The Atlantic blue crab (Callinectes sapidus), an invasive alien species in the Mediterranean Sea, is the focus of a joint project between the Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe) and the Italian Ministry of Agriculture, Food Sovereignty, and Forestry (MASAF). The project, coordinated by the Fish and Seafood Specialist Centre at IZSVe, aims to assess the health status of the blue crab, with particular attention to the presence of pathogens that may influence the population dynamics of this species in the main coastal lagoons of the Northern Adriatic Sea.

Among the most significant diseases affecting the blue crab stands the Bitter Crab Disease (BCD), caused by the parasitic dinoflagellate of the genus Hematodinium. Crustaceans infected with BCD typically show distinctive clinical signs such as lethargy, cloudy haemolymph, and reduced vitality.

Infection with Hematodinium sp. induces a range of physiological changes in the tissues and circulating hemolymph of the crustaceans, including a significant reduction in the number of cells involved in the immune response. In particular, the parasite’s rapid proliferation leads to high nutrient consumption, which results in decreased glucose levels in the hemolymph and glycogen storage in the hepatopancreas, further compromising the animal’s survival capacity and altering its organoleptic properties. Indeed, the meat of severely parasitized crustaceans, once cooked, may develop a distinct bitter taste, hence the popular name “Bitter Crab Disease,” which can compromise its palatability for the consumers.

The Atlantic blue crab (Callinectes sapidus), an invasive alien species in the Mediterranean Sea, is the focus of a joint project between the IZSVe and the Italian Ministry of Agriculture, Food Sovereignty, and Forestry. The project aims to assess the health status of the blue crab, with particular attention to the presence of pathogens that may influence the population dynamics of this species in the main coastal lagoons of the Northern Adriatic Sea. Among the most significant diseases affecting the blue crab stands the Bitter Crab Disease (BCD).

Epizootics caused by this parasite are a priority for research, as Hematodinium sp. is known for its ability to infect various marine crustacean species, causing declines in native natural populations, ecological impacts, and economic losses for the commercial fishing industry.

Between April and May 2024, 225 commercial-sized specimens of C. sapidus were collected and analyzed from seven location: Grado, Marano Lagunare, Caorle, Chioggia, Scardovari, Goro, and Marina di Ravenna. Thanks to the collaboration with local fish markets and cooperatives operating in the study areas, researchers collected at least 30 commercially sized blue crabs from each site. To investigate the prevalence of the parasite in the studied populations, various diagnostic techniques were applied, including molecular analyses (real-time PCR) on haemolymph samples coupled with cytological and histological analyses to pinpoint the parasite in tissue samples.

Preliminary results confirmed the presence of Hematodinium sp. in the collected blue crabs, highlighting significant variability in infection rates across the different transitional areas studied. In the lagoon areas of Friuli Venezia Giulia, the parasite was not detected, while in Veneto and Emilia-Romagna regions, the prevalence of individuals positive for Hematodinium sp. was 33% and 97%, respectively. As a matter of fact, during late spring 2024 in the Emilian sites, lethargic or moribund specimens, characterized by a lower viability to transport and handling were reported by fishing operators and lately confirmed to be strongly positive for Hematodinium sp. These observations support the hypothesis that this infection can negatively affect the commercial value of the crabs.

Hematodinium sp. does not have zoonotic potential, i.e. it is not transmissible and does not cause infection and disease in humans, however, the consumption of raw or undercooked blue crab may pose other potential health risks, such as acute gastroenteritis caused by bacteria of the genus Vibrio (especially V. parahaemolyticus) present on the exoskeleton or in the meat. It is therefore suggested to consume blue crab after adequate cooking.