039 | Age and growth of the mesopelagic fish Electrona risso (myctophidae) from the Strait of Messina (central Mediterranean sea)

Calogero Fontana¹, Alice Vaccaro², Francesco Longo¹, Danilo Malara³, Emanuela Fanelli^2|4, Pietro Battaglia^1|4 | ¹Stazione Zoologica Anton Dohrn, Sicily Marine Centre, Messina, Italy; ²Università Politecnica delle Marche UNIVPM, Dipartimento di Scienze della Vita e dell’Ambiente, Ancona, Italy; ³Northern Territory Government of Australia, Department of Agriculture and Fisheries, Fisheries Division, Berrimah, NT, Australia; ⁴National Biodiversity Future Center, Palermo, Italy.

Electrona risso (Cocco, 1829) is a mesopelagic fish belonging to the family Myctophidae and contributes significantly to the 400m Deep Scattering Layer (DSL) biomass in the Mediterranean Sea. It is an important component of the Mediterranean pelagic food web and commonly found in the stomach contents of several pelagic predators, such as bluefin tuna. There is limited information available on the biology and ecology of this species, particularly about age and growth. The present study provides a first assessment of the age and growth of E. risso from the Strait of Messina (central Mediterranean sea). Overall, 161 fresh individuals were collected stranded in the study area, and their otoliths were removed for age analysis. The research examined the length-weight relationship (LWR), the microstructure of the sagittal otoliths as well as the growth patterns, counting daily microincrements. The multi-model inference approach was used to assess the growth of E. risso, by fitting three different non-linear growth models: von Bertalanffy model (VBGF), Gompertz's model, and logistic growth function. The LWR showed a positive allometric growth (b =3,143636). Analysis of daily micro-increments of otoliths revealed a short life cycle, with estimated ages ranging from 95 to 524 days in our individuals. Application of the multi-model inference approach revealed sex-specific growth dynamics: the VBGF model effectively describes males (L∞ = 66.72 mm; k = 0.003), while the logistic model is optimal for females (L∞ = 51.25 mm; k = 0.0096). This difference suggests an energy trade-off in females, where somatic growth slows down to favour reproductive effort. Overall, the analyses conducted and data obtained in this study contribute to expanding the biological and ecological knowledge of E. risso, a species that needs further investigation in the Mediterranean context.