Intraspecific variability in several isolates of Philasterides dicentrarchi (syn. Miamiensis avidus), a scuticociliate parasite of farmed turbot.

Research on intraspecific variation in ciliates is scarce, and in scuticociliate parasite of fish, virtually nonexistent. In this study, seven isolates obtained from turbots affected by scuticociliatosis in different parts of the Iberian Peninsula (northwest Spain and southwest Portugal) were morphologically and genetically characterized to investigate the intraspecific divergence in these amphizoic ciliates. The isolates were stained with ammoniacal silver carbonate and examined in an optical microscope; all were found to have the typical morphological characteristics described for Philasterides dicentrarchi (syn. Miamiensis avidus). Sixteen biometric characteristics of the seven isolates were used in a canonical discrimination analysis (CDA) to select a subset of those that best identified each isolate. Discriminant analysis indicated that the OPK3 width, length of the PM2, length of the buccal field, the body width, L:W ratio, the body length, the OPK1 width and the distance between OPK2 and OPK3 were the most important morphological variables for discriminating the isolates. The first three canonical functions accounted for 86% of the total variance. The scatter plots of the first two canonical variables grouped and separated the P. dicentrarchi isolates into five clusters. Flow cytometry analysis of isolates also indicated intraspecific polymorphisms among P. dicentrarchi isolates. Nuclear markers (a 349-bp and a 390-bp fragment of 18S rRNA and ß-tubulin genes) and a 398-bp of the mitochondrial cytocrome oxidase subunit I (Cox1) gene were then used to investigate the intraspecific genetic variation in P. dicentrarchi. Haplotype analysis and neighbour-joining phylogenies of nucleotide sequences of seven isolates revealed a high degree of intraspecific genetic variation among the isolates. Analysis of Cox1 and ß-tubulin genes revealed six haplotypes (and clusters) in both cases; however, analysis of the 18S rRNA gene revealed only two haplotypes. The results show clear intraspecific variation at morphological and genetic levels in the scuticociliate P. dicentrarchi, and verify the suitability of mitochondrial (Cox1) and nuclear (ß-tubulin) genes for detecting intraspecific genetic variation within populations of scuticociliates that infect cultured turbot. The existence of this intraspecific variation must be taken into account in the design of an effective vaccine to control scuticociliatosis.

The activity of several components of the innate immune system in diploid and triploid turbot.

The use of triploid fish may be of interest in research, e.g. study of how this condition affects the size and activity of cells. In addition, triploid fish are sterile and production of triploids in fish species that are marketed after reaching sexual maturity may be of economic interest. In the present study, the effects of triploidy on the activity of several components of the innate immune system of turbot (Psetta maxima L) were determined. Triploid turbot had bigger cells (erythrocytes and neutrophils) but the number of blood erythrocytes, leucocytes and thrombocytes was lower than in diploid fish. The differential cell count was similar in both types of fish. The respiratory burst and the phagocytic activities were higher in neutrophils of triploid turbot. However, because the number of neutrophils was higher in diploids, the total respiratory burst activity and the phagocytosis per microliter of blood was similar in both types of fish. No differences were found in serum complement, lysozyme or bactericidal activities. The results indicate that the activities of the humoral components of the innate immune system tested are similar in diploid and triploid fish and that the lower leucocyte number found in triploids is compensated for by higher cell activity.