Effects of ovarian fluid on motility characteristics of rainbow trout (Oncorhynchus mykiss Walbaum) spermatozoa

Summary The objective of this work was to determine sperm motility characteristics in rainbow trout (Oncorhynchus mykiss Walbaum) (nine males) and assess the motility enhancement potential of ovarian fluid of nine females in order to test gender effects on sperm motion. Spermatozoa motility characteristics were obtained using computer-assisted sperm analysis (CASA). Ovarian fluid enhanced sperm motility and this was not attributed to the percentage of motile sperm in the samples but rather to the speed and trajectory of movement. For example straight-line velocity (VSL) increased from 32.3 to 85.8 μm s−1 and amplitude of lateral head displacement (ALH) decreased from 20.11 to 10.25 μm. Some females produced ovarian fluid with clearly different sperm motility-enhancement capacity. Furthermore, spermatozoa of some males performed differently regardless of the origin of the ovarian fluid. These data indirectly suggest the existence of cryptic female choice in rainbow trout.