Differential processing of yolk proteins during oocyte hydration in marine fishes (Labridae) that spawn benthic and pelagic eggs

Abstract

The yolk proteins and free amino acids (FAA) were investigated during oocyte maturation in 4 species of Labridae with either benthic or pelagic eggs. Benthic eggs and oocytes of both types had a small FAA pool dominated by taurine, while pelagic eggs had a large and characteristic FAA pool with about equal amounts of indispensable and dispensable amino acids. Electrophoresis (SDS-PAGE) of the yolk proteins revealed the presence of high molecular weight yolk proteins in the oocytes of all 4 species. In 2 species with benthic eggs (Labrus bergylta, L. mixtus), no buildup of an FAA pool occurred (nmol µg-1 dry mass) during final maturation, and the yolk protein profile remained essentially unchanged. In a third species (Crenilabrus melops) with benthic eggs, partial degradation of a 112 kDa protein coincided with the buildup of a small FAA pool. In the species with pelagic eggs (Ctenolabrus rupestris), the buildup of a large FAA pool coincided with the disappearance of the 112 kDa yolk protein. The calculated yield of FAA by hydrolysis of the disappearing fraction of the 112 kDa yolk protein for both species matched well with the measured increase in the FAA pool. It is suggested that differential processing of the high molecular yolk proteins causes differences in teleost egg behaviour, benthic or pelagic.