Storage of unfertilized eggs of rainbow trout (Oncorhynchus mykiss) in artificial media

Unfertilized eggs of rainbow trout (Oncorhynchus mykiss) were stood in coel omic fluid and in Cortland medium (devoid of bicarbonate and phosphate), wh ich was buffered with 20 mM Hepes (4-(2-hydroxyethyl)-1-piperazineethanesul fonic acid) or Tris-HCl (Tris hydroxymethyl aminomethane hydrochloride) and adjusted to a pH of 8.5. Eggs stored in these solutions for 24 and 48 h, w ere fertilized using sperm derived from 4-6 males. The sperm was applied in a dilutant (127 mM NaCl, 20 mM Tris-HCl, pH 9.5). The percentage of embryo s reaching the eyed and hatching stages was recorded as an index of fertili ty. Unfertilized trout eggs stored for 48 h at 12-13 degrees C in Cortland medium buffered with Hepes or Tris exhibited the same fertility as eggs fer tilized prior to storage. In fact, the percentage of embryos reaching the e yed stage was significantly greater in eggs stored in the modified Cortland solutions than in eggs stored for the same amount of time in coelomic flui d. It appears that fertility may be better in eggs stored in Cortland mediu m containing Hepes than in medium containing Tris. Since serine protease in hibitors have been shown to enhance fertility of goldfish eggs, the effect of a soybean trypsin inhibitor on egg fertility was investigated. Trout egg s stored for 24 h in Cortland medium containing 2.0 mg soybean trypsin inhi bitor/ml were almost completely infertile. Eggs stored in modified Cortland medium and fertilized in the direct presence of soybean trypsin inhibitor (0.01 mg/ml sperm dilutant) exhibited the same percentage of eyed and hatch ed embryos as eggs stored in Cortland medium alone, This suggests that the inhibitor did not directly block fertilization but had an effect during sto rage. The results indicate that modified Cortland medium can be used for th e storage of trout eggs for at least 2 days. Furthermore, washing and stora ge for a short time in this medium may actually enhance the fertilization o f the eggs of some females. (C) 2000 Elsevier Science B.V. All rights reser ved.