Morphological and ecophysiological adaptations of wild gilthead seabream Sparus aurata associated with tuna farms

Abstract

Morphological and ecophysiological traits of wild, farmed and wild farm-associated gilthead seabream Sparus aurata were used to assess the degree of phenotypic adaptation of the species to their respective environments. Geometric morphometrics revealed clear body shape differentiation amongst the 3 types of populations, whereby sig nificant differences were noted in head profile and the anterior-body region of the fish. Morphological resemblance was recorded among 2 gilthead seabream populations associated with tuna farms, indicating that they share the same phenotypic responsiveness pattern. Adaptation in reproductive investment strategy was observed in individuals from farm-associated origin, displaying the highest gonadosomatic index but lowest condition in comparison to their farmed and wild counterparts. Multinomial logistic regression revealed that sex change from male to female with increasing length was more pronounced in farm-associated fish than in farmed and and wild fish. These findings demonstrate a significant influence of the environmental factors inherent to tuna farms on the phenotypic characteristics of gilthead seabream, providing a basis for further research on the ecological effects of tuna farms on local marine populations.

Assignment of Gilthead Seabream Sparus aurata to Its Origin through Scale Shape and Microchemistry Composition: Management Implications for Aquaculture Escapees

“…Based on the results presented above, multiple lines of inference are reported herein. Clear divergence of farmed fish scale shape from the shapes of wild and wild farm-associated fish was shown, with divergence patterns analogous to those previously documented based on the analyses of genetic and whole-body shape from the same population dataset [6,8]. The typical shape generated by farming condition was characterized with a more elongated lateral axis of the exposed portion of the scale and convexed posterior scale edge, enabling the highest classification origin score (85.2%), with outline analysis displaying a 17.41% more correct classification rate than GM (see Table 2).…”

“…Recent studies have shown that scale shape can be used as a good discriminator between congeneric species [27], sympatric phenotypes [28], populations [29] or geographic variants [30]. Here, we explored morphological and microchemistry patterns of gilthead seabream scales from different population origins, i.e., wild, wild farm-associated and farmed, sampled over a relatively small spatial scale that were previously characterized genetically and morphologically (whole-body shape) [6,8]. Based on the results presented above, multiple lines of inference are reported herein.…”

“…In recent years, increased numbers of wild gilthead seabream have been observed in the Adriatic Sea, and it has been suggested that rapid expansion of sea-cage farming, with the escape of fish from sea-cages and the positive effect of ocean warming on larval survival, have contributed to population increases for this subtropical species [5,6]. Several recent studies have confirmed that Adriatic tuna farms are areas of permanent residency of highly abundant wild seabream [7,8]. This aggregative behaviour has been attributed to the permanent and increased availability of tuna baitfish losses, composed of small pelagic species.…”

“…This aggregative behaviour has been attributed to the permanent and increased availability of tuna baitfish losses, composed of small pelagic species. Such an altered environment has triggered the temporarily stable adaptation of both morphological and physiological traits, where wild farm-associated populations show a different head profile, body shape and enhanced reproductive fitness in comparison to those of wild or farmed fish origin [8]. Further on, at a very small spatial scale (<4000 km 2 ), these populations showed genetic differentiation with wild populations not associated with aquaculture sites, when 19 microsatellite loci were employed to investigate gilthead seabream population structure in the eastern Adriatic [6].…”

“…At present, no studies have compared the performance of scale shape or scale microchemistry composition as proxies for origin selection of gilthead seabream. Thus, we employed three different approaches, i.e., landmark-and outline-based scale morphometrics, trace element chemistry profiles, and scale microstructure characteristics to test three hypotheses: (i) different environmental pressures can promote population differentiations over small geographical areas, (ii) scale shape has the same discrimination power as body shape of the same fish (from Talijančić et al [8]), and (iii) different methodologies may enhance the reliability and applicability of the data for monitoring and fisheries management. Scales were sourced from population origins with a known genetic background [6].…”