Diet of Mediterranean moray, Muraena helena (Actinopterygii: Anguilliformes: Muraenidae), from the north-eastern Tunisian coast (central Mediterranean)

Background. The feeding behaviour of Mediterranean moray, Muraena helena Linnaeus, 1758, from the coast of Tunisia (central Mediterranean) is poorly know and this study is a first step in determining prey consumption by M. helena as main information for improving fishery monitoring and management in the study area. Materials and methods. Of the 411 sampled Mediterranean morays, 237 were males and 174 females. The stomach contents were removed, sorted, identified to the lowest possible taxon, counted, and weighed. For diet description, we calculated vacuity index (VI), abundance (mean number of preys) (NM), frequency of occurrence (F%), relative abundance (N%), and frequency by weight  (W%). The contribution of each prey in the diet was also estimated with Index of Relative Importance (IRI) and its standardized value (%IRI). The trophic level (TROPH) was calculated for total sample to determine the diet of the species, but it was also related to the sex, size, and seasons. Results. The relation between the total length and the total body weight showed a positive allometry for both males and females. VI presented high values, for total sample, sex, size, and season. Muraena helena under study consumed a variety of prey items including 3 higher taxa, 13 families, and 20 species. Osteichthyans were the dominant preys with 15 taxa, representing 96.84% of weight, 78.83% of number, 84.21%, of frequency, and %IRI = 98.51. Crustaceans and cephalopods and sea grass were also ingested by M. helena, with lower %IRI (0.65, 0.66), and no ontogenetic changes in the diet were recorded related to sex, size, and seasons. The most common prey species were Diplodus annularis (Linnaeus, 1758) and D. vulgaris (Geoffroy Saint-Hilaire, 1817) with  %IRI = 28.52 and 7.45, respectively while Serranus cabrilla (Linnaeus, 1758) was also consumed with %IRI = 1.84. The calculated TROPH was 4.27 (SE = 0.74); changes were recorded with seasons but not significantly different. Conclusion. Muraena helena is a carnivorous species feeding on prey items representing three higher taxa, osteichthyans being the most common in stomach contents and such findings suggest that it should be considered as a piscivorous species. The high value of trophic level pointed out that M. helena is a top predator.