Chilled storage of walking catfish ( Clarias macrocephalus) semen

Abstract

The aim of the present study was to determine changes in sperm quality of walking catfish ( Clarias macrocephalus) during its spawning season, and develop a simple and efficient protocol for the chilled storage of semen at 4 °C. Semen samples were evaluated monthly during April–November in 2006. Percentage of spermiating males and sperm motility peaked during the middle of the spawning season, June–September. Sperm density and seminal plasma osmolality increased significantly ( P < 0.05) throughout the spawning season, while semen pH did not change during this period. The effects of extender, dilution ratio and timing of chilled storage on successful storage period of extended semen were examined during the years 2006–2007. Fresh semen was diluted 1:1 with several sperm extenders, calcium-free Hanks' balanced salt solution (Ca–F HBSS), Hanks' balanced salt solution (HBSS), extender 7 (NaCl 5.780 g, KCl 2.558 g, CaCl 2·2H 2O 0.103 g, NaHCO 3 0.235 g, MgCl 2·6H 2O 0.220 g, pyruvate 6.0 g, citric acid 0.100 g, HEPES buffer 2.380 g in 1000 mL distilled water), extender 13 (NaCl 8.760 g in 1000 mL distilled water), and modified Cortland, in tissue culture flasks. Longest successful storage period of sperm was 10 days with Ca–F HBSS. Semen diluted with Ca–F HBSS at 1:1, 1:2 or 1:4 ratios significantly lengthened ( P < 0.05) the storage period over those at dilutions of 1:9 or 1:19. To determine the effect of season on the success of chilled storage, semen diluted with Ca–F HBSS at a ratio of 1:4 was prepared at three sampling intervals in the beginning (May), middle (August) and end (November) of spawning season in 2007. Extended semen prepared in August remained motile (20 ± 3.1%) for as long as 10 days, whereas those prepared in May or November were immotile on days 9 and 7 of storage, respectively. Extender-preserved semen was capable of fertilizing eggs as efficiently as fresh semen within two days of storage. A significant decrease in fertilization and hatching rates of extender-preserved semen compared to fresh semen on days 4 and 6 was due to low sperm motility. These results demonstrate that semen of walking catfish can be stored for short term at 4 °C without appreciably affecting motility and fertilization.