Mediterranean Aquaculture Industry Research Articles

Carbon footprint values as a climate change assessment criterion of the partial harvests of European seabass and meagre in earthen pond aquaculture

Abstract Turkey's Mediterranean aquaculture industry is the world leader in European seabass aquaculture and the European leader in meagre aquaculture. In this study, carbon footprint (CF) values of four partial harvests of European seabass in earthen pond aquaculture (EPES) and meagre in earthen pond aquaculture (EPM) were determined. The average values of total CF expended for EPES and EPM, which reached a final harvest weight of approximately 1,500 g in 1,061 and 633 days were 3.38 and 2.26 kg CO2e kg−1, respectively. The lowest and highest rates of CF expended on consumed compound diet (CFCD) were 63.92 and 65.59% in EPES, and 62.44 and 66.70% in EPM, respectively. The rates of CF general management were 32.0 and 33.57% in EPES and 30.98 and 34.98% in EPM, respectively. Against this high proportion of the compound diet, the second highest value was the lowest and highest proportion of partial harvests of electricity, 28.20 and 29.59% in EPES and 27.09 and 30.51% in EPM, respectively. CF input and CF output per kg values of meagre were decreased with increasing weight, therefore meagre can be defined as a species with high global food security and resilience against climate change.

Mediterranean Sea heatwaves jeopardize greater amberjack’s (Seriola dumerili) aquaculture productivity through impacts on the fish microbiota

Climate change is dramatically increasing the frequency and severity of marine heatwaves (MHWs) in the Mediterranean basin, strongly affecting marine food production systems. However, how it will shape the ecology of aquaculture systems, and the cascading effects on productivity, is still a major knowledge gap. The present work aims to increase our understanding of future impacts, caused by raising water temperatures, on the interaction between water and fish microbiotas, and consequential effects upon fish growth. Thus, the bacterial communities present in the water tanks, and mucosal tissues (skin, gills and gut), of greater amberjack farmed in recirculatory aquaculture systems (RAS), at three different temperatures (24, 29 and 33 °C), were characterized in a longitudinal study. The greater amberjack (Seriola dumerili) is a teleost species with high potential for EU aquaculture diversification due to its fast growth, excellent flesh quality and global market. We show that higher water temperatures disrupt the greater amberjack’s microbiota. Our results demonstrate the causal mediation exerted by this bacterial community shifts on the reduction of fish growth. The abundance of members of the Pseudoalteromonas is positively correlated with fish performance, whereas members of the Psychrobacter, Chryseomicrobium, Paracoccus and Enterovibrio are suggested as biomarkers for dysbiosis, at higher water temperatures. Hence, opening new evidence-based avenues for the development of targeted microbiota-based biotechnological tools, designed to increase the resilience and adaptation to climate change of the Mediterranean aquaculture industry.

Essential fatty acid requirement of juvenile meagre (Argyrosomus regius)

Meagre (Argyrosomus regius) is a fast-growing marine teleost and a promising candidate for the diversification of the Mediterranean aquaculture industry. Information on specific dietary requirements is necessary to improve the competitiveness of meagre farming. While the essential fatty acids (EFA) requirement of meagre fingerlings was previously estimated, knowledge regarding the EFA requirement of on-growing meagre juveniles is still lacking. To assess the EFA requirement of juvenile meagre, six isolipidic, isoproteic, semi-purified diets with different levels of n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) contents 0.0%, 0.3%, 0.6%, 0.9%, 1.2%, and 1.5% of diet dry matter (DM) were formulated and fed three times daily to triplicate groups of juvenile meagres of 35.6 ± 0.3 g for twelve weeks. Growth rates, whole body composition and fatty acid profile, liver lipid content as well as fatty acid profiles were assessed. In addition, the incidence of hepatic steatosis and granulomatosis was evaluated. Juvenile meagre fed the 0.0% n-3 LC-PUFA diet showed significantly lower growth and final body weight compared to all other treatments. There was an increase in growth of meagre with increasing dietary n-3 LC-PUFA levels and weight gain plateaued at levels above 0.9% n-3 LC-PUFA. Occurrence of granulomas examined in the liver supported the data on growth as the hepatic granulomatosis incidence in the groups fed <0.9% n-3 LC-PUFA were greater compared to fish fed diets containing higher levels of n-3 LC-PUFA. The findings of this study showed that the dietary n-3 LC-PUFA requirement of juvenile meagre for optimal growth and liver health status lays between 0.7 and 0.8% of the dietary dry matter.

Whole Genome Sequencing Provides Information on the Genomic Architecture and Diversity of Cultivated Gilthead Seabream (Sparus aurata) Broodstock Nuclei.

The gilthead seabream (Sparus aurata) is a species of relevance for the Mediterranean aquaculture industry. Despite the advancement of genetic tools for the species, breeding programs still do not often include genomics. In this study, we designed a genomic strategy to identify signatures of selection and genomic regions of high differentiation among populations of farmed fish stocks. A comparative DNA pooling sequencing approach was applied to identify signatures of selection in gilthead seabream from the same hatchery and from different nuclei that had not been subjected to genetic selection. Identified genomic regions were further investigated to detect SNPs with predicted high impact. The analyses underlined major genomic differences in the proportion of fixed alleles among the investigated nuclei. Some of these differences highlighted genomic regions, including genes involved in general metabolism and development already detected in QTL for growth, size, skeletal deformity, and adaptation to variation of oxygen levels in other teleosts. The obtained results pointed out the need to control the genetic effect of breeding programs in this species to avoid the reduction of genetic variability within populations and the increase in inbreeding level that, in turn, might lead to an increased frequency of alleles with deleterious effects.

Changes of the Mediterranean fish farm sector towards a more sustainable approach: A closer look at temporal, spatial and technical shifts

The Mediterranean is a miniature of the world with 22 countries sharing the its coastline. In the past few decades aquaculture production in Mediterranean showed an increasing trend but brought with it several environmental and socio-economic issues. In order to establish sustainable development, the Mediterranean aquaculture sector has adopted integrated management plans. Within this framework, our aim was to evaluate the state of the Mediterranean aquaculture industry with respect to sustainable growth, focusing mostly on the spatial scale. We used the evaluation framework for ICZM proposed by Billé (2007) that takes into consideration how multiple policies can be accountable for sustainable management practices. In order to identify the different management regimes and trends in the area, satellite images were processed as a diagnostic tool to locate and analyse the characteristics of the Mediterranean fish farms in cages over time. Google Earth historical images were used to map the characteristics of the Mediterranean fish farms in three different periods between 2006 and 2017. The average coastal surface occupied by the fish cages in the Mediterranean was 0.01%; only two countries currently exceed this percentage due to having a large number of cages (Turkey and Greece) and five others due to their limited coastline. In total, 15,499 cages were counted in recent years in the Mediterranean area, 46.5% of them belonging to larger cluster aggregations. Over time, square steel cages have been gradually replaced by larger and technically more advanced circular cages that significantly increased the finfish production rates. To understand the level of integration done by Mediterranean aquaculture we examined four dimensions of aquaculture issues: (i) policy and management; (ii) environment; (iii) economy - industry and (iv) social. State-of-the-art aquaculture policy and management systems were integrated in national legislations, boosting the production, ensuring at the same time better environmental quality from and for the aquaculture. Despite these positive results for the Mediterranean aquaculture industry, other factors, such as social issues related with the general bad image of aquaculture and the conflicts with local stakeholders, seem to inhibit the further development of aquaculture production. Thus, studies like this can identify factors that have favoured the expansion of aquaculture but also the evolving needs of the stakeholders in the context of changing market and social conditions.

Genetic Variation, GWAS and Accuracy of Prediction for Host Resistance to Sparicotyle chrysophrii in Farmed Gilthead Sea Bream (Sparus aurata).

Gilthead sea bream (Sparus aurata) belongs to a group of teleost which has high importance in Mediterranean aquaculture industry. However, industrial production is increasingly compromised by an elevated outbreak of diseases in sea cages, especially a disease caused by monogeneans parasite Sparicotyle chrysophrii. This parasite mainly colonizes gill tissues of host and causes considerable economical losses with mortality and reduction in growth. The aim of current study was to explore the genetics of host resistance against S. chrysophrii and investigate the potential for genomic selection to possibly accelerate genetic progress. To achieve the desired goals, a test population derived from the breeding nucleus of Andromeda Group was produced. This experimental population was established by crossing of parents mated in partial factorial crosses of ∼8 × 8 using 58 sires and 62 dams. The progeny obtained from this mating design was challenged with S. chrysophrii using a controllable cohabitation infection model. At the end of the challenge, fish were recorded for parasite count, and all the recorded fish were tissue sampled for genotyping by sequencing using 2b-RAD methodology. The initial (before challenge test) and the final body weight (after challenge test) of the fish were also recorded. The results obtained through the analysis of phenotypic records (n = 615) and the genotypic data (n = 841, 724 offspring and 117 parents) revealed that the resistance against this parasite is lowly heritable (h2 = 0.147 with pedigree and 0.137 with genomic information). We observed moderately favorable genetic correlation (Rg = −0.549 to −0.807) between production traits (i.e., body weight and specific growth rate) and parasite count, which signals a possibility of indirect selection. A locus at linkage group 17 was identified that surpassed chromosome-wide Bonferroni threshold which explained 22.68% of the total genetic variance, and might be playing role in producing genetic variation. The accuracy of prediction was improved by 8% with genomic information compared to pedigree.

Detection of Betanodavirus in experimentally infected European seabass (Dicentrarchus labrax, Linnaeus 1758) using non‐lethal sampling methods

One of the major disease threats affecting the Mediterranean aquaculture industry is viral encephalopathy and retinopathy (VER). The target organs for Betanodavirus detection are the brain and eyes, obtained through lethal sampling. This study aimed to evaluate the efficacy and suitability of non-lethal samples for detecting Betanodavirus in European seabass (Dicentrarchus labrax). European seabass juveniles were infected with Betanodavirus, by either an intramuscular injection or immersion (107 TCID50 /ml and 106 TCID50 /ml, respectively), and samples collected 7, 15 and 30 days post-infection (dpi). The brain was collected as a lethal sample, and gills, caudal fin and blood as non-lethal tissues for detecting Betanodavirus by quantitative reverse transcription PCR (RT-qPCR). The presence of virus in non-lethal tissues was inconsistent, with lower viral loads than in the brain. For blood, higher viral loads were detected in intramuscular-infected fish at 15 dpi until the end of the challenge. Serum antibodies against Betanodavirus were assessed using an enzyme-linked immunosorbent assay (ELISA). Antibodies were detected as early as 7 dpi, with higher mean antibody titres at 15 and 30 dpi. The presence of Betanodavirus-specific antibodies indicates that this is a suitable evaluation method for detecting early stages of the infection.

Spawning and rearing ofHolothuria tubulosa: A new candidate for aquaculture in the Mediterranean region

Holothuria tubulosa (Gmelin, 1788) has recently shown an increased demand in Asian markets, becoming one of the intensively exploited holothurian species in the Mediterranean Sea. A risk is that over-harvesting is likely affecting both the species' natural stocks and the benthic communities. In this scenario, sea ranching and restocking through aquaculture could assist in mitigating its overexploitation. This study is the first to demonstrate the successful artificial breeding and rearing of H. tubulosa, and its consequent potential as a new species for the Mediterranean aquaculture industry. Here we describe the spawning induction, larval development and early juvenile growth in hatchery cultures, aimed at developing a spawning and rearing protocol for this species. The trials were conducted from July to October in both 2014 and 2015. Holothuria tubulosa was induced to spawn by testing four different methods. Thermal stimulation plus thermal shock emerged as the most efficient method to obtain active and healthy gametes. Larval development in H. tubulosa progressed through five stages, reaching the juvenile stage in 27 days. Two different microalgal feeding regimens were tested for larval breeding. Under the best feeding conditions, 7% of the larvae metamorphosed into settled juveniles, adhering to artificial substrates previously conditioned with benthic biofilm. Our results indicate that H. tubulosa shows good performance in hatchery rearing during the larval phases, indicating that this species could be a new candidate for aquaculture in the Mediterranean region, both for production and restocking proposes.

Genomic Prediction of Resistance to Pasteurellosis in Gilthead Sea Bream (Sparus aurata) Using 2b-RAD Sequencing.

Gilthead sea bream (Sparus aurata) is a species of paramount importance to the Mediterranean aquaculture industry, with an annual production exceeding 140,000 metric tons. Pasteurellosis due to the Gram-negative bacterium Photobacterium damselae subsp. piscicida (Phdp) causes significant mortality, especially during larval and juvenile stages, and poses a serious threat to bream production. Selective breeding for improved resistance to pasteurellosis is a promising avenue for disease control, and the use of genetic markers to predict breeding values can improve the accuracy of selection, and allow accurate calculation of estimated breeding values of nonchallenged animals. In the current study, a population of 825 sea bream juveniles, originating from a factorial cross between 67 broodfish (32 sires, 35 dams), were challenged by 30 min immersion with 1 × 105 CFU virulent Phdp. Mortalities and survivors were recorded and sampled for genotyping by sequencing. The restriction-site associated DNA sequencing approach, 2b-RAD, was used to generate genome-wide single nucleotide polymorphism (SNP) genotypes for all samples. A high-density linkage map containing 12,085 SNPs grouped into 24 linkage groups (consistent with the karyotype) was constructed. The heritability of surviving days (censored data) was 0.22 (95% highest density interval: 0.11–0.36) and 0.28 (95% highest density interval: 0.17–0.4) using the pedigree and the genomic relationship matrix respectively. A genome-wide association study did not reveal individual SNPs significantly associated with resistance at a genome-wide significance level. Genomic prediction approaches were tested to investigate the potential of the SNPs obtained by 2b-RAD for estimating breeding values for resistance. The accuracy of the genomic prediction models (r = 0.38–0.46) outperformed the traditional BLUP approach based on pedigree records (r = 0.30). Overall results suggest that major quantitative trait loci affecting resistance to pasteurellosis were not present in this population, but highlight the effectiveness of 2b-RAD genotyping by sequencing for genomic selection in a mass spawning fish species.

Monitoring of trace metals, biochemical composition and growth of Axillary seabream (Pagellus acarne Risso, 1827) in offshore Copper alloy net cage

The study was conducted to assess trace metal contents, biochemical composition and growth performance of axillary seabream (Pagellus acarne Risso, 1827) cultured in a copper alloy mesh cage. A total of 400 axillary seabream (initial mean weight: 176.0±14.0 g), a new candidate species for the Mediterranean aquaculture, were stocked into a high-density polyethylene frame gravity cage and fed a commercial seabream diet for a period of 6 months. At the end of the feeding trial, fish reached a final weight of 264.8±16.8 g with a weight increase of 88.8 g and a feed conversion rate of 2.51. Overall, relative growth rate, specific growth rate and feed conversion ratio were satisfactory and comparable to the pelagic fishes such as gilthead seabream or European seabass, which are presently the main fish species for the Mediterranean aquaculture industry. Trace elements in fish grown in copper alloy net cages over a 6-month period showed satisfactory results, as the metal concentrations in fish tissues such as liver, skin, muscle and gills were below the reported upper limits for human consumption, indicating that copper alloy net is an acceptable and safe material for finfish cage aquaculture. Furthermore, from the growth performance data obtained in the present study, it can be concluded that axillary seabream showed potential for cage farming, and thus is a promising new candidate for the Mediterranean aquaculture industry.

Sensitivity of Mediterranean Bivalve Mollusc Aquaculture to Climate Change, Ocean Acidification, and Other Environmental Pressures: Findings from a Producer Survey

Human-induced climate change and ocean acidification are global environmental phenomena with a common driver: anthropogenic emissions of carbon dioxide. Both processes potentially threaten the Mediterranean bivalve mollusc aquaculture sector, which is economically relevant to several regions and countries. Detrimental effects on bivalve mollusc species might arise from the associated increase in sea surface temperature, pH reduction, higher frequency of extreme climatic events, and possible synergies with other nonclimatic stressors, such as harmful algal blooms and mollusc diseases. This paper presents the results of a questionnaire-based study of Mediterranean bivalve mollusc producers from 12 coastal regions and six countries, the latter including those with the highest production share in the Mediterranean region. This study aims to assess knowledge and perception of threat of climatic and nonclimatic environmental stressors within the Mediterranean aquaculture industry. Furthermore, it collects information about the (geographical) impacts of summer heat waves and ocean acidification. The results suggest that ocean acidification is still a relatively unknown phenomenon and generally poorly understood.Moreover, it is considered a secondary threat compared with other pressures. Summer heat waves are presently perceived as the highest threat, having been observed in amajority of the studied production sites in past years,with effects on seed (spat), adultmortality, and byssus attachment.

Dose-dependent effect of a single GnRHa injection on the spawning of meagre (Argyrosomus regius) broodstock reared in captivity

The present study aimed to determine the spawning efficacy, egg quality and quantity of captive breed meagre induced with a single gonadotrophin‐releasing hormone agonist (GnRHa) injection of 0, 1, 5, 10, 15, 20, 25, 30, 40 or 50 µg kg-1 to determine a recommended optimum dose to induce spawning. The doses 10, 15 and 20 μg kg-1 gave eggs with the highest quality (measured as: percentage of viability, floating, fertilisation and hatch) and quantity (measured as: total number of eggs, number of viable eggs, number of floating eggs, number of hatched larvae and number of larvae that reabsorbed the yolk sac). All egg quantity parameters were described by Gaussian regression analysis with R2=0.89 or R2=0.88. The Gaussian regression analysis identified that the optimal dose used was 15 μg kg-1. The regression analysis highlighted that this comprehensive study examined doses that ranged from low doses insufficient to stimulate a high spawning response (significantly lower egg quantities, p&lt;0.05) compared to 15 μg kg-1 through to high doses that stimulated the spawning of significantly lower egg quantities and eggs with significantly lower quality (egg viability). In addition, the latency period (time from hormone application to spawning) decreased with increasing doses to give a regression (R2=0.93) which suggests that higher doses accelerated oocyte development that in turn reduced egg quality and quantity. The identification of an optimal dose for the spawning of meagre, which has high aquaculture potential, represents an important advance for the Mediterranean aquaculture industry.

Second generation genetic linkage map for the gilthead sea bream Sparus aurata L.

An updated second linkage map was constructed for the gilthead sea bream, Sparus aurata L., a fish species of great economic importance for the Mediterranean aquaculture industry. In contrast to the first linkage map which mainly consisted of genomic microsatellites (SSRs), the new linkage map is highly enriched with SSRs found in Expressed Sequence Tags (EST-SSRs), which greatly facilitates comparative mapping with other teleosts. The new map consists of 321 genetic markers in 27 linkage groups (LGs): 232 genomic microsatellites, 85 EST-SSRs and 4 SNPs; of those, 13 markers were linked to LGs but were not ordered. Eleven markers (5 SSRs, 5 EST-SSRs and 1 SNP) are not assigned to any LG. The total length of the sex-averaged map is 1769.7cM, 42% longer than the previously published one, and the number of markers in each LG ranges from 2 to 30. The inter-marker distance varies from 0 to 75.6cM, with an average of 5.75cM. The male and female maps have a length of 1349.2 and 2172.1cM, respectively, and the average distance between markers is 4.38 and 7.05cM, respectively. Comparative mapping with the three-spined stickleback (Gasterosteus acuulatus) chromosomes and scaffolds showed conserved synteny with 132 S. aurata markers (42.9% of those mapped) having a hit on the stickleback genome.

Do the visual conditions at the point of escape affect European sea bass escape behavior?

European sea bass (Dicentrarchus labrax), an important species for the Mediterranean aquaculture industry, has been reported to escape from sea cage installations. Fish escapes are caused mainly by operational and technical failures that eventually result into a creation of a tear. Escapees may interact with wild stocks through interbreeding, transfer of pathogens and competition for food. The aim of this study was to examine at which extent the presence of a visible obstacle close to a tear on the net have an influence on sea bass propensity to escape. Fish were initially confined into small sea cages, with a tear at one side. The escape behavior was tested under experimental conditions. It is clearly demonstrated that sea bass was able to locate a tear on the net pen, immediately after its appearance. Crossings occurred in all cages, in singles or in a series of up to seven individuals. The presence of an obstacle close to the net tear altered the escape behavior of D. labrax resulting in a delay that eventually reduced the escape rate. Concluding, it is highly recommended that sea bass cages should be kept internally the culture array. Furthermore, the placement of artificial obstacles close to the sea cages could be an efficient practice that mitigates the escape risk after severe environmental conditions.

Do the visual conditions at the point of escape affect European sea bass escape behavior?

European sea bass (Dicentrarchus labrax), an important species for the Mediterranean aquaculture industry, has been reported to escape from sea cage installations. Fish escapes are caused mainly by operational and technical failures that eventually result into a creation of a tear. Escapees may interact with wild stocks through interbreeding, transfer of pathogens and competition for food. The aim of this study was to examine at which extent the presence of a visible obstacle close to a tear on the net have an influence on sea bass propensity to escape. Fish were initially confined into small sea cages, with a tear at one side. The escape behavior was tested under experimental conditions. It is clearly demonstrated that sea bass was able to locate a tear on the net pen, immediately after its appearance. Crossings occurred in all cages, in singles or in a series of up to seven individuals. The presence of an obstacle close to the net tear altered the escape behavior of D. labrax resulting in a delay that eventually reduced the escape rate. Concluding, it is highly recommended that sea bass cages should be kept internally the culture array. Furthermore, the placement of artificial obstacles close to the sea cages could be an efficient practice that mitigates the escape risk after severe environmental conditions.

Evaluation of soybean meal as protein source for Argyrosomus Regius (Asso, 1801) (Sciaenidae)

The meagre (Argyrosomus regius) is a carnivorous fish which requires diets with higher protein content, causing an increment in diets cost. A way to diminish this cost is to use vegetable meals like soybean meal (SB). So the aim of this trial was to determine the optimum inclusion level of defatted soybean meal in experimental diets for this species. 800 fishes (165 g) were distributed in 8 tanks, two replicates per treatment. Four isoproteic (50% CP) and isolipidic (17% Cl) diets were formulated with four levels of soybean meal inclusion, 0, 15, 30 and 45%. The trial lasted 107 days. Meagre fed diets 15 and 30% obtained the highest final weight. There were no significant differences among treatments in the feed conversion rate (FCR) and the protein efficiency (PER). According to the quadratic regression, the optimum SB inclusion to maximize thermal growth coefficient (TGC) was 26.4% and for FCR was 27.6%. No significant differences were observed in energy, protein and amino acid retention among diets. The inclusion of SB in meagre diets can generate a decrease in the use of fish meal and in turn reduce the cost of producing meagre Mediterranean aquaculture industry. Key words: Argyrosomus regius, fish meal replacement, defatted soybean meal, economic analysis.