Experimental transmission of Cryptosporidium molnari (Apicomplexa: Coccidia) to gilthead sea bream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax L.).

Cryptosporidium molnari was experimentally transmitted to gilthead sea bream (Sparus aurata) and European sea bass (Dicentrachus labrax) by oral infection with infected stomach scrapings. The infection was also cross-transmitted from infected gilthead sea bream to sea bass by cohabitation. The course of the infection was assessed after necropsy by three microscopic diagnostic methods and their sensitivity was compared. At the end of all the experiments the prevalence of infection reached 100%. In the oral experiments, both fish hosts appeared infected as early as 7 days post exposure (p.e.), but gilthead sea bream exhibited a higher intensity of infection and infection proceeded at a faster rate than in sea bass. The cellular host reaction was stronger in sea bass than in sea bream, whereas the histopathological effect was lower in the former. Transmission could be favoured by cannibalism among cohabiting fish. This is the first report on piscine Cryptosporidium transmission. The implications for the aquaculture industry are discussed.