Silvering process of female European eel in the north Adriatic: Who is really ready to migrate?

During the 1970s and 2010, the population of Anguilla anguilla declined significantly, and the species is now classified as a critically endangered species by the International Union for Conservation of Nature (IUCN). Considering its social, economic, and ecological importance, it is necessary to understand the biological mechanism that controls population dynamics, in particular the passage from the resident phase to the migratory phase. During this phase of their life cycle, the environment plays a key role in the maturation of the spawners which will eventually undertake a long spawning migration to the Sargasso Sea. An assessment of the morphological characteristics of eels during their silvering process and reproductive activity was conducted by collecting 1513 female eels from seven lagoons in the North Adriatic Sea. Morphometric analyses show that eels classified as pre-migratory according to the Silver Index are histologically (65% of eels with oocytes in the most advanced stage of development) and morphologically ready to migrate. Accordingly, pre-migrant eels treated with hormone induction performed similarly to migrant eels. They mated and spawned spontaneously in the tank with a percentage of 81.0%, and 88.2% of them produced viable eggs. The results showed how the North Adriatic lagoons could present favourable conditions that permit the fast development of females with high reproductive potential. This data can be used to develop successful strategies to conserve and manage eel populations

Induced Reproduction of Aphanius fasciatus by Ecophysiological Conditioning and Hormonal Treatment in Fresh and Marine Water

The Mediterranean toothcarp (Aphanius fasciatus) can be used to biologically control mosquito larvae. The reproductive performance of 234 Mediterranean toothcarp (180 females and 54 males) was investigated. Reproductive factors were determined in fish kept in fresh or saline water (males and females together), and in fish kept separately by sex in saline water and hormonally-treated with carp pituitary extract (CPE). In the hormonally-treated group, the combined effect of temperature, photoperiod, and hormonal treatment induced the best ovary maturation and larvae production rates. The rate of reproduction was very high (average eggs/female: 5.9-10.5) compared to natural reproduction in the wild (average eggs/female: 2-4). Additionally, the hatching rate was 97-100%. The results of this study show that reproduction of Mediterranean toothcarp can be controlled in an artificial environment: the lack of mortality in adults during acclimation and conditioning in fresh and marine waters indicates good domestication and plasticity in reproductive parameters

Gonadal Development in European Eel Populations of North Adriatic Lagoons at Different Silvering Stages

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 m 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

Sexual behaviour and reproductive performance of the endangered European eel Anguilla anguilla (Linnaeus, 1758) based on direct observationsand paternity assignment in semi-natural conditions

European eel Anguilla anguilla is among the highly valued species for aquaculture. Since its peculiar biology, it is not yet possible to complete the whole life cycle in artificial conditions and its supply depends entirely on wild catches. In the last 50 years this species has suffered a population reduction of 99 % mainly due to overfishing. In a conservation perspective, it is of fundamental importance to improve the aquaculture production of European eel, to avoid the extinction of this species and preserve its residual genetic variability, allowing at the same time the fulfilling of costumers request without increasing its harvesting pressure. In this study we aimed to deepen the knowledge about the mechanisms at the basis of reproduction of the European eel in semi-natural conditions, through direct observation of spawning behaviour and through the paternity assignment using microsatellite markers. The systematic and prolonged observation of the reproductive behaviour of European eel and the contextual parentage analyses we carried out for the very first time in this species on 39 adults and 432 F1 randomly collected. We contributed to unravel the sexual behaviour of this species in the most common artificial reproduction conditions (polyandry), and define the precise courtship sequence until the release of gametes, and the male-male hierarchy in courtship. We characterized for the first time three main types of male: dominant (the first who starts the courtship, and the one with the majority of F1 assigned), subordinate (which starts the courtship only in a second time and with a minor percentage of F1 ascribed) and ineffective (which sometime appears totally disinterested to courtship and has few F1 or none). The evidences here produced represent an important attempt for developing good reproduction practices of the critically endangered European eel, providing a good starting point for its future aquaculture production

Effects of environmental enrichment on the behavior of Octopus vulgaris in a recirculating aquaculture system

Octopus vulgaris is a commercially valuable species. It is overexploited in the natural envi-24 ronment and is considered to be an innovative species for aquaculture. However, large-scale farm-25 ing is generally designed only based on economic requirements, disregarding any form of enrich-26 ment that to induce the natural behavior of aquatic species. Although many studies have shown the 27 influence of environmental enrichment on terrestrial vertebrates, fish, and cephalopod mollusks, 28 information on the effect of environmental enrichment on the body patterns of O. vulgaris is limited. 29 Therefore, in this study, we assessed how different environmental conditions (Basic vs. Enriched) 30 affect sub-adults of O. vulgaris kept in recirculation systems, through qualitative–quantitative stud-31 ies of the main body patterns and their potential application in the commercial production of this 32 species. The results indicated that octopuses kept in the enriched environment showed several body 33 patterns and gained a significantly higher weight than those kept in the basic environment. The 34 body patterns displayed by the individuals kept in the basic environment were similar to those 35 exhibited under situations of hostility and inter/intra-specific conflict. Hence, the environment of 36 octopuses needs to be enriched, especially for the large-scale production of this species

Effects of Environmental Enrichment on the Behavior of Octopus vulgaris in a Recirculating Aquaculture System

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

Yeast-extracted nucleotides and nucleic acids as promising feed additives for European sea bass (Dicentrarchus labrax) juveniles

Nowadays functional ingredients have a significant potential for improving current low fish meal (FM) aquafeed formulation in sustaining growth and enhancing animal robustness for Mediterranean aquaculture. Among them, nucleotides (NT) and nucleic acids (NA) drew attention for their application in the last two decades. NT are organic molecules involved in many life-supporting pathways, and are the building blocks of NA, which stand as genetic repositories. NT are naturally present in organic ingredients, and among them FM is known to be one of the highest NT sources. When this NT source is seriously limited, fish might be under the minimum NT requirements, especially in fast growing life stages of carnivorous species. Hence, a trial on European sea bass juveniles was carried out, testing two dietary FM levels (FM10, FM20 as 10% and 20% FM, respectively) supplemented with 500 mg kg-1 yeast-originate NT or NA dose over 80 days. Thereafter, fish were exposed to one week of sub-optimal thermal and dissolved oxygen condition (30°C and 4.0 mg/L O2) to further explore the effect of NT and NA inclusion on immune response and gut microbiome alteration. At the end of the growth period NT increased feed intake at both FM dietary levels. FM20 combined with NA and NT further improved growth performance, enhancing lipid efficiency and increased anti-inflammatory TGF-b. After sub-optimal environmental conditions both NT and NA exerted prebiotic functions on gut microbiome by promoting beneficial lactic acid bacteria such as Weissella and Leuconostoc. At the same time NT in 10% FM diet increased the abundance of Bacillus taxon. In conclusion, the combination of NT/NA included at 500 mg kg-1 was able to promote growth when included in 20% FM level, assuming higher nutritional NT requirement when combined with 10% FM. On the other hand, NT/NA added in 10% FM upregulate proinflammatory IL-1b and favor beneficial gut bacterial taxa