The advent of molecular technologies allow for identification of organisms that were previously challenging or not possible. Conventional polymerase chain reaction analyses of a segment of the small subunit ribosomal RNA gene from trypanorhynch plerocerci obtained from cultured and wild caught amberjacks, Seriola dumerili, and Seriola rivoliana of the family Carangidae from Hawai‘i and Japan were found to be 100% identical, indicating that the cestodes from Japan and Hawai‘i are the same species, Protogrillotia zerbiae. The prevalence of the trypanorhynch plerocerci found in the musculature of Hawai‘i wild‐caught S. dumerili and S. rivoliana was 86.9 and 72.7%, respectively. In stark contrast, no trypanorhynch plerocerci have been detected in S. rivoliana cultured in Hawai‘i and they are only rarely seen in S. dumerili cultured in Japan. Trypanorhynch plerocerci are part of a complex life cycle that involves the transmission in at least two intermediate hosts before finally residing in a host shark species. The results of this study indicate that artificial propagation of the amberjacks using manipulated diets has most likely disrupted the life cycle of this tapeworm, thus reducing the prevalence of this parasite in farmed amberjacks and enhancing the marketability of cultured amberjack.

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A 25-week immersion challenge was conducted exposing Oreochromis mossambicus, Oreochromis aureus and Oreochromis urolepis hornorum to Francisella noatunensis subsp. orientalis (Fno). Two populations were compared for each fish species; 'resident fish' were defined as fish maintained in tanks since week 0 of challenge, whereas 'naïve fish' were defined as fish added to tanks once temperature in water reached <26 °C at 21 weeks post-challenge. Fno genome equivalents (GEs) in water were similar in all treatments 1 h post-challenge; however, significantly lower Fno GEs were detected 2 weeks post-challenge in all tanks, and the only treatment with detectable Fno GE after 4 weeks of challenge were the O. mossambicus tanks. Twenty-one weeks post-challenge, naïve fish were stocked with 'resident' cohorts. Over a 4-week period, mortalities occurred consistently only in O. mossambicus naïve cohorts. Overall presence of granulomas in spleen of survivors was similar (>55%) in all resident populations; however, in naïve populations, only O. mossambicus presented granulomas. Similarly, only O. mossambicus presented viable Fno in the spleen of survivors, and Fno GEs were only detected in O. mossambicus, and in resident O. aureus. In conclusion, the results of this study suggest different susceptibility of tilapia species to piscine francisellosis.

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