Alien fish’s first Mediterranean appearance is in Malta

In a confirmation of the impact of global warming on Maltese waters, the number of non-indigenous species in Maltese waters is approaching the 100 mark, an increase that includes predatory fish with the ability to put greater pressure on local ecosystems.

The latest addition to Malta’s marine biodiversity was documented by the ‘Spot the Alien Fish’ citizen-science campaign in which divers and fishermen are encouraged to report alien species for documentation.

The newcomer, a fish species, belongs to the ten-pounder Elops genus, for which a single individual was caught off Delimara in October 2019. The specimen consisted of a long, slender, silvery specimen  estimated to have a total length of 55-60cm. The fish had elongated and pointed fins, including a deeply-forked caudal fin.

According to Dr Alan Deidun, from the Department of Geosciences, and coordinator of the Spot the Alien Fish citizen science campaign, this latest discovery was consistent with the progressive warming trend of the Mediterranean, given that Elops species are native to tropical and sub-tropical regions of the global ocean.

The fact that the fish was first recorded in the Mediterranean basin in Maltese waters is considered “anomalous”, especially since the genus is not used in the aquarium or pet industry, therefore ruling out any deliberate release of the species within Maltese waters.

One possibility is that the spread of the fish may have been brought about through ballast water-mediated transport, when the fish was in larval form. “However, given the relatively large dimensions of the specimen, a passive range-expansion mode of introduction is more likely.”

While the capture of a single Elops in the Mediterranean might represent a vagrant adult, its occurrence suggests it could potentially survive in these waters.

Further surveys with fishermen are necessary to monitor the species. Only one photograph of the fish was submitted, which makes it hard to identify it given that there are seven Elops species that are morphologically very similar to each other.

According to one study, over 90% of the stomach contents of sampled Elops individuals consisted of fish, which indicates the kind of pressure it could exert on local ecosystems.