Mexican scientists first noticed the Indo-Pacific damselfish in the Southwestern Gulf of Mexico in 2013. Now Neopomacentrus cyanomos is so well established that it can number as many as 100 per square meter on oil platforms there, reports Smithsonian staff scientist Ross Robertson, who estimated a population of as many as 100,000 living on the stilts of a single small oil rig, in a study published early this year.

“It is an incredible density, all of alien fish, with virtually no native damselfishes present on that same oil rig,” says Robertson, who believes the fish were transported to the Mexican offshore oil fields by one or more oil rigs towed from Singapore or other construction sites in the northwest Pacific or northern Indian Ocean.

The discovery sets in motion numerous new avenues of research. Firstly, Robertson and colleagues want to figure out why the shiny grey-and-blue damselfish has been so successful and if it will have an impact on the native marine fauna.

“A lot of people tend to regard species like this as all bad,” says Robertson, who plans another research trip to the Gulf of Mexico this summer. “My hunch is they’re not going to do very much. They’re just another mouth and morsel added to the fauna.”

The fish are planktivores and may compete with a couple of local species. But, if they don’t become so abundant they squeeze out native fishes, they may benefit the larger ecosystem by simply be an additional food option for predators further up the food chain. It also appears they left their native parasites behind — samples so far show that the few parasites they carry are all native to the gulf.

N. cyanomos in Mexico comes in the two different lineages found in the Indian Ocean and the Northwest Pacific. Robertson and colleagues are studying their genetic makeup to better understand their relationship to their kin on the other side of the globe.

They also plan to investigate if they are undergoing genetic changes due to local selection pressure in their new environment.

“Genetically these two lineages are different enough that in some cases people would say they are two different species,” says Robertson.

Citation: D.R. Robertson, O. Dominguez-Dominguez, Benjamin Victor and Nuno Simoes. 2018. An Indo-Pacific damselfish (Neopomacentrus cyanomos) in the Gulf of Mexico: origin and mode of introduction. PeerJ 6:e4328, doi:10.77717/peerj.4328