REPRODUCTIVE-CYCLE AND FECUNDITY OF THE DATE MUSSEL LITHOPHAGA-LITHOPHAGA (BIVALVIA, MYTILIDAE)

The reproductive cycle and fecundity of the date mussel Lithophaga lit hophaga, L. a well-known, edible species has been examined. Sexes are separate and the mean number of eggs per each gonad is 1.894 x 10(6) /- 1.044 x 10(6) S.D. Reproduction first occurs at an age of 2(+) year s and al a shell length greater than 0.9 cm. Gonad activity is annual and is observed at all ages. The sex ratio for individuals up to 7 cm is 3:1 in favour of the males, whereas it becomes 1:1 for individuals greater than 7 cm. The release of gametes by males and females occurs almost simultaneously and begins immediately after a decline in the hi ghest water temperature (less than or equal to 27 degrees C), an incre ase in salinity (> 31 parts per thousand) and a decrease in the dissol ved oxygen (6.5 ppm). Small percentages of mature individuals appear d uring the first winter months thus lengthening the reproductive period . This phenomenon is attributed to the temperature difference in deepe r waters, the delay in gamete release by young individuals, tide, wave action and changes in salinity. The fecundity of Lithophaga lithophag a is high because its life-cycle is adversely affected by environmenta l factors such as waves and tides. Fecundity increases with shell leng th, more so with total wet weight and mainly with the age of the anima ls. Summer seems to be the suitable season to exploit the date mussel of shell lengths > 5 cm.