THE EFFECT OF SALINITY ON THE INDUCTION OF SPAWNING AND FERTILIZATION IN THE STRIPED MULLET, MUGIL-CEPHALUS

Induced spawning was carried out in both 100% seawater (32-34 parts per thousand) and 50% seawater (15-17 parts per thousand). Spawning was induced at both salinities, suggesting that final maturation and ovulation can take place across the salinities tested (15-34 parts per thousand). However, the number of fertilized eggs obtained was significantly lower in the spawning conducted at 50% seawater. Initiation of sperm motility was also found to vary in response to variations in salinity. No motility could be initiated in salinities below 13.8 parts per thousand, initiation of motility was variable between 14-17 parts per thousand and above 17 parts per thousand motility was consistently induced. In addition, initiation of sperm motility was determined to be in response to a change in osmolality and not in response to changes in specific ions. From the results of the current investigation, a supply of 100% seawater is recommended for use during the spawning phase of the hatchery production of striped mullet.