The culture of the Patagonian pejerrey (Odontesthes hatcheri ), a native species of Patagonia, is currently at an experimental stage and represents a promising alternative for diversifying regional aquaculture. However, the presence of pathogens such as oomycetes of the order Saprolegniales poses a significant health risk during the larval stage. This study assessed the pathogenicity of a Saprolegnia diclina strain in Patagonian pejerrey larvae fed with different diets under controlled experimental conditions.
Eight-day post-hatch larvae were distributed into groups of 15 individuals and fed one of three diets: Artemia salina nauplii, formulated feed (Table 1), or a combination of both. Groups were exposed for 10 days to an initial concentration of 2.6 × 10² zoospores·mL⁻¹ of S. diclina at 15 ± 3 °C. Daily mortality was recorded, and clinical as well as histopathological signs of infection were examined. Larvae receiving formulated feed, either alone or in combination, exhibited higher mortality and infection rates compared to those fed exclusively on Artemia (Table 2). Hyphae were detected in the digestive tract, abdominal cavity, integument, kidney, and muscle, and were associated with inflammatory, degenerative, and necrotic processes (Figure 1). In addition, hyphae were observed on residual formulated feed settled at the bottom of the tanks.
These findings indicate that diet influences both the route and severity of S. diclina infection. The results suggest that the presence of formulated feed favours zoospore germination within the digestive tract, initiating infection from inside the host. We conclude that diet is a critical factor influencing susceptibility to saprolegniasis during the larval phase of Patagonian pejerrey and emphasize the importance of optimizing both feed formulation and health management strategies in the culture of this species.
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