TILAPIA AQUACULTURE IN HAWAII: LESSONS ABOUT FNO DISTRIBUTION AND SPECIES COMPOSITION FROM ISLAND STREAMS

Tilapia aquaculture continues to grow worldwide, with global production of 6.5 MT in 2017. However, due to the state's isolated geography, tilapia production in Hawaii is affected by international competition with lower market costs, while local farmers are subjected to state laws that restrict importation of certain tilapia species. Additionally, due to a disease outbreak caused by the bacteria Francisella noatuanensis subsp. orientalis (Fno) around Oahu in 1994, the export of Oahu tilapia to other Hawaiian Islands is prohibited. Here we sampled tilapia from feral populations of the main Hawaiian Islands to evaluate species composition and the geographic distribution of Fno.

The research presented here includes field work on ten feral streams from five main Hawaiian Islands - Oahu, Maui, Kauai, Molokai, and Hawaii (aka Big Island) - in which tilapia were screened  for species composition and Fno presence using real-time PCR . Fno was found in tilapia from Oahu, Kauai, and Maui streams.  Detected species include Oreochromis mossambicus , O. aureus ,  and  O. niloticus on the Big Island. T he potential hybrid  O. niloticus x O. aureus was  also found on the Big Island, while the potential hybrid , O. niloticus x  O. mossambicus , was found in Big Island, Maui and Molokai streams (Figure 1). Although Fno was found predominantly in the Black Chin Tilapia (Sarotherodon melanotheron ) on Oahu and Kauai, Fno positive tilapia from Maui were from two potential  O. niloticus x  O. mossambicus hybrids and three tilapia of the Captodon rendalli/zillii strain. Since Fno is found in many species around the world, it is not surprising to find this bacteria outside Oahu as historically thought.