Factors responsible for successful chilled storage of unfertilized rainbow trout (Oncorhynchus mykiss) eggs

A series of 7 experiments was conducted to explore suitable conditions for storing of unfertilized rainbow trout eggs in a chilled state. The eggs were stored in small vials at a temperature of 2 ± 1 °C. The factors studied were: duration of storage, number of egg layers, weight of eggs and the provision of aerobic conditions. Indicator of success was the proportion of eggs reaching the eyed stage when inseminated with cryopreserved semen. The outcome of the first 3 experiments indicated that, if eggs are stored two layers deep, for up to 10 days the best results will be obtained under an atmosphere of air. For large quantities of eggs stored several layers deep, and for extended periods of time (up to 20 days), pure oxygen proved to be more suitable. It is, however, advisable to not exceed a storage depth of 4 layers. The physical weight of the eggs stored up to 9 layers deep exerted no detrimental effect (Experiment 4). With increasing storage time, pH and oxygen concentration in the samples decreased, indicating intensive metabolic activity on the part of the eggs. The correlation coefficient between oxygen concentration in coelomic fluid and its pH was r = 0.76 (P < 0.001) (Experiment 5). Attempts to supply oxygen to the eggs by gassing the coelomic fluid with air or oxygen, proved to be less effective than the provision of a suitable gas atmosphere. Nevertheless, the fertilization rates in aerated samples were slightly better than in the non-aerated controls (Experiments 6 and 7). The outcome of this series of experiments supplies a number of clues that will prove useful for the establishment of storage conditions that will permit holding and shipping of unfertilized rainbow trout eggs for extended periods while retaining an acceptable level of fertilizing capacity. Follow-up experiments will have to show to what extent the present findings will hold under practical conditions with batches of 1000 eggs or more.