Exploring the efficacy of vaccine techniques in juvenile sablefish,Anoplopoma fimbria

Wild sablefish, Anoplopoma fimbria, are a valuable commercial species whose populations are declining. Fortunately, sablefish are excellent species for commercial aquaculture. Sablefish raised under high‐density conditions in the marine environment require the use of efficacious vaccines to control disease. Sablefish impacted by disease in net pens may have poor flesh quality and high mortality during grow‐out. As a result, disease can cause financial hardship for sablefish aquaculture operators. The efficacy of a multivalent vaccine preparation for sablefish, administered either by intraperitoneal (i.p.) injection or by immersion, against atypical and typical Aeromonas salmonicida, the causative agents of atypical and typical furunculosis, respectively, was examined. A. salmonicida can affect sablefish at any age and size. Consequently, an efficacious vaccine that can be appropriately and optimally administered to all life stages is desirable. Sablefish vaccinated by immersion at ~1.5 or ~4.5 g with a whole‐cell multivalent vaccine were not protected against either typical or atypical A. salmonicida. Factors that may have contributed to the ineffectiveness of the immersion vaccine are discussed. By contrast, the relative per cent survival (RPS) or potency of the whole‐cell multivalent vaccine injected i.p. in juvenile sablefish at ~50 g against typical and atypical A. salmonicida was 94.3% and 81.7% respectively. The high RPS values indicated that the vaccine successfully initiated an immune response in sablefish upon a second encounter with the pathogen.     

养殖裸盖鱼(Anoplopoma fimbria)疥疮病病原菌的分离与鉴定

裸盖鱼(Anoplopoma fimbria)是一种名贵的冷水经济鱼类,已在我国北方地区开展小规模的工厂化繁育和养成.目前,我国关于裸盖鱼的病害研究仍是空白.本研究对山东烟台一养殖场自然发生疥疮病的裸盖鱼进行了病原分析,从发病鱼体内分离得到形态一致的优势菌株,命名为AF-1,并对其进行了致病性检测、菌种鉴定及药物敏感性研究.人工感染实验证明,AF-1对裸盖鱼有致病性,呈现症状与自然发病状态一致;结合形态观察、革兰氏染色、生理生化特征、16S rRNA和gyrB基因序列进化树分析,将AF-1鉴定为杀鲑气单胞菌(Aeromonas salmonicida);药物敏感性实验结果显示,AF-1对青霉素、阿莫西林、头孢噻吩等13种抗生素具有耐药性,对氟苯尼考、氟甲喹等16种抗生素敏感.综上所述,本研究首次报道了我国养殖裸盖鱼感染杀鲑气单胞菌病例,为裸盖鱼养殖过程中的疾病防控和疫苗开发提供了参考.     

Diel vertical migration of sablefish (Anoplopoma fimbria)

To investigate their diel vertical migration (DVM), 599 sablefish (Anoplopoma fimbria) were implanted with electronic archival tags in the Gulf of Alaska, Aleutian Islands, and the eastern Bering Sea. Of these tags, 98 were recovered with usable depth data (7,852,773 recordings representing 81,233 days) that we used to identify DVM and to classify DVM into one of two types: normal DVM (rise from the bottom during nighttime) and reverse DVM (rise from the bottom during daytime). The results of our study highlight three important attributes of DVM for sablefish. First, all tagged sablefish carried out DVM, although the occurrence was intermittent (26% of the days with usable data) and most commonly for short durations (10 days or less). Second, bottom depth for normal DVM was about 78 m shallower than for reverse DVM. Third, normal DVM occurred most often in fall and least often in spring, whereas this high/low pattern was shifted about 3 months later for reverse DVM; reverse DVM occurred most often in winter and least often in summer. Normal DVM likely occurred to increase foraging opportunity (e.g., nightly shift to match depth of prey). Reverse DVM more commonly occurred during winter and may represent an increase in foraging by sablefish during the daytime to compensate for decreased pelagic resources. The default foraging strategy for sablefish may be benthic because of the uncertainty of vertically migrating to a location where the occurrence of prey is not guaranteed; sablefish may invoke DVM when the non‐DVM foraging benefit is reduced.     

Oceanographic drivers of sablefish recruitment in the California Current

Oceanographic processes and ecological interactions can strongly influence recruitment success in marine fishes. Here, we develop an environmental index of sablefish recruitment with the goal of elucidating recruitment‐environment relationships and informing stock assessment. We start with a conceptual life‐history model for sablefish Anoplopoma fimbria on the US west coast to generate stage‐ and spatio‐temporally‐specific hypotheses regarding the oceanographic and biological variables likely influencing sablefish recruitment. Our model includes seven stages from pre‐spawn female condition through benthic recruitment (age‐0 fish) for the northern portion of the west coast U.S. sablefish stock (40°N–50°N). We then fit linear models and use model comparison to select predictors. We use residuals from the stock‐recruitment relationship in the 2015 sablefish assessment as the dependent variable (thus removing the effect of spawning stock biomass). Predictor variables were drawn primarily from ROMS model outputs for the California Current Ecosystem. We also include indices of prey and predator abundance and freshwater input. Five variables explained 57% of the variation in recruitment not accounted for by the stock‐recruitment relationship in the sablefish assessment. Recruitment deviations were positively correlated with (i) colder conditions during the spawner preconditioning period, (ii) warmer water temperatures during the egg stage, (iii) stronger cross‐shelf transport to near‐shore nursery habitats during the egg stage, (iv) stronger long‐shore transport to the north during the yolk‐sac stage, and (v) cold surface water temperatures during the larval stage. This result suggests that multiple mechanisms likely affect sablefish recruitment at different points in their life history.     

Validation of otolith increment daily periodicity in captive juvenile sablefish (Anoplopoma fimbria) experimentally immersed in strontium chloride (SrCl2)

We used a chemical marking experiment to validate the daily periodicity of otolith increment deposition in juvenile sablefish, Anoplopoma fimbria. The sagittal otoliths of 26 live juvenile sablefish were marked twice by immersion in saltwater baths containing elevated levels of strontium chloride (SrCl₂) during June–August of their first year of life (age 0). The number of otolith increments detected between strontium bands from three readings (median 15–20) was compared to the number of days between marking events (15–17 days). Median discrepancies between otolith increment counts and days between strontium bands were small (mean 1.1, S.E. 0.81, n = 20) and suggest that otolith increment counts from age 0 juvenile sablefish may provide a useful proxy for daily age. However, median discrepancies in June (mean 4.7, S.E. 0.65, n = 9 otoliths) were significantly (^*P ≤ 0.05) higher than those in July (mean −1.8, S.E. 0.40, n = 6) and August (mean −1.8, S.E. 0.66, n = 5). Increment banding patterns were more difficult to identify in otoliths marked in June (mean sablefish size 84.9 mm FL) because of changes in the structure of the sagittae associated with the formation of accessory primordia.     

What goes up must come down: Diel vertical migration in the deep‐water sablefish (Anoplopoma fimbria) revealed by pop‐up satellite archival tags

The sablefish (Anoplopoma fimbria) is a long‐lived species with wide distribution throughout the North Pacific Ocean. While adult sablefish are considered a deep‐water fish, diet analyses suggest that they undergo vertical migrations that could be related to prey movement and feeding. Pop‐up satellite archival tags (PSATs) were used to observe the fine‐scale depth selection behavior of adult sablefish tagged off the Washington coast during the summer from June to August. Tags were physically retrieved after they surfaced using direction‐finding equipment so that complete datasets over the entire deployment were obtained from 14 tags. PSATs that recorded depth and temperature every 4 min during the deployment confirm that sablefish inhabit depths of 750 m or greater. However, a majority of the tagged fish underwent extensive vertical migrations that averaged 254.4 m overall and occurred at a 24 hr periodicity. Variations were observed among individuals in the amount of the deployment during which vertical migrations occurred, ranging from 12.37% to 63.48% of the time. During the vertical migration, fish ascended towards the surface at night and descended prior to daylight (i.e., diel vertical migration). Sablefish generally inhabited temperatures of 5°C but during the vertical migrations were found at temperatures from 6 to 10°C. Sablefish are opportunistic feeders with a large proportion of their diet being fish, euphausiids and cephalopods. Because these prey items also exhibit diel vertical migrations, it is possible that the vertical migratory behavior displayed by the sablefish was in response to the movements or the location of their prey.     

Renibacterium salmoninarum bar forms: characterization, occurrence, and evidence of a host response to a R. salmoninarum infection

Unique-staining Renibacterium salmoninarum (Rs) cells, termed bar forms, first observed in a coho salmon, Oncorhynchus kisutch (Walbaum), in 1983, could not be cultured, making their characterization difficult and significance obscure. They can be detected only by the fluorescent-antibody technique (FAT) and their numbers estimated only by a quantitative FAT (QFAT). Data collected over a 10-year period showed that bar forms were observed only in vivo and appeared associated with a host response. Bar forms were observed in 10 salmonid species from five countries and in fish from < 1 g to spawning adults. They were observed in 50.1% of kidney smears prepared from 10,061 Rs positive chinook, O. tshawytscha (Walbaum), coho, and Atlantic salmon, Salmo salar L. Bar forms were shown to be Rs cells based on absorption studies, their reaction with an Rs-specific FAT and enzyme-linked immunosorbent assay, and a transition from 'typical' Rs cells to bar forms in naturally and experimentally infected fish. Bar forms were determined to be non-virulent, damaged or dead Rs cells, based on fluorescence and electron microscopy observations, the inability to culture them, and mortality data. Bar forms appeared to represent visual markers of recovery from an Rs infection.     

Co‐infection of rainbow trout (Oncorhynchus mykiss) with infectious hematopoietic necrosis virus and Flavobacterium psychrophilum

Co‐infection of rainbow trout with infections haematopoietic necrosis virus (IHNV) and Flavobacterium psychrophilum is known to occur, and it has been speculated that a combined infection can result in dramatic losses. Both pathogens can persist in fish in an asymptomatic carrier state, but the impact of co‐infection has not been well characterized or documented. In this study, it was hypothesized that fish co‐infected with F. psychrophilum and IHNV would exhibit greater mortality than fish infected with either pathogen alone. To test this, juvenile rainbow trout were co‐infected with low doses of either IHNV or F. psychrophilum, and at 2 days post‐initial challenge, they were given a low dose of the reciprocal pathogen. This combined infection caused high mortality (76.2%–100%), while mortality from a single pathogen infection with the same respective dose was low (5%–20%). The onset of mortality was earlier in the co‐infected group (3–4 days) when compared with fish infected with F. psychrophilum alone (6 days) or IHNV (5 days), confirming the synergistic interaction between both pathogens. Co‐infection led to a significant increase in the number of F. psychrophilum colony‐forming units and IHNV plaque‐forming units within tissues. This finding confirms that when present together in co‐infected fish, both pathogens are more efficiently recovered from tissues. Furthermore, pathogen genes were significantly increased in co‐infected groups, which parallel the findings of increased systemic pathogen load. Extensive tissue necrosis and abundant pathogen present intracellularly and extracellularly in haematopoietic tissue. This was pronounced in co‐infected fish and likely contributed to the exacerbated clinical signs and higher mortality. This study provides novel insight into host–pathogen interactions related to co‐infection by aquatic bacterial and viral pathogens and supports our hypothesis. Such findings confirm that mortality in fish exposed to both pathogens is greatly elevated compared to a single pathogen infection.     

The use of Western blot and electroimmunotransfer blot assays to monitor bacterial kidney disease in experimentally challenged Atlantic salmon, Salmo salar L.

Abstract. Western blot (WB) and electroimmunotransfer blot (EITB) methods were used to monitor bacterial soluble antigens and scroconversion profiles, respectively, in Atlantic salmon, Salmo salar L., experimentally challenged with Renibacterium salmoninarum. The two challenged populations exhibited differences in susceptibility to R. salmoninarum permitting an evaluation of the methods in fish populations harbouring different levels of the pathogen, WB detection of R. salmoninarum soluble antigens in serum provided a sensitive method for detecting pathogen presence during the active infection stages. For comparison, results for drop-plate culture and direct fluorescent antibody techniques were obtained. During the recovery phase, surviving fish were negative for the pathogen by these methods. However, >90% of challenged fish sampled from early infection stages to the end of the experimental period (141 days post-infection) were scropositive by the EITB assay for Atlantic salmon immunoglobulin reactive with R. salmoninarum soluble antigens. The results suggest that these methods for detecting R. salmoninarum or its soluble antigens may be useful during active infections. However, asymptomatic fish populations exposed to the pathogen, perhaps having recovered from an active infection and representing potential disease carrier sources, may be more readily identified by antigen-specific antibodies using methods such as the EITB assay.     

The pathology of the early stages of the crustacean parasite, Lernaeocera branchialis (L.), on Atlantic cod, Gadus morhua L

Lernaeocera branchialis is a penellid copepod, the adults of which are commonly found on gadoids in the North Atlantic and North Sea. L. branchialis has a severe negative impact on wild gadoids and is a potentially serious pathogen of farmed cod, Gadus morhua. This paper describes an experimental infection by cohabiting the intermediate host, the flounder, Platichthys flesus, heavily infected with juvenile stages of L. branchialis, with hatchery-reared cod in order to study the pathology of the early stages of infection of the final host. Early stages of L. branchialis induce extensive local gill hyperplasia, large intravascular thrombus formation and a moderate cellular immune response in the cardiac and branchial tissues of G. morhua. The parasite appears to migrate within the lumen of the afferent branchial artery, ventral aorta and in turn, that of the bulbus arteriosus. These findings are consistent with the presence of a haematophagous, voluminous and rapidly invasive parasite.     

Physiological Response to Dolops carvalhoi (Crustacea: Branchiura) Infection by Pacu,Piaractus mesopotamicus,Subjected to Short Cycles of Food Restriction and Refeeding

Feeding strategies that reduce feed and promote compensatory growth could be an interesting tool to reduce costs in the fish production. However, fish health must be monitored to evaluate if their physiological response to adverse conditions, such as parasite infection, does not become compromised. A 12‐wk growth trial was conducted to determine the physiological responses of pacu, Piaractus mesopotamicus, that were subjected to different fasting/refeeding cycles and infected with the Dolops carvalhoi. The schemes were: (i) control group fish (FD), (ii) food‐restricted and controlled refeeding group (FR/Rc), and (iii) food‐restricted and refeeding to satiation group (FR/Rs). After 84 d, the fish were exposed to D. carvalhoi for 30 h. The fish subjected to food restriction did not exhibit compensatory growth. Cortisol levels decreased in all groups within 30 h after infection. Glucose levels increased 6 h after the D. carvalhoi in the FR/Rs and 30 h after infection in the FD. In all of the fish groups, the hematocrit values were reduced after infection, and it was associated with a reduction in the mean corpuscular volume and erythrocytes. At 30 h after infection, the number of erythroblasts increased. The use of the feeding schemes does not indicate a failure of the pacu physiological responses.     

Economic performance of mechanised trawlers in the state of Kerala,India

The rapid growth in the fleet of small mechanised shrimp trawlers in Kerala from 769 trawlers day⁻¹ in 1973 to 3500 trawlers day⁻¹ in 1980 resulted in considerable erosion in the estimated annual net profit trawler⁻¹ from a maximum of Rs 537.5 × 10³ im 1976 to a minimum of Rs 5805 in 1982. This study proposes to optimise the fleet at 1460 trawlers day⁻¹ at which the net profit day⁻¹ for the trawler sector in Kerala would be Rs 2.127 × 10⁶ (or Rs 457.305 × 10⁶ year⁻¹ of 215 fishing days). At this economically optimum level of fishing effort, the yield from trawl fishery is estimated at 91 323 tons, comprising 44 931 tons of shrimps and 46 392 tons of finfish. The optimum number of trawlers may be chosen each year by about March or April by lot. The surplus vessels may be deployed in alternative fisheries such as for whitebait, rock perches, red snappers, breams, cephalopods, sharks and larger pelagics.     

Interannual changes in sablefish (Anoplopoma fimbria) recruitment in relation to oceanographic conditions within the California Current System

Sablefish (Anoplopoma fimbria) supports substantial fisheries in both the eastern and western Pacific Oceans. Juvenile recruitment along the west coast of the continental United States has been highly variable over the past three decades. Using a generalized additive model, we demonstrate that physical oceanographic variables within the California Current System have significant effects on sablefish recruitment. Significant relationships were found between juvenile recruitment and northward Ekman transport, eastward Ekman transport, and sea level during key times and at key locations within the habitat of this species. The model explains nearly 70% of the variability in sablefish recruitment between the years 1974 and 2000. The predictive power of the model was demonstrated by refitting without the last 5 yr of data and subsequent prediction of those years. Bootstrap assessments of bias associated with parameter estimates and jackknife‐after‐bootstrap assessments of the influence of individual data on parameter estimates are presented and discussed. Using this model, it is possible to draw preliminary conclusions concerning year‐class strength of cohorts not yet available to the survey gear as well as historic year‐class strengths. We discuss changes in zooplankton abundance and shifts in species of copepods associated with fluctuations in the physical variables that appear to have a major influence on sablefish recruitment.     

Effect of light intensity and feed density on feeding behaviour,growth and survival of larval sablefish Anoplopoma fimbria

We studied the effects of light intensity on larval activity, feeding behaviour, growth and survival of a candidate species for aquaculture – sablefish (Anoplopoma fimbria). Of six light intensities ranging from 2 to 750 lux at the water surface, the greatest surviving biomass in small tanks was observed at 12–42 lux. In another experiment in larger tanks, behavioural observations showed that larvae fed poorly under light brighter than 800 lux but fed better at lower light intensities, depending on tank type. In a separate experiment, where live feed densities were varied between 2.5 and 17.5 rotifers per mL of tank water, surviving biomass and dry weight increased with higher feed densities. These experiments help refine methods for rearing larval sablefish by demonstrating effects of light intensity and feed density on larval performance.     

Effects of different batches of Neoparamoeba perurans and fish stocking densities on the severity of amoebic gill disease in experimental infection of Atlantic salmon,Salmo salar L.

Currently, there are two methods of inducing laboratory‐based amoebic gill disease (AGD) in Atlantic salmon, Salmo salar L.: cohabitation with infected fish or exposure to a suspension of amoebae. Amoebic gill disease cannot be induced with cultured amoebae; therefore, the only source of the infective organism is salmon with the disease. For experimental purposes and to maintain pathogen supply, salmon are kept in an infection tank and amoebae are isolated from salmon once the disease establishes. In this way, discrete batches of amoebae are collected periodically. This study investigated the infective ability of different batches of amoebae. Furthermore, the effect of stocking density of salmon on the progression of AGD was also examined. The infective ability of different batches of amoebae isolated periodically from AGD‐affected salmon varied in terms of quantifiable pathology. Salmon stocking density had a significant impact on survival after amoebae challenge, with morbidity beginning 23 days post challenge in tanks stocked at 5.0 kg m^?3 and 29 days for those stocked at 1.7 kg m^?3. For uniform initiation of AGD in multiple tanks, amoebae batches should be equally divided and added to tanks until the required concentration is reached and to maintain a standard biomass between replicate tanks and treatments.     

Decadal-scale patterns in the relative year class success of sablefish (Anoplopoma fimbria)

Climate–ocean regimes in the north-east Pacific translate into decadal-scale patterns in the relative success of sablefish ( Anoplopoma fimbria ). By combining estimates of year class abundance determined from commercial catches and research surveys for adults and juveniles, we were able to construct an index of year class success. Year classes from 1960 to 1976 were generally below average, with little indication of good year class success. The 1977 year class was exceptionally large and year classes from 1978 to 1990 were generally above average. Year classes following 1990 were generally below average. The periods with above-average year classes were generally characterized by intense Aleutian Lows, above-average frequency of south-westerly winds and warmer coastal sea surface temperatures off the west coast of Vancouver Island. Decadal-scale patterns in the production of sablefish suggest stability in long-term periods of similar recruitment but different mean levels of productivity across periods. However, rapid shifts between periods remain unpredictable and therefore complicate the incorporation of decadal-scale dynamics in management.     

Diagnosis of bacterial kidney disease by detection of Renibacterium salmoninarum by real-time PCR

Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum (Rs), is a serious threat to salmon in aquaculture as well as to wild populations. We have developed a real-time polymerase chain reaction (PCR) for detection of Rs in kidney samples. The PCR is based on detection of unique parts of the 16S rRNA gene of Rs and DNA equivalent to 1-10 Rs genomes was detected per reaction. No cross-reactivity with other fish pathogenic or related bacteria could be demonstrated. Analysis of individual kidney samples collected from BKD classified populations identified 39.9% of the fish as positive by real-time PCR compared with 28.0% by polyclonal enzyme-linked immunosorbent assay (ELISA). The real-time PCR assay was found to be well suited for complementary use with ELISA for diagnosis of BKD, with the ability to detect clinical as well as covert Rs infections. The infection level determined by the polyclonal ELISA and by real-time PCR was significantly correlated.     

Growth performance,oxidative stress,and non-specific immune responses in juvenile sablefish, <Emphasis Type="Italic">Anoplopoma fimbria</Emphasis>, by changes of water temperature and salinity

Juvenile sablefish, Anoplopoma fimbria (mean length 15.5 ± 1.9 cm, mean weight 68.5 ± 4.8 g), were used to evaluate the effects on growth, oxidative stress, and non-specific immune responses by changes of water temperature (8, 10, 12, 14, 16, 18, and 20 °C) and salinity (100 (35.0), 90 (31.5), 80 (28.0), 70 (24.5), 60 (21.0), 50 (17.5), and 40% (14.0) (‰)) for 4 months. The growth performance was significantly increased at the temperature of 12 and 14 °C, and the feed efficiency was notably decreased at the temperature of 18 °C. The growth performance and feed efficiency were also significantly decreased at low salinity. The antioxidant responses such as superoxide dismutase and catalase were significantly increased by the high temperature and decreased by the low salinity. The immune responses such as lysozyme and phagocytosis were elevated by the temperature of 18 °C and decreased by the salinity of 50%. The results of this study indicate that the growth performance of juvenile sablefish, A. fimbria, is influenced by the temperature and salinity, and the excessive temperature and salinity levels can affect the antioxidant and immune responses.     

A viral dermatitis of the smooth dogfish, Mustelus canis (Mitchill)

Abstract. A viral infection of the smooth dogfish, Mustelus canis (Mitchill), a squaliform shark, is described. The disease was found and observed in wild, laboratory-maintained and aquaria-displayed populations of smooth dogfish of the Woods Hole area of Massachusetts during a 2.5-year period. The disease was characterized by the progressive development of gross and microscopic herpes-like skin lesions. Electron microscopic examination revealed cellular pathology, viral replication and transport, and virions that conformed to those of herpesvirus infection. This study is the first report of a viral infection in elasmobranchs. The comparative pathology and implication for wild and captive shark populations is discussed.     

Histology,immunocytochemistry and qRT‐PCR analysis of Atlantic salmon,Salmo salar L., post‐smolts following infection with infectious pancreatic necrosis virus (IPNV)

Infectious pancreatic necrosis (IPN) is a very serious viral disease in terms of its impact on production of Atlantic salmon, Salmo salar L., fry and post‐smolts. Post‐smolts of Atlantic salmon were injected with infectious pancreatic necrosis virus (IPNV) and cohabited with naive fish to produce natural infection. Cohabitant fish were sampled every 2 days, up to day 36 post‐infection (p.i.). From 90 cohabitant fish, 11 (12.2%) were positive by immunohistochemistry (IHC). The first detection of IPNV by IHC occurred on day 16 p.i. which coincided with the onset of mortality in this group. Besides the pancreas, the liver was found to be a key target organ for IPNV. For the first time, the virus was observed in the islets of Langerhans and in the kidney corpuscles of Stannius which suggests that the virus could affect the fish’s metabolism. The liver of two fish, which showed the most widespread presence of IPNV by IHC, had a pathology including focal necrosis and widespread presence of apoptotic hepatocytes, many of which did not stain for virus by IHC. Up‐regulation of cytokine gene expression was found only in the IHC‐positive (IHC+ve) fish and reflected the level of infection as determined by IHC positivity of the liver. In most fish, interferon (IFN), Mx, γIFN and γIP were up‐regulated in liver and kidney, while only IFN and Mx were up‐regulated in gill. IL1β and TNFα were not induced in any tissue. The gill showed variable levels of constitutive expression of IL1β and γIFN. The two fish with liver pathology had the highest level of IFN expression, especially relative to the level of Mx expression, in the liver compared with the other IHC+ve fish which did not have a liver pathology. The results suggest that following widespread infection of hepatocytes, the cells may over‐produce IFN, resulting in apoptosis of neighbouring cells with subsequent death from liver failure.