An Assessment of the Asian Swamp Eel (Monopterus albus) in Florida

Abstract

The Asian swamp eel (Monopterus albus) is an air-breathing, sex-reversing, eel-like exotic fish that was first reported from Florida waters in 1997. This illegally introduced fish is now abundant in four major southeastern Florida canal systems, and it continues to slowly spread into nearby areas, including the Everglades. Swamp eel feed on a wide variety of organisms, the most common of which are small fishes, crustaceans (mostly crayfish), and insects. In a laboratory study, swamp eel died at temperatures ≤8°C. No deleterious ecological effects associated with the swamp eel's presence were detected during the 11 years we studied this species, nor was there any evidence that it makes overland movements. Based on these data and observations, the swamp eel in Florida is best described as an illegally introduced, opportunistic and successful predator that feeds on a variety of small prey; fortunately, however, it is unlikely to perpetrate major ecological or economic disturbances.

Keywords:

• exotic fishes
• fecundity
• fish populations
• food habits
• lower lethal temperature

ACKNOWLEDGMENTS

We thank FWC colleagues Larry Connor, who assisted with statistical analyses, and Ted Lange, who provided the edible muscle mercury analyses. And we thank J. Fury, J. Galvez, S. Hardin, J. Hill, J. Kline, K. Liem, W. Loftus, J. Trexler, J. Williams, and J. Troxel for valuable personal communications. We also thank the following individuals for reviewing and providing valuable comments on early drafts of this paper: S. Hardin, T. Reinert, J. Troxel, C. Watson, and P. Zajicek.

Notes

^a 1987: 2% of total biomass contributed by one Orinoco sailfin catfish (Pterygoplichthys multiradiatus); < 1% by number); no grass carp (Ctenopharyngodon idella) collected; spotted tilapia (Tilapia mariae) made up 38% of biomass (46% by number); spotted tilapia, striped mullet (Mugil cephalus), and Florida gar (Lepisosteus platyrhincus) collectively made up 70% of biomass.

^b 1999: 25% of total biomass contributed by one grass carp (< 1% by number); 18% by 20 Orinoco sailfin catfish (2% by number).

^c 2000: 8% of total biomass contributed by five Orinoco sailfin catfish (< 1% by number); no grass carp collected.

^d 2001: 46% of total biomass contributed by six grass carp (< 1% by number), 15% by 18 Orinoco sailfin catfish (1% by number), and 5% by one tarpon (Megalops atlantica; < 1% by number); therefore, 25 fish (< 2% by number) made up 67% of total biomass.

^e 2002: Most of biomass increase due to Orinoco sailfin catfish (45 kg/ha; n = 23), Florida gar (13 kg/ha; n = 4), grass carp (10 kg/ha; n = 2), and common snook (Centropomis undecimalis; 8 kg/ha; n = 2). Collectively, these species comprised 66% of total biomass but only 3% by number.

^f 2005: 23% of total biomass contributed by five Orinoco sailfin catfish (1% by number); no grass carp collected.

^a Values are composites of two vegetated and two non-vegetated blocknet sites for 1999 and 2000; only one blocknet site sampled in 2001, 2002, and 2005; 1999 samples were done in January, all others in May.

^a Since more than one category of prey item were found in some stomachs, the total number of stomachs containing prey items (FO) is not a simple sum.

^a Other = small turtle, head of a snake, fish eggs, frog.

^a Other = turtle, head of a snake, fish eggs, frog.