Changes in milt volume and sperm quality with time after an injection of recombinant Japanese eel luteinizing hormone in male Japanese eels

Fifteen males of the Japanese eel (9 as the Japanese eel recombinant LH (rLH) group and 6 as the 0.9% NaCl group), which had received 7 weekly injections of rLH (500 μg/kg BW/wk), were used in the experiment. Two days after the 7th injection, milt was collected until the males were spent just before an injection of rLH (500 μg/kg BW) or 0.9% NaCl solution. After the injection, the amount of expressible milt weight and its quality (percentage motility, the velocity of the sperm movement, and sperm density of the milt) were examined every 6 h until 48 h after injection (h AI). In the 0.9% NaCl group, the amount of expressible milt remained small throughout the experimental period. In the rLH group, however, expressible milt increased after 12 h AI and peaked at 18-24 h AI before decreasing thereafter. The total weight of obtainable milt from each male up to 48 h AI was 13.7 times more in the rLH group compared to that of the 0.9% NaCl group. The percentage motility of sperm increased after 6 h AI of rLH and was maintained at high values (> 60%) until 42 h AI. Thus, a large quantity of high-quality milt was transported at 18-24 h AI from the testes to the sperm duct for storage when treated with rLH. Because female eels that have completed egg yolk formation release eggs within 13 to 14 h after the administration of a maturation-inducing steroid (MIS), the administration of rLH as the final shot for males should be given at 6 h before the MIS injection to females for the effective induction of spontaneous spawning.