Effect of Temperature on post ovulated oocyte quality maintenance in female rainbow trou, oncorhynchus mykiss

ABSTRACT

Effect of temperature on the duration of post ovulated oocyte quality maintenance in abdominal cavity of female rainbow trout, Oncorhynchus mykiss, was assessed to determine suitable time of stripping. Egg quality measurement was done through assessing the eying and hatching rates of eggs. Regarding the best temperature range reported for salmonid brood fish in breeding season [3-10 C] the study was undertaken in two temperatures of 2 +/- 0.5 C and 8 +/- 0.5 C. In each of the noted temperatures, 15 female brood fish were used as 15 replicates and stripped 5 times. Time interval of each two spawnings was 7 days. Results indicated that temperature has a significant effect on the suitable time of stripping. When the temperature increased from 2 C to 8 C, the optimum eyeing and hatching rates were transferred from second week to the first one. Also, eyeing rate was decreased from 83% for the fifth treatment at 2 C to 3.6% at 8 C. The same trend was observed for the hatching rates. The decrease of post ovulatory suitable stripping time from 30 days in 2 C to two weeks in 8 C, shows the role of temperature on egg quality maintenance and confirms that the increase of water temperature in optimal living range, shortens the suitable post ovulatory time of stripping. This time duration estimated at least 21 DPO at 2 C and 14 DPO at 8 C. Also the time needed for overripening of the eggs estimated more than 224 Degree-Days. So the time duration of post ovulated oocyte quality maintenance in abdominal cavity of female rainbow trout is highly dependent on water temperature