Yersinia ruckeri infection activates local skin and gill B cell responses in rainbow trout.

Teleost fish lack organized structures in mucosal tissues such as those of mammals, but instead contain dispersed B and T cells with the capacity to respond to external stimuli. Nonetheless, there is still a great lack of knowledge regarding how B cells differentiate to plasmablasts/plasma cells in these mucosal surfaces. To contribute to a further understanding of the mechanisms through which fish mucosal B cells are activated, in the current study, we have studied the B cell responses in the skin and gills of rainbow trout (Oncorhynchus mykiss) exposed to Yersinia ruckeri. We have first analyzed the transcription levels of genes related to B cell function in both mucosal surfaces, and in spleen and kidney for comparative purposes. In a second experiment, we have evaluated how the infection affects the presence and size of B cells in both skin and gills, as well as the presence of plasmablasts secreting total or specific IgMs. The results obtained in both experiments support the local differentiation of B cells to plasmablasts/plasma cells in the skin and gills of rainbow trout in response to Y. ruckeri. Interestingly, these plasmablasts/plasma cells were shown to secrete specific IgMs as soon as 5 days after the exposure. These findings contribute to a further understanding of how B cells in the periphery respond to immune stimulation in teleost fish.

Subjective and objective assessment of fish sperm motility: when the technique and technicians matter.

Fish sperm motility is nowadays considered the best sperm quality biomarker in fish, and can be evaluated both by subjective and computerized methods. With the aim to compare the precision and accuracy of both techniques, fish sperm samples were assessed by subjective methods and by a computer-assisted sperm analysis (CASA-Mot) system, and simultaneously by three different technicians with different degrees of expertise on the sperm quality analysis. Statistical dispersion parameters (CV, coefficient of variation; and RG, range) were estimated in order to determine the precision and accuracy of the techniques and the influence of laboratory staff on sperm motion assessments. Concerning precision, there were not much significant differences between the technical support staff (high, medium, and low experimented technician), and statistical dispersion parameters were quite similar between them independent of the technique used and the sperm motility class analyzed. However, concerning accuracy, experimented technician reported subjective motility values very closed to the values provided by the CASA-Mot system, only 10 percentage points away from the data provided by a CASA-Mot system. However, medium and low experimented technicians often overestimate the CASA-Mot values, and amplitudes up to 30 percentage points were detected in several sperm assessments. To sum up, both the technique (subjective or objective) and the technician (degree of expertise) became key factors in order to reach accurate motility estimations, so the use of both qualified staff and novel CASA-Mot systems seems to be a critical requirement for obtaining satisfying results in fish species with similar motility patterns.

Using specific recombinant gonadotropins to induce spermatogenesis and spermiation in the European eel (Anguilla anguilla).

New specific European eel (Anguilla anguilla) recombinant gonadotropins (aarGths) produced in the ovarian cells of Chinese hamsters (CHO) were used to induce maturation in captive male eels. In the first experiment, five different hormonal treatments were assayed: one group was given a constant dose of recombinant European eel follicle-stimulating hormone (aarFsh; 4 µg/fish) for 9 weeks, and the second group received a constant dose of recombinant European eel luteinizing hormone (aarLh; 2 µg/fish) also for 9 weeks. The other three groups were injected with different combinations of both aarGths (some doses constant, some variable). All five treatments stimulated androgen synthesis, but the increase was more pronounced in the fish treated with a combination of both aarGths. Unlike aarLh, aarFsh alone was able to induce spermiation, the best results were achieved in the fish that were treated with a constant dose of aarFSH and an increasing dose of aarLH, with spermiation being induced (20% motile cells) despite the fact that these fish were immature at the start of the experiment. In order to improve sperm quality, a second experiment was performed. Immature males received three constant doses of aarFsh (2.8, 1.4 or 0.7 µg/fish) and increasing doses of aarLh (every 3 weeks; 1, 2, 6 µg/fish). All the treatments induced spermiation, however the best sperm quality (with ≥50% motile cells) was observed in the males treated with the highest dose of aarFsh. In conclusion, these specific recombinant gonadotropins have demonstrated their capacity to induce spermatogenesis and spermiation in vivo in a teleost fish, the European eel.