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Organic acids and their salts are used as additives in aquafeeds, as their participation in some metabolic pathways and energy generation in organisms increases the nutritional value. Benzoic acid (BA; C6H5‐COOH), a white crystalline substance with a chemical structure that contains carboxylic acid attached to a benzene ring, is naturally found in plant and animal tissues. It is one of the most used organic acids due to its antifungal properties, and it acts as a preservative for a variety of human consumption products. Additionally, it demonstrates health and growth benefits when included in feeds by modifying the energy metabolism, microbiota, and intestinal tract morphology. Information on BA inclusion in aquatic food is rare, and such information for Pacific white shrimp Penaeus vannamei is nonexistent. This study evaluated the effects on growth, survival, feed conversion ratio, energy content, and health status (through lipid quantification in the hepatopancreas, histological examination, and salinity stress tests) of Pacific white shrimp juveniles by including BA at different concentrations (0.0, 1.0, 1.5, and 2.0 g/kg) in a commercial feed. Diets with BA inclusion produced significant differences in the hepatosomatic index, hepatopancreas lipid content, and histopathological index value (reflecting damage to the hepatopancreas and antennal gland atrophy) at all BA concentrations. The lowest survival obtained was 94.44% at a BA concentration of 1.0 g/kg. The feed conversion ratio was in accordance with the range established by the Food and Agriculture Organization of the United Nations except for values obtained at 0 g/kg. Calorimetric analysis and BA detection in muscle revealed no significant differences between concentrations. Due to the results obtained in this study, the evaluated inclusions of BA are not recommended for use in juvenile Pacific white shrimp diets. [ABSTRACT FROM AUTHOR]

PirAB toxins secreted by Vibrio parahaemolyticus (Vp) harbor the pVA1 virulence plasmid, which causes acute hepatopancreatic necrosis disease (AHPND), an emerging disease in Penaeid shrimp that can cause 70–100% mortality and that has resulted in great economic losses since its first appearance. The cytotoxic effect of PirABVp on the epithelial cells of the shrimp hepatopancreas (Hp) has been extensively documented. New insights into the biological role of the PirBVp subunit show that it has lectin-like activity and recognizes mucin-like O-glycosidic structures in the shrimp Hp. The search for toxin receptors can lead to a better understanding of the infection mechanisms of the pathogen and the prevention of the host disease by blocking toxin–receptor interactions using a mimetic antagonist. There is also evidence that Vp AHPND changes the community structure of the microbiota in the surrounding water, resulting in a significant reduction of several bacterial taxa, especially Neptuniibacter spp. Considering these findings, the PirABvp toxin could exhibit a dual role of damaging the shrimp Hp while killing the surrounding bacteria. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate the nutrigenomic effect of feeding pike silverside larvae with rotifer versus a formulated microdiet. Survival of larvae was evaluated across the experiment, while growth performance and transcriptional expression profiles in both dietary treatments were compared at the end. Larvae fed with rotifers achieved higher growth and survival, and in accordance, relevant genes associated with growth and development were overexpressed. Moreover, genes associated with digestive enzymes were overexpressed in larvae fed with rotifers, suggesting this to be an average expression profile that may give insight into the digestive status/capacity of pike silverside larvae. On the contrary, the overexpression of genes related to stress, genome instability and epigenetic marks could explain the low larval performance observed in the microdiet fed larvae. These findings point out the relevance of a nutrigenomic approach as an important tool to assess artificial diet performance in fish and the necessity to re‐evaluate formulation, type and proportion of the ingredients in the microdiet which may reflect similar expression profiles found in the rotifer group and provide adequate growth in early larval stages of pike silverside. This information contributes to the knowledge of the limitations of microdiets in pike silverside and other fish larvae. [ABSTRACT FROM AUTHOR]

The phenotypic characteristics and growth kinetics at several temperatures, salinities, and pH values of three Vibrio parahaemolyticus (Vp) strains with different virulence and one nonpathogenic strain were evaluated. Independent of the virulence of the strain, a high metabolic diversity was found, which yielded different colored phenotypes on the CHROMagar™ Vibrio. All strains were resistant to ampicillin and carbenicillin, and Vp AHPND+ organisms were the most sensitive to enrofloxacin. The exponential growth of Vp strains started at 1–2 hr of incubation, although no relationship was observed between the bacterial density and degree of virulence. Moreover, the growth of the most virulent strain was independent of the nutrients in the incubation media during the initial hour postinoculation. No strain grew at 4°C in 0% NaCl and pH 4, but only Vp AHPND+ grew at 44°C. For all strains, the lag phase was proportional to the NaCl concentration, and the growth was better at pH 8–9. However, the Vp AHPND− strain displayed a greater variability, was more sensitive to extreme conditions, and showed a lag phase of 9 hr independent of the pH. [ABSTRACT FROM AUTHOR]

To determine if exposure to a sublethal mixture of metals (Cd, Cu, Fe, Mn, Pb and Zn) increases susceptibility to White spot syndrome virus (WSSV) infection, Litopenaeus vannamei juveniles were fed WSSV‐infected shrimp tissues after 21 days of exposure to the metal mixture (WS‐MM treatment). Other treatments consisted of shrimp not exposed to metals and fed infected tissues (WS), and shrimp fed healthy tissues and exposed (MM) or not exposed to metals (C). The presence of viral DNA and inclusion bodies was detected at 32 hr postinfection (hpi) in the stomach epithelium of shrimp from the WS treatment, and eight hours later in shrimp from the WS‐MM treatment, possibly because of an initial negative effect of metals in viral replication. At 40 hpi, the severity of infection represented by the histopathological index increased in both WS and WS‐MM treatments, and values were higher in WS‐MM than in WS shrimp at the end of the experiment. From 56 hpi to the end of experiment, total hemocyte counts were lower in both WS‐MM and WS treatments, and concentrations were particularly low in WS‐MM shrimp. Conversely, phenoloxidase activity was higher in the WS‐MM treatment from 32 to 56 hpi, suggesting a possible role of the prophenoloxidase (proPO) system in the antiviral defense against WSSV. The presence of heavy metals at sublethal concentrations may increase shrimp susceptibility to WSSV; this is supported by a decrease in circulating hemocytes, an increase in the humoral response, and the development of a higher number of WSSV inclusion bodies. [ABSTRACT FROM AUTHOR]

The article discusses a study on the exposure of white shrimp Litopenaeus vannamei juveniles to Cu2+ concentrations for 25 days. It cites the use of Cu2+ concentrations in Mexican shrimp farms to assess the possible histological effects on shrimp. The sampling procesures and acclimation of seas-water grown Litopenaeus vannamei juveniles are discussed. The study showed the absence of mortalities in controls and treatments and the lack of histological alterations in the shrimps' midgut, gills and hepatopancreas.

Juvenile C. viridis (5.26 ± 0.72 g) were intraperitoneally injected with three doses of Vibrio ponticus (Vp) CAIM 1751 from 104 to 106 CFU/g, and histological analysis, haemolytic activity assessment and putative virulence genes identification were performed. The time of experimental challenge was 168 h. The virulence of Vp was dose-dependent. The mortality after 25 h post infection (p.i.) was 100% at 3.1 × 106 CFU/g and, 83% at 60 h p.i. at 2.9 × 105 CFU/g. The LC 50 was 2.9 × 105 CFU/g at 32 h p.i. Congestion and petechial haemorrhages in the ventral area were observed in the infected fish. Similar histological lesions were observed at the three doses as necrosis, congestion and bacterial masses in different organs and tissues. This is the first report where Vp caused in C. viridis pathological changes associated with an acute peritonitis that caused irreversible damage to the internal organs, except in the kidney. Greater severity was identified in the liver and pancreas of the organisms exposed to the higher dose and in the stomach, intestine and nervous system of the fish infected with the lower dose. The main virulence genes of Vp CAIM 1751 were auto inducers, toxins and iron acquisition, including three types of haemolysins and metalloproteases. Furthermore, this strain had a strong β-haemolytic reaction on erythrocytes of the Pacific white snook. The combined action of the proteases and haemolysins may be responsible for the vascular fragility allowing for the rupture of small vessels and haemorrhages in the tissues. This study contributes to our understanding of Vibrio ponticus as an emerging finfish aquaculture pathogen. • Doses of 2 x 105 and 3 x 106 CFU/g of Vibrio ponticus CAIM 1751 caused 83 and 100 % mortality, respectively at 24 hr p.i. • Vp CAIM 1751 caused acute peritonitis in fish, with irreversible damage to the internal organs, except in the kidney. • Greater severity was identified in the liver and pancreas of fish exposed to the higher dose of V. ponticus • The combined action of bacterial proteases and haemolysins may be responsible for organ dysfunction and death. [ABSTRACT FROM AUTHOR]

Moribund shrimp affected by acute hepatopancreatic necrosis disease (AHPND) from farms in northwestern Mexico were sampled for bacteriological and histological analysis. Bacterial isolates were molecularly identified as Vibrio parahaemolyticus by the presence of the tlh gene. The tdh-negative, trh-negative, and tlh-positive V. parahaemolyticus strains were further characterized by repetitive extragenic palindromic element-PCR (rep-PCR), and primers AP1, AP2, AP3, and AP and an ems2 IQ2000 detection kit (GeneReach, Taiwan) were used in the diagnostic tests for AHPND. The V. parahaemolyticus strains were used in immersion challenges with shrimp, and farmed and challenged shrimp presented the same clinical and pathological symptoms: lethargy, empty gut, pale and aqueous hepatopancreas, and expanded chromatophores. Using histological analysis and bacterial density count, three stages of AHNPD (initial, acute, and terminal) were identified in the affected shrimp. The pathognomonic lesions indicating severe desquamation of tubular epithelial cells of the hepatopancreas were observed in both challenged and pond-infected shrimp. The results showed that different V. parahaemolyticus strains have different virulences; some of the less virulent strains do not induce 100% mortality, and mortality rates also rise more slowly than they do for the more virulent strains. The virulence of V. parahaemolyticus strains was dose dependent, where the threshold infective density was 104 CFU ml-1; below that density, no mortality was observed. The AP3 primer set had the best sensitivity and specificity. Field and experimental results showed that the V. parahaemolyticus strain that causes AHPND acts as a primary pathogen for shrimp in Mexico compared with the V. parahaemolyticus strains reported to date. [ABSTRACT FROM AUTHOR]

Abstract: Exposure to different levels of a mixture in equitoxic concentrations of Cd, Cu, Fe, Hg, Mn, Pb and Zn, equivalent to between 5 and 0.5% the individual respective 96-h median lethal concentrations (0.05–0.005AF: application factors) caused dose- and time-dependent damages to the hepatopancreas, gills, epipodites and midgut tissues of Litopenaeus vannamei juveniles. After between 1 and 3–4 weeks, there was between 50 and 100% loss of the hepatopancreas R cells and of the tubules regular structure. Gill alterations were observed between 2 and 3 weeks with 0.05–0.025 and 0.005AF, respectively. Epipodites showed time- and dose-dependent increasing degrees of melanization, and hemocytic enteritis was observed with 0.025 and 0.01AF. Exposure to 0.05 and 0.025AF caused also 50 and 12% mortalities after 2 and 3 weeks respectively, showing that even at these low levels the mixture of these metals may have a mid-term lethal effect. For this reason, the assessment of risk and of safe levels of toxic substances added to any natural environment through human or natural sources, should not neglect the effects on biological systems caused by the interaction of minute amounts of toxicants, which would be harmless unless present in combination. [Copyright &y& Elsevier]