Comparative gonad histology and semen quality of normal (XY) and neo‐males (XX) of Atlantic salmon (Salmo salar)

Abstract

With an overarching objective of improving the hatchery production of Atlantic salmon (Salmo salar) all‐female progeny, this study comparatively evaluated the reproductive parameters between normal (genotype XY) and neo‐males (genotype XX). Four normal (XY) and seven neo‐ (XX) males, from the same brood stock, distinguished by their ability to or lack of expressing semen, respectively, were comparatively evaluated. The left testicular lobe was used for histomorphometric analyses, while the right for semen collection and sperm quality analyses. Histomorphometric observations revealed that neo‐male testes are irregularly shaped, and have poorly formed seminiferous ducts, higher proportions of interstitial tissue and lower gonadosomatic index (p < .05). In addition, hypertrophied and cyst forming Sertoli cells were found in these individuals which collectively appear to form a physical barrier, precluding the semen collection by standard stripping techniques and reducing sperm quality. Particularly, semen motility (80.69 ± 2.4% and 57.2 ± 36.5% for XY and XX respectively) and duration of motility (99.31 ± 28.03 s and 66.84 ± 23.83 s for XY and XX respectively) of neo‐males were most compromised (p < .05). Interestingly, the TUNEL assay indicated no signs of apoptotic tissue suggesting that the histological differences may relate to delayed physiological/sexual maturity of neo‐males.

Characteristics and Cryopreservation of Semen of Sex-Reversed Females of Salmonid Fish

“…For example, for rainbow trout, the average sperm concentration of SRF testicular semen amounts to approximately 30 × 10 9 spermatozoa mL −1 , which is about three times higher than the stripped semen of normal males [ 55 , 56 , 57 ]. Moreover, the sperm concentration values of the testicular semen of SRF are usually similar to values recorded for the testicular semen of normal males [ 3 , 49 , 52 ].…”

“…The current knowledge concerning sperm motility of testicular semen of SRF is primarily based on the characteristics of SRF rainbow trout, which have been characterised in 19 publications (see Table 3 ). The sperm motility percentages in SRF Atlantic salmon and brook trout were presented only in single publications and were between 53.0–59.0%, which is similar to that in SRF rainbow trout [ 52 , 58 ]. Moreover, significantly higher values of sperm motility in the testicular semen of normal male Atlantic salmon (81%) than in the testicular semen of SRFs (57%) were recorded [ 52 ].…”

“…Additionally, the cysts of epithelial hyperplasia were found. This tissue, filling the lobule, perhaps consists of hypertrophied Sertoli cells, which were also identified in SRF Atlantic salmon [ 52 ]. It should be noted that the rate and quality of spermatogenesis are determined by the number and functionality of Sertoli cells present, and therefore, complications with their development can be responsible for pathological processes resulting in reduced semen quality in SRFs [ 53 ].…”

“…SRFs have less developed testes and there is usually a lack of spermatic ducts, where the final maturation of spermatozoa occurs [ 3 ]. Owing to the lack of spermatic duct secretions, the sperm of SRFs resembles testicular rather than ejaculated sperm and is often characterised by low and highly variable sperm quality (including increased sperm concentration and reduced motility parameters) compared to that of ejaculated sperm from normal males [ 52 , 54 , 55 ].…”

“…It should be also noted that the motility duration of SRF rainbow trout spermatozoa lasts up to 40 s and do not differ from values recorded for normal males [ 3 ]. However, the motility duration of Atlantic salmon testicular sperm is much longer for normal males (up to 100 s) than for SRFs (up to 67 s; [ 52 ]). It must be underlined that information regarding the motility characteristics of SRF semen is often gathered from experiments concerning semen cryopreservation.…”