Fig. 7
Reproductive hormone receptor gene expression in male Atlantic salmon (experiment 2) exposed to normal light (NL) or to continuous additional light (LL). Based on testicular proliferation activity (see Fig. 4) and independent of the photoperiod, individuals showing type A spermatogonia (SGA) as the furthest developed germ cell type were assigned to groups with a low or a high proliferation activity (Plow and Phigh, respectively). Within the further developed stages showing type B spermatogonia (SGB), or spermatocytes/spermatids (SC/ST), all males showed high proliferation activity, irrespective of the photoperiod. a Pituitary gnrhr4 mRNA levels; b testicular ara1 and c ara2 mRNA levels; d testicular fshr and e lhcgr mRNA levels. The number of individuals analyzed per group is given under the respective bars, showing means and SEM. In the LL group in the SC/ST stage in a statistical comparison has not been included due to the small sample size and the individual values are shown. Statistical differences within a given graph between recruited fish showing elevated proliferation activity (Phigh) or non-recruited fish showing low proliferation activity (Plow) and between NL- or LL-exposed fish in the same stage of spermatogenic development are indicated by asterisks (Student t-test; *, p < 0.05; **, p < 0.01); the absence of an asterisk indicates the absence of statistically significant differences.