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Identification of the potential habitat of European anchovy ( Engraulis encrasicolus) at different life stages in relation to environmental conditions is an interesting subject from both ecological and management points of view. For this purpose, acoustic data from different seasons and different parts of the Mediterranean Sea along with satellite environmental and bathymetry data were modelled using generalized additive models. Similarly, egg distribution data from summer ichthyoplankton surveys were used to model potential spawning habitat. Selected models were used to produce maps presenting the probability of anchovy presence (adults, juveniles and eggs) in the entire Mediterranean basin, as a measure of habitat adequacy. Bottom depth and sea surface chlorophyll concentration were the variables found important in all models. Potential anchovy habitats were located over the continental shelf for all life stages examined. An expansion of the potential habitat from the peak spawning (early summer) to the late spawning season (early autumn) was observed. However, the most suitable areas for the presence of anchovy spawners seem to maintain the same size between seasons. Potential juvenile habitats were associated with highly productive inshore waters, being less extended and closer to coast during winter than late autumn. Potential spawning habitat in June and July based on ichthyoplankton surveys overlapped but were wider in extent compared with adult potential habitat from acoustics in the same season. Similarities and dissimilarities between the anchovy habitats as well as comparisons with sardine habitats in the oligotrophic Mediterranean Sea and other ecosystems with higher productivity are discussed. [ABSTRACT FROM AUTHOR]

The gonosomatic or gonadosomatic index [GSI=(ovary weight/fish weight)×100] has been widely used in fisheries science and experimental reproductive studies as a simple, low-cost measure of reproductive condition. However, its properties have not been fully evaluated, and several pitfalls, such as size-dependence and changes in ovarian allometry, may invalidate its use. In the present study, we examined ovarian allometry and the appropriateness of GSI for assessing ovarian activity in the Mediterranean sardineSardina pilchardus. The analysis was based on a large sample of histologically scored females collected over an annual cycle in the eastern Mediterranean (Aegean and Ionian Seas). First, we examined GSI dependence on fish size by comparing ovary weight-on-fish weight relationships in different stages of oocyte development. The effects of recent spawning (incidence of postovulatory follicles) and intensity of follicular atresia were also addressed. In a subsequent step of the analysis, we applied generalized linear models (GLMs) to analyze the relationship between GSI and histological stage, taking into account the parallel effects of additional factors related to geographical region, month of capture, fish length and energetic reserves (fat stage, hepatosomatic index-HSI). Ovarian growth was isometric in all stages of oocyte development and states of atresia, but altered to positive allometric at the stage of oocyte hydration. Oocyte growth and intensity of atresia significantly affected GSI. Fish length, geographical region, month of capture, fat stage and HSI did not substantially affect GSI, further strengthening the appropriateness of the index for the Mediterranean sardine. Finally, we provide first evidence, based mainly on available (but yet limited) published information for other fish species, that: (1) the pattern of ovarian allometry may not be altered by fecundity variations and (2) the pattern of ovarian allometry may reflect the pattern of oocyte growth (i.e. isometric vs. allometric ovarian growth could reflect group-synchronous vs. -asynchronous oocyte development). Alternatively, the pattern of ovarian allometry could reflect the presence or absence of size dependency in the relative fecundity (eggs per gram of body weight) and/or egg size. The isometric ovarian growth in the Mediterranean sardine could be attributed to the lack of such size-dependent effects. [ABSTRACT FROM AUTHOR]

Forage species with high biomass, such as anchovies and sardines, play a key role in pelagic ecosystems and make up a significant proportion of the world's capture fisheries production. In recent years, condition indices have gained interest as significant indicators for assessing the effects of environmental and human pressures on these species and the quality of their habitats. In the present study, we examined, for the first time in the North Aegean Sea (eastern Mediterranean), the year-round variation in somatic and gonadal condition, energy density, and percentage of lipid content of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). Energy density was measured with bomb calorimetry and percentage lipid content with the fatmeter, a portable electronic device. Finally, the monthly changes in gonadal and energetic condition were examined in relation to the annual cycle of temperature and mesozooplankton biomass, simulated by the implementation of a coupled hydrodynamic-biogeochemical model (POM-ERSEM). There was a strong relationship between fish energy density (kJ g -1 ) and percentage dry weight. Furthermore, the mean monthly energy density and fatmeter measurements were strongly correlated, especially in sardine. Overall, the monthly changes in energetic condition were indicative of the species' different strategies for energy acquisition and allocation to reproduction (capital vs. income breeding): sardine exhibited low energy density and percentage lipid content during the winter spawning period (November-March) and markedly higher energetic condition from spring to autumn (April-October). Anchovy spawning period, as inferred from gonadal condition, lasted from April to September, i.e., during the warm period of the year but its energy density and percentage lipid content did not exhibit any seasonal changes and were markedly lower than in sardine from April to October. Finally, the simulated mesozooplankton biomass was higher from January to July, which corresponded to the second half of the spawning season for sardine, but first half of the spawning season for anchovy., (© 2024 The Author(s). Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

The invasion of the tetrodotoxin (TTX)-bearing silver-cheeked toadfish and potential poisoning due to its consumption (tetrodotoxication) threatens public safety in the Mediterranean Sea. In this study, TTX and TTX analogues of Lagocephalus sceleratus (Gmelin, 1789) were measured using liquid chromatography tandem mass spectrometry (LC-MS/MS) in fish collected off the island of Crete (Southern Mediterranean). We tested the synergistic effect of a suite of factors potentially affecting toxins' levels and tetrodotoxication risk using general and generalized linear models, respectively. The type of tissue, geographic origin (Cretan Sea, Libyan Sea), sex, and fish maturity stage were significant predictors of toxin concentrations. Mean TTX was higher in gonads and lower in muscles, higher in the Libyan Sea and in female fish, and lower in juvenile (virgin) fish. The concentration of TTX was also significantly and positively correlated with the concentration of several TTX analogues (4-epiTTX, 4,9-anhydroTTX, 11-deoxyTTX, 5,11/6,11-dideoxyTTX, 5,6,11-trideoxyTTX, 11-norTTX-6-ol). The analysis showed that fish originating from the Libyan Sea had significantly higher probability to cause tetrodotoxication in case of consumption. The variability explained by the models developed in this study was relatively low, indicating that toxin levels are hard to predict and the consumption of L. sceleratus should therefore be avoided.

Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild-caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild-caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild-caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (O P ) than wild-caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for O P and all except one shape descriptors (harmonics 2-7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks., (© 2020 Fisheries Society of the British Isles.)

A 1-D full-life-cycle, Individual-based model (IBM), two-way coupled with a hydrodynamic/biogeochemical model, is demonstrated for anchovy and sardine in the N. Aegean Sea (Eastern Mediterranean). The model is stage-specific and includes a 'Wisconsin' type bioenergetics, a diel vertical migration and a population dynamics module, with the incorporation of known differences in biological attributes between the anchovy and sardine stocks. A new energy allocation/egg production algorithm was developed, allowing for breeding pattern to move along the capital-income breeding continuum. Fish growth was calibrated against available size-at-age data by tuning food consumption (the half saturation coefficients) using a genetic algorithm. After a ten-years spin up, the model reproduced well the magnitude of population biomasses and spawning periods of the two species in the N. Aegean Sea. Surprisingly, model simulations revealed that anchovy depends primarily on stored energy for egg production (mostly capital breeder) whereas sardine depends heavily on direct food intake (income breeder). This is related to the peculiar phenology of plankton production in the area, with mesozooplankton concentration exhibiting a sharp decrease from early summer to autumn and a subsequent increase from winter to early summer. Monthly changes in somatic condition of fish collected on board the commercial purse seine fleet followed closely the simulated mesozooplankton concentration. Finally, model simulations showed that, when both the anchovy and sardine stocks are overexploited, the mesozooplankton concentration increases, which may open up ecological space for competing species. The importance of protecting the recruit spawners was highlighted with model simulations testing the effect of changing the timing of the existing 2.5-months closed period. Optimum timing for fishery closure is different for anchovy and sardine because of their opposite spawning and recruitment periods., Competing Interests: The authors have declared that no competing interests exist.

Marine litter is a threat to marine life and an economic burden for coastal communities, but efforts to address the issue are hampered by the lack of data for many countries. We performed the first harmonized assessment of seafloor litter (trawl and visual surveys) in six countries of the Adriatic-Ionian macroregion. Seafloor litter showed an uneven distribution throughout the area, with large differences in litter densities and composition among countries and locations. An emerging problem in the area resulted in short-term & single-use objects that represented the largest fraction of litter. Packaging was the economic sector contributing most to seafloor litter on the continental shelf and upper slope, while in some areas aquaculture (mussel farming) represented a key activity producing marine litter. In coastal areas and bays (e.g. Boka Kotorska bay, Montenegro), seafloor litter was mainly related to construction activities and electronic goods, which are a consequence of fly-tipping/illegal dumping., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Geostatistical techniques were applied and a series of spatial indicators were calculated (occupation, aggregation, location, dispersion, spatial autocorrelation and overlap) to characterize the spatial distributions of European anchovy and sardine during summer. Two ecosystems were compared for this purpose, both located in the Mediterranean Sea: the Strait of Sicily (upwelling area) and the North Aegean Sea (continental shelf area, influenced by freshwater). Although the biomass of anchovy and sardine presented high interannual variability in both areas, the location of the centres of gravity and the main spatial patches of their populations were very similar between years. The size of the patches representing the dominant part of the abundance (80%) was mostly ecosystem- and species-specific. Occupation (area of presence) appears to be shaped by the extent of suitable habitats in each ecosystem whereas aggregation patterns (how the populations are distributed within the area of presence) were species-specific and related to levels of population biomass. In the upwelling area, both species showed consistently higher occupation values compared to the continental shelf area. Certain characteristics of the spatial distribution of sardine (e.g. spreading area, overlapping with anchovy) differed substantially between the two ecosystems. Principal component analysis of geostatistical and spatial indicators revealed that biomass was significantly related to a suite of, rather than single, spatial indicators. At the spatial scale of our study, strong correlations emerged between biomass and the first principal component axis with highly positive loadings for occupation, aggregation and patchiness, independently of species and ecosystem. Overlapping between anchovy and sardine increased with the increase of sardine biomass but decreased with the increase of anchovy. This contrasting pattern was attributed to the location of the respective major patches combined with the specific occupation patterns of the two species. The potential use of spatial indices as auxiliary stock monitoring indicators is discussed.

A new type of vertebral malformation is described, consisting of deformed cartilaginous neural and haemal processes and the compression and fusion of vertebral bodies. The malformation is designated as haemal vertebral compression and fusion (haemal VCF). We studied the aetiology of the malformations and described microanatomical histopathological alterations. The malformations were detected during routine quality control in one of six monitored Gilthead sea bream populations. Haemal VCF affected the posterior part of the vertebral column (haemal vertebrae). In 20% of the deformed specimens, haemal VCF was combined with lordosis. At 35 dph (days post-hatching), early anatomical signs of the haemal VCF consisted of abnormal centrum mineralization, malformed cartilaginous neural and haemal processes and developing lordotic alterations. The histological examination of the deformed individuals revealed that haemal VCF is preceded by notochord abnormalities. The frequency of deformed individuals was three times higher at 35 than at 61 dph (50.3% vs. 17.2%, n = 157 and n = 250, respectively). No signs of repair or reversion of malformations have been observed. Thus, the steep decrease in deformities in older animals suggests that haemal VCF is linked to high mortality rates. The results are discussed in respect of the possible causative factors of haemal VCF., (© 2013 John Wiley & Sons Ltd.)

A number of scientific papers in the last few years singled out the influence of environmental conditions on the spatial distribution of fish species, highlighting the need for the fisheries scientific community to investigate, besides biomass estimates, also the habitat selection of commercially important fish species. The Mediterranean Sea, although generally oligotrophic, is characterized by high habitat variability and represents an ideal study area to investigate the adaptive behavior of small pelagics under different environmental conditions. In this study the habitat selection of European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus is analyzed in two areas of the Mediterranean Sea that largely differentiate in terms of environmental regimes: the Strait of Sicily and the North Aegean Sea. A number of environmental parameters were used to investigate factors influencing anchovy and sardine habitat selection. Acoustic surveys data, collected during the summer period 2002-2010, were used for this purpose. The quotient analysis was used to identify the association between high density values and environmental variables; it was applied to the entire dataset in each area in order to identify similarities or differences in the "mean" spatial behavioral pattern for each species. Principal component analysis was applied to selected environmental variables in order to identify those environmental regimes which drive each of the two ecosystems. The analysis revealed the effect of food availability along with bottom depth selection on the spatial distribution of both species. Furthermore PCA results highlighted that observed selectivity for shallower waters is mainly associated to specific environmental processes that locally increase productivity. The common trends in habitat selection of the two species, as observed in the two regions although they present marked differences in hydrodynamics, seem to be driven by the oligotrophic character of the study areas, highlighting the role of areas where the local environmental regimes meet 'the ocean triad hypothesis'.

To test the hypothesis that sex determination in the European sea bass (Dicentrarchus labrax L.) Can be affected by the incubating temperature during the very early developmental stages, eggs from the same batch of spontaneously spawned broodstock were divided at the stage of half-epiboly into three groups according to rearing temperature: G13 = 13 degrees C, G15 = 15 degrees C, and G20 = 20 degrees C. Temperature treatment lasted until the middle of metamorphosis (17-18 mm total length, [TL]), and, with the exclusion of water temperature, all biotic and abiotic conditions were identical for the three experimental groups. The on-growing phase was performed under ambient photoperiod and temperature conditions for all groups. Sex proportions were determined by histological examination of the gonads of fish at 308, 467, and 568 days posthatch (DPH). At 308 DPH (TL: 135-201 mm), 100% of the specimens had differentiated into males and females. A significantly higher (P < 0.01) proportion of females was found in groups G13 (72-74%) and G15 (67-73%) than in group G20 (24-28%). At the final sampling there was no statistically significant difference in body weight between the experimental groups. However, in all groups, female fish were larger than males (P < 0.001). Results provide for the first time clear evidence that temperature during the very early developmental stages is the crucial factor affecting the process of sex differentiation of the sea bass, with low rearing temperatures (13 or 15 degrees C) resulting in sex proportions consistently skewed in favor of females.