Seasonal variations in the biological characteristics and biochemical composition of bluemouth rockfish, Helicolenus dactylopterus (Actinopterygii, Perciformes, Sebastidae), in the central Mediterranean Sea

This study provides a comprehensive analysis of the annual biological cycle and biochemical composition of the bluemouth rockfish, Helicolenus dactylopterus (Delaroche, 1809), collected in 2022, from the northern Tunisian coast. We investigated seasonal variations in biological indices (condition, gonadosomatic, and relative growth) and biochemical constituents (lipids, proteins, glycogen, and fatty acids). Our key finding is a defined cold-season (winter) spawning period, evidenced by a significant peak in the gonadosomatic index (GSI) coinciding with a depletion of somatic condition, hepatic glycogen, and lipid reserves. Spawning was associated with a pronounced shift in energy allocation, with lipid and glycogen levels in muscle tissue decreasing by up to 92% and 88%, respectively, in winter. Biochemically, the species exhibited high protein content (41–77 mg · g –1 ) and was rich in omega-3 fatty acids, particularly in warm seasons (PUFA n-3 = 28%). The fatty acid profile (FA) was dominated by PUFA > MUFA > SFA year-round, with notable differences in energy reserves between sexes, as females showed higher energy mobilization for reproduction. These results provide crucial insights into the reproductive biology and energy allocation strategy of H. dactylopterus , underscoring its vulnerability to fishing pressure during spawning and its consistent nutritional value, which is vital for sustainable management in the Mediterranean.