Diversity of Metazoan Parasites of the Little Tunny (Euthynnus alletteratus Rafinesque, 1810) from the Tunisian Coast of Gulf of Gabes (Mediterranean Sea).

Purpose: Euthynnus alletteratus (Scombridae) is widely distributed in the Atlantic Ocean including Tunisian coast. This species appears to be a promising species for aquaculture due to its rapid growth and the quality of its flesh. The present study aims to identify the metazoan parasites fauna of E. alletteratus in the Gulf of Gabes and analyze parasitism variation according to sex, age, and season.

Methods: A total of 341 specimens of E. alletteratus (175 females and 166 males) of 21-66 cm long were collected in the Gulf of Gabes between February 2024 and January 2025 for parasitological analysis.

Results: Six metazoan parasites species were identified. Three were found on the gills: Capsala manteri (Monopisthocotyla), Neohexostoma euthynni (Polyopisthocotyla) and Pseudocycnus appendiculatus (Copepoda). Notably, C. manteri and P. appendiculatus are reported here for the first time in Tunisia. In the stomach, the digenean Lecithochirium texanum was identified, while Anisakis type I larvae were observed on the viscera, and the acanthocephalan Rhadinorhynchus pristis was found in the intestine. Parasite prevalence and abundance were significantly influenced by seasonal and host-related factors. Prevalence generally declined in winter, while abundance peaked in spring and summer. Among all species, only N. euthynni showed a significant association between prevalence and host age, increasing in older males. The abundance of N. euthynni, P. appendiculatus and Anisakis type I larvae also increased in older hosts. These trends were further shaped by seasonal variation.

Conclusion: This study provides new insights into the parasitic fauna in the Gulf of Gabes. Our findings show that prevalence and abundance of studied parasites are primarily driven by seasonal dynamics and host characteristics. The age-related patterns, particularly in N. euthynni, highlight the complex interplay between host development and parasite life cycles, emphasizing the dynamic nature of host-parasite interactions in marine ecosystems.