Abstract
Tolerance and adaptability to changing environmental parameters have made Nile tilapia Oreochromis niloticus (Linnaeus, 1758) a hardy and desirable aquaculture species. These traits have also enabled this fish to become a highly successful invasive species into temperate and subtropical aquatic environments. Otolith-based ages of Nile tilapia (41.3 – 400.0 mm TL, 1.34 – 1,293 g WW, n = 259) collected from a power plant cooling reservoir and the Pascagoula River proper indicated that feral populations overwintered reaching ages up to 4+ years old in coastal Mississippi, USA; these data confirm their establishment. A survey of mean daily winter (December – February) water temperatures from 2004 – 2010 in this region showed minimum lethal temperatures of < 10°C to occur nearly 11% of the time attesting to the adaptability of the Nile tilapia as an invasive species. One annulus (opaque zone) per year was being deposited from April to August based on marginal increment analysis along with sulcal groove length-age estimation of the young-of-the-year Nile tilapia. Additionally, life history metrics measured for this temperate population of Nile tilapia were nearly identical to those reported from African environments, indicating they are flourishing in this non-native habitat.
Highlights
Nile tilapia Oreochromis niloticus (Linnaeus, 1758) is native to Africa, ranging from the upper Nile River south to the equator and west to the Atlantic coast (Trewavas 1983)
Peterson et al (2005) found populations of Nile tilapia thriving along thermal gradients associated with aquaculture facility effluents in coastal Mississippi, USA and suggested thermal refugia coupled with the characteristic oligomesohaline habitats of many estuarine areas would increase the likelihood of survival and establishment of non-native Nile tilapia
Opaque zone formation has been attributed to a variety of factors such as food resources, spawning, and climate (Beckman and Wilson 1995), for species in tropical areas (Fowler 1995)
Summary
Nile tilapia Oreochromis niloticus (Linnaeus, 1758) is native to Africa, ranging from the upper Nile River south to the equator and west to the Atlantic coast (Trewavas 1983). The species is favored among aquaculturists due to its ability to tolerate a wide range of environmental conditions, fast growth, successful reproductive strategies, and ability to feed at different trophic levels These same traits allow them to be an extremely successful invasive species in subtropical and temperate environments (Peterson et al 2005). Non-native Nile tilapia has recently been reported from Nevsehir, Turkey, the northern most locality of introduction in the Mediterranean region (Mert and Cicek 2010) In this region, monthly winter surface water temperatures were similar to, if not slightly lower than, those observed on the Mississippi Gulf Coast, indicating water temperatures in these areas may not reach fatal minimums for feral Nile tilapia as once perceived. Recent experimental research has pointed out that Nile tilapia can have important detrimental effects on the structure of the northern Gulf of Mexico food webs through agonistic behavior (Martin et al 2010), with many invasive cichlids reducing growth and reproduction of native species as well (Lorenz and O'Connell 2008; Doupé et al 2009; Lorenz et al 2011)
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