Refining the Occurrence of Viral Encephalopathy and Retinopathy, Photobacteriosis, and Vibriosis in Connection with Seawater Physicochemical Parameters: A Five-Year Case Study

The marine environment and its physicochemical parameters play a pivotal role in the context of fish farming. Fundamental physicochemical factors of water, including temperature (T°C), salinity (S psu), dissolved oxygen (D.O. mg/l), and pH, exert a profound influence on the physiology of farmed aquatic animals and the composition of microbial communities. This study aimed to establish correlations between documented disease occurrences in sea bass intensive rearing and the prevailing physicochemical parameters of water. The objective was to analyse the significance of these parameters in disease outbreaks and develop a predictive model for the outbreak risk of key diseases. To this end, real-time physicochemical data were collected daily over five years (2011-2015) from two fish farms (A and B) located in the Gulf of Argostoli, island of Cephalonia, Western Greece. The focus was on incidences of Viral Encephalopathy and Retinopathy (VER), Photobacteriosis caused by Photobacterium damselae subsp. piscicida (PHDP) and Vibriosis caused by Vibrio anguillarum serotype O1 (VAO1). Statistically significant correlations were found between increasing water temperature and salinity and the occurrence of VER, PHDP, and VAO1 diseases. The reduction of dissolved oxygen, when combined with other parameters, synergistically triggered the manifestation of these three diseases. The study’s findings were discussed within the context of their potential to predict disease outbreaks based on fluctuations in the physicochemical parameters of water and anticipated climate change scenarios

Antibacterial Activity of Ulva Lactuca Against Important Aquaculture Bacterial Strains

Efforts are made to produce functional aquaculture diets capable of promoting fish growth and health while being sustainable at social, economic and environmental levels. One of the emerging threats in aquaculture has become the antibiotic resistance phenomena due to antimicrobial drugs. Therefore, functional feed additives of marine origin have been introduced globally as an alternative to fish antibiotics. Towards the selection of natural and sustainable resources of bioactive compounds, seaweed has been proven to be a source of valuable substances showing antibacterial activity. Aim of this study is to evaluate the inhibition of bacterial growth caused by an ethanolic extract of the macroalgae Ulva lactuca against important aquaculture bacterial strains. Vibrio anguillarum O1, Photobacterium damselae sub. piscicida and Tenacibaculum maritimum, were incubated for 48 hours in sterile Brain Heart Infusion Broth and tested for resistance to the extract using broth cultures. The algal extract successfully inhibited the growth of all strains. The optimum inhibition was achieved for VAO1 and PHDP by the undiluted and 1:1 diluted extract, while for TMAR, by the 1:3 dilution as well. The antibacterial activity that the extract provided is considered to be the result of the containing bioactive compounds of the algal strain, such as polysaccharides, carotenoids and phenolic compounds

Correlations of betanodavirus load in the brain of experimentally infected sea bass (Dicentrarchus labrax, L.) with varying levels of resistance to viral nervous necrosis

The red-spotted grouper nervous necrosis virus (RGNNV) genotype of Betanodavirus causes significant losses to the European sea bass aquaculture industry. The lack of widely available vaccines against this genotype has led researchers and the industry to investigate other avenues for reducing mortality caused by the disease, such as the selection of resistant stocks. The objectives of this study were: a) to assess the presence of natural resistance in sea bass families propagated in the genetic improvement program of Nireus S.A., Greece and, b) to test an ELISA method able to detect viral coat antigen and measure viral load in the brain of tested fish. The second objective was to investigate virus antigen fluctuations during the course of the infection and its correlation with disease development, mortality and resistance. Further aspects of disease pathogenesis were investigated. A population of sea bass consisting of 89 families was experimentally infected with an RGNNV genotype of Betanodavirus; mortalities were recorded and brain samples from dead and survived fish were collected. Experimental infection of fish resulted in a typical pattern of mortality development that reached 56%. Different levels of natural resistance between families were found with cumulative mortality ranging from 20% to 86.2%. There was no statistical difference between the weight of dead fish and the resistant and susceptible families, except when extreme phenotypes were tested, indicating that the weight of fish that died was not a significant factor of final mortality. Brain virus load in the population as a whole increased sharply until D6 post-infection and then gradually dropped until the end of the experiment. When the viral load in the population (dead and survived fish) was tested against time of death, no correlation was found. In fish that survived the infection, the virus load remained high. The viral load per mg of brain tissue in samples taken from dead fish was not a factor that influenced family cumulative % mortality. Brain samples from survived fish reproduced the disease after infection of healthy fish. This study revealed a natural resistance of sea bass to Betanodavirus infection. This important finding can be used as an additional tool in reducing the mortality of cultured stocks. Additionally, there was clear evidence that fish surviving infection become subclinical carriers of the pathogen. Apparently, survival may not be associated with mechanisms of viral clearance but to other mechanisms that may suspend viral replication or aid infected cell endurance. These findings may assist in developing future vaccines and stock selection. A combination of effective vaccination and resistant stocks could be the way ahead

Supplementation of a Commercial Diet of European Seabass by an Algal Ethanolic Extract of Ulva lactuca

Ulva spp. has been investigated as a feed additive with promising results, while literature concerning the use of its ethanolic extracts on the European seabass diet is scarce. Such extracts have shown promising results towards the reduction of the use of antibiotics and the improvement of the final product quality in the aquaculture industry. The objective of this study was to investigate the effects of a Ulva lactuca extract of high antioxidant activity as a result of extraction process optimization on the growth performance and flesh biochemical composition of Dicentrarchus labrax. 450 fingerlings were separated into three experimental groups, and fed with supplemented diets at 1% and 3% w/w Ulva extract inclusion for 8 weeks. The specific growth rate of fish subjected to 3% inclusion increased at a rate of ~28% during the trial, while flesh mineral content was found to be ~15% higher than the control population (p0.05). Results of this study indicate that the targeted extraction of bioactive compounds from algae can potentially result in overcoming drawbacks regarding their digestibility and subsequently improve their use in the aquaculture industry

Marker assisted selection for resistance against viral nervous necrosis in European seabass (Dicentrarchus labrax)

publishedVersio

Genetic Basis for Resistance Against Viral Nervous Necrosis: GWAS and Potential of Genomic Prediction Explored in Farmed European Sea Bass (Dicentrarchus labrax)

Viral nervous necrosis (VNN) is an infectious disease caused by the red-spotted grouper nervous necrosis virus (RGNNV) in European sea bass and is considered a serious concern for the aquaculture industry with fry and juveniles being highly susceptible. To understand the genetic basis for resistance against VNN, a survival phenotype through the challenge test against the RGNNV was recorded in populations from multiple year classes (YC2016 and YC2017). A total of 4,851 individuals from 181 families were tested, and a subset (n∼1,535) belonging to 122 families was genotyped using a ∼57K Affymetrix Axiom array. The survival against the RGNNV showed low to moderate heritability with observed scale estimates of 0.18 and 0.25 obtained using pedigree vs. genomic information, respectively. The genome-wide association analysis showed a strong signal of quantitative trait loci (QTL) at LG12 which explained ∼33% of the genetic variance. The QTL region contained multiple genes (ITPK1, PLK4, HSPA4L, REEP1, CHMP2, MRPL35, and SCUBE) with HSPA4L and/or REEP1 genes being highly relevant with a likely effect on host response in managing disease-associated symptoms. The results on the accuracy of predicting breeding values presented 20–43% advantage in accuracy using genomic over pedigree-based information which varied across model types and applied validation schemes.publishedVersio

In vitro antibacterial activity of essential oils from medicinal plants against major fish pathogens in Mediterranean aquaculture

A rise of intensive Mediterranean aquaculture has been associated with vulnerability to bacterial infections, necessitating alternative approaches to conventional antibiotics. This study evaluated the antibacterial and bactericidal activity of essential oils derived from fifteen medicinal plants against four key bacterial pathogens affecting Mediterranean marine aquaculture: Aeromonas veronii biovar veronii, Aeromonas veronii biovar sobria, Vibrio harveyi, and Tenacibaculum maritimum. Essential oils were screened using disc diffusion assays, and the most effective oils—thyme, oregano, cinnamon, and absinthe—underwent further evaluation through broth microdilution methods. Results demonstrated that these four oils exhibited notable inhibitory and bactericidal effects, with thyme and oregano showing the strongest overall activity across multiple pathogens. Notably, this is among the first studies to document the in vitro efficacy of essential oils against Tenacibaculum maritimum, a major pathogen with limited treatment options. The findings support the potential use of selected essential oils as sustainable and natural antibacterial agents in fish health management, contributing to reduced reliance on antibiotics in aquaculture

<i>Pontobdella muricata</i> infection of <i>Raja clavata</i> and <i>Dasyatis pastinaca</i> off the coast of Lesvos, Greece

An investigation of ectoparasites of skates caught off the coast of Lesvos Island, north-eastern Aegean, Greece was performed from May 2010 to February 2012. One parasite, identified as the marine leech Pontobdella muricata, was found on the skin of 0.43% of Raja clavata and 3.6% of Dasyatis pastinaca specimens examined during the investigation period. This is the first record of D. pastinaca as being a host to P. muricata. Macroscopic and microscopic observation of the lesions caused by the parasitism, revealed haemorrhages and swelling of the skin of R. clavata, a milder inflammation of the skin of D. pastinaca, congestion, necrosis and liquefaction of the skin at the site of leech attachment and a lesion with disappearance of upper skin layers after the detachment of the leech.</jats:p

Quantitative and qualitative analysis of sea bream,<i>Sparus aurata</i>(L.), humoral immune response, vaccinated with commercial and experimental vaccines against vibriosis and photobacteriosis

The specific humoral immune response of sea bream,Sparus aurata(L.), againstVibrio anguillarumO1 andPhotobacterium damselaesubsp.piscicida(Phdp) after immunization with commercial and experimental bacterins was analysed quantitatively and qualitatively. Specific anti-V. anguillarumO1 and anti-Phdp levels provoked by the adjuvanted commercial vaccine reached higher levels in comparison to the aqueous commercial and experimental bacterins. Infection of vaccinated fish withV. anguillarumO1 bacterial cells acted as a boost of the humoral immune response, except for the sera of the group vaccinated with the adjuvanted vaccine. Infection with Phdp acted as a boost of the humoral immune response mainly for the group vaccinated with a monovalent Phdp bacterin and to a lesser degree for the group vaccinated with the aqueous commercial vaccine. Western blot analysis of the sera againstV. anguillarumO1 whole cell antigens revealed strong reactions to only a few antigens below 54 kD and above 15 kD and weak reactions to other antigens. Similar reactions were observed from the sera isolated from the controls. Western blot analysis of the sera against Phdp whole cell antigens revealed strong reactions to only a handful of antigens below 20.7 and below 6.4 kD. Sera from the control group, as in the case ofV. anguillarumO1, reacted with Phdp whole cell antigens. No differences regarding antigen reactions between monovalent and bivalent formulations were noted, in contrast to the adjuvanted and aqueous bacterins.</jats:p