Changes in the number of germ cells in the gonads of the rainbow trout (Salmo gairdneri) during the first 10 post-hatching weeks

Abstract

Summary. The number of germ cells in fry gonads was determined from histological sections sampled periodically over a 10-week post-hatching period. Several The number of germ cells increased regularly from 47 ± 35 (SD) after hatching (PGC) to 166 ± 25 at 2 post-hatching weeks (G!). At 5 post-hatching weeks, two groups of fish could be distinguished by the number of their germ cells (G 2 ) -one group had less than 926 cells and the other more than 1 577 ― and by their gonadal morphology (filiform or with an enlarged anterior part due to germ cell concentration). At 6 post-hatching weeks, the ovary differentiated with organization of the ovarian lamellae and the appearance of oocytes in meiotic prophase (4 out of 10 trout). The gonads of the other fish stayed at the indifferent stage. The number of germ cells was significantly higher in female-type gonads (6 335 ± 3 558) than in indifferent gonads (1 696 + 467). The situation was the same at 8 to 10 weeks.Introduction.

Characterization of early molecular sex differentiation in rainbow trout, Oncorhynchus mykiss

“…These germ cells are recognized by their large, pale, round nuclei with a single nucleolus and correspond to primordial germ cells (PGCs) previously described by Lebrun et al (1982). These PGCs were surrounded by undifferentiated somatic cells (35 dpf, Fig.…”

“…Using histological criteria, this differentiating period is observed in rainbow trout around 5 weeks post-hatching at 10°C (ϳ67 dpf) with the first detection of oocyte meiosis and the concomitant formation of ovarian lamellae in females (Lebrun et al, 1982). Using gene expression profiling and ISH, we were able to demonstrate that gonadal differentiation occurred much sooner, i.e., shortly after hatching and at least one month before the first signs of morphological gonadal differentiation.…”

“…1), delimited by some connective tissue. Inside the ovarian lamellae, germ cells are characterized by their pale, round nuclei with several nucleoli corresponding to gonocytes described by Lebrun et al (1982). Somatic cells located between germ cells are characterized by an elongated nucleus.…”

Sex Differentiation in an All-Female (XX) Rainbow Trout Population with a Genetically Governed Masculinization Phenotype

“…The histology of gonads undergoing normal sex differentiation in the rainbow trout has been well described [Takashima et al, 1980;Lebrun et al, 1982;Vizziano et al, 2007;Nagler et al, 2011]. At a rearing temperature of approximately 11 ° C, the morphological features of ovarian differentiation are not detectable until 4-5 weeks after hatching, and clear testis differentiation with cystic organization does not appear until approximately 3 months after fertilization, at which time sex can be unambiguously assigned by histological observation.…”

“…The samplings ( fig. 1 ) were cho-sen according to the following known developmental landmarks [Takashima et al, 1980;Lebrun et al, 1982;Vizziano et al, 2007;Nagler et al, 2011]: the increase in the primordial germ cells in both sexes between 35 to 61dpf (i.e. 350-691 degrees × days (° Cdays) in the present experiment), the earlier (from 69 dpf; 784 ° Cdays) increase in the number of germ cells in the differentiating ovary than in the future testis, and the earlier (at around approximately 69 dpf) meiotic entry of female germ cells concomitant with the beginning of ovarian lamellae organization and germinal epithelium lateralization of the ovary.…”