Rainbow trout (Oncorhynchus mykiss) sperm extender protocols can differ considerably with regards to composition of the extenders and handling. The objective of this study was to determine the effect of pH for 5 extenders on rainbow trout sperm motility and activation during storage at 5°C. Two-year-old sexually mature rainbow trout males (n = 46) weighing 1.5 to 2.5 kg were caught at Aquaculture Farm Tatakay in Jilotzingo, Estado de México, México. One semen sample per male was collected by abdominal massage. For the experiments, 100 mL of each extender (306, 512, Mounibs, Erdahl and Graham, and Hanks’ Balanced Salt Solution) was made, with pH adjusted to 6 levels (7.0, 7.2, 7.4, 7.8, 8.0, and 8.2). To evaluate pH dynamics in each extender, pH was tested daily over an 8-day storage interval. Trout sperm was added to each of the extenders in a ratio of 1:1 and motility recorded. Afterwards, each activator solution [DIA 532, saline solution (0.85%) and pond water] was added separately to a sample of the extended sperm, to initiate sperm activation. Motility was evaluated subjectively at 400× and monitored until ~99% of the sperm stopped moving (on average, in 40 s). A one-way ANOVA was used and statistical differences were set at α < 0.05. Extender 512 activated sperm motility when pH was >7.4, whereas extender 306 activated motility at every pH. Hanks’ Balanced Salt Solution activated motility at very low percentages for various pH levels, whereas Mounibs and Erdahal and Graham solutions did not activate motility for any pH tested. The 512 extender with a pH of 7 performed best (P < 0.05) as a storage solution, producing a sperm motility of 54% after activation using DIA 532. These results demonstrated the importance of evaluating effects of sperm extender pH over both short- and medium-term storage.
Effect of pH on rainbow trout (Oncorhynchus mykiss) sperm motility using five extender solutions