Phenotypic Convergence in Sea Bass (Dicentrarchus labrax) Escaping From Fish Farms: The Onset of Feralization?

Kilian Toledo-Guedes,Carlos Garcia De Leaniz,Alberto Brito

doi:10.3389/fmars.2021.674635

Kilian Toledo-Guedes, Carlos Garcia De Leaniz + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2021.674635

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Abstract

The impact of fish escaping from fish farms may depend on the extent to which escapees adapt to the natural environment, resemble wild conspecifics, and become feral. Yet, little is known about the process of feralization in marine fish. We examined phenotypic changes in body shape, body condition, and scale growth profiles of sea bass escaping from fish farms in the Canary Islands and quantified the extent to which escapees had diverged from farmed conspecifics. Most feral sea bass had sizes that overlapped with those of farmed fish, indicating that they had escaped throughout the production cycle. However, 29% of escapees were larger than the maximum size at harvesting, indicating growth in the wild. Analysis of scale growth profiles showed that some escapees had grown in the wild as fast as cultured fish, albeit at more variable growth rates. Feral sea bass tended to converge towards a similar body shape, having more streamlined bodies, lower body condition, and lower hepatosomatic indices (HSI) than fish in cages. Although our study cannot discriminate between phenotypic plasticity and differential mortality of escapees, we interpret phenotypic convergence as the likely result of a period of initial starvation, phenotypic plasticity, and selection against maladapted phenotypes. Our results warn against the risks of rearing sea bass in open-net cages and suggest that sea bass escapees could pose a threat to shallow coastal assemblages, particularly in areas where the species is not naturally found.

Highlights

Not all aquaculture escapees survive and reproduce in the wild, but some do, and minimizing their impact on wild fish has become an issue of global concern (Naylor et al, 2005)
We examined three phenotypic traits directly affected by growth and which are likely to change during the transition from captive to natural environments: growth rate—based in the analysis of growth rings found on fish scales, body condition—inferred from the hepatosomatic index and the condition factor, and body shape—derived from measurements of multiple morphological traits obtained through digital photography
Our study reveals that sea bass escaping from fish farms undergo significant phenotypic changes in the wild and tend to converge toward a more similar phenotype compared to farmed

Summary

INTRODUCTION

Not all aquaculture escapees survive and reproduce in the wild, but some do, and minimizing their impact on wild fish has become an issue of global concern (Naylor et al, 2005). Fish escaping from aquaculture facilities can be expected to undergo changes in phenotypic traits during feralization (the process of domestication in reverse; Price, 2002; Zeder, 2012) and these can provide cues about the differential response of fish to artificial and natural selection. Such information will be useful for mitigating the impacts of aquaculture escapes because improvements in the adaptation of fish to captivity (domestication) should translate into loss of fitness in the wild. We examined the process of feralization by quantifying the phenotypic changes that are displayed by sea bass when they escape into the wild

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ETHICS STATEMENT