Seasonal dynamics of proximate composition, fatty acid profile, and mineral content in muscle tissue of Diplodus annularis and Zosterisessor ophiocephalus fishes

Abstract

Seasonal variability significantly affects nutritional quality and the dietary and commercial value of marine fish. This study includes an in-depth seasonal analysis of proximate composition, energetic content, fatty acid profile, and mineral content of Diplodus annularis and Zosterisessor ophiocephalus extracted once a month in the Gulf of Gabes (Tunisia) for 1 year. Muscle samples were screened for moisture, protein, lipid, and ash with respect to sex and season, and fatty acid methyl esters were identified using gas chromatography and mineral compositions by ICP-OES. Biochemical changes associated with reproduction were examined using biological indices. Significant seasonal variation of the species was noted. D. annularis displayed the obvious appearance of high lipid accumulation during autumn and winter, when the muscle fat number is greater than 5%, classifying it as fatty fish. Z. ophiocephalus had consistently low lipid levels (<1%) throughout the year, which confirmed a lean classification. Protein also remained high in both species regardless of the season. Fatty acid profiles were largely dominated by palmitic and oleic acids with elevated levels of ω-3 polyunsaturated fatty acids (PUFAs). Calcium, potassium, sodium, and magnesium are the major elements in mineral analysis. These trends exhibit unmistakable species-based and season-dependent nutritional profiles, with D. annularis as a highly energetically concentrated fish and Z. ophiocephalus representing a low-fat, high-protein choice, and consequently their dietary value and sustainable exploitation in the Mediterranean.