Plastic Responses of Gilthead Seabream Sparus aurata to Wild and Aquaculture Pressured Environments

Igor Talijančić,Leon Grubišić,Jasna Šiljić,Tanja Šegvić-Bubić,Viktorija Kiridžija,Iva Žužul,Jelka Pleadin

doi:10.3389/fmars.2021.694627

Abstract

Fish farms, as artificial marine structures with a constant food supply, have a high capacity to attract surrounding wild fish. Different phenotypes of abundant gilthead seabream have been recorded in natural and aquaculture pressured environments in the eastern Adriatic Sea, where the influence of tuna farming on plastic traits associated with habitat use and foraging behaviour remains largely unknown. Several traits, such as body and otolith shape, external colouration, diet preference, and proximate tissue content, were analysed to examine habitat selection of the tuna farm-associated phenotype in comparison to wild and farmed phenotypes. Foraging behavioural shifts in prey selectivity, from hard-shelled bivalves towards soft textured baitfish feed, and local hydrodynamic conditions have initiated plastic responses in farm-associated seabream. Consequently, morphological traits connected with feeding and swimming performance and paler vs. vivid body colouration patterns differed between wild and farm-associated fish, highlighting the existence of resource polymorphism in gilthead seabream. While otolith shape proved to be a reliable phenotypic tracer in distinguishing farmed from wild and farm-associated fish, reduced sensitivity was found between individuals residing in the vicinity of tuna farms and wild ones. To fully understand the impact of fish farms on associated gilthead seabream and its plastic response with a distinctive morph outcome, the underlying molecular mechanisms involved in the regulation of alternative phenotypes needs to be investigated.

Highlights

Interaction and compatibility of aquaculture with the environment is one of the main debated issues linked to the sustainability of this food industry
As farmed populations have been modified by their cultured environment and artificial selection, so have the farm-associated populations been shaped by their interactions with tuna farms, with cues such as resource availability and local hydrodynamics
To fully understand the different phenotypic outcomes of farm-associated gilthead seabream and whether this can be considered a distinctive morph stemming from resource polymorphism, the associated molecular mechanisms, both genetic and epigenetic, involved in the regulation of phenotypically plastic traits, should be studied

Summary

Introduction

Interaction and compatibility of aquaculture with the environment is one of the main debated issues linked to the sustainability of this food industry. With an annual finfish production of 1.9 million tonnes (FAO, 2020) and over 21,000 finfish and tuna cages in the Mediterranean (Trujillo et al, 2012), farm leasehold areas act as high-quality habitats that enhance the productivity of coastal fish assemblages (Sanchez-Jerez et al, 2011; Bayle-Sempere et al, 2013; Staglicicet al., 2017). Farming installations attract large fish aggregations by introducing structures and a constant food supply in form of uneaten feed into the pelagic environment, thereby enhancing the attractive effect on local populations by affecting their presence, abundance, residence time and diet (Dempster et al, 2002; Sanchez-Jerez et al, 2011; Šegvic-Bubicet al., 2011a; Staglicicet al., 2017). A common feature emerging from Mediterranean studies is the consistent record of the family Sparidae around finfish and tuna farms, despite their discrepancies in attracted fish assemblages due to different site selection, i.e., coastal vs semioffshore, and the proportion of uneaten and type of feed, i.e., pellets vs baitfish (Valle et al, 2007; Šegvic-Bubicet al., 2011a; Bacher et al, 2012; Staglicicet al., 2017)

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