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Anatomical and Histological Organization of the Testes of the Inseminating Catfish Trachelyopterus striatulus (Steindachner, 1877) (Siluriformes: Auchenipteridae)

The testicular morphology, spermatogenesis and occurrence of sperm in the ovarian lumen of Trachelyopterus striatulus were studied using anatomical, histological and biometric techniques. A total of 50 catfish (T. striatulus) were captured, measuring 14.9 ± 2.5 cm of standard length, body weight was 81.2 ± 34.5 g and their testes weighed 16.9 ± 6.1 g. The testes of T. striatulus are paired organs, showing two distinct regions: cranial, which shows a compact medial part and with fringes ventrally, and caudal region, which is formed of the seminal vesicle with fringes laterally and two saculiform expansions. The testes presented a length of 35.2 ± 6.9 mm, and the fringes showed a cranial length of 12.1 ± 3.8 mm and caudal length of 6.4 ± 2.6 mm. Histologically, the cranial fringes are spermatogenic and showed cells with significantly different nuclear diameters, ranging from 8.2 ± 1.5 μm (primary spermatogonia) to 1.88 ± 0.3 μm (spermatid). The seminal vesicles and saculiform expansions showed tubules with a simple prismatic secretory epithelium containing spermatozoa and secretion into the lumen. The caudal fringes are exclusively for secretory flow, consisting of tubules with a simple cuboidal epithelium. The common spermatic duct showed a simple cuboidal epithelium and contained spermatozoa with secretion into the lumen. The secretion of the caudal region is acidophilic, with neutral glycoproteins and sialomucin. T. striatulus ovaries showed free spermatozoa or were organized in spermatozeugmata into the ovarian lumen and between the ovuligers lamellae.