Parasitic copepod (Lernanthropus kroyeri) on caged sea bass (Dicentrarchus labrax): An estimation of abundance and internal infestation pressure.

Infestation by parasitic copepods is a substantial problem in the cage culture of European sea bass (Dicentrarchus labrax). The Copepoda parasite, Lernanthropus kroyeri (Lernanthropidae), is one of the threats to the mariculture of sea bass. In the present study, we evaluated the data of abundance for L. kroyeri pre-adults and adult males (PAAM) and ovigerous adult females (AF ) to estimate the internal infection pressure (IIP) in the same cage environment. The sea bass infested by L. kroyeri was collected from grow-out sea cages located in Gulluk Bay (Turkey) in September and October 2019. Mean fish weight and length of sea bass were 75.79 ± 1.66 g and 21.40 ± 0.56 cm, respectively. The fixed lag method was used to predict the abundance of L. kroyeri adult females. The overall prevalence of L. kroyeri was 60%. The mean abundance of PAAM and AF varied from 0.8 ± 0.24 to 2.5 ± 0.67 and 2.9 ± 0.40 to 4.3 ± 0.55, respectively. The abundance of AF was strongly correlated with PAAM. The pattern of AF and PAAM was interpreted as an indication of the continuous infestation of L. kroyeri on sea bass. Our results showed that the correlation of AF abundance for five consecutive weeks was significant, representing the main determinative factor for the continuity of the parasitic load. In our approach, internal infestation pressure is the quantitative estimation of the potential infective copepodids, which are mainly characterized by AF abundance and the prevalence. We predicted that the internal infestation pressure could be high, even exceeding the 50.000 × 10 potential infective copepodids for one sea cage with the fish density of 20 sea bass/m .