Unusual abundance of invasive Tilapia species in coastal waters of Devipattinam, Palk Bay, India

Abstract

Worldwide, Tilapia sp. has gained a reputation as a highly sought-after, culturable species in the aquaculture industry thanks to its higher growth rate, excellent adaptive nature, low disease rate, and prolific breeding. Aquaculture is the only means to satisfy the dietary demand for fish protein in India, which has the highest population in the world. The first Tilapia species used for extensive aquaculture was Oreochromis mossambicus, which was introduced in India in the early 1950s under government patronage. Since then, aquaculture farms have been developed to culture Tilapia all over India, from the warmer tropical brackish waterbodies of Tamil Nadu to the cooler Himalayan regions.

The past few decades have witnessed a huge surge in Tilapia abundance in various natural water bodies, posing a serious threat to indigenous fish species. These highly adaptive fishes have now been observed surviving in fully marine environments in Palk Bay. Local fishermen are aware of the presence of these invasive species and regularly harvest them from the inshore waters. Several specimens of different ages have been found and recorded during a survey in coastal areas near Devipattinam, Tamil Nadu. It is assumed that these exotic species have found their way to the ocean from local aquaculture farms to local canals, eventually ending up in the ocean.

In a recent survey in January, 2023, adult specimens with fertile gonads were recorded. But most of the specimens found were juveniles and sexually immature, indicating that the inshore water of the Palk Bay region serves as a breeding and nursery ground for young ones. Surveys have shown that they are more abundantly found in coastal waters with an average depth of 2–5 meters, dominated by several sea grass species. Survival success is influenced by their ability to withstand oceanographic conditions and their interactive credibility with native indigenous species.