The European eel (Anguilla anguilla, Linnaeus 1758) is a catadromous fish with significant cultural, scientific, and commercial value. The protection of this species is particularly difficult because the biology of the eel life cycle remains unknown in many aspects. The European eel (A. anguilla) population has declined alarmingly over the past 30 years; this condition has led to questions about the long-term welfare of this species. This work aims to perform a histological analysis on gonad samples from European eels coming from four different lagoons of the North Adriatic at different stages of silvering, and to evaluate the maturation of the gonads. For this study, a total of 859 wild eels were captured from four different lagoons using the “lavoriero”. Subsequently, the biometric parameters were collected. Seventy-nine female eels were randomly selected, dissected, and the gonads were removed for histological analysis. Sections of 4 µm were cut and stained with hematoxylin and eosin (H&E). Histological observations of germ cells at the light microscopy level allowed for the characterization of six steps of oocyte maturation. Valle di Comacchio had the highest levels of oocyte maturation, while Valle Ca’ Pasta had the lowest. Eels with silver index III had an oocyte maturation nearly equal to that of eels at stages IV and V of silvering. Considering the results, we can affirm that eels from North Adriatic lagoons have high oocyte maturation levels and high GSI value indices at silvering stage III. The following experimental work shows that the levels of oocyte maturation are higher even at lower silver index levels. It can be hypothesized that in these eels, the transition from yellow to silver eel occurs faster in relation to the high trophic availability in North Adriatic lagoons.

The European eel, Anguilla anguilla (Linnaeus, 1758), is a species of high conservation and commercial value. Also, with a high aquacultural value, it was one of the most farmed species in Europe before its decline. Conservation measures for this species are currently being implemented, some of which are the release of adults to allow them to migrate to spawning grounds and artificial reproduction to minimise the impact of overfishing. Much progress has been made regarding the closing of the life cycle, but several problems remain to be solved, such as the weaning and growth of larvae. In this regard, the study of local populations and the identification of the best spawners could be a good way forward as it would help to identify spawners with high reproductive potential and good offspring quality. In this study, we compared the reproductive performance of female eels from migratory areas of the Northern Adriatic Sea at different maturation stages (10 pre-migrant stage; 10 migrant stage), treating both groups with the same hormonal protocol (weekly carp pituitary extract, injection of 17α,20β-Dihydroxy-4-pregnen-3-one at complete oocyte maturation). The research showed that eels at the beginning of metamorphosis (SI III), i.e., eels not yet ready to undertake migration, achieve reproductive performance equal to that of eels ready for migration (SI IV). Their performance was on par in both qualitative and quantitative terms. The optimal results in hatching (with values of 65.8 ± 3.2% for pre-migrant and 68.2 ± 4.1% for migrant) and survival rates (with value of 25.7 ± 5.4% pre-migrants; 27.2 ± 3.7% migrants), as well as the results about the time to reach full gonadal maturation, may have positive implications when considering release and restocking measures.

Octopus vulgaris is a commercially valuable species. It is overexploited in the natural environment and is considered to be an innovative species for aquaculture. However, large-scale farming is generally designed only based on economic requirements, disregarding any form of enrichment that induces the natural behavior of aquatic species. Although many studies have shown the influence of environmental enrichment on terrestrial vertebrates, fish, and cephalopod mollusks, information on the effect of environmental enrichment on the body patterns of O. vulgaris is limited. Therefore, in this study, we assessed how different environmental conditions (Basic vs. Enriched) affect sub-adults of O. vulgaris kept in recirculation systems, through qualitative–quantitative studies of the main body patterns and their potential application in the commercial production of this species. The results indicated that octopuses kept in the enriched environment showed several body patterns and gained a significantly higher weight than those kept in the basic environment. The body patterns displayed by the individuals kept in the basic environment were similar to those exhibited under situations of hostility and inter/intra-specific conflict. Hence, the environment of octopuses needs to be enriched, especially for the large-scale production of this species.

Evaluating milt samples before their preservation and/or reproductive use is critical to correctly develop assisted reproductive strategies for teleost species. This is especially true in case of “critically endangered” species, like the European eel (Anguilla anguilla), whose life cycle is not closed yet, leading to the necessity of capturing younglings from natural populations for both research and productive purposes. Despite androgens being involved in spermatogenesis and playing pivotal roles in the pre-migratory morphological and physiological changes, their quantification in different biological tissues is still to be refined in European eels. The aim of this study was to evaluate the feasibility of extraction and quantification of testosterone (T) and 11-ketotestosterone (11-KT) from male European eel milts. The secondary aim was to investigate potential differences in androgens’ profiles and/or functional characteristics of spermatozoa between wild-caught and farmed specimens. Twenty-four male European eels obtained from the North Adriatic region (14 wild-caught and 10 farmed) underwent a maturation-inducing hormonal treatment for milt production; blood and milt samples were then collected for androgens quantification upon ELISA and RIA methodologies. Spermatozoa were also evaluated for viability and objective motility. Plasma showed average T and 11-KT levels of 2.32 and 6.88 ng/mL, respectively, while milt 0.24 (T) and 1.09 ng/mL (11-KT). Significantly higher spermatozoa concentrations and motility were observed in farmed eels’ milts. This work contributes to deepening the knowledge on teleost physiology, being the first report quantifying T and 11-KT from European eels’ seminal plasma and comparing the quality of milts of farmed vs wild specimens.

The population of the blue crab Callinectes sapidus is rapidly expanding in the Mediterranean Sea, where it is causing increasing ecological and economic impacts. However, biological information from recently colonised areas remains limited. This study combined controlled experiments and reproductive analyses to investigate the key biological traits of C. sapidus in the northern Adriatic Sea. Feeding trials were conducted under controlled conditions to assess prey consumption and feeding behaviours using Manila clams (Ruditapes philippinarum) and Mediterranean mussels (Mytilus galloprovincialis), offered as monospecific and mixed diets. The results showed that, while the number of prey items consumed did not differ markedly between species, mussels provided a significantly higher edible biomass, indicating greater energetic profitability. Handling and consumption times were comparable between prey types, suggesting compensatory differences between opening and feeding phases. Food intake was strongly influenced by temperature, with peak consumption observed between 25 and 28 °C and reduced feeding at both lower and higher temperatures. Reproductive analysis of ovigerous females revealed high fecundity, with a mean of 1.63 ± 0.53 million eggs per individual and a positive relationship between fecundity and body size. Overall, the results confirm that C. sapidus combines trophic flexibility with high reproductive output—traits that support its invasive success. These findings improve the understanding of the blue crab’s ecological role in the northern Adriatic, providing useful insights for assessing its impact on shellfish aquaculture and developing management strategies.