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Development of a highly permissive cell line from spotted knifejaw (Oplegnathus punctatus) for red sea bream iridovirus

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Yasuhiko Kawato, Hirofumi Yamashita, Kei Yuasa, Satoshi Miwa, Kazuhiro Nakajima

We developed a cell line (SKF-9) from spotted knifejaw (Oplegnathus punctatus), which is highly susceptible to red sea bream iridovirus (RSIV). Cytopathic effect (CPE) characterized by rounding and enlargement was clearly observed in RSIV-infected SKF-9 cells. The amount of viral production of SKF-9 cells was approximately 100 times greater than that of GF cells, which is conventionally used for RSIV research. The viral titer was not decreased through passages using SKF-9 cells, whereas a considerable reduction in the titer was observed when GF cells were used. On the other hand, control of appropriate passage numbers (<50) of the cell line was important to maintain the high permissiveness of SKF-9. Mortality rate was 100% when culture supernatant of RSIV propagated with SKF-9 cells was injected into spotted knifejaw with dilutions of 100, 105, and 106. Thus, the SKF-9 cell line can be a useful tool for research of RSIV (and ISKNV) and for vaccine production.





How does a domestication process modulate oogenesis and reproduction performance in Eurasian perch?

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Amine Khendek, Maud Alix, Sandrine Viot, Yannick Ledoré, Camille Rousseau, Robert Mandiki, Patrick Kestemont, Tomas Policar, Pascal Fontaine, Sylvain Milla

The domestication process is accompanied by adaptation of the animals to captive conditions. It induces changes at different levels thereby affecting a variety of biological functions. While there is abundant literature on the domestication effects on growth and stress response in teleosts, the effects on reproduction have received limited attention. In this work, we investigated the domestication effect on the reproductive ability of Eurasian perch (Perca fluviatilis L.), a promising candidate for the development of European aquaculture and whose reproductive physiological processes through the domestication history have not been questioned yet. To address this question, two populations of F1 and “domesticated” females were subjected to a photothermal program allowing the control of gonadogenesis advancement. Gonadosomatic index, 17β-Estradiol levels, and oocyte diameter were significantly higher in the “domesticated” population than in F1 population. In contrast, testosterone, 11-ketotestosterone, and vitellogenin levels were found to be higher in F1 females than in their “domesticated” counterparts. Lower reproductive performance was observed in the “domesticated” population compared to the F1 population in terms of embryo survival, percentage of eyed-stage larvae, hatching and percentage of malformation rates. In conclusion, this study shows that despite a positive effect on advancing gonadogenesis and vitellogenesis, this domestication route negatively affected the reproductive performance under our conditions. Statement of relevance This work will give information to producers to choose good broodstock populations (wild or domesticated) to have optimal reproductive performances in Eurasian perch, and thus improve fish production.





Comparison of lacZ reporter gene expression in gilthead sea bream (Sparus aurata) following oral or intramuscular administration of plasmid DNA in chitosan nanoparticles

Published on 24/3/2017
Publication date: 1 May 2017
Source:Aquaculture, Volume 474

Author(s): M.I. Sáez, A.J. Vizcaíno, F.J. Alarcón, T.F. Martínez

The development of non-parenteral delivery systems allowing efficient intestinal absorption in fish is a current research topic drawing much interest. Different aspects would benefit from such oral delivery, especially those related to immunization, owing to the convenience of this route in terms of time saving, safety, and lack of stressful effects among others. In the last years, DNA vaccines are evidencing their suitability for fish immunization, although commercial preparations currently available require parenteral administration. In this regard, this work was aimed at assessing a chitosan-based oral delivery system for plasmid DNA (pDNA) in fish. Plasmid pCMVβ was encapsulated in chitosan nanoparticles with the aim of evaluating the ability of inert capsules to retain and protect pDNA from in vitro conditions mimicking the fish gut environment. Furthermore, the feasibility of in vivo oral gene delivery was also assessed in fish by administrating pDNA nanoparticles comparing oral and intramuscular routes. The results indicated that lacZ gene expression (β-galactosidase activity) could be detected in fish tissues following both oral and i.m. administration of pDNA-chitosan nanoparticles up to 60days. However, organ distribution of the reporter gene expression was more evident after oral (β-gal activity measured in gut, liver and muscle) than after parenteral administration (mostly restricted to adjacent tissues). The results suggest that chitosan nanoparticles enabled efficient oral delivery of pDNA, followed by organ migration and further sustained expression of the reporter gene encoding for β-galactosidase. The intensity of such expression was similar to that obtained by intramuscular injection, a fact that might suppose valuable practical applications in terms of on-farm administration of DNA-based vaccines to fish.

Graphical abstract






Performance evaluation of reciprocal hybrids derived from the two brackish oysters, Crassostrea hongkongensis and Crassostrea sikamea in southern China

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Yuehuan Zhang, Jun Li, Yang Zhang, Haitao Ma, Shu Xiao, Zhiming Xiang, Ziniu Yu

Interspecific hybridization has been used as an important tool for genetic manipulation in oyster culture with the aim to produce a new strains having desired traits from both the parental species. A two by two factorial cross between sympatric oyster species, Hong Kong oyster (Crassostrea hongkongensis) and Kumamoto oyster (Crassostrea sikamea), yielded hybrids that were fast growing (a characteristic of Hong Kong oyster) and had superior meat quality (characteristic to Kumamoto oyster). Reciprocal hybrids were obtained by the acceptable level of fertilization and hatching rate compared to these of two parental species. The survival rate of the hybrids was similar to that of the parental species. The hybrids exhibited fully developed gonads and gametes when sexually mature. Relative to C. sikamea, the hybrids also showed significant growth advantages as in shell height and wet weight. The shell morphology of the hybrid was dictated by maternal inheritance. Our results revealed that reciprocal hybrids exhibited larger growth heterosis and survival advantage (in terms of C. sikamea), as well as a higher meat weight, showing great potential for application in the oyster aquaculture industry in southern China. Statement of relevance We firstly conducted the interspecific hybridization between the largest (Crassostrea hongkongensis) and smallest oysters (C. sikamea) in Crassostea genus, and then obtained reciprocal hybrids with obvious the heterosis (in terms of C. sikamea). These hybrids are very useful as a new stock for the oyster aquaculture industry.





Multifactorial interactions and optimization in biomass harvesting of marine picoalga Picochlorum maculatum MACC3 with different flocculants

Published on 24/3/2017
Publication date: 1 May 2017
Source:Aquaculture, Volume 474

Author(s): Arun Augustine, Jisha Kumaran, Jayesh Puthumana, Sanyo Sabu, I.S. Bright Singh, Valsamma Joseph

Cost effective harvesting of biomass is a major challenge in microalgal industries as it involves the recovery of small sized algal cells from large volumes of culture medium. The present work evaluated the potential of chitosan and aluminium sulfate (AS) in the flocculation of the marine picoalga, Picochlorum maculatum MACC3 using response surface methodology based optimization of flocculation conditions. The viability and integrity of the flocculated cells were assessed using Evan's blue staining and scanning electron microscopy. Under optimized conditions, flocculation efficiency of >95% was achieved with a chitosan concentration of 63mgL1 at pH8.5, and aluminium sulfate concentration of 150mgL1 at pH9.7 with algal biomass concentration of 1.5gL1. Based on flocculation efficiency, cell viability and cell integrity chitosan was selected as an efficient flocculant for biomass harvesting of P. maculatum. The flocculated biomass of this newly isolated nutritionally rich microalga can be further explored for feed applications in aquaculture after accomplishing studies under laboratory and field conditions.





Bacteriophage therapy for the control of Vibrio harveyi in greenlip abalone (Haliotis laevigata)

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Yanhui Wang, Mary Barton, Lisa Elliott, Xiaoxu Li, Sam Abraham, Mark O'Dea, James Munro

Bacteriophage therapy has demonstrated promising results towards the control of bacterial infections within the aquaculture industry as an alternative therapy to antibiotics. This current research describes the efficacy of bacteriophage therapy in controlling vibriosis within abalone (Haliotis laevigata). Two bacteriophages were isolated and used in in vitro assays to determine the effect of each specific phage on the growth of specific Vibrio harveyi isolates. To demonstrate efficacy, an in vivo bioassay was performed using abalone (H. laevigata) at a water temperature of 24°C. Characterisation of the two isolated phages revealed they were from the family, Siphoviridae. The phages had different antimicrobial abilities towards different Vibrio harveyi isolates in the in vitro assays and the bioassay demonstrated improved survival of abalone treated with bacteriophage. The results of the bioassay showed that the negative control and phage control were statistically identical, with 100% survival, but they were different from the positive bacterial control, with a 0% survival. The bacteria + phage treated group showed increased accumulative survival of 70% compared to the positive control. This is the first study to demonstrate the efficacy of bacteriophage therapy treatment for abalone. The study demonstrates that if abalones are treated with bacteriophage shortly after Vibrio harveyi infection, the accumulative survival could be significantly increased.





Combined or individual effects of dietary vitamin E and selenium nanoparticles on humoral immune status and serum parameters of rainbow trout (Oncorhynchus mykiss) under high stocking density

Published on 24/3/2017
Publication date: 1 May 2017
Source:Aquaculture, Volume 474

Author(s): Mahdi Naderi, Saeed Keyvanshokooh, Amir Parviz Salati, Alireza Ghaedi

A 60day feeding experiment was conducted to evaluate the effects of dietary vitamin E (vit E), selenium nanoparticles (nanoSe), and their combination on humoral immune status and serum parameters of rainbow trout under high density condition. A total of 1275 rainbow trout with an average weight of 42.6±2.3g were acclimatized, distributed into 15 tanks and divided into five experimental groups according to stocking density and diet: Normal control (20kgm3; basal diet), Dense control (80kgm3; basal diet), Vit E (80kgm3; 500mgkg1 vit E-supplemented diet), NanoSe (80kgm3; 1mgkg1 nanoSe-supplemented diet), and Combination (80kgm3; 500mgkg1 vit E and 1mgkg1 nanoSe-supplemented diet). Each group consisted of three tanks. High stocking density reduced weigh gain, specific growth rate, feed intake, feed conversion ratio, serum agglutination antibody titer, total antioxidant capacity, and globulin level, but increased lysozyme, albumin, and cholesterol levels when basal diet was fed. However, vit E supplementation to diets significantly improved growth performance and health status of rainbow trout. While the combination of nanoSe with vit E promoted the performance of the fish, supplementation with nanoSe had no significant effects on performance in rainbow trout under high density conditions, suggesting that the beneficial effects observed in the performance of the Combination group may be due to vitamin E alone.





Olive mill wastewater-enriched diet positively affects growth, oxidative and immune status and intestinal microbiota in the crayfish, Astacus leptodactylus

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Lucia Parrillo, Elena Coccia, Maria Grazia Volpe, Francesco Siano, Caterina Pagliarulo, Elisa Scioscia, Ettore Varricchio, Omid Safari, Tufan Eroldogan, Marina Paolucci

In the present study, the effects of polyphenols extracted from olive mill wastewaters (OMWW) were investigated in the narrow clawed Astacus leptodactylus in a 24week-feeding trial. 0.5 and 5.0g of OMWW polyphenolic extract were mixed with 1kg of basic diet to generate OMWW-LC (Low Concentration) diet and OMWW-HC (High Concentration) diet. Growth performances, antioxidant and immunological parameters, microbiota, and FA composition were evaluated. Growth performances (specific growth rate; feed conversion ratio; protein, lipid and carbohydrate efficiency ratio) and survival rate significantly improved in crayfish fed OMWW-enriched diets, in a polyphenol concentration-related manner. The activities of the oxidative enzymes GP, GR and CA were evaluated in the hepatopancreas. GP activity did not statistically changed. The increase in GR activity was statistically significant only in the OMWW-HC group. The increase in CA activity was statistically significant in both OMWW-LC and OMWW-HC groups. The immunological parameters (total haemocytes, phenoloxidase activity) significantly increased in OMWW-LC and OMWW-HC groups with respect to the control group. Superoxide anion production in the hemocytes statistically decreased only in the OMWW-HC group. No pathological changes in the midgut and hindgut after OMWW-enriched diets were detected by histological analysis. In crayfish fed on OMWW-enriched diet, total intestinal microbiota decreased, with the exception of anaerobes and yeasts. A significant increase in PUFA and decrease in MUFA was registered in the hepatopancreas. The emerging picture indicates that diets enriched with polyphenols extracted from OMWW had beneficial effects on crayfish growth and health and hence could be successfully employed in aquaculture and considered as a novel strategy of development to the feed industry sector.





Effects of reduced water exchange rate and oxygen saturation on growth and stress indicators of juvenile lumpfish (Cyclopterus lumpus L.) in aquaculture

Published on 24/3/2017
Publication date: 1 May 2017
Source:Aquaculture, Volume 474

Author(s): Even H. Jørgensen, Ada Haatuft, Velmurugu Puvanendran, Atle Mortensen

Lumpfish (Cyclopterus lumpus) is currently used as cleaner fish in Norwegian Atlantic salmon (Salmo salar) farming to control parasitic lice on salmon. The need for high numbers of lumpfish necessitates intensive farming of this species but very limited knowledge is available on the environmental requirements of lumpfish in culture. The present study was therefore carried out to investigate the tolerance of lumpfish to varying water exchange rates and oxygen saturations. Four triplicated treatment groups were established at different water exchange rates, which caused oxygen saturations of 55% (0.7Lmin1), 69% (1.2Lmin1), 81% (1.9Lmin1) and 96% (6Lmin1). Decreasing water exchange rate and oxygen saturations negatively affected growth, even in the fish groups held at 81% oxygen saturation. The fish group held at 55% oxygen saturation had almost no growth in body mass and showed sign of fin-infections and were terminated halfway through the experiment. A high workload associated with oxygen extraction and reduced appetite is considered the reason for reduced growth at lower oxygen saturations. While plasma cortisol levels in the groups held at 81 and 96% oxygen saturation corresponded to those considered typical for unstressed fish (<10ngmL1), the levels of plasma cortisol of fish in the 69 and 55% oxygen saturation groups were above 20ngmL1 in November, indicating a state of chronic stress. A fast, albeit weak, cortisol response to stressors in the lumpfish was confirmed in a separate, 2h long acute handling and hypoxia experiment. Lack of differences between treatments in plasma lactate levels indicates that the lumpfish reduced their food intake and locomotory activity sufficiently to avoid resorting to anaerobic metabolism when exposed to reduced oxygen saturations. It is concluded that the juvenile lumpfish is sensitive to reduced water oxygen saturations and that oxygen saturations below 80% in aquaculture should be avoided.





Transmission of Ostreid herpesvirus-1 microvariant in seawater: Detection of viral DNA in seawater, filter retentates, filter membranes and sentinel Crassostrea gigas spat in upwellers

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Olivia Evans, Paul Hick, Bruce Alford, Richard J. Whittington

To understand the transmission of Ostreid herpesvirus-1 microvariant(s) (OsHV-1) in seawater, it is necessary to understand the temporal pattern of occurrence of the virus in seawater in relation to demonstrated infection events in oysters. The aims of the current study were: (1) to investigate the temporal sequence of detection of OsHV-1 in seawater and Crassostrea gigas spat in an upweller system, (2) to assess whether filtration or ageing of seawater reduced the detection of OsHV-1 in seawater and spat, and (3) to assess whether retentate or membranes from filters that were installed to enable continuous sampling of particles in seawater could be used for OsHV-1 surveillance and to investigate OsHV-1 particulate attachment. This study is the first to detect OsHV-1 DNA in 5μm retentates and membranes used to continuously filter natural seawater. OsHV-1 DNA was detected in seawater before it was detected in oysters in 65.4% of the 26 detection events examined across 6 trials in an OsHV-1 endemic estuary. The time of sampling (morning or afternoon) did not affect the detection of OsHV-1 DNA in seawater. Seawater treatment by filtration or ageing did not reduce the frequency of detection of OsHV-1 DNA in seawater. In contrast, the odds of detecting OsHV-1 DNA in the tissues of oysters kept in aged seawater and some filtered seawater treatments were reduced (odds ratios: 0.16–0.36) in comparison to the control. Although OsHV-1 DNA was detected in the retentate from 5μm filtration, it is unlikely these samples will be useful for investigating OsHV-1 particle attachment due to low viral signals. Similarly, OsHV-1 DNA was detected on the 5μm filter membranes, however further investigation is required to ascertain their usefulness in assessing OsHV-1 particle attachment. Despite this and with further development, 5μm filter retentates and filter membranes may prove to be useful samples for the surveillance of OsHV-1 in seawater.





Fitness component assessments of wild-type and growth hormone transgenic coho salmon reared in seawater mesocosms

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Rosalind A. Leggatt, Carlo A. Biagi, Dionne Sakhrani, Robert Dominelli, Erika J. Eliason, Anthony P. Farrell, Robert H. Devlin

Growth hormone (GH) transgenic fish have been proposed for use in aquaculture to enhance production efficiency. As part of a risk analysis for use of such fish, the influence of GH transgenesis on the potential to persist and succeed in natural ecosystems is being examined in confined laboratory conditions. GH transgenesis can greatly accelerate growth and, in culture conditions, is associated with secondary effects such as poor swimming capacity and spawning success. However, standard culture has also been shown to negatively affect fitness components of wild-type fish, raising the question of whether culture conditions influence fitness components of transgenic fish in a similar way. To examine factors influencing the phenotype of marine-stage GH transgenic salmon (T), and to determine if genotype-by-environment interactions exist at this life stage, we grew T and wild-type (NT) coho salmon (Oncorhynchus kisutch) over six cohort years in 350,000L seawater tanks (termed mesocosms) designed to minimize effects of standard culture conditions. Mesocosm rearing partially facilitated development of normal size and morphology of NT fish relative to nature-reared counterparts, but altered overall body shape, indicating mesocosm conditions do not fully mimic natural environmental effects on coho salmon phenotype. T fish reared in mesocosms had larger mass at maturity than mesocosm- or nature-reared NT fish, indicating GH transgenesis can alter maximum obtainable mass in salmon. Unlike NT, T fish obtained maximum size at maturity across environments, suggesting marine environmental conditions may affect T growth less than NT growth. Screening parents for a common disease agent (Renibacterium salmoninarum) improved seawater survival, and T fish had lower survival than NT fish when from unscreened parents and inconsistent relative survival when from screened parents, indicating GH transgenesis may constitute an advantage or disadvantage in terms of survival. Transgenic salmon had lower swimming capacity and aerobic scope, but similar routine metabolic rate and thermal tolerance, demonstrating transgenesis can have different influences depending on what phenotype is examined. Using an alternate strain of T fish in phenotypic comparisons did not greatly influence most fitness components, although had a strong effect on female fecundity. The inconsistent influence of GH transgenesis on different fitness components, and existence of genotype-by-environment interactions during the marine life stage, complicates extrapolation of laboratory data for transgenic fish to natural environments. However, current and previous data do not provide evidence that overall increased performance of GH transgenic salmon over wild-type fish would arise in the marine environment. Statement of relevance Rearing in seawater mesocosms demonstrate that growth hormone transgenesis has inconsistent effects on marine fitness components in coho salmon.





Growth and oxidative parameters of Rhamdia quelen fed dietary levels of vitamin A

Published on 24/3/2017
Publication date: 1 May 2017
Source:Aquaculture, Volume 474

Author(s): Eduardo K. Battisti, Samuel Marasca, Emerson G. Durigon, Valesca S. Villes, Thamara L.S. Schneider, Juliano Uczay, Nilce C. Peixoto, Rafael Lazzari

Vitamin A, a fat soluble compound is an essential nutrient for fish. The present study evaluated the effects of dietary vitamin A administered to juvenile silver catfish (Rhamdia quelen). Fish were fed semi-purified diets formulated to meet the protein and energy requirements of the species (37% CP and 3400kcalkg1 DE). Five vitamin A levels were tested: 1090, 1180, 1750, 2610 or 2880IUkg1 of diet. The growth, body composition, metabolic and blood parameters and oxidative stress biomarkers of juvenile silver catfish were studied after 70days. Fish growth increased with an increase in vitamin A. The fish that were fed a 2610IUkg1 vitamin A diet had better quality fillets, with more protein and less fat. No effects on hematological and biochemical parameters were noted. The high levels (1750, 2610 and 2880IUkg1) of vitamin A improved the fish antioxidant defense system. Lower activity was observed for enzymes that act as antioxidants because retinoids and carotenoids acted as scavengers and donated electrons to reactive oxygen species, conferring enzymatic protection and contributing to the animal's energy economy. Based on the growth and fillet quality and oxidative results, we recommend a 2610IUkg1 vitamin A diet for juvenile R. quelen. Statement of relevance Important to assess the nutrition and health of the silver catfish.





Maxi-Gen™ Plus: A nucleotide-containing product that reduces stress indicators and improves growth performance during smoltification in Atlantic salmon (Salmo salar)

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Minhao Fu, Stephanie A. Collins, Derek M. Anderson

Three trials were conducted to determine the effects of dietary nucleotides fed as Maxi-Gen™ Plus on the stress level, growth performance and intestinal histology of in-season and off-season Atlantic salmon smolts. Twenty-four hour, 40ppt salinity tests determined the hypo-osmoregulatory ability of Atlantic salmon during smoltification gradually improved as the dietary inclusion rate of Maxi-Gen™ Plus increased from 0.05 to 0.60%, which indicates an extended period of time for effective transfer to seawater. Growth performance evaluated as weight gain, feed consumption and feed conversion ratio showed diets containing 0.40 to 0.60% Maxi-Gen™ Plus enhanced the growth performance of Atlantic salmon smolts. Fish fed the diet containing 0.60% Maxi-Gen™ Plus exhibited lower plasma cortisol levels. The villus height, width and apparent surface area of both mid and distal intestines were not influenced by including Maxi-Gen™ Plus in the diet. Statement of relevance Three experiments assessed the effect of the inclusion of dietary nucleotides fed as Maxi-Gen™ Plus on the stress level, growth performance and intestinal histology of in-season and off-season Atlantic salmon smolts. Increasing the dietary inclusion level of Maxi-Gen™ led to improved hypo-osmoregulatory ability and growth performance with no noted effect on the intestinal histology of Atlantic salmon. This indicates as the dietary inclusion level of Maxi-Gen™ increased from 0.05% to 0.60%, so did the “smolt window,” or period of time when the smolts can be transferred from fresh to salt water.





A model of the process of spillover and adaption leading to potential emergence of disease in salmon held with cleaner fish used to control lice

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Alexander G Murray

Sea lice control is a very important issue for sustainable salmon aquaculture, and cleaner fish (largely wrasse and lumpfish) are increasingly used as a key tool for this control. Such fish can carry pathogens, which they can potentially spread to the salmon. A modelling approach is used to help guide practice on cleaner fish use. The model simulates transmission of pathogens within and between cleaner fish and salmon populations. A function modifying the coefficient of infection allows simulation of pathogens input with cleaner fish to adaptation to salmon with passage. Adaption may require different numbers of passage events and may face obstacles that make adaption easier or more difficult, allowing the exploration of a range of potential emergent pathogens with different properties. The model includes the production cycle of salmon, whereby all salmon are periodically removed and replaced with naïve fish, but a proportion of the cleaner fish may be reused in the next production cycle. An assessment of the likely consequence of emergent diseases relative to consequence of sea lice infection is made using an analysis of literature. The modelling concludes that any emergent disease is unlikely to be of as serious consequence as sea lice already are, and therefore the risk from emergent disease is low relative to benefit of controlling lice. This risk can be further reduced by practices that limit input of infection and by restricting reused of cleaner fish in subsequent production cycle. The risk from reusing small numbers is generally substantially lower than reusing larger numbers, but avoiding reuse is more effective, especially if there is limited input of pathogens with new cleaner fish. More data as cleaner fish are increasingly used will allow more accurate assessment of risk, but the model provides a flexible framework for assessing risk of emergence of potential new pathogens and advising on good practice while information is limited and a precautionary approach is inappropriate owing to the clear benefits of effective lice control.





Water temperature and oxygen: The effect of triploidy on performance and metabolism in farmed Atlantic salmon (Salmo salar L.) post-smolts

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Florian Sambraus, Rolf Erik Olsen, Mette Remen, Tom Johnny Hansen, Thomas Torgersen, Per Gunnar Fjelldal

The use of sterile triploids in Atlantic salmon aquaculture would mitigate the environmental risks associated with introgressive hybridization between escaped farmed and wild Atlantic salmon. However, production of farmed triploid salmon is limited due to reports of poorer growth and higher mortality when compared to diploids, in particular under sub-optimal environmental conditions. To address these concerns, we monitored triploid and diploid Atlantic salmon post-smolts at temperatures between 3 and 18°C and 100% oxygen saturation (O2 sat), and additional periods of 60% O2 sat (hypoxia) at 6 or 18°C, respectively. Feed intake and oxygen consumption rate were monitored throughout the experimental period. Muscle and blood samples were collected at 100 and 60% O2 sat at 6 and 18°C for analysis of white muscle energy phosphates (creatine phosphate, adenosine triphosphate) and carbohydrate fuels (glucose, glycogen) as well as blood clinical chemistry (whole blood: hematocrit; plasma: Na+, K+, Cl, glucose, lactate, pH, triacylglycerol). Mortality was similar between ploidies, but higher in triploids compared to diploids during reduced O2 sat at 18°C. Compared to diploids, triploids had higher feed intake (% biomass) at ≤9°C, but lower feed intake at ≥15°C. Feed intake peaked at 12 and 15°C for triploids and diploids, respectively. Triploids progressively reduced feed intake with increasing temperature after peak feeding, indicating reduced scope for specific dynamic action with increasing water temperature. During hypoxia, triploids had lower feed intake than diploids at 6 and 18°C. The difference in feed intake was not associated with any ploidy effect on body weight gain or feed conversion ratio, but triploids had greater body length growth compared to diploids. At ≥15°C triploids consumed less oxygen than diploids. In the white musculature, the only observed difference between ploidies was a lower level of glycogen in triploids compared to diploids at 18°C and 100% O2 sat. In the blood plasma, the concentration of ions was lower and glucose level higher in triploids compared to diploids at 18°C and 60% O2 sat. The results of this study indicate that triploid Atlantic salmon post-smolts can substitute diploids, but are less tolerant to high seawater temperature and low O2 sat. For sea-cage farming of triploid salmon post-smolts, this would favour production areas with maximum temperatures of 15°C and sufficient oxygen. Statement of Relevance This study demonstrates that triploid Atlantic salmon post-smolts have lower temperature optima for feeding and growth than diploids, a similar physiological response to high temperatures, but higher mortality under suboptimal conditions. Consequently triploid Atlantic salmon post-smolts may be well suited for commercial farming in geographical regions with moderate water temperatures in the summer and autumn months.





The roles of probiotic purple nonsulfur bacteria to control water quality and prevent acute hepatopancreatic necrosis disease (AHPND) for enhancement growth with higher survival in white shrimp (Litopenaeus vannamei) during cultivation

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Supaporn Chumpol, Duangporn Kantachote, Teruhiko Nitoda, Hiroshi Kanzaki

This study aimed to investigate the potential of a mixed probiotic purple nonsulfur bacteria (PNSB) for controlling water quality and preventing acute hepatopancreatic necrosis disease (AHPND) to promote growth performance and increase survival of white shrimp (Litopenaeus vannamei) in postlarval stage during cultivation. Four probiotic PNSB (Rhodobacter sphaeroides strains SS15, S3W10, TKW17 and Afifella marina STW181) were investigated for controlling water quality using a mixed culture at a ratio of 1: 1 (roughly 1×108 cellsmL1 for each, every week 1–7) as follows; T1 (S3W10+SS15), T2 (S3W10+TKW17) and T3 (S3W10+STW181) and found that throughout 8weeks shrimp cultivation the most effective sets to reduce NH4 + and promote shrimp growth (based on weight and total length) were T1 and T3, respectively. Hence, PNSB strains (SS15, S3W10 and STW181) were used as a mixed culture (1: 1: 1, roughly 1×108 cellsmL1 for each at weeks 1, 2 and 3) assessing their potential to prevent AHPND by challenge test on shrimp with a virulent strain AHPND-causing Vibrio parahaemolyticus SR2 (roughly 1×105 cellsmL1 at day 15) during shrimp cultivation for 30days. Inoculated PNSB sets (positive control: only PNSB inoculation, and treatment: both PNSB and SR2 inoculations) significantly decreased (P <0.05) the levels of NH4 +, NO2 , NO3 and chemical oxygen demand (COD) with significantly higher (P <0.05) of dissolved oxygen (DO) compared to native control (no inoculation) and challenge test (only SR2 inoculation). The maximal growth performance of shrimp was observed in the positive control; while no significant difference (P >0.05) was observed for other sets. PNSB survived and colonized in intestinal shrimp tract to prevent AHPND by increasing 11% survival rate of infected shrimp by strain SR2. The correlation coefficient between PNSB population and shrimp survival showed a positive strong correlation, but a negative strong correlation between vibrios population and shrimp survival. Overall results proved that a mixed three probiotic PNSB are a good candidate for applying in white shrimp cultivation to maintain water quality and to protect shrimp diseases for promoting shrimp growth with higher survival rate.





Pseudomonas aeruginosa strain PAO1 infection impairs locomotor activity in experimentally infected Rhamdia quelen: Interplay between a stress response and brain neurotransmitters

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Matheus D. Baldissera, Carine F. Souza, Roberto C.V. Santos, Luiz Vinicius C. da Rosa, Denis B. Rosemberg, Bernardo Baldisserotto

The aim of this study was to evaluate whether infection by Pseudomonas aeruginosa, an important opportunistic Gram-negative bacterium, causes behavioral alterations in Rhamdia quelen, as well as to investigate the involvement of markers of stress response and brain neurotransmitters in experimentally infected fish. For this, twelve animals were divided in two groups: uninfected (negative control) and experimentally infected animals with P. aeruginosa (positive control), in order to assess the behavioral parameters, plasma cortisol levels, as well as the Na+, K+-ATPase and acetylcholinesterase (AChE) activities. Animals infected with P. aeruginosa presented a behavioral impairment linked with hyperlocomotion. Also, the plasma cortisol and reactive oxygen species (ROS) levels increased in infected fish compared to uninfected ones. Cerebral Na+, K+-ATPase activity decreased in infected animals, while cerebral AChE activity increased compared to uninfected animals. In summary, fish experimentally infected with P. aeruginosa presented behavioral impairments, which are associated with stress and hyperlocomotion. Moreover, the impairment of the cerebral Na+, K+-ATPase pump and cholinergic system may directly contribute to this behavior, since dysfunction in the synapse is promoted, and levels of ACh, an important neurotransmitter involved in several behavioral functions, is decreased.





Physiological response to relaxation as pre-operative therapy to pearl formation in the winged pearl oyster Pteria sterna

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Andrés Granados-Amores, Ángel I. Campa-Córdova, Carmen Rodríguez-Jaramillo, José M. Mazón-Suástegui, Dariel Tovar-Ramírez, Pedro E. Saucedo

This study expands on the criteria for selecting relaxants used in commercial production of pearls, based on the hypothesis that relaxation, before acting at a cellular level, is a stressor that triggers a battery of physiological responses. Four relaxants at two concentrations each were tested for survival, relaxation and recovery, incidence of spawning, condition index, glycogen index, mucopolysaccharide index, and lipofuscin index in the winged pearl oyster Pteria sterna. The relaxants are: propylene phenoxetol (1.5 and 2.5mLL1), benzocaine (0.15 and 0.25gL1), magnesium chloride (15 and 30gL1), and clove oil (0.25 and 0.50mLL1). Benzocaine (0.25gL1) and propylene phenoxetol (2.5mLL1) promoted >85% relaxation in <45min, but induced the oysters to spontaneously spawn. The poorest efficiency for relaxation and recovery of oysters occurred with magnesium chloride at both concentrations. In all treatments, the glycogen index decreased in adductor muscle and increased in the gonad >50% with benzocaine, suggesting mobilization of energy reserves likely tied to spawning. In the digestive gland, the glycogen index also decreased by 30% with clove oil (0.5mLL1), but the response with this relaxant is attributed to oxidative stress and use of glycogen reserves to cover other physiological needs, such as immune protection. Relaxing with benzocaine caused a significant accumulation of lipofuscins in the gills and mantle, again as possible indicator of oxidative stress. Based on these results, we recommend using propylene phenoxetol at 1.5mLL1 for maximum relaxation with minimum deleterious effects in P. sterna.





Transcriptomic screening of the innate immune response in delta smelt during an Ichthyophthirius multifiliis infection

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Daniel F. Frank, Matthias Hasenbein, Kai Eder, Ken M. Jeffries, Juergen Geist, Nann A. Fangue, Richard E. Connon

Fish health can be affected by many environmental factors including infection with pathogens. Infectious disease can lead to high mortality in wild populations and in aquaculture, resulting in significant economic losses. Teleost fishes share a highly conserved response to pathogen infections, starting with an immediate activation of the innate immune response before shifting to an adaptive immune response. Fishes also show altered transcriptomic expression in stress-related genes during acute and chronic infections. The ciliate Ichthyophthirius multifiliis (Ich) is one of the most widely distributed ectoparasites for freshwater fish, providing the possibility to identify infection severity via phenotypical assessments. Molecular markers are increasingly incorporated in health assessments and to determine sublethal physiological responses to stressors. We evaluated the effects of an infection with Ich using the pelagic fish species delta smelt (Hypomesus transpacificus) as a model. We investigated transcriptional changes of ten genes belonging to the innate immune response and five heat shock genes related to thermal and general stress response. Molecular assessments were conducted in three tissues (gill, spleen and kidney), and collected from fish with different infection intensities. The combination of molecular markers, including immune and stress-related genes, resulted in significant differentiation between infection levels in all tissue types. The strongest results were observed in gill and kidney, however, the detection of infection severity was most effective when combining the transcriptomic results from all tissues. Chemokine cxcb was the most responsive gene in all tissues and provided significant upregulation in fish with visible Ich-infection. The identification of molecular markers targeting fundamental host responses associated with infections is contributing to the establishment of techniques to assess fish health in natural habitats and in aquaculture.





Identification of Tilapia Lake Virus in Egypt in Nile tilapia affected by ‘summer mortality’ syndrome

Published on 24/3/2017
Publication date: 20 April 2017
Source:Aquaculture, Volume 473

Author(s): Mohamed Fathi, Cathryn Dickson, Malcolm Dickson, William Leschen, Johanna Baily, Fiona Muir, Kristina Ulrich, Manfred Weidmann

Egyptian fish farms have faced unexplained mortality of tilapia during the summer months in recent years. Epidemiological surveys indicated that 37% of fish farms were affected in 2015 with an average mortality rate of 9.2% and a potential economic impact of around US$ 100 million. Despite a number of researchers and organizations investigating potential causes results so far have been inconclusive. Meanwhile recent reports emerged of the presence of a new orthomyxovirus, Tilapia Lake Virus (TiLV) in Israel, which shares a border and migrating avifauna with Egypt. Tissue samples from seven farms affected by ‘summer mortality’ were tested at the University of Stirling for TiLV. Samples from three of seven farms tested positive using PCR; the first time that TiLV has been identified in Egypt. Sequence analysis yielded a TiLV sequence with 93% homology to the published TiLV sequence described from Israel. More research is required to determine if TiLV is linked to ‘summer mortality’.





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