Caligus elongatus and Photobacterium damsela subsp piscicida are pathogens of serious infections in European seabass, Dicentrarchus labrax. In this study, both agents were concomitantly isolated from moribund broodstock European seabass cultured within the hatchery unit at El-Max Research Station (NIOF), Alexandria governorate, Egypt. Externally, fish were heavily infested with Caligus elongatus ectoparasitic copepods. The overall prevalence, mean intensity and mean abundance of C. elongatus on examined fish were 92.3%, 23.3 and 21.5; respectively. Majority of samples noticed sever haemorrhages on the external body surface and fins. Internally, moribund fish showed characteristic whitish nodules and extensive adhesions of visceral organs. 88.46% of investigated fish were concurrently found to be infected with P. damsela subsp piscicida. No other bacterial species were detected. P. damsela subsp piscicida was also isolated from C. elongatus infesting clinically diseased fish. All P. damsela subsp piscicida isolates were confirmed by sequencing of the16S rRNA gene. Microscopically, multiple granulomas were regularly observed in haemopoietic organs. Our results as a whole indicate that C. elongatus may serve as a potential vector for P. damsela subsp piscicida and possibly enhance photobacteriosis dissemination among cohabitant fish, thus suggesting the desirability of redesigning the protocols presently used for microbial recognition during fish epidemiological studies to improve fish health.