بررسي تاًثير دما ، شوري و دروه نوري در القاء رسيدگي جنسي و رفتارهاي توليد مثلي كرم نرئيس (Nereis diversicolor)

The effects of temperature, salinity and photoperiod on sexual maturity and concomitant reproduction behavior in Nereis diversicolor

Nereis diversicolor worms were collected from the Anzali lagoon during the years 2004- 2006 using Van Veen grab sampler with a surface area of 400cm2. Water salinity, temperature and total organic matter (TOM) of sediments in the sampling region was determined. The worms were maintained in 0.5 tons (lxlm2) tanks until they reached a weight of 200-300mg. Sexual maturity in the samples was attained at 4-6°C and spawning occurred at approximately 16°C. The first gametes were observed after the temperature increased from 6 to 16°C. Sexual maturity was studied at various salinities (0.5, 5, 12, and 15 %o). Results indicated that the worm attains sexual maturity at salinity 15%o in a shorter period as compared to other salinities. No significant differences were observed between sexual maturity attained at salinities 12 and 15%o (P>0.05). The effect of light and photoperiod in synchronizing reproduction in male and female N. diversicolor was also studied. We observed that reproduction behavior in adult worms increased for a period of one week at the end of each month after they were exposed to a prolonged photoperiod (L:D 16:8) followed by a period of dim light. Mature males crawled around outside the tubes in search of a female. In the presence of a mature female, the males released sperm directly in front of the female tube. Soon after, there was an increase in the activity of the females which showed intense ventilation movements. The female worms with their eggs already released began to carry the sperm into their tube. The ripe females nearby which had not yet laid eggs in their tubes released their gametes a few minutes after the male and began to carry sperm into their tubes. The fertilized eggs remained inside the tube protected by the female. The benthic larvae developed fast, feeding on the mucus and microbial film on the tube wall. After 10 to 14 days, larvae began to leave the tube. A few days later the females died.