Although the involvement of β-endorphin (β-ERP) in vertebrate reproduction has been suggested, its role in testicular activity is not clear in fish. We describe the influence of β-ERP on spermatogenesis in a cichlid fish in the present paper. In comparison to the control group, the administration of β-ERP (3 µg) caused a significant increase in the number of spermatogonia-A and spermatids. Following treatment with β-ERP (6 µg), a significant increase in the number of spermatogonia-A was observed, whereas the numbers of all the other germ cells, excluding spermatogonia-B, significantly decreased in comparison to those in the control group. In addition, treatment of fish with 6 µg β-ERP resulted in a significant reduction in the dimensions of the lumen and seminiferous lobules, the level of immunopositive androgen receptor (AR) expression in Sertoli cells, and the percentage of luteinizing hormone (LH) immunolabeled in the pituitary compared to those in the control group or the group treated with 3 µg β-ERP. In contrast, the intensity of AR immunoreactivity and the percentage of LH immunolabeling were substantially increased in fish treated with 3 µg β-ERP compared to those in the control group. These findings reveal for the first time that a low dose of β-ERP stimulates the recruitment of spermatogonia as well as spermateleosis, whereas a high concentration affects the recruitment of germ cells prior to meiotic division in tilapia. These results suggest that β-ERP exerts modulatory effects at the testicular and hypophysial levels through alterations in AR expression and LH secretory activity, respectively, in teleosts.

尽管β-内啡肽（β-ERP）已被认为参与脊椎动物的繁殖，但其在鱼类睾丸活动中的作用尚不清楚。我们在本文中描述了 β-ERP 对慈鲷精子发生的影响。与对照组相比，β-ERP（3 µg）的施用导致精原细胞-A和精子细胞的数量显着增加。用 β-ERP（6 µg）治疗后，观察到精原细胞 A 的数量显着增加，而除精原细胞 B 之外的所有其他生殖细胞的数量与对照组相比显着减少。此外，用 6 µg β-ERP 处理鱼可显着降低管腔和曲细精小叶的尺寸、支持细胞中免疫阳性雄激素受体 (AR) 的表达水平以及黄体生成素 (LH) 的百分比与对照组或用 3 µg β-ERP 治疗的组相比，垂体中进行了免疫标记。相反，与对照组相比，用 3 µg β-ERP 处理的鱼的 AR 免疫反应强度和 LH 免疫标记百分比显着增加。这些研究结果首次揭示，低剂量的β-ERP会刺激精原细胞的募集以及精原细胞的形成，而高浓度的β-ERP会影响罗非鱼减数分裂之前生殖细胞的募集。这些结果表明，在硬骨鱼中，β-ERP 分别通过改变 AR 表达和 LH 分泌活性，在睾丸和垂体水平发挥调节作用。