| In order to produce better marine pearls, the growth, pearl performance, digestive enzyme activities, pearl-sac formation of two different sized Pinctada martensii were compared. The results were as follows.Four groups were designed in the present studies: A group, individuals (2 years old) with nuclei-operation; B group, individuals (2 years old) without nuclei-operation; C group, individuals (1 year old) with nuclei-operation; D group, individuals (1 year old) without nuclei-operation. Growth traits of the four groups were evaluated based on the measurement data at days 1, 3, 5, 10, 15, 20, 30, 60, 180, 270 after nucleus-inserting operation. Survival rate, pearl size and weight among the groups were also compared. The results showed that within the first month after nucleus-inserting, the net increase in the A and C groups was significantly lower than the control groups (B and D) (P<0.05), showing the surgery operation affected the growth of the species. At 30-60 days, the experimental groups (A and C) grew rapidly and had a compensatory growth phenomenon. A 1-60 days, the net growth increase of the one-year-old animals was significantly higher than that of the 2-year-old ones (P<0.05). Therefore the one-year-old oysters had a more rapid growth rate. At 60-180 day, when it was winter, the temperature of seawater was lower and the growth of oyster was slow. At 180-270 days, when it was between May and July, due with the excretion of gonad, the growth of oysters was slow, even negative.There were significant differences in mortality rates among the four groups. The mortality rates of the A, B, C and D groups were 18.8%, 5.2%, 12.7% and 2.7%, respectively. Nuclei retention rates of the C group (60.6%) were higher than the A group (47.9%). At 6 months after nuclei-inserting operation, pearl sizes of the one- and two-years old oysters were 5.019±0.532mm and 6.203±0.452 mm, respectively; pearl weight of the one- and two-years old oysters were 0.262±0.063g and 0.365±0.095g, respectively. Pearl weight of the one- and two-years old oysters were 0.262±0.063g and 0.365±0.095g, respectively. Pearl thickness of the one- and two-years old oysters were 0.308±0.032mm and 0.323±0.024 mm, respectively. At 9 months after nuclei-inserting operation, pearl sizes and weight of the C group were significantly smaller and the D group. The pearl sizes of the C and A groups were 5.221±0.478mm and 6.318±0.314 mm, respectively; Pearl weight of the C and A groups were 0.268±0.046g and 0.368±0.074g, respectively. Pearl thickness of the one- and two-years old oysters were 0.320±0.017mm and 0.356±0.007mm, respectively.We can conclude that more high quality of pearls can be obtained from the two-year- old oysters, while higher production can be got by the one-year- old ones.The activity of three digestive enzyme (amylase, cellulase, protease) from liver- pancreas of each group were measured and compared at days1, 3, 5, 10, 15, 20, 30, 60, after nucleus-inserting operation. The results showed the difference of the activity of digestive enzymes among the four groups (P>0.05). The activity of protease was much lower than those of amylase and cellulase. The activity of amylase and cellulase of two-year-old and one-year-old oysters after nucleus-inserting decreased and then increased, while the down-trend of the activity of protease was not obvious. The activities of digestive enzyme in the tested groups (A and C) were lower than the ones in the control groups (B and D). In addition, the activities of digestive enzyme of one-year-old oysters were slightly lower than the ones of two-year-old ones.The pearl sac of the one- and two-year old oysters was observed and compared through histological techniques at days 1, 3, 5, 10, 15, 20, 30 after the day of nucleus-inserting operation. The results showed that there were no evident differences between the one- and two-year-old oysters in the early stages of the pearl-sac formation. More columnar epithelial cells were observed at days 30 after nucleus-inserting operation, which had the same morphological characteristics as that of the two-year-old oysters at days 20. The epidermal cells of pearl sac of the two-year-old oysters had changed from the columnar epithelial cells into much more shorter columnar cells at days 30 after nucleus-inserting operation, which became the nacre secreting stable structure. |
PDF Full Text Request