Formalin‐fixed gonad tissues from sterile and fertile males and females (n = 6–10 per group) were processed overnight in Tissue Processor (Logos; Milestone). Paraffin embedded tissues were sectioned (2 μm) using a rotary microtome (Leica) and stained with hematoxylin and eosin (Merck) in auto‐stainer (Leica) at the Norwegian Veterinary Institute, Harstad. All slides were then analyzed at Nofima, Tromsø, using light microscopy and the QuPath (Quantitative Pathology & Bioimage Analysis) software. Germ cells were detected by immunohistochemical analysis of a subset of gonads using polyclonal rabbit antibodies against Atlantic salmon Vasa (Škugor et al., 2016 (link)) as primary antibodies and the ImmPRESS polymerized reporter enzyme staining system (Vector) with horseradish peroxidase anti‐rabbit immunoglobulin G as secondary antibody according to manufacturer's protocol. Sections treated without the primary antibody were used as negative controls.