Suitability of a semipermeable membrane to cap storage vials for rainbow trout (Oncorhynchus mykiss) eggs

Successful storage of rainbow trout (Oncorhynchus mykiss) eggs is dependant upon several factors including the oxygen pressure of the atmosphere under which they are stored. On the other hand, transportation of eggs in uncovered containers is impractical. The present experiment was designed to test if closure of storage vials with a semipermeable membrane ("BioFolie 25", Sartorius, Goettingen, Germany) will allow the eggs to survive. Freshly stripped unfertilized rainbow trout eggs from 3 to 5 year old females were stored 2 or 4 layers deep in vials either uncapped or capped with BioFolie at a temperature + 2degreesC under a moisture-saturated oxygen atmosphere for up to 30 days. To control bacterial growth, antibiotics at a concentration of 125 IU penicillin and 125 mug streptomycin per g of eggs and coelomic fluid were added. Batches of eggs were fertilized with uniform frozen-thawed semen after either 0, 15, 20, 25 or 30 days of storage. Freshly collected eggs served as controls. The fertilization and hatching rates were expressed as percent of controls. The percentage of eyed eggs was taken as indicator of fertility. The experiment was conducted with five replications. Fertility of the eggs declined significantly during storage (P < 0.05). However, fertilization rates around 50% were achieved up to 20 days of storage. Thereafter fertilization rates dropped sharply, reaching levels below 10% by day 30. No significant difference in fertility of eggs was observed between treatments and number of layers over the storage period with the exception of eggs stored for 30 days where there was a slight, though significant reduction in fertility of eggs stored in uncapped vials vs capped vials (P < 0.05). Either dehydration, despite the humidified gas atmosphere supplied, or an enhanced metabolic rate due to excessive exposure to oxygen may serve as explanation. Thus, the results show that the capping of egg-containing vials with BioFolie is possible without impairment of fertility in eggs stored for extended periods of time.