A combination of traditional and emerging methodologies was used to assess the trade‐offs between several life‐history traits (linked to reproduction and condition) and parasitism in a commercially‐exploited cold‐water species, blue whiting Micromesistius poutassou, in the Mediterranean Sea. The use of histological and gravimetric methods revealed conflicting evidence as to the fecundity type (indeterminate or determinate) of this species. Moreover, there seem to be condition‐mediated compensations between egg quality and egg quantity. The effects of parasitism on reproduction and condition are species‐specific and occur mainly at high intensities of infection; they include a lower batch fecundity (affecting reproductive potential), a higher hepatosomatic index and a higher spleen‐somatic index. Considering the fact that larger fish spawn more eggs and that the minimum landing size is lower than the size at maturity, these results may have implications for the future management of M. poutassou stocks in the Mediterranean Sea. Local environmental conditions may account for geographical differences regarding infection in M. poutassou. Altogether, the results support the idea that the complex trade‐offs between parasitism, reproduction and condition need to be considered in order to understand the status of cold‐water species such as M. poutassou.

To achieve sustainable fisheries implies that resources' management is carried out in accordance with biologically and ecologically relevant processes. In this context, to infer the boundaries of the genetic stocks along their distribution is crucial to avoid the depletion of genetic diversity induced by fishing pressure. Despite its remarkable ecological role and commercial interest, there are still many uncertainties about the genetic population structure and local adaptation processes of the European sardine (Sardina pilchardus) along its distributional range. Our analysis revealed that in addition to the uneven genetic study effort throughout its distribution, there are discrepancies when it comes to delimiting populations, especially in the waters surrounding the Iberian Peninsula. Also, powers of the genetic markers applied in the studies were examined, showing that allozymes detected a larger number of significant pairwise values of genetic differentiation, while mtDNA-RFLP detected a greater degree of differentiation among genetic stocks. Moreover, large values of genetic diversity in all the locations were identified regardless of marker type. Thereby, we provide a discussion of updated knowledge, contributing to shape long-term and genetically sustainable harvest strategies for this pelagic fish, since our findings indicate a mismatch between the genetic stocks and the managed stocks currently defined.

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The small pelagic European sardine presents high commercial and ecological values. Due to its cold-temperate water affinity, stocks are affected by global warming. Water temperature rise may change primary productivity patterns, negatively affecting fish condition and increasing parasite incidence. In this context, sardine health status was evaluated through the annual cycle on the Catalan Coast using thermal regimes comparison. Morphogravimetric parameters, sex and gonadal stages were assessed; infection by nematodes was characterised, and body condition was estimated by the Le Cren Factor and lipid content measured using a fish fat meter. Significant statistical differences were observed in spawning dynamics, body condition, and parasite infection between thermal regimes. Sardines from the colder north area had better condition and an earlier spawning, with lower parasite incidence (in terms of total prevalence, mean intensity and abundance) than those from the southern coast. Hysterothylacium spp. was the most abundant nematode, while Anisakis spp. prevalence was null in the two locations. Seasonal differences in nematode load were observed along the Catalan Coast, with lower prevalence during the summer and higher in winter-spring. Although previous studies have underestimated parasite influence on sardine health status, parasite abundance and sardine condition were negatively correlated. Seawater temperature and primary productivity are the proposed factors promoting differentiation in nematode infection and fish condition throughout the annual cycle and between locations.

The European sardine’s condition is reflected in its reproductive potential, and therefore, in its status as a fishery resource. These values depend on the stock’s distribution and resource availability, which is highly determined by environmental characteristics. Sardines from the productive Gulf of Trieste (in the North Adriatic), located in the northernmost section of the most septentrional Mediterranean sub-basin in which sardine exploitation has traditionally been intensive, were analysed. The reproductive cycle and gonadosomatic index (GSI) were studied. Tissue and mesenteric fat values, as well as vacuity (% V), relative condition (Kn), and hepatosomatic (HSI) indices were evaluated due to their potential relationships with reproductive performance. The results suggested opposite patterns between fat reserves and GSI, while Kn showed a relationship neither with GSI, nor with reproductive stage, which led us to conclude that it is more advisable to apply direct lipid indices to project their contribution to reproductive potential. Moreover, the females’ condition was generally better than that of the males, added to an advanced gonadal development during spring and summer, albeit males and females reached the spawning season together. Moreover, females’ GSIs were significantly higher during active spawning. Furthermore, correlation analyses showed that SST was related with the parameters evaluated, as well as the available portion of productivity for the fish (OPFish), which may explain the sardines’ better condition and GSIs than their chlorophyll concentration.