Artificial spawning in cultured sterlet sturgeon, Acipenser ruthenus L., with special emphasis on hermaphrodites

Abstract

International audienceHormonal stimulation of sterlet sturgeon, Acipenser ruthenus, was carried out with carp pituitary extract at 2 and 5 mg kg−1 body weight for males on the one hand, females and hermaphrodites on the other hand. Within our experimental stock, reproductive performances defined by relative number of ovulated females, fertilisation rate, and relative number of good quality semen samples had begun to decline in fish older than 14-16 years. Ovarian cycle have proved to be mostly annual recurring cycles with a 1-year interval (40% to 50%) or 2-year interval (27% to 34%). Spawnable females ranged from 39% to 86% in our experimental period 1994 to 2000. Selection of spawnable females was mainly based on a minimum size of oocytes of 2.5-2.6 mm. For the first time, hermaphrodites have been reported in farmed sterlet sturgeon. Few sequential and simultaneous hermaphrodites have been observed. Most of the time both gametes proved to be functional in either mating. Embryonic survival of self-fertilised eggs ranged from 0% to 70%. Progeny was obtained twice. Out of 102 (1994) to 76 (2000) individuals representing an equilibrated sex ratio, 2 to 4 individuals, respectively, were hermaphrodites. The number of hermaphrodites increased with the age of the fish. Anatomical and physiological aspects are discussed. The modelling of our data demonstrates that fertilisation depends on gamete interaction, of which practical consequences are discussed. Artificial reproduction of hermaphrodite fish was confirmed by genetic analysis. Microsatellite analysis produced a homozygous excess of two alleles, both polymorphic loci