Characterization of semen of Baryancistrus xanthellus Rapp Py-Daniel, Zuanon & Ribeiro de Oliveira, 2011 (Siluriformes, Loricariidae), an endemic catfish species from the Xingu River, Pará, Brazil

Baryancistrus xanthellus is an endemic species of the Xingu River, known as “Gold Nugget Pleco”. Its color pattern arouses interest in the aquarium fish trade, making this species highly valued in the global market. Its natural populations suffer ecological impacts due to overfishing and environmental changes especially by the Belo Monte Hydroelectric Power Plant. Despite its economic and ecological relevance, conservation efforts including, artificial breeding, becomes necessary, although no record of artificial breeding. The objective of this study is to analyze the sperm characteristics of wild-caught Baryancistrus xanthellus to support ex-situ conservation strategies and facilitate the development of technologies and studies related to the species' reproduction. For this purpose, 10 adult mature males (weight 315.3 ± 17.48 g; standard length 23.06 ± 0.69 cm) were collected during the spawning season (October 2022 to February 2023). Seminal samples were collected without hormonal treatment for using a 1000-µm pipette in the urogenital papillae, and immediately diluted in immobilizing solution. Sperm activation achieved by a 11-fold dilution using distilled water, and motility analysis was conducted using computer-assisted sperm analysis (CASA) from video sequences obtained from the microscope. Data were analyzed considering the significance value of P < 0.05 , with ANOVA succeeded by Pearson’s correlation test. Surprisingly, the species presented motility duration of 424.80 ± 278.40 s, with a significant decrease on motility after 180 s. Negative correlations were observed between sperm abnormalities, motility and kinetic patterns. However, abnormalities in the midpiece of spermatozoa seem to impair the percentage motile spermatozoa. Males released 75.00 ± 60.09 µL of semen and sperm concentration was 1.10 ± 0.93 × 10 7 sptz.mL −1 . Our study demonstrated that it is possible to collect semen from wild-caught Baryancistrus xanthellus during spawning season, and no hormonal treatment is necessary. A progressive motility of long duration was observed in the species, suggesting good fertilization capacity. All the results showed above are innovative, and the first step for future conservation efforts including germplasm conservation and subsequent in vitro fertilization. • Semen from wild-caught Baryancistrus xanthellus can be collected without hormonal treatment during the spawning season. • Seminal characterization is the first step for subsequent conservation and aquacultural purposes. • Practical tips for collecting and analysing sperm and new findings are found Loricariidae family.