Effects of pH on sperm motility in several Salmoniformes species: Oncorhynchus mykiss, Salvelinus fontinalis, Salmo trutta, Salmo salar and Thymallus thymallus

Abstract

In this study we investigated the effect of pH (range 5.5–10.5) on sperm motility of rainbow trout (Oncorhynchus mykiss) and other fish species from family Salmonidae: brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), Atlantic salmon (Salmo salar), and grayling (Thymallus thymallus). Video recordings of sperm motility were analyzed using Hobson Sperm Tracker. Since urine contamination of milt was suspected to modulate motility, the effect of pH on rainbow trout spermatozoa was re-evaluated with the use of semen collected with a catheter. Spermatozoa of all the species except for rainbow trout were characterized by a broad pH range for the motility. At a pH of 5.5, motile sperm was observed for both brook trout and brown trout, 31 and 38%, respectively. For rainbow trout spermatozoa collected by stripping, no motility was observed at pH 7.0 and below. On the contrary, when sperm from rainbow trout was collected using a catheter we observed motility at low pH values. Our results demonstrated that salmonid spermatozoa can be motile in a wide range of pH values, including the acidic range. Our results suggest that urine contamination significantly affects pH-dependence of sperm motility activation in fish.