Background. Salmonid spermatozoa are characterised by a very short time of activity in the water, therefore sudden water pollution in the form of increased salinity on the spawning grounds may have a negative effect on the sperm motility parameters, thus affecting the subsequent egg fertilisation and, consequently, the number of hatched individuals of the species. The aim of this study was to determine the effect of water salinity on the motility parameters of spermatozoa of brook trout, Salvelinus fontinalis (Mitchill, 1814). Materials and methods. Sperm motility was monitored with a camera (Basler A312fc) coupled with Nikon Eclipse 50i light microscope from the moment of their activation (contact with water) until the cessation of movement. The following water-salinity treatments were tested: 1.0‰, 3.0‰, 5.0‰, and 10.0‰. The motility parameters: VCL, VSL, VAP, ALH, BCF, LIN, STR, WOB, and MOT, were analysed with Computer Assisted Sperm Analysis (CASA). Results. The mean values of the studied motility parameters of the brook trout spermatozoa (obtained within 30 s), whose activation took place in the water of 0.35‰ salinity and in water of 1.0‰ and 3.0‰ salinity, did not differ significantly. The highest mean values of motility parameters were recorded for the water of 5.0‰ salinity.  The 10.0‰ treatment caused a distinct decrease in the values of all the studied parameters. The percentage of MOT was the highest (37.5%) in the sample activated in the water used for fish rearing (0.35‰). In the remaining samples the MOT was lower, and in the water of 10.0‰ salinity it was only 9.1%. No spermatozoa movement of any kind was recorded in the 35th second of the experiment. Conclusion. The values of the motility parameters as well as the percentage of motile spermatozoa (MOT) in the semen decrease with increasing salinity of the water used for activation, and with increasing time of exposure.

sperm quality, CASA, salinity, brook trout, Salvelinus fontinalis