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Oomycetes of the genus Saprolegnia are widespread in freshwater environment and are among the main path- ogens causing economic losses in salmonid aquaculture. Infections by mycotic agents in fish farming are generally considered to result from chronic stress and poor fish condition associated with water quality problems, adverse environmental conditions, frequent/rough/incorrect handling, concurrent infections, physiological changes associated with reproduction and immunocompromised animals. To identify risk factors for Saprolegnia infections in trout and Atlantic salmon farming, longitudinal studies were carried out in different Italian, Spanish, and Scottish fish farms. Prevalence of saprolegniosis and fish mortality were monitored over time and statistically analysed with respect to husbandry and environmental factors. Overall, statistical results by production cycle (trout vs salmon farming) and by country indicate that the prevalence of Saprolegnia may be influenced by peculiarities of the culture system and farming environment. Nevertheless, a specific set of parameters, including lower water temperature, and handling procedures increased Saprolegnia prevalence in all the considered farms. Particularly, in trout farms Saprolegnia infections represented an important contribution to mortality, and prevalence was influenced by water temperature and pH, and by fish density within the tanks. Similarly, temperature and water quality were the main factors influencing the prev- alence of Saprolegnia in Atlantic salmon farms. Moreover, molecular analyses confirmed the role of S. parasitica as the main pathogenic oomycete in trout and salmon farming in the considered countries. The identification of risk factors for introduction and increase of Saprolegnia infection in fish farms will allow the correct design of bio- security and pathogen control strategies

INTRODUCTION. Eustrongylides spp. are parasitic nematodes of piscivorous birds and freshwater fish, which act as their definitive and intermediate/paratenic hosts respectively, and are as well recognized as potentially zoonotic parasites. To date, Eustrongylides has been reported from fish and birds from different areas of central Italy (Dezfuli et al., 2015Parasites Vectors. 8: 227; Mazzone et al., 2019 J Parasitol. 105: 882-89; Guardone et al., 2021 Food Control. 120: 107517); therefore, the purpose of this study was to investigate the presence of the parasite in fish populations from areas not yet studied in northern Italy. MATERIALS AND METHODS. A total of 2130 specimens belonging to a wide range of fish species (Perca fluviatilis, Lepomis gibbosus, Micropterus salmoides, Squalius cephalus, Scardinius erythrophthalmus, Carassius carassius, Rutilus rutilus, Alburnus arborella, Ameiurus melas, Silurus glanis) were collected with the help of local fishermen from six lakes in northern Italy (Garda, Nero, Alice, Pistono, Sirio, Candia) and subjected to a full parasitological examination. Collected nematodes were fixed in 70% ethanol and identified morphologically through light and scanning electron microscopy; a subset of larvae was analyzed with molecular methods (amplification and sequencing of ITS rDNA) for species confirmation. RESULTS AND CONCLUSIONS. Overall, Eustrongylides larvae were recovered in 4.88% of the examined fish and were exclusively found in the species P. fluviatilis, L. gibbosus and M. salmoides, with particularly high prevalence in L. gibbosus (as high as 95.45% in Candia lake). The parasite occurrence was confirmed in all six surveyed lakes with prevalence values higher in Candia lake (65.15%) and lower in Sirio lake (1.42%). Morphological and molecular analyses allowed to confirm that all larvae belonged to the species Eustrongylides excisus. The distribution of E. excisus in all the lakes under study and the high prevalence values reported in some fish species throughout the present investigation highlight a possible emergence of this parasitic infection, which could represent an important health issue for piscivorous birds, being particularly pathogenic for nestlings, as well as a potential zoonotic risk.

The diffusion of new eating habits and the increase of fish products demand have been raising concerns in the European countries, including Italy, about the transmission risk of zoonotic fish parasites to consumers, leading to the current EU "Hygiene Package" Regulations. In relation to the mandatory freezing treatment for “products intended to be consumed raw, or marinated, salted and any other treated fishery products, if the treatment is insufficient to kill the viable parasite”, an exception is included in the Reg. (EU) No 1276/2011 for farmed Atlantic salmon (Salmo salar), for which the risk was considered negligible according to EFSA Opinion (2010), but not for other fish species farmed in Europe. With the aim to collect the necessary epidemiological information on the presence/absence of zoonotic parasites in EU aquaculture, in the framework of the EU H2020 project ParaFishControl (www.parafishcontrol.eu), an extensive parasitological survey has been carried out on the main farmed fish species in Italy and other countries such as Spain, Greece, Denmark, Norway and Hungary. The present work reports the results from Italy. From 2016 to 2018 a total of 4728 farmed fish have been examined from 6 freshwater and 5 marine farms located in Italy: 1594 rainbow trout (Oncorhynchus mykiss), 1571 European sea bass (Dicentrachus labrax) and 1563 gilthead sea bream (Sparus aurata) have been collected based on a random polietapic and stratified sampling plan with a confidence level of 99% and a margin of error (MoE) of 4-8%. Besides harvest quality fish, runts were also examined in order to consider even the most predisposed hosts to acquire parasites through the natural food web. Parasitological analyses to search for anisakid nematodes in marine fish and diphyllobothriid cestodes and Opisthorchioidea digeneans in freshwater fish were performed utilizing methodologies such as visual inspection and candling as provided by the EU regulation, integrated by UV-press method, muscle compression/artificial digestion followed by microscopic examination when required (e.g. for Opisthorchioidea). No zoonotic parasites were found in any of the examined fish, including runts. The data obtained from this extensive survey show the absence of zoonotic parasites in the fish examined and are comparable to those reported in previous studies, leading to consider as negligible the risk of infections due to zoonotic helminths in the most important fish species of Italian aquaculture. Similar results have been obtained for the examined farmed fish in other countries involved in ParaFishControl Project. The results allow to assess the risk of the presence of zoonotic parasites in farmed rainbow trout, European sea bass and gilthead sea bream as negligible, indicating that also these farmed fish species should be considered suitable to benefit from the exemption from freezing treatment provided by EU Regulation No 1276/2011 for Atlantic salmon. Furthermore, the monitoring approach employed could be adopted for planning surveillance activities in EU fish farming systems, as it appears implementable also by industry, to better guarantee the safety of aquaculture products.

The class Oomycota comprises species that are pathogenic to plants and animals, including humans, and are able to cause severe economic losses in agriculture and aquaculture industry worldwide. Phytophthora infestans causes losses in potato and tomato crops for more than 6 billion per year, as well as damage to ecosystems; Plasmopara viticola is responsible for downy mildew, which is one of the most damaging grapevine diseases. The genus Phytium, includes species that are pathogenic to both plants and animals, particularly, Phytium insidiosum has been reported to cause disease in humans and in other mammals. Oomycetes of the order Saprolegniales are widely distributed in freshwater environments, causing infections in different taxa of aquatic animals. Among these, members of the genus Saprolegnia represent a severe problem in freshwater fish farms, where production losses from 10 to 50% are reported. Despite the wide distribution and the impact of oomycetes on economic activities and on animal health, there are no effective available molecules against these agents. Following the current classification of malachite green and formalin among carcinogens, there are limited possibilities to control oomycete infections in aquaculture. The aim of this work was to test in vitro the activity of dimethomorph, a fungicide used in agriculture to control oomycete infections, on different species of Saprolegnia and Pythium isolated from fish and aquatic environment. Although no complete inhibition was observed at tested concentrations (0.1; 1; 5; 10; 50; 100 mg/L) mycelial growth was slowed down at highest concentrations. Furthermore our results suggest a different susceptibility of dimethomorph on the tested oomycete species.

Oomycetes from the genus Saprolegnia are opportunistic pathogens that cause significant losses in salmonid aquaculture. Despite this, studies reporting dominant Saprolegnia species in different fish farming facilities, as well as analyses of their spreading to natural environments, are still scarce. In this study, we have for the first time identified oomycete species present in four different trout farms in Croatia. We have collected 220 oomycete isolates, both from affected tissue (46 in total: adult trout - 28, eggs - 13, and alevins - 5) and from water (174 in total: in the fish farm – 78, upstream – 50, and downstream - 46). We have used Bayesian inference to reconstruct phylogenetic relationship among the internal transcribed spacer (ITS) sequences of the collected isolates and referent strains, and determined that the isolates belonged to three different oomycete genera: Saprolegnia (64% of isolates), Pythium (35%), and Leptolegnia (1%). Saprolegnia isolates were classified into four species: S. parasitica with 53 isolates, S. australis - 52, S. delica – 25, and S. ferax – 11. Pythium and Leptolegnia isolates couldn't be identified to the species level and probably belong to so far undescribed species since their sequences didn't group with previously described species. Next, isolates from the affected tissue were mostly S. parasitica (32), while S. australis, S. delica, and S. ferax were less common (≤ 4 isolates per species). Furthermore, we used hempseed baits to capture oomycetes from water and positioned them inside the fish farms, as well as upstream (between 55 and 155 m) and downstream (between 95 and 140 m) of the fish farms. According to correspondence analysis, Saprolegnia species showed a strong association with fish farms and downstream locations, while upstream locations were associated with Pythium species, highlighting a possible role of trout farms as a source of spreading Saprolegnia species into the environment.

Specimens of common smooth-hound, Mustelus mustelus, fished as bycatch in the Northwestern Adriatic Sea, were subjected to a complete parasitological examination. Parasites were processed for morphological and morphometric analyses aimed at identifying them to the species level. Parasite identity was confirmed through amplification and sequencing of 28S rDNA. The nematode Acanthocheilus rotundatus was recovered from the stomach and the proximal intestine, while the cestode Calliobothrium verticillatum was collected from the spiral valve. Our results confirm the occurrence of C. verticillatum in M. mustelus from the Mediterranean Sea and provide the first sequence data of A. rotundatus from the same area. Updated knowledge on the parasite fauna of M. mustelus from Adriatic Sea contributes to elucidating aspects of the ecology, biology and health status of elasmobranchs from the Mediterranean Sea, providing useful information for their proper management and conservation.

The fish parasites Saprolegnia spp. (Oomycota) and Amyloodinium ocellatum (Dinophyceae) cause important losses in freshwater and marine aquaculture industry, respectively. The possible adverse effects of compounds used to control these parasites in aquaculture resulted in increased interest on the search for natural products with antiparasitic activity. In this work, eighteen plant-derived compounds (2′,4′-Dihydroxychalcone; 7-Hydroxyflavone; Artemisinin; Camphor (1R); Diallyl sulfide; Esculetin; Eucalyptol; Garlicin 80%; Harmalol hydrochloride dihydrate; Palmatine chloride; Piperine; Plumbagin; Resveratrol; Rosmarinic acid; Sclareolide; Tomatine, Umbelliferone, and Usnic Acid) have been tested in vitro. Sixteen of these were used to determine their effects on the gill cell line G1B (ATCC®CRL-2536™) and on the motility of viable dinospores of Amyloodinium ocellatum, and thirteen were screened for inhibitory activity against Saprolegnia spp. The cytotoxicity results on G1B cells determined that only two compounds (2′,4′-Dihydroxychalcone and Tomatine) exhibited dose-dependent toxic effects. The highest surveyed concentrations (0.1 and 0.01 mM) reduced cell viability by 80%. Upon lowering the compound concentration the percentage of dead cells was lower than 20%. The same two compounds revealed to be potential antiparasitics by reducing in a dose-dependent manner the motility of A. ocellatum dinospores up to 100%. With respect to Saprolegnia, a Minimum Inhibitory Concentration was found for Tomatine (0.1 mM), Piperine and Plumbagin (0.25 mM), while 2′,4′-Dihydroxychalcone considerably slowed down mycelial growth for 24 h at a concentration of 0.1 mM. Therefore, this research allowed to identify two compounds, Tomatine and 2′,4′-Dihydroxychalcone, effective against both parasites. These compounds could represent promising candidates for the treatment of amyloodiniosis and saprolegniosis in aquaculture. Nevertheless, further in vitro and in vivo tests are required in order to determine concentrations that are effective against the considered pathogens but at the same time safe for hosts, environment and consumers.

Introduction: Marine Protected Areas (MPAs) represent a privileged observatory to monitor disease outbreaks in the marine environment. Recently, several episodes of mass mortality events (MME) of the noble pen shell Pinna nobilis occurred in different parts of the Mediterranean Sea. In the present work we report a MME occurred in 2018, involving a protected population of P. nobilis within the MPA of Porto Cesareo (Southern Italy, Ionian Sea) which had been previously characterized and monitored within the framework of the “Marine Strategy” Directive (2008/56/EC). Methodology: Data on abundance and size structure of the P. nobilis population had been collected since September 2017 through scuba diving visual census. Following a MME occurred in June 2018, one moribund specimen was sampled by professional divers of Porto Cesareo MPA within the reserve boundaries. The specimen was subjected to a complete diagnostic exam, including parasitological, histopathological and molecular analyses. Results: The mortality affected 100% of the protected population. The diagnostic exams allowed to detect the presence of Haplosporidium pinnae, identified through amplification and sequencing of partial 18S rDNA region, in the intestine and digestive gland. Histopathological analyses revealed the presence of haplosporidian-like protozoa in different life cycle stages within the digestive gland. The epithelium of digestive tubuli showed a diffused degeneration with extended infiltrate of brownish pigment referable to brown cells, which replaced almost completely the decaying glandular tissue. Conclusion: Haplosporidium pinnae has been already indicated as responsible for other MME of P. nobilis occurred in Western and Central Mediterranean Sea. The implementation of routine monitoring programs to assess the presence and distribution of transmissible agents in wild marine environment is an essential step to protect biodiversity. Such procedures are especially relevant within the context of a MPA, and should focus on the identification of sanitary risks that could impair conservation efforts. With respect to H. pinnae, further studies aimed at elucidating the life-cycle of the parasite and its causative role in recent MME of noble pen shell are of primary importance.

Introduction: Oomycetes belonging to the genus Saprolegnia cause high mortality rates in freshwater fish culture. The lack of alternative treatment with effectiveness comparable to the banned malachite green (MG), urge the identification of new molecules active against this pathogen. This work focused on an in vitro screening aimed at assessing the effectiveness of 35 compounds against Saprolegnia spp. in order to select molecules that could be of major interest for further in vivo investigations and applications in aquaculture. Methodology: In vitro trials were carried out on two Saprolegnia parasitica strains and one S. delica strain. Tests were performed according to existing protocols to determine the Minimum Inhibitory Concentration (MIC) in agar and the Minimum Lethal Concentration (MLC) after one hour of contact in water. Compounds were provided diluted in DMSO at a concentration of 10 mM (with the exception of Dequalinium Chloride, diluted at 2 mM) that were further diluted to working concentrations of 0.00001; 0.0001; 0.001; 0.01; 0.1 and 0.25 mM. Pure DMSO was also screened at the same amount present in different concentrations, until 1mM, in order to check its own inhibitory or lethal effects. Each strain was tested in triplicate. Results: Triplicates were consistent among each other. DMSO showed no inhibitory effects against Saprolegnia at concentrations from 0.00001 to 0.25 mM, but was able to inhibit the oomycete at higher concentrations also when used alone. MICs were determined for 15 out of 35 compounds examined. The lowest MIC was defined for zinc pyrithione (0.01 mM). Seven compounds had a MIC of 0.1 mM, seven of 0.25 mM, while the other 20 were ineffective at the tested concentrations. Conclusion: Although it was not possible to define MICs for several compounds at the tested concentrations, most of the molecules showed the ability to slow down the radial growth and/or to inhibit the aerial mycelium. These compounds, although not showing a high efficacy against Saprolegnia in in vitro trials, could be effective in decreasing the invasive capacity of the oomycete in the host, therefore representing good candidates for further in vivo studies.

13 pages, 6 figures, 2 tables, Coccidian parasites of the genus Aggregata are known to parasitize cephalopods as definitive hosts, however one of the genus members, A. octopiana, has shown an unresolved phylogeny within the same definitive host, the common octopus (Octopus vulgaris). Our study represents a large-scale investigation aimed at characterizing morphological traits and phylogeny of A. octopiana isolated from O. vulgaris inhabiting three distinct geographic areas of the central Mediterranean: The Adriatic, Ionian and Tyrrhenian Seas. The morphology of sporogonic stages of the parasite in octopus tissues was assessed by light and electron microscopy; molecular characterization has been carried out using the 18S rRNA locus. Our results support the hypothesis that two morphologically and genetically different A. octopiana infect O. vulgaris in the investigated areas of the Mediterranean Sea. Additional nuclear and mitochondrial markers for Aggregata should provide further information and better resolution of its phylogeny, This work has been initiated through the networking initiatives of the COST Action FA1301 (CephsInAction) and thanks to the support of a COST FA1301-Short Term Scientific Mission (P. Tedesco, from Italy to Vigo, Spain). The study has been supported through RITMARE Flagship project (MIUR-SZN) to PT and GF. G. Catanese would like to thank INIA for the INIA/CCAA research contract program

A redescription of Philometra globiceps (Rudolphi 1819), the type species of Philometra Costa 1845 (Philometridae), is provided on the basis of specimens collected from the gonads, stomach, pyloric caeca, intestine and gallbladder of the marine fish Uranoscopus scaber Linnaeus (Uranoscopidae, Perciformes) caught in the Ionian Sea off Ugento, southern Italy. Light microscopical and scanning electron microscopical examinations (latter used for the first time in this species) of the specimens revealed some previously unreported morphological features, such as the location of submedian pairs of cephalic papillae of external circle on four elevated cuticular lobes in gravid females, the presence of amphids, genital papillae and phasmids in males, the lamellate structure of the distal end of gubernaculum appearing as a dorsal protuberance in lateral view and the structure of the male caudal end. A taxonomically important feature of P. globiceps is the details in the dorsal transverse lamella-like structures on the distal end of the gubernaculum, by which this species can be separated from other gonad-infecting species of this genus. Apparently, P. globiceps is a specific parasite of U. scaber and all previous records of this species from hosts belonging to other fish families are evidently based on misidentifications.

INTRODUCTION. Monogeneans of the Family Calceostomatidae Parona & Perugia, 1890 parasitize different species of Sciaenids worldwide: among these, the calceostomatid Ktariella polyorchis Vala & Euzet, 1977 has been described infecting the gills of wild meagre Argyrosomus regius (Asso, 1801) caught off Tunisia and Egypt. The present investigation reports for the first time the occurrence of K. polyorchis in broodstock of A. regius from a Croatian farm. MATERIALS AND METHODS. At the farm, gills samples and skin scrapings were collected from heavily infected fish and preserved in 70% ethanol and 10% buffered formalin. Ethanol-fixed parasites were subjected to morphological analysis following clarification in Amman’s lactophenol. Before clearing the parasites, a section of the body without diagnostic characters was excised with a sterile scalpel and processed for molecular analysis, amplifying and sequencing the complete ITS and partial 28S rDNA. For observation in Scanning Electron Microscopy (SEM), formalin-fixed specimens were dehydrated in a graded ethanol series, critical point dried and sputter coated with gold-palladium. RESULTS AND CONCLUSIONS. Although being reported mainly from the gills, in our samples K. polyorchis were mainly found on the fins and skin, while the gills were infected with another monogenean species, the diplectanid Diplectanum sciaenae Van Beneden & Hesse, 1863; this finding may indicate a possible displacement of K. polyorchis in concurrent heavy infections with D. sciaenae. Originally assigned to the genus Calceostoma Van Beneden, 1958 based on the morphology of the anterior region and of the armature in the haptor, K. polyorchis was subsequently assigned to a separate genus based on the morphology of the male reproductive system. Our study adds further morphological information, providing the first detailed description of the parasite surface by SEM analysis, and the first molecular data, useful in future taxonomical and phylogenetic studies.

The work focused on ultrastructural and molecular characterization of protozoan parasites of the genus Aggregata (Apicomplexa, Aggregatidae) in specimens of the common octopus Octopus vulgaris obtained from Ionian and Tyrrhenian seas (Southern Italy, Central Mediterranean). Aggregata spp. are reported to parasitize cephalopod species and to be responsible of severe pathologies, which seem to be mostly evident in cultured cephalopods. In the Central Mediterranean the parasite is known to occur with high prevalence, however its taxonomic status in this area is still under debate. Following detection and purification of parasitic stages from octopus tissues, genomic DNA was extracted from Aggregata sporocysts. 18S rRNA gene of the parasite was amplified by PCR using specific primers and the sequences obtained were compared to those available from Aggregata octopiana type species infecting O. vulgaris in Northeastern Atlantic. Samples for Transmission Electron Microscopy (TEM) were treated using standardized protocols specifically designed for the processing of Aggregata spp. parasites. Histological preparations obtained from samples of infected oesphagus, crop, caecum, intestine and mantle of O. vulgaris showed the presence of both gamogonic and sporogonic stages of Aggregata and allowed the use of a semiquantitative method to compare the intensity of infection per each sampled locality. Information from histology was integrated with the analysis of parasite ultrastructure by TEM, which allowed the observation of important taxonomic features to distinguish between different species of Aggregata.

Cephalopods have been included in the European Directive (EU Directive 63/2010), that rules the use of animals for scientific purposes. Therefore, animals welfare and health should be assured. Considering cephalopods, only few information are available on their microbiological status, microbiological agents affecting them and the micro-organism host interaction. The Working Group ‘Stress and diseases’ of the COST Action FA1301, CephsInAction, is aimed to classify diseases of cephalopods and establish guidelines for diseases prevention. Diseases can affect animals on different levels: they could show clinical signs (lesions, ulcer, bleeding), behavioural abnormalities (i.e. lethargy, being not attracted by the prey, inking) or can not respond as usual to normal stimuli. Therefore, experiments can be not reproducible, data can be highly affected and the research can be not robust at all. Nowadays, veterinarians, researchers and technical personnel involved in cephalopods projects don’t have many available tools for monitoring the health status and there are only few qualified experts to evaluate the cephalopods well-being. For this reason, we have collected all papers available on clinical reports and experimental infections and we have analysed them for all scientific information reported. Based on these annotations, we propose a cephalopods diseases database, including pathogens, hosts, symptoms, tissues affected, diagnostic methods, survival rate and possible treatment. Filters for pathogens or for symptoms can be applied. Moreover, the database is correlated to one atlas corresponding to lesions and symptoms. Animal care-takers, researchers running experiments and technician will have the tool to discriminate lesions (physiology vs pathology), to recognize and study the pathogen, to reduce the spread of infection and to find possible treatment. Moreover, the personnel responsible for the animal welfare, designated veterinarians and officers will have one possible tool to check if animals are kept in a good health status and according to the authorized experimental project. In the future, this database will be continuously updated with case-reports and to make it available to researchers, designated veterinarians and officers.

Cephalopods are known to harbor parasitic organisms in almost every organ of their body. The growing importance of cephalopods for both commercial and research purposes requires a better understanding about their health and welfare, which includes a detailed characterization of their parasites and diseases, especially of those infectious agents that are able to affect the physiology of cephalopod hosts or their marketability as fishery products. Information about the parasitic fauna of cephalopods also prove very useful for scientists since it may help elucidating some aspects of cephalopod biology and ecology in natural environment. During the last decades, the development of new investigation techniques, such as the increased use of molecular tools, allowed the identification of new parasite species and helped to solve the taxonomic uncertainty resulting from difficulties associated with morphological identification of small-sized and often cryptic organisms, which had produced, over time, a high synonymy rate among parasitic taxa. The present work intends provide an update of the last 25 years of research about cephalopod infectious agents, by considering over two hundred new publications, since they were first extensively surveyed in 1990. The number of new parasite descriptions, new host records and new infection reports was reviewed as well as the geographic distribution of reports in order to characterize the worldwide pattern of research efforts in cephalopod parasites. The total amount of literature available so far was also considered and analyzed in order to detect potential variations in parasite biodiversity among cephalopod groups as well as among geographic areas and to identify parasitic groups, host groups and geographic areas that require more investigation. Special attention is paid to potentially pathogenetic agents and to treatments available or attempted so far.

Introduction and Aims Octopus vulgaris is a highly valuable food resource and good candidate for marine aquaculture. Over the past years, more than a hundred of published papers have been devoted to increase the growth performance of captive octopuses and overcome the problems associated with the adaptation of these animals to farming conditions. Despite this effort, the farming of O. vulgaris is still far from being a large-scale, economically profitable activity due to high costs, heavy losses in terms of mortality and inadequate growth. Malabsorption syndrome due to parasite load, and competition for food due to elevated territoriality of animals in the cages have been considered as the main limiting factors for a successful ongrowing of O. vulgaris. Approaches and Results In order to explore possible factors limiting growth of animals, historical long-term data on the growth of O. vulgaris in standardized uniform maintenance conditions have been correlated with confounding factors such as season, temperature, genetic factors, parasitic infections. In addition, effect of habituation to a social context have been applied to increase the willingness of octopuses to actively feeding on administered prey items. We show that parasitic load is not directly correlated with decreased growth, but to metabolic factors linked to genetic differences and possibly to changes of temperature in the holding conditions. Habituation to a social condition, allow subordinate individuals to re-equilibrate the feeding hierarchy and reduce the competition for food, thus also increasing the chances for a more uniform growth of animals held in the same cage. Standardized Fulton Condition Index confirm the view that inter-individual differences in animals’ growth are largely linked to metabolic and genetic factors Conclusions Non invasive strategies to facilitate selection of individuals for the rearing are suggested, thus to maximize animals’ growth. In addition, improvement of aquaculture success is presented through the application of a behavioral-welfare approach.