Analysis of bacterial populations in the gut of developing cod larvae and identification of Vibrio logei, Vibrio anguillarum and Vibrio splendidus as pathogens of cod larvae

Poor larval survival rates currently limit production in aquaculture and a better understanding of the bacterial flora in the larval digestive tract is essential to improving survival in hatchery reared larval fish. Identification of bacteria alone is insufficient, as the concentrations of key bacterial species may be important in determining survival. Here, we analysed bacteria, principally vibrios, in developing cod larvae from a Scottish hatchery. Six tanks of larvae were sampled weekly in parallel to monitor the microbial populations in larvae successively fed on rotifers and Artemia before weaning onto dry feed. When cod larvae were fed on rotifers the digestive tract microbiota was dominated by Ruegeria/Roseobacter, Pseudoalteromonas, and Microbacterium but when the diet was changed to Artemia over 90% of the microbiota consisted of vibrios. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis was used to identify the vibrios present and this showed that the microbiota was affected by changes in larval diet. Whilst feeding on Artemia, the larval digestive tract microbiota was dominated by Vibrio alginolyticus, but the population rapidly switched to one dominated by V. splendidus when larvae were weaned onto dry feed. Other Vibrio species were detected at lower levels at various times. During the survey, one tank experienced heavy mortalities associated with an elevated level of Vibrio anguillarum. The V. anguillarum isolates differed from those typically associated with mortalities in gadoid fish. Apparently healthy larvae from the tank experiencing heavy mortalities had a culturable microbiota almost equally represented by V. anguillarum and V. logei. Both species, as well as a V. splendidus strain isolated from turbot larvae, were pathogenic to cod larvae in laboratory experiments, and these vibrios could be targets for intervention to control the microbial flora of the larval digestive trac

Salinity effects on immune parameters of Ruditapes philippinarum challenged with Vibrio tapetis

The occurrence of brown ring disease (BRD) in farmed Manila clams Ruditapes philippinarum is seasonal. Development of the disease is believed to require the presence of the infective agent Vibrio tapetis and particular environmental conditions. This paper studies the effect of salinity (20 to 40‰) on measurable immune parameters of Manila clams, and the progression of BRD in experimentally infected individuals. At 20‰ salinity, the total haemocyte count was reduced and disease prevalence was highest. At 40‰ salinity significantly fewer clams presented signs of BRD, and this was correlated with increases in the total haemocyte count, hyalinocyte count, phenoloxidase levels and phagocytic activity of haemocytes. Inoculation of clams with V. tapetis did not have a significant effect on the immune parameters measured. Thus, this laboratory-based study relates environmental stress to disease development

The effect of temperature on the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) tail meat during storage

Abstract AimsGÇé The aim of the present study was to update and extend our knowledge of the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) under commercially relevant storage conditions in order to optimise handling procedures. Methods and ResultsGÇé Total viable counts were performed at different storage temperatures (0, 4, 8, 10, 12 or 16 -¦C) and after different storage times (1-7 days). Storage at 16 -¦C was found to be most detrimental and storage at 0 -¦C was found to be optimal. 16S-rRNA sequencing was utilised to determine the composition of the bacteria within the microflora. In this way Photobacterium isolates, especially P. phosphoreum, were identified as the main specific spoilage organisms (SSOs). The abilities to reduce TMAO and to produce H2S were analysed in a selection of bacterial isolates. The higher the incubation temperature during storage the more isolates were found to reduce TMAO and produce H2S. ConclusionsGÇé N. norvegicus possesses an unusually high initial microbial load when fresh. Storage temperature is the most crucial factor affecting microbial growth, microbial activity and spoilage potential in N. norvegicus produce. Spoilage can be attributed mainly to P. phosphoreum. Significance and Impact of StudyGÇé This study presents significant new findings with regard to the progression and causative agents of spoilage in N. norvegicus. Based on the results we can recommend that N. norvegicus tails should be stored in a 0 -¦C environment immediately after catch. Stored this way the growth and spoilage activity of the microflora may be reduced significantly and an extension of shelf life might be attained