Impact of Semen Dilution and Sperm to Egg Ratio on Fertilization Success in Snowtrout (Schizothorax richardsonii)

A study was conducted to know the optimum semen dilution and sperm to egg ratio on egg fertilization in snowtrout (Schizothorax richardsonii). During the present study, very high fertilization percentage (98.80 ±0.13%) was recorded with fresh undiluted semen (sperm concentration 3.59 ±0.12x108 sperm/ml) at sperm-egg ratio of 29.5 ±0.09x104:1. At 1:4 and 1:10 semen dilution, almost equally high fertilization rate (98.73 ±0.11% & 97.06 ±0.11%) similar to control was recorded. Our results on sperm-egg ratio reveal that approximately 18,600 motile sperm per egg are required to achieve ~90% fertilization rate, while 26,900 sperm are required for an egg to achieve ~97% fertilization rate at sperm motility rating 4 (>75 to 100% motility) in a semen sample. Sperm-egg ratio of 18,600 sperm–egg and 26,900 sperm–egg were obtained at 1:15 and 1:10 semen dilution (semen: extender) respectively, when its one ml sperm dilution was used to fertilize ~1200 eggs. It was observed that control and dilution ratio 1:4 are not significantly different (P ns, n=3). However, dilution ratio 1:4 is found significantly superior to all other dilutions of semen, viz. 1:10 (P