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Over the past few decades, the fishing industry and species conservationists have grown increasingly concerned about the decrease in catches and poor health of European sardines (Sardina pilchardus), particularly in the northwestern Mediterranean region. The species is threatened by a number of factors, including parasite illnesses, rising seawater temperatures, and overfishing. Increasing seawater temperatures due to climate change might lead to the proliferation of protistan parasites, such as Ichthyodinium chabelardi. This parasite has been documented in the literature to cause 100% larval mortality in sardines, which may have detrimental effects on fish populations and the fishing industry. We confirmed the existence of I. chabelardi in pelagic eggs and the ovaries of European sardines from the Catalan coast (northwestern Mediterranean) by means of stereomicroscopic analysis and a genetic methodology for parasite identification. The incidence of this infection was 22.5% in ovarian tissue and 11.5% in eggs. In this study, we present new data on the vertical transmission of I. chabelardi from one generation to another in sardines captured in the Mediterranean region. Interpreting outbreaks of I. chabelardi, especially in sardine populations, requires further research into the transmission of infection and improving our understanding of protozoan parasites.

One-Health is an umbrella term that integrates the health of the environment, humans and non-human animals. This approach is applied here to elucidate the impact of non-native invasive species on aquaculture and food security. Despite inherent biases against these species, a better understanding of their characteristics allows for the identification of those of greatest concern, minimizing the risk of food shortages and infectious diseases. This review summarises the positive and negative impacts of non-native species, delineating the specific areas they may impact. Additionally, this review gives an insight to the expertise and stakeholders that would need to be included if a “One-Health” approach were to be implemented by policymakers to better control non-native species. Detailed examples illustrate the consequences of non-native species on trophic dynamics, ecosystem health, water chemistry, and human health, emphasizing the importance of managing them within a multidimensional framework. The “One-Health” approach is explained, and suggestions are made on how certain non-native species could be used to contribute to food security in low- and middle-income countries. Furthermore, recommendations are made to promote a more inclusive management strategy.

Rearing density directly impacts fish welfare, which, in turn, affects productivity in aquaculture. Previous studies have indicated that high-density rearing during sexual development in fish can induce stress, resulting in a tendency towards male-biased sex ratios in the populations. In recent years, research has defined the relevance of the interactions between the environment and epigenetics playing a key role in the final phenotype. However, the underlying epigenetic mechanisms of individuals exposed to confinement remain elucidated. By using zebrafish (Danio rerio), the DNA methylation promotor region and the gene expression patterns of six genes, namely dnmt1, cyp19a1a, dmrt1, cyp11c1, hsd17b1, and hsd11b2, involved in the DNA maintenance methylation, reproduction, and stress were assessed. Zebrafish larvae were subjected to two high-density conditions (9 and 66 fish/L) during two periods of overlapping sex differentiation of this species (7 to 18 and 18 to 45 days post-fertilization, dpf). Results showed a significant masculinization in the populations of fish subjected to high densities from 18 to 45 dpf. In adulthood, the dnmt1 gene was differentially hypomethylated in ovaries and its expression was significantly downregulated in the testes of fish exposed to high-density. Further, the cyp19a1a gene showed downregulation of gene expression in the ovaries of fish subjected to elevated density, as previously observed in other studies. We proposed dnmt1 as a potential testicular epimarker and the expression of ovarian cyp19a1a as a potential biomarker for predicting stress originated from high densities during the early stages of development. These findings highlight the importance of rearing densities by long-lasting effects in adulthood conveying cautions for stocking protocols in fish hatcheries.

Rearing density directly impacts fish welfare, which, in turn, affects productivity in aquaculture. Previous studies have indicated that high-density rearing during sexual development in fish can induce stress, resulting in a tendency towards male-biased sex ratios in the populations. In recent years, research has defined the relevance of the interactions between the environment and epigenetics playing a key role in the final phenotype. However, the underlying epigenetic mechanisms of individuals exposed to confinement remain elucidated. By using zebrafish (Danio rerio), the DNA methylation promotor region and the gene expression patterns of six genes, namely dnmt1, cyp19a1a, dmrt1, cyp11c1, hsd17b1, and hsd11b2, involved in the DNA maintenance methylation, reproduction, and stress were assessed. Zebrafish larvae were subjected to two high-density conditions (9 and 66 fish/L) during two periods of overlapping sex differentiation of this species (7 to 18 and 18 to 45 days post-fertilization, dpf). Results showed a significant masculinization in the populations of fish subjected to high densities from 18 to 45 dpf. In adulthood, the dnmt1 gene was differentially hypomethylated in ovaries and its expression was significantly downregulated in the testes of fish exposed to high-density. Further, the cyp19a1a gene showed downregulation of gene expression in the ovaries of fish subjected to elevated density, as previously observed in other studies. We proposed dnmt1 as a potential testicular epimarker and the expression of ovarian cyp19a1a as a potential biomarker for predicting stress originated from high densities during the early stages of development. These findings highlight the importance of rearing densities by long-lasting effects in adulthood conveying cautions for stocking protocols in fish hatcheries.

Small pelagic fish are key elements of marine trophic networks and are of great importance to the total landing of marine species. Over the last decades, a decrease in biomass and catches of European sardine has been described, especially in the Mediterranean Sea, as an indication of a drop in stock condition. Multiple causes, including direct and indirect anthropogenic factors, seem to affect this ecologically and economically important species. To address this issue, it is important to identify the current variability in sardine status and understand the strategies for energy allocation, which are intimately related to reproductive potential and recruitment. We analyzed the somatic condition through tissue and mesenteric lipid measurements, relative condition (Kn) and hepatosomatic (HSI) indices, and reproductive condition with the gonadosomatic index (GSI) in four subareas of the Mediterranean (Northern Alboran, Northern Spain, the Northern Adriatic, and the Aegean Sea) and an outgroup from the Atlantic. The analyses were performed within the gonadal development cycle since translocation to reproduction may mask the state of actual energy reserves for comparison. The results revealed marked differences in health status among subareas, highlighting the low condition of Northern Spain sardines throughout the annual cycle. The uniform condition throughout gonadal development in the Northern Adriatic suggests that resource availability modulates the reproductive strategy since in this locality, sardines would have high dependence on immediate reserves, not behaving as strict capital breeders. Moreover, similarities between Alboran and Atlantic stocks are discussed, highlighting the marked energy replenishment of the latter after reproduction compared to the Mediterranean stocks. The Aegean stock was the fastest to reach its maximum after spawning, presenting low condition values from the developing to actively spawning period, but with the greatest recovery at the re

Body condition and reproduction data are broadly used to assess the health status of fish because of its implications for recruitment and ecosystem structure. Sardina pilchardus is a small pelagic distributed throughout both Mediterranean and Eastern Atlantic. Seasonal trend analysis of energy storage and reproduction was carried out in sardines from two areas along the Atlantic-Mediterranean transition: Southern Portugal-Gulf of Cádiz (POR-GC) (Atlantic Ocean) and Alboran Sea (Alb) (Mediterranean Sea) from 2019 to 2021. Energetic condition was estimated using tissue and mesenteric fat content, hepatosomatic index (HSI), and the relative condition factor (Kn). Sex, reproductive developmental stage, and gonadosomatic index (GSI) were also obtained. In addition, the oceanographic and meteorological characteristics of the areas were analysed. Results showed that seasonal Kn, tissue and mesenteric fat content, and HSI values of POR-GC specimens exceeded Alb's with summer arrival, period in which sardine acquires reserves to allocate them to reproduction. These differences could be associated to greater productivity of the former area mainly due to rivers discharges and trade winds intensification during summer (from July to September). Furthermore, gonad maturation of POR-GC stock occurred before the Alb. However, no spawning capable individuals were identified until February in POR-GC. In contrast, in Alb it was observed a remarkable fraction of spawning capable and active spawner individuals in October. We hypothesized the migration of mature individuals from POR-GC to the spawning areas located in the Alb. Seasonal genetic population studies are required to untangle it and reliably evaluate the environmental effect on the stocks.

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

Zebrafish is a worldwide used animal model to better understand cultured fish species; thus, in the last two decades, zebrafish facilities have been created in many aquaculture research centres. However, and despite the attempts of rigorous aseptic conditions for animal husbandry in wet laboratory facilities, the presence of parasites cannot be underestimated. The microsporidium Pseudoloma neurophilia, which mostly affects the central nervous system, has been listed as the most prevalent parasite in reared zebrafish. The emergence of P. neurophilia is usually detected when the individual presents irreversible morphological and/or behavioural symptoms, and consequently, the spread of the disease is inevitable, indicating that the infection is expanded across rearing tanks. This review attempts, for the first time, to collect and discuss the current information on P. neurophilia life cycle, target tissues and symptomatology of the infection occurred in zebrafish. Due to its vertical transmission together with the increasing presence of zebrafish as a model in reproduction-related problems found in aquaculture, it is highlighted, among others, the sexual dimorphism of the pathogenic effects and the possible transgenerational implications of parasitic infections. Further, to date none effective treatments have been described, so here we provide in detail available diagnostic methods, discussing the importance of the early detection, giving safety-rearing recommendations to decrease the presence of P. neurophilia. Our intention is to minimize parasite outbreaks in zebrafish facilities, which, on the one hand, can compromise zebrafish welfare, and on the other hand, could interfere furtively in the resulting research previously designed for improving aquaculture production but also other biomedical-related research.

Zebrafish is a worldwide used animal model to better understand cultured fish species; thus, in the last two decades, zebrafish facilities have been created in many aquaculture research centres. However, and despite the attempts of rigorous aseptic conditions for animal husbandry in wet laboratory facilities, the presence of parasites cannot be underestimated. The microsporidium Pseudoloma neurophilia, which mostly affects the central nervous system, has been listed as the most prevalent parasite in reared zebrafish. The emergence of P. neurophilia is usually detected when the individual presents irreversible morphological and/or behavioural symptoms, and consequently, the spread of the disease is inevitable, indicating that the infection is expanded across rearing tanks. This review attempts, for the first time, to collect and discuss the current information on P. neurophilia life cycle, target tissues and symptomatology of the infection occurred in zebrafish. Due to its vertical transmission together with the increasing presence of zebrafish as a model in reproduction-related problems found in aquaculture, it is highlighted, among others, the sexual dimorphism of the pathogenic effects and the possible transgenerational implications of parasitic infections. Further, to date none effective treatments have been described, so here we provide in detail available diagnostic methods, discussing the importance of the early detection, giving safety-rearing recommendations to decrease the presence of P. neurophilia. Our intention is to minimize parasite outbreaks in zebrafish facilities, which, on the one hand, can compromise zebrafish welfare, and on the other hand, could interfere furtively in the resulting research previously designed for improving aquaculture production but also other biomedical-related research

Changes in the fish fauna composition of North-eastern Atlantic Ocean have been recorded based on the occurrence of warm affinity species. Individuals of Anthias anthias (Serranidae), Callanthias ruber (Callanthiidae), Dactylopterus volitans (Dactylopteridae), Halobatrachus didactylus (Batrachoididae), Seriola rivoliana (Carangidae), and Sphyraena sphyraena (Sphyraenidae) have been found along Galician waters, considered unusual species in this biogeographic transition zone. To classify them as seasonal migrant visitors or local spawners with settlement potential, gonad histological analyses were performed, showing that at least A. anthias, C. ruber, and H. didactylus were spawning capable when present in the area. In turn, this work sheds light on the reproductive biology of these species, of which gonadal histological data were limited or non-existent. In fact, this study represents the first gonad histological analyses of A. anthias, C. ruber, and D. volitans. Our results described important traits of the reproductive strategies of the species analysed, having classified a C. ruber female as asynchronous batch spawner, and identifying lobular type and cystic spermatogonial testis in A. anthias, C. ruber, and H. didactylus males. Males of A. anthias and C. ruber presented potential histological evidence of protogyny with the description of melanomacrophage centres in both species.

Fish farmed for human consumption are reared in artificial environments that are very different from conditions that species experience in the wild. Consequently, the environment influences many aspects of the biology of cultured animals, including sexual phenotype through epigenetic mechanisms (Feeney et al., 2014). Disease outbreaks occur eventually in fish farms, causing economic loses. However, the epigenetic consequences that these reiterating infections can potentially cause in fish during their development and whether these can alter the reproductive system, remain unknown. Here we present a study for which two model research tools have been selected; the zebrafish as a suitable model for aquaculture research (Ribas and Piferrer, 2014) and the lipopolysaccharide (LPS) from Gram negative bacterial wall as a model to stimulate the immune system in fish(Forn-Cuní et al., 2017). The aim of this work is to develop a suitable in vivo system to study whether infections occurring in fishduring sex differentiation are able to alter the finalgonadal phenotype throughout epigenetic changes