Abstract
Diplodus annularis are common public seafood in Libya. Parasites like crustaceans are dangerous threats to fish species because they can lead to less quality seafood production besides the shortcuts of the fish life cycle that significantly affects marine life's biodiversity. So, it was recommended to follow up the health status of fish by identifying and counting different parasites spread in Libyan seawater, especially around Tripoli. This research aims to evaluate the common parasites of D. annularis. About ~ 3300 g of fish samples (60 individual units) were examined for the presence of helminthes endoparasites, copepods, branchiura, and isopoda. Results evaluated in terms of prevalence percentage with different ranges of length and weight of fish samples in addition to maturity. Results prove that branchiura (Argulus purpureus) and isopoda (Ceratothoa oestroides) are the common parasites that lived on D. annularis with the highest percentage of infestation ~ 10.34 and 4.35 % for (12-14) and (14-16) cm length respectively. The sex of a D. annularis species was confirmed by examining the genital papilla located behind the anus and finding a balance between the numbers of males and females, but male are more infested than female samples. A correlation between length, maturity and infection was theoretically confirmed by applying a mathematical exponential model to male and female and hence probability function of maturity and parasitological infection of D. annularis can be expected within a particular length range.