinus, Chalcalburnus chalcoides mento, Esox sp., Lota lota and 1‐eggs in cichlids), hexagonal patterns (e.g., in many percids and in channichthyids), villi‐like protuberances (= attaching‐plugs; in many cyprinids), attaching‐filaments (e.g., in gobies and blennies, p‐eggs in cichlids, piranhas and clariids), a jelly layer (Perca fluviatilis) or a muco‐follicle epithelium (Silunis glanis). This enables not only an attachment to the substrate but the eggs also can be placed in clusters and may be protected by the fish species which guard their egg deposits. In water bodies which have little or greatly reduced available oxygen, the eggs may be attached to plant tips and thus help to ensure adequate supplies of oxygen.