Introduction
The Carpione (Salmo carpio L.) is an endangered salmonid endemic to Lake Garda and represents a promising candidate for aquaculture diversification in the Autonomous Province of Trento, Italy. Carpione inhabits deep pelagic waters at depths exceeding 150 m. Its reproductive cycle involves seasonal migrations from the central-southern basin toward northern spawning grounds, where it seeks gravelly-sandy substrates at depths of 150 – 200 m, typically 200 – 500 m offshore (Raunich et al., 1990). Sexual maturity is generally reached at approximately 3 years for males and 4 years for females (Melotto & Alessio, 1990). While spawning phenology remains a subject of debate, two distinct periods are generally recognized: a primary winter peak (December–February) and a secondary summer event (July–August) (Gandolfi et al., 2006). Interestingly, some females may spawn twice within a single year, a phenomenon likely driven by rapid post-spawning vitellogenesis (Melotto & Alessio, 1990). Following reproduction, adults migrate back to the southern basin to feed (Raunich et al., 1990). Despite its potential, limited understanding of the species' reproductive physiology currently constrains both commercial production and conservation efforts.
The aim of the "Filiera Astro" project is to improve the local aquaculture industry through the adoption of precision fish farming principles, a better understanding of farm-environment interactions, and strategies to limit pressure on ecosystems. Additionally, the project focuses on the reuse of fish-farming by-products and the application of new technologies to reduce feed waste and environmental impacts. A part of the project focuses on developing farming protocols for S. carpio. This study assessed reproductive performance and key physiological indicators in captive broodstock during the 2025 spawning season, with emphasis on endocrine status, histological analysis, and stress responses associated with stripping procedures.
Material and methods
Reproductive monitoring was conducted from February to July 2025. A total of 479 females and 264 males were spawned, yielding 64 L of eggs with an average fertility of 40.4%. A marked production peak occurred in April. To evaluate physiological responses to handling and reproduction, females were sampled at three time points (15 individuals per group): prestripping (PRE), 24 h poststripping (POST1), and 21 days poststripping (POST21). The following parameters were monitored in fish plasma: 17β-estradiol (E2), testosterone (T), progesterone (P4), glucose, superoxide dismutase (SOD), catalase (CAT), and glutathione Peroxidase (GPx). Ovaries were analysed through histology using hematoxylin and eosin Y (H&E) and periodic acid-Schiff (PAS) staining procedures to evaluate the ovarian cellular structure
Results and Discussion
Contrary to published reports of first maturation occurring at age 3 for males and age 4 for females, a substantial proportion of 2-year-old individuals (62%) in this study reproduced successfully in captivity. However, these younger fish exhibited significantly higher post-spawning mortality compared to 3-year-old broodstock. This suggests that precocious maturation—likely accelerated by consistent feeding and reduced energetic costs in a controlled environment—may compromise long-term survival. For commercial production, delaying first maturation until age 3 may enhance both animal welfare and overall reproductive efficiency.
Regarding physiological indicators, plasma concentrations of estradiol, testosterone, and progesterone did not differ significantly between groups, indicating stable steroidogenic activity throughout the sampling period. Histological analysis confirmed ongoing reproductive activity, with ovaries at various maturity stages observed in POST21 females and no evidence of anatomical damage resulting from the stripping procedure.
In contrast, cortisol levels increased significantly (p < 0.05) by POST21. This elevation was accompanied by increased activity of antioxidant enzymes, specifically superoxide dismutase (SOD) and catalase (CAT), revealing a delayed stress and oxidative response. Notably, glucose levels remained stable.
These findings indicate that while the stripping procedure does not acutely suppress steroid production or cause physical tissue damage, the cumulative impact of handling and reproductive effort induces measurable stress after three weeks. Younger broodstock appear particularly vulnerable, highlighting the necessity of optimizing management practices and minimizing handling frequency to preserve the welfare and reproductive performance of S. carpio.
Acknowledgment
Project "Filiera ASTRO: Competitiveness and Sustainability of Mountain Aquaculture" (CUP J38H23001450007), funded by the "Piano Nazionale Complementare – PNC" of the Ministry of Agriculture, Food Sovereignty and Forests (MASAF).
References
Gandolfi, A., Ciutti, F., & Grando, M. S. (2006). l carpione del Garda (Salmo carpio): Variabilit�� genetica e relazioni filogenetiche rispetto al complesso Salmo trutta. BIOLOGIA AMBIENTALE, 20(1), 7–12.
Melotto, S., & Alessio, G. (1990). Biology of carpione, Salmo carpio L., an endemic species of Lake Garda (Italy). Journal of Fish Biology, 37(5), 687–698. https://doi.org/10.1111/j.1095-8649.1990.tb02533.x
Raunich, L., Balestra, V., & Zaccanti, F. (1990). Observations on the reproductive period of the Lake Garda salmonid carpione. Rivista di Idrobiologia, 29(3), 847–859.