The Isopod Parasite Ceratothoa oestroides (Cymothoidae) in European Sea Bass (Dicentrarchus labrax): Estimation of Initial Reproductive Maturity and Fecundity

Abstract

Ceratothoa oestroides (Cymothoidea, Isopoda) is a crustacean parasite that primarily affects European sea bass (Dicentrarchus labrax) in Mediterranean aquaculture. The study aimed to estimate first reproductive maturity and fecundity using degree days (DD). Samples were collected from farmed European sea bass in the central Eastern Adriatic Sea between July 2017 and November 2022. Data were collected from six generations of European sea bass aged < 1 year during vaccination, with water temperatures of 13-25°C and DD of 1080-6869. Parasites were found in all samples, with 70.8% containing mature females. Samples of fish with immature female parasites (29.2%) were recorded at DD values ranging from 1080 to 3330. Mature females were recorded at DD values from 1873 to 6869. The proportion of mature females in samples ranged from 1% to 42%. A total of 2281 mature females were examined, with fecundity ranging from 7 to 327, averaging 91. Both DD and host size influenced parasite size, age at first maturity, and reproductive output. Fecundity increased significantly with DD, indicating a link to age and size. Understanding the reproductive biology of this parasite can enhance sustainable aquaculture practices and provide insight into how aquaculture may impact nearby wild fish populations.