Stochastic modelling of direct costs of pancreas disease (PD) in Norwegian farmed Atlantic salmon (Salmo salar L.)

An economic model for estimating the direct costs of disease in industrial aquaculture was developed to include the following areas: biological losses, extraordinary costs, costs of treatment, costs of prevention and insurance pay-out. Direct costs of a pancreas disease (PD) outbreak in Norwegian farmed Atlantic salmon were estimated in the model, using probability distributions for the biological losses and expenditures associated with the disease. The biological effects of PD on mortality, growth, feed conversion and carcass quality and their correlations, together with costs of prevention were established using elicited data from an expert panel, and combined with basal losses in a control model. Extraordinary costs and costs associated with treatment were collected through a questionnaire sent to staff managing disease outbreaks. Norwegian national statistics for 2007 were used for prices and production costs in the model. Direct costs associated with a PD-outbreak in a site stocked with 500,000 smolts (vs. a similar site without the disease) were estimated to NOK (Norwegian kroner) 14.4 million (5% and 95% percentile: 10.5 and 17.8) (NOK = €0.12 or $0.17 for 2007). Production was reduced to 70% (5% and 95% percentile: 57% and 81%) saleable biomass, and at an increased production cost of NOK 6.0 per kg (5% and 95% percentile: 3.5 and 8.7).     

Three statistical approaches for genetic analysis of disease resistance to vibriosis in Atlantic cod (Gadus morhua L.)

The objective of this study was to estimate and compare variance components and sire breeding values for disease resistance to vibriosis in Atlantic cod (Gadus morhua L.) using 3 statistical approaches. A total of 3,576 individually tagged juvenile cod from 50 full-sib families were infected with Vibrio anguillarum, which causes vibriosis, a frequently reported disease in cod aquaculture. The experimental fish were progeny of captured wild cod from populations of southern coastal cod (POP1), and northern coastal cod and northeast Arctic cod (combined as POP2 in the genetic analyses). Fish were randomly assigned to 1 of 3 test tanks, and daily mortality was recorded until the termination of the experiment at d 31 postinfection. Variance components were estimated separately for the 2 populations using a Cox regression model, univariate linear model, and a linear model that accounted for censoring. With all approaches, the additive genetic sire variance estimated from POP1 was greater than for POP2. Heritability estimates across populations varied from 0.08 to 0.17 depending on the method used. The Cox regression model and univariate linear model resulted in greater heritability estimates for POP1 (0.10 and 0.16) than for POP2 (0.08 and 0.13), whereas the contrary was true with a linear model that accounted for censoring (0.17 vs. 0.14). The predicted breeding values for the sires from the 3 approaches were highly correlated (0.97 to 0.99). This is likely due to the fact that censoring only occurred at the end of the test; i.e., observations of the most resistant fish were censored. The considerable genetic variation found in this study suggests that vibriosis resistance may be improved through selective breeding. The univariate linear model, even without censoring of the data, was robust for the estimation of breeding values using the present data. Therefore, inclusion of vibriosis resistance in the multivariate linear estimation of breeding values for the traits of economic importance in Atlantic cod seems appropriate.     

State of the art and future trends of European and Italian aquaculture

This paper describes the main features of fish aquaculture in Europe and Italy focusing attention on single sectors of the farmed species and their trend for the future. Over recent years, European and Italian aquaculture have shown a markedly different trend from that of world aquatic production. Asia, particularly China, has recorded a constant and rapid growth and Latin America a moderate development. Nowadays, European farmers are concerned with adapting their product to market demand and diversifying the fish species reared. After a discussion about the main European production statistics regarding finfish aquaculture production, we consider the most important aspects in the promotion of production and consequent consumption of farmed fish.     

State of the art and future trends of European and Italian aquaculture

This paper describes the main features of fish aquaculture in Europe and Italy focusing attention on single sectors of the farmed species and their trend for the future. Over recent years, European and Italian aquaculture have shown a markedly different trend from that of world aquatic production. Asia, particularly China, has recorded a constant and rapid growth and Latin America a moderate development. Nowadays, European farmers are concerned with adapting their product to market demand and diversifying the fish species reared. After a discussion about the main European production statistics regarding finfish aquaculture production, we consider the most important aspects in the promotion of production and consequent consumption of farmed fish.     

Complete diallel cross between five strains of Atlantic salmonCroisement diallèle complet entre cinq souches de saumon de l'AtlantiqueVollständige diallele paarung zwischen fünf herkünften des Atlantik- lachses

The effect of cross-breeding on survival, growth and maturity when crossing five Norwegian strains of Atlantic salmon has been investigated. A diallel cross including purebred strains and their reciprocal crosses was used. Additive, maternal and heterosis effects were studied. Total heterosis was partitioned into average, general and specific heterosis. Growth of maturing and immature males and females was also considered.Significant total heterosis was found for survival of fry, survival of fish after marking (marked at one year of age), body weight of fingerlings and body weight of adults. However, average heterosis was low for all traits. For survival of eyed-eggs, alevins and fingerlings, dressing percentage and maturity, total heterosis was not significantly different from zero.It is concluded that cross-breeding Norwegian strains of Atlantic salmon seems to have little practical significance in a future breeding program.     

Francisella infections in farmed and wild aquatic organisms

ABSTRACT: Over the last 10 years or so, infections caused by bacteria belonging to a particular branch of the genus Francisella have become increasingly recognised in farmed fish and molluscs worldwide. While the increasing incidence of diagnoses may in part be due to the development and widespread availability of molecular detection techniques, the domestication of new organisms has undoubtedly instigated emergence of clinical disease in some species. Francisellosis in fish develops in a similar fashion independent of host species and is commonly characterised by the presence of multi-organ granuloma and high morbidity, with varying associated mortality levels. A number of fish species are affected including Atlantic cod, Gadus morhua; tilapia, Oreochromis sp.; Atlantic salmon, Salmo salar; hybrid striped bass, Morone chrysops × M. saxatilis and three-lined grunt, Parapristipoma trilinineatum. The disease is highly infectious and often prevalent in affected stocks. Most, if not all strains isolated from teleost fish belong to either F. noatunensis subsp. orientalis in warm water fish species or Francisella noatunensis subsp. noatunensis in coldwater fish species. The disease is quite readily diagnosed following histological examination and identification of the aetiological bacterium by culture on cysteine rich media or PCR. The available evidence may indicate a degree of host specificity for the various Francisella strains, although this area requires further study. No effective vaccine is currently available. Investigation of the virulence mechanisms and host response shows similarity to those known from Francisella tularensis infection in mammals. However, no evidence exists for zoonotic potential amongst the fish pathogenic Francisella.     

Isolation of putative probionts from cod rearing environment

Survival problems are encountered at early stages of intensive fish rearing and antibiotics are widely used to remedy the situation. Probiotics may provide a potential alternative method to protect larvae from opportunistic and pathogenic bacteria and promote a balanced environment. This study was designed to search for new probiotics to target this critical period in cod rearing. Potential probionts were selected from the natural microbiota of cod aquacultural environment. The selection was based on several criteria: pathogen inhibition potential, growth characteristics, strain identification, metabolite production and adhesion to fish cell lines. Our study demonstrated that 14% of screened bacteria (n=188) had antagonistic properties towards fish pathogens. The majority of these isolates were Gram-positive (81%), belonging to Firmicutes (69.2%) and Actinobacteria (11.5%) phyla based on 16S rRNA gene sequencing. Only 6 (3.2%) of 188 isolates could inhibit all three pathogens tested: Vibrio anguillarum, Aeromonas salmonicida subsp. achromogenes and Vibrio salmonicida. Differences observed in activity intensity and spectrum among inhibitory isolates emphasise the need to develop probiotic mixtures for efficient prophylactic methods. Comparison of growth behaviour of inhibitory isolates and pathogens at cod rearing temperatures, metabolite production and adhesion capacity were considered for final probiont selection. Four promising isolates that could be used as a mixed supplement to rearing water were identified as putative probiotic bacteria. This study emphasises the importance and potential of lactic acid bacteria in aquaculture.     

Utilization of dichlorvos and trichlorfon in salmonid farming in Norway during 1981-1988

The main objectives of this investigation were to quantify the use of dichlorvos and trichlorfon in the treatment of salmon lice infestations, to evaluate the prescribing of these drugs, and to estimate possible changes in the salmon lice problem by use of drug statistics. This study has shown that the use of trichlorfon increased from 4.9 tons in 1981 to 28.3 tons in 1985. This figure declined to 3.2 tons in 1988. The use of dichlorvos increased from 0.3 tons in 1986 to 3.2 tons in 1988. The change in the prescribing from trichlorfon to dichlorvos has dramatically reduced the pollution caused by these substances in the marine environment. Moreover, if necessary safety rules are observed, this change reduces the exposure of the workers on fish farms to these drugs, and also reduces the possibilities of intoxications of the fish during the treatment procedure. The sales figures of dichlorvos and trichlorfon, related to the calculated biomass of farmed salmonids in the sea, indicate a dramatic increase in the salmon lice problem.     

Clostridium botulinum in fish.

1407 fish caught in Scandinavian waters, the North Sea and the North Atlantic have been examined for the presence of Cl. botulinum. The incidence in gut samples expressed as percentage of fish tested was generally highest in fish from Scandinavian coastal waters and the Baltic Sea (4--43%), decreasing in fish from the North Sea (0--8%), and the organism was practically absent in fish from the North Atlantic. When gut samples were examined, the incidence was highest in demersal fish (cod and flatfish) as compared with pelagic fish (herring). The latter fish species were mainly contaminated on outer surfaces and gills. Only type E was detected in this survey, and Cl. botulinum was not detected in any wild fresh water fish. It is suggested that type E spores may originate in the sea bed and that they be spread by fish and water currents.     

Streptococcus iniae: an aquatic pathogen of global veterinary significance and a challenging candidate for reliable vaccination

Streptococcus iniae has become one the most serious aquatic pathogens in the last decade causing high losses in farmed marine and freshwater finfish in warmer regions. Although first identified in 1976 from a captive Amazon freshwater dolphin, from which it derives its name, disease outbreaks had most likely been occurring for several decades in marine aquaculture in Japan. S. iniae is globally distributed throughout warm water finfish aquaculture. In common with other encapsulated beta-haemolytic streptococci and in direct contradiction to the phenomenal success story of bacterial vaccines in finfish aquaculture, control of S. iniae by vaccination has met with limited success. Thus, antibiotic usage is the current practice for reducing mortality and consequent economic loss. Vaccine failure appears to result in part from serotypic variation and, whilst 2 serotypes have been named, variation would appear to be more complex. S. iniae also has zoonotic potential, with human infections identified in the USA, Canada, and throughout Asia. In humans, infection is clearly opportunistic with all cases to date associated with direct infection of puncture wounds during preparation of contaminated fish, and generally in elderly or immunocompromised individuals. Significant progress has been made in terms of research into pathogenic mechanisms of S. iniae, with recent research elucidating the role of capsule in virulence for fish through antiopsonic activity. In light of this recent coverage in the literature, the present review centres on areas of direct veterinary interest including identification, epidemiology, therapy and prevention in farmed finfish. Clearly as the prevalence of S. iniae and associated economic losses continue to increase, further work towards developing a reliable vaccine is essential. This would appear to require a much better understanding of cell-surface variability amongst S. iniae isolates.     

Selective breeding in fish and conservation of genetic resources for aquaculture

To satisfy increasing demands for fish as food, progress must occur towards greater aquaculture productivity whilst retaining the wild and farmed genetic resources that underpin global fish production. We review the main selection methods that have been developed for genetic improvement in aquaculture, and discuss their virtues and shortcomings. Examples of the application of mass, cohort, within family, and combined between-family and within-family selection are given. In addition, we review the manner in which fish genetic resources can be lost at the intra-specific, species and ecosystem levels and discuss options to best prevent this. We illustrate that fundamental principles of genetic management are common in the implementation of both selective breeding and conservation programmes, and should be emphasized in capacity development efforts. We highlight the value of applied genetics approaches for increasing aquaculture productivity and the conservation of fish genetic resources.     

Primary Isolation and Characterization of Tenacibaculum maritimum from Chilean Atlantic Salmon Mortalities Associated with a Pseudochattonella spp. Algal Bloom

Abstract

This study presents the first isolation of Tenacibaculum maritimum from farmed Atlantic Salmon Salmo salar in Chile. The isolate, designated T. maritimum Ch-2402, was isolated from gills of Atlantic Salmon at a farm located in region X, Los Lagos, Chile, during the harmful algal bloom caused by Pseudochattonella spp. in February 2016. The algal bloom is reported to have caused 40,000 metric tons of mortality in this salmon farming area. The bacterium T. maritimum, which causes tenacibaculosis, is recognized as an important pathogen of marine fish worldwide. Genetic, phylogenetic, and phenotypic characterizations were used to describe the T. maritimum Ch-2402 isolate. The isolate was similar to the type strain of T. maritimum but was genetically unique. Tenacibaculum dicentrarchi isolates were also recovered during sampling from the same farm. Based on the fact that T. maritimum has been shown to cause disease in Atlantic Salmon in other regions, the presence of this bacterium poses a potential risk of disease to fish in the Chilean aquaculture industry.

Received November 6, 2016; accepted May 29, 2017 Published online July 26, 2017     

A framework for understanding the potential for emerging diseases in aquaculture

Numerous diseases have emerged as serious economic or ecological problems in aquaculture species. The combination of factors behind the emergence of each disease is unique, but various common factors are apparent. We combine risk-analysis methods and virulence theory with historical examples (mainly from salmonid production) to identify key disease-emergence risk factors. Diseases have emerged through pathogen exchange with wild populations, evolution from non-pathogenic micro-organisms and anthropogenic transfer of stocks. Aquacultural practices frequently result in high population densities and other stresses (such as intercurrent disease) which increase the risk of infection establishment and spread. As aquaculture expands and new species are farmed, diseases will continue to emerge and affect both wild and farmed fish adversely. The rate and extent of emergence can be reduced by the application of biosecurity programmes designed to mitigate the risk factors for disease emergence.