Thorolf Magnesen

Characterisation of the bacterial community associated with early stages of Great Scallop (Pecten maximus), using denaturing gradient gel electrophoresis (DGGE).

Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA was used to characterise and compare bacterial communities associated with scallop larvae (Pecten maximus), in different production units in a shellfish hatchery. Water and larvae samples were collected from three different aquaculture systems; stagnant, flow-through and a flow- through system with seawater treated with ozone. Samples were also collected from different algal cultures, inlet tanks and water pipes leading to the different aquaculture systems. Clear differences were seen between the bacterial community associated with the larvae and in the water from the different aquaculture systems. However, there were high similarities in the community composition between different water samples and between larvae samples collected at different time periods, indicating a high stability in the bacterial communities. Fifty three percent of the sequences from these samples were similar to 16S rRNA gene sequences of members of the gamma-subclass of the Proteobacteria. The different algal cultures had different bacterial communities, however 73 percent of the sequences were similar to 16S rRNA gene sequences of members of the alpha-subclass of the Proteobacteria. Differences in the DGGE profiles were also seen between the samples taken from the inlet tanks and water pipes, indicating a change in the bacterial community composition as the water passed through the pipes. To our knowledge this is the first study investigating bacterial communities associated with Great Scallop larvae in different aquaculture systems including noncultured components.

Distribution, development, and production of Calanus finmarchicus (Gunnerus) in Lindåspollene, western Norway, 1979

The Calanus finmarchicus population in Spjeldnesosen, a ‘poll’ in the landlocked fjord system, Lindaspollene, in western Norway was investigated during 1979 and early 1980. The bottom water was renewed during the winter 1978–1979. This led to a well aerated water column in 1979 compared to earlier years. Differences were observed between the horizontal distributions of the various copepodid stages. This is thought to be due to migration away from the shore as the individuals grew older. One yearly generation with one spring spawning was observed. Residence times were estimated as 2, 4, 6, 13, and 250 days for copepodid stages I to V respectively. The estimated mortality was greater than 10 % per day when the younger stages were represented in the samples, and less than 1 % per day when stage V was dominant. Of about 72 000 ind./m2 recruited to copepodid stage I, about 800 ind./m2 of the total population survived until the end of 1979. Estimated production was 1 g dry weight/m2 per year on the average for ...

Bacteria associated with early life stages of the great scallop, Pecten maximus : impact on larval survival

A bacteriological study was carried out at a scallop (Pecten maximus) hatchery near Bergen, western Norway following a severe increase in mortality rates during the larval stages of the scallops. No larvae survived to settling, except for those in groups treated prophylactically with chloramphenicol. In order to identify pathogenic strains of bacteria, we performed a challenge test on 10- to 16-day-old larvae using isolated bacterial strains from the hatchery. Infection with six of these strains produced mortalities that were not statistically different from that resulting from infection with the known pathogen Vibrio pectenicida. However, about 5% of the strains tested in the challenge experiment produced higher motility rates than found in the unchallenged control group, indicating a possible probiotic effect. On the basis of 16S rDNA analysis on these strains, the phylogenetic tree indicated two groups of apparent pathogens: (1) one strain, LT13, grouped together with Alteromonas/Pseudoalteromonas; (2) a cluster of strains grouped together with Vibrio splendidus (LT06, LT21, LT73, PMV18 and PMV19). Strain LT13 was isolated from cultures of the microalga Chaetoceros calcitrans used for feed, while the other strains were isolated from larval cultures. Transmission electron microscopy showed intracellular bacteria that resembled bacteria in the groups Chlamydiaceae and Rickettsiaceae.

Hatchery Production of Scallop Larvae (Pecten maximus) – Survival in Different Rearing Systems

Scallop farms in Norway rely exclusively on hatchery production of spat. Larval rearing is one of the most difficult parts of the production, and several experiments have been performed during the last years to improve the larval systems. This paper describes results from commercial and experimental trials obtained between 1996 and 2001. Four different rearing systems were compared: untreated batch cultures, chloramphenicol-treated batch cultures, flow-through cultures with filtered water and flow-through cultures with water from a biofilter. The chloramphenicol-treated batch cultures had overall significantly higher survival rates than the untreated and flow-through cultures. There were no significant differences in survival between untreated and flow-through cultures. The average survival rates for the untreated, treated and flow-through cultures were 6.8, 23.0 and 8.6%, respectively. No significant seasonal differences were found for the untreated and treated larval groups, whereas for larvae reared in flow-through systems survival was significantly higher in the winter than the spring. Overall best results were obtained during winter in years with high salinity water in the fjord.

SUSPENSION CULTURE OF THE GREAT SCALLOP Pecten maximus IN GALICIA, NW SPAIN: INTERMEDIATE SECONDARY CULTURE FROM JUVENILES TO YOUNG ADULTS

Abstract A strategy for producing juvenile Pecten maximus to a suitable size for final culture (≈20–60 mm shell-height) within a year is suggested. Effects of stocking density, fouling on cages and shells, and handling frequency (every 1, 2, or 3 mo) on scallop growth and survival were investigated. Small juveniles (16.8 ± 3.0 mm) were initially stocked in August at densities of 24, 36, and 48 scallops quarter−1 (17% to 34% coverage), and 35.5 ± 5.1 mm scallops were restocked in January to 6, 12, 18, and 24 quarter−1 (18% to 73%). Survival was neither affected by stocking density nor handling, and was 98% the first period and from 93.2% to 96.9% between January and July. Shell-growth was mainly affected by stocking density and less affected by handling frequency. Growth slowed down during the winter months, and stocking density influenced growth during all seasons. Juveniles kept at the lowest densities obtained highest growth. Final mean shell-height was 54.8–67.2 mm and coverage 22% to 165%. Scallops handled monthly and bimonthly had significantly larger sizes than scallops handled every three months. Fouling on the cages increased with rising sea temperature, whereas high stocking density significantly reduced fouling on cages. Effective production during intermediate secondary culture in Galicia should include high initial stocking density in August, restocking to low density in January, and changes or cleaning of cages every second month.

Salinity tolerance of juvenile scallops (Pecten maximus L.) at low temperature

Abstract The effects of reduced salinity on survival, filtration rate and behaviour of juvenile scallops ( Pecten maximus ) were studied at 5.0°C and 9.4°C. Daily observations of mortality and behaviour, and weekly measurements of filtration were made for 30 days at the original salinity of 33 ppt, and at reduced salinities (29, 26, 23, 20 ppt, and weekly fluctuating between 27 and 29 ppt) and thereafter for a 15-day recovery period at the original salinity. The results show that there was no mortality in scallops at 9°C at salinities above 20 ppt and only low mortality at 20 ppt, while the scallops at 5°C had high mortality (> 50%) at salinities lower than 26 ppt. The filtration rate showed little variation between salinities above 20 ppt at 9°C, and between salinities at 5°C and 20 ppt at 9°C. The filtration rate in salinities over 20 ppt at 9°C was 4–5 times higher than at 5°C. The scallops responded to reduced temperature and salinity by retracting tentacles and mantle edge or closing valves. It is recommended that scallop farms in western Norway should be located in areas where salinity seldom drops below 29 ppt.

Preliminary Studies on the Vertical Distribution of Size-Fractions in the Zooplankton Community in Lindaspollene, Western Norway

Zooplankton collected with Clarke-Bumpus plankton samplers equipped with 180 µm mesh-size nets in 10 m depth-strata and with 2–3 hours time intervals in Lindaspollene 2–3 October 1979 and 12–13 May 1981 revealed distinct differences with regard to the vertical distribution of size-fractions in the plankton. Thus, the major part of the biomass of the > 1000 µm size-fraction in October 1979 was concentrated in the deepest 20 m throughout the sampling period, but a smaller part of the size-fraction, composed particularly of Sagitta elegans and Aglantha digitale, performed distinct vertical migrations. In May 1981 the same size-fraction was concentrated particularly in the upper 20 m, and no diel vertical migration could be ascertained. However, the species S. elegans and A. digitale displayed diel vertical migrations similar to those observed in October 1979. The major part of the biomass of the 180–500µm and the 500–1000 µm size-fractions was concentrated in the upper 20 m in October 1979, and a weak diel v...

Treatment of the early life stages of scallop (Pecten maximus) with antimicrobial agents; searching for an alternative to chloramphenicol

High mortality rates are often observed in rearing the early stages of the great scallop, Pecten maximus. The addition of antibacterial agents has been necessary to improve larval survival. However, as one antibacterial agent, chloramphenicol, is banned in Norway and Europe the aim of this study is to investigate alternative antibacterial agents. The therapeutic agents investigated in this study were florfenicol, oxytetracycline, oxolinic acid, neomycin and Pyceze. The mean minimum inhibitory concentration (MIC) values were determined for oxytetracycline, oxolinic acid and Pyceze against bacteria isolated from scallop larvae. Two types of treatment regime were investigated on an intermediate scale (20 L). One regime involved continuous exposure of scallop larvae to the therapeutic agent while the other involved a short exposure lasting two hours. All intermediate scale treatments were performed in parallel to large-scale production (800 L) treatment with chloramphenicol. Of the therapeutants investigated, oxolinic acid was the most effective, although only at high concentrations. The short exposure of two hours was ineffective for all therapeutics.

Arcobacter lekithochrous sp. nov., a new species isolated from a molluscan hatchery in Norway.

Four bacterial strains, LFT 1.7T, LT2C 2.5, LT4C 2.8 and TM 4.6, were isolated from great scallop (Pecten maximus) larvae and tank seawater in a Norwegian hatchery and characterized by a polyphasic approach including determination of phenotypic, chemotaxonomic and genomic traits. All were Gram-stain-negative, motile rods, oxidase- and catalase-positive and required sea salts for growth. Major fatty acids present were summed feature 3 (C16 : 1ω7c/C16 : 1ω6c), summed feature 8 (C18 : 1ω7c or C18 : 1ω6c), C16 : 0, C14 : 0, summed feature 2 (C14 : 0 3-OH/iso-C16 : 1 I), C12 : 0 3-OH and C12 : 0. Strain LFT 1.7T contained menaquinone MK-6 as the sole respiratory quinone. Phylogenetic analysis based on 16S rRNA gene sequences indicated that all strains formed a distinct lineage within the genus Arcobacter with a low similarity to known species (94.77-95.32 %). The DNA G+C content was 28.7 mol%. Results of in silico DNA-DNA hybridization and average nucleotide identity confirmed that the isolates constitute a novel species of Arcobacter, for which the name Arcobacter lekithochrous sp. nov. is proposed. The type strain is LFT 1.7T (=CECT 8942T=DSM 100870T).

Vertical distribution of size-fractions in the zooplakton community in Lindåspollene, Western Norway. 2. diel variations

Abstract At mid-day and midnight in May, June, August, September. and October 1983. and in April and May 1984 samples were collected in horizontal depth strata between the surface and 30 m (50 m 1984). The total zooplankton biomass (> 60 μm) was fractioned into five size-classes. Diel migrations could not be revealed in the two smallest size-classes, 60–125 and 125–250 μm. In the 250-500-μm size-class upward vertical migrations occurred in May and September, while the 500-1000-μm size-class performed vertical migrations on all occasions. except for June. At night more than 90 % of the biomass in this size-class could be found in the upper layer (0-15 m) compared to 50-70 % at mid-day. The diel variations in the largest size-class (> 1000 μm) were small in 1983. but in 1984 distinct vertical migrations occurred. The change in migrational patterns between the two years was due to a change in species composition caused by renewal of water masses. Calanus finmarchicus, Pseudocalanus elongatus, and Temora long...