Incubation time for the cultivation of Renibacterium salmoninarum from Atlantic salmon, Salmo salar L., broodfish

Abstract. Cultivation plates for the primary isolation of Renibacterium salmoninarum were incubated for 12 or more weeks over 3.5 years. The incubation time for sample of two groups of Atlantic salmon, Salmo solar L., broodfish on a selective agar medium is reported. Samples turned positive over a long time-span. but the longest incubation time recorded for growth of the bacterium was 19 week. In one group, 79% of all positive samples form fish with macroscopic signs of bacterial kidney disease were positive after 6 weeks of incubation and the highest incidence of positive samples occured during the sixth week. From covertly infected fish within the same group.42% of sample were positive after 6 weeks of incubation, and the highest incidence of positive sample occured during the sixth and the ninth weeks of incubation. The growth pattern of the bacterium at primary isolation was characterized by a prolonged lag phase followed by a relatively growth in one week from microscopic to macroscopic size of the colonies.     

A simple non-destructive biometric method for estimating fat levels in Atlantic salmon, Salmo salar L., parr

Abstract. Simple body measurements were used to predict the fat content of Atlantic salmon parr. For three different sizes (wet weights 18–98g, 44–207g and 137-151·8g) at two times of year (November/December and July) the percentage body fat (as measured by lipid extraction) could be predicted accurately using multiple regressions based on a combination of the following measurements: wet weight, fork length, opercular height, dorsal height, opercular width, dorsal width, anal width, adipose fin length and condition factor. In every case predictions based on multiple regression equations were more accurate than condition factor alone. This biometric method is easily employed and can potentially be used both in biological studies and on fish farms to assess body condition of individual fish. Since it is non-destructive it has the additional advantage of allowing repeated monitoring of fat levels in the same fish.     

A comparison of five external marks for Atlantic salmon, Salmo salar L.

Five external marks (Panjet, visible implant tag, hot brand, anal finclip and fluorescent pigment) were compared for retention and effect on marine survival in Atlantic salmon, Salmo salar L., ranching experiments aimed at complementing coded wire tagging. Only fluorescent pigment marks and Panjet marks were found to be effective, with retention rates of 76.9% and 90.0% respectively, after one year at sea. The Panjet was the only mark to significantly reduce marine survival ( P < 0.001) compared with controls.     

Incidence of hybridization between Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Ireland

The substantial growth of the farmed salmon industry in Europe since the 1970s has highlighted concerns regarding the genetic impact of escaped farmed salmon on wild salmonid stocks. High incidences of salmon × trout hybrids have been recorded in rivers situated near intensive salmon farming in Norway and Scotland, which may be indicative of a breakdown in reproductive isolation between salmon, Salmo salar L., and brown trout, Salmo trutta L. In the present study, salmonid fry and 0+ parr were collected from rivers in western Ireland. Allozyme and minisatellite DNA analysis were carried out on fry to determine the frequency of F1 hybrids from 10 rivers located within 38 km of salmon farms and three rivers at least 80 km from salmon farms. A total of 49 hybrids were recorded from 4135 salmonid fry (frequency = 1.2%). Mitochondrial DNA analysis showed that all hybrids arose from Atlantic salmon female × brown trout male crosses. Hybrid parr were recorded from one of the low-risk rivers (1.0%), but were present in seven out of the 10 catchments located within 38 km of salmon farms, with frequencies ranging from 0.7% to 3.1%. The results of the present survey, which represents the first extensive record of the levels of salmon-trout hybridization in Ireland, are discussed in relation to the continued growth of salmon farming in this country.     

Minimum requirement of vitamin E for Atlantic salmon, Salmo salar L., at first feeding

The minimum requirement of vitamin E for Atlantic salmon, Salmo salar L., at first feeding was found to be 60 mg dl-α-tocopheryl acetate per kg dry diet. The dry diet contained 5.6% polyunsaturated fatty acids, which is similar to that used in practical diets at first feeding. Preliminary results indicate that the optimal dietary vitamin E level is 120 mg dl-α-tocopheryl acetate per kg dry diet, or more. Further research is necessary to confirm this hypothesis.     

Atlantic salmon, Salmo salar L., feed in Scottish coastal waters

Abstract. The stomach contents of 256 Atlantic salmon, Salmo salar L., of fork lengths 53–66cm, caught in bag nets on the Scottish west coast near Ullapool, were examined between June 1983 and July 1986. A total of 61 fish contained fish in the stomach or had faecal pellets containing fish bones in the gut. All recognizable whole fish were sandeels, Ammodytes marinus Raitt, ranging in size from 4.5 to 15cm. No evidence for crustacean or other non-fish prey items was found. Results indicate that feeding salmon were caught up to a certain cut-off point in June or early July, after which all salmon sampled were not feeding. It is suggested that either there is a local feeding stock of salmon or that fish feed during migration from the Faroe Isles or other possible distant water origins.     

Screamer disease in Atlantic salmon, Salmo salar L., in Chile

Investigation of cranial and spinal deformities in Atlantic salmon smolts from Chile immediately after sea transfer, over two successive crops, demonstrated ankylosis of the mandibular articulation, spinal foreshortening, fracture of vertebrae and rarefaction of osseous and cartilaginous tissues including the operculum. As a result the mouth was permanently agape and opercula could be folded back on themselves. All affected fish had been transferred to sea water at 20 °C plus and fed on particular commercial diets. Fish in cooler areas, or on diets high in vitamin C and phosphorus in the high temperature zone, were clinically normal. The condition has not recurred following dietary adjustment.     

Field testing of adjuvanted furunculosis vaccines in Atlantic salmon, Salmo salar L.

Abstract. Two different commercial vaccines against furunculosis, caused by Aeromonas salmonicida subsp. salmonicida , were tested in Atlantic salmon on seven fish farms. Both vaccines were based on formalin-inaclivated bacterins containing aluminium salts as adjuvants. The fish were vaccinated by intraperitoneal injection in the spring approximately one month prior to transfer to sea water, and they were challenged by natural outbreaks of furunculosis. During the first year, six of the farms experienced disease outbreaks. The overall mortality was 7·14% in vaccinated fish and 21·7% in unvaccinated controls, giving a relative percentage survival (RPS) of 67%. In the seventh farm, outbreaks of furunculosis more than one year after vaccination revealed that there was still a trend towards lower mortality in vaccinated fish, though the mean RPS fell to 22%. The use of adjuvants in the vaccines resulted in local lesions in the abdominal cavity of vaccinated fish. However, the severity of the lesions declined gradually, and they did not influence fish quality at the time of slaughtering. Vaccination also had a moderately adverse impact on fish weight gain in most cases.     

Pathogenicity of Saprolegnia spp. to Atlantic salmon, Salmo salar L., eggs

Live and dead Atlantic salmon eyed eggs were challenged with eight different Saprolegnia isolates, selected because of their varied origins, known morphological characteristics and growth/germination pattern. Some isolates were also tested for pathogenicity to Atlantic salmon parr. Challenge of eggs was performed by exposure to spores in suspension or by co-incubation of live eggs with infected dead eggs. The phenotypic characteristics of the isolates were evaluated in relation to their observed pathogenicity from the challenge experiment, to identify possible virulence factors leading to egg-infection by Saprolegnia. The results from the experiments confirm that live eggs are refractory to infection with Saprolegnia spores in suspension and that an infection of live eggs can only occur from an infection nucleus represented by dead eggs or debris. It was observed that strains pathogenic to salmon parr were not particularly infective towards eggs, and the isolates that gave the highest infection rates to eggs were species considered to be saprotrophs.     

Nocardiosis in tank-reared Atlantic salmon, Salmo salar L.

Nocardiosis is an infection caused by aerobic Gram-positive, branching, filamentous rods of the genus Nocardia . The organism is resident in both soil and plants ( Austin & Austin 1993 ; Frerichs 1993 ), and is closely related to Mycobacterium spp. Nocardiosis caused by Nocardia asteroides and N. seriolae (previously N. kampachi ) has been reported in several finfish species, both freshwater and marine. The first reported incidence was recorded by Valdez & Conroy (1963) in neon tetras, Hyphessobrycon innesi (Myers), and subsequently in other fish species, some of commercial significance including rainbow trout, Oncorhynchus mykiss (Walbaum) ( Snieszko, Bullock, Dunbar & Pettijohn 1964 ), brook trout, Salvelinus fontinalis (Mitchill), ( Campbell & MacKelvie 1968 ) and yellowtail, Seriola quinqueradiata (Temminck & Schlegel; Kubota, Kariya, Nakamura & Kira 1968 ). Despite two of these incidences occurring in salmonids, infection by Nocardia spp. in Atlantic salmon, Salmo salar L., has not previously been reported.     

Reproductive strategies in Atlantic salmon, Salmo salar L.

Abstract. Life-history strategies are means by which animals solve the problems of successful reproduction in varying environments. Their development patterns are consequences of responses to the opportunities the environment offers them. Understanding them requires an understanding of the way they evolved, their ontogenetic development, their physiological control, and their adaptive value. The present paper views the salmonids as marine fishes, which have radiated into fresh water through using river beds as protected spawning grounds. It also takes the view that the maturation process has priority over somatic growth in fish, and that it has already been initiated by the time of first feeding. Its completion is environmentally dependent, and can be arrested annually. Whether or not it will be arrested depends on the status of the energy stores of the individual at particular critical times of year. This mechanism has adaptive value both for immediate reproductive success — adequate energy to provision the next generation — and for later overwinter survival, ensuring that if energy stores are inadequate for reproduction they are spared. Atlantic salmon show variation in their reproductive patterns, and examples are given from laboratory and aquaculture experiments to demonstrate some environmental controls which result in these variations. A hypothetical model is presented to account for the operation of these controls.     

Target spawning requirements for Atlantic salmon, Salmo salar L., in Newfoundland rivers

Abstract In recent years, there has been increasing pressure from user groups in Newfoundland and Labrador, Canada, to manage Atlantic salmon, Salmo salar L., on a river-specific basis. The requirement to maximize benefits to users while ensuring that conservation goals are met has resulted in an initiative to develop river-specific target spawning requirements. In Newfoundland, anadromous juvenile Atlantic salmon make widespread use of lacustrine habitat for rearing. Depending on the river, lacustrine habitat can account for a substantial proportion of total production. Therefore, target spawning requirements for a number of rivers in several management areas were derived in terms of the contribution of both riverine and lacustrine habitats. The approach adopted, and derivations of associated parameter values, are reviewed, and limitations and research needs are discussed.     

Comparison of the effectiveness of three different growth media for primary isolation of Renibacterium salmoninarum from Atlantic salmon, Salmo salar L., broodfish

Abstract. The effectiveness of three different growth media KDM-2, S-KDM and S-KDM-C for primary isolation of Renibacterium salmoninarum was examined over a 14-week incubation period. Kidney samples were taken from Atlantic salmon, Salmo salar L., broodfish returning to a sea ranch after 2 years at sea. Homogenized samples were inoculated onto two selective media, S-KDM supplemented with lamb serum and S-KDM-C supplemented with activated charcoal. The third medium was the non-selective serum supplemented KDM-2. Renibacterium salmoninarum was isolated from 112 samples on one or more of the media used. Of all positive samples, 91% were positive on S-KDM, 60% on S-KDM-C and 35% on KDM-2. These results demonstrate that selectivity significantly enhances the isolation capacity of the medium and that supplementing with serum is significantly more effective than supplementing with charcoal.