| Via experimental ecology, morphology, microanatomy, marine aquaculture, in vivo and in vitro techniques approaches, and using ovarian index, proportion of spawning females, time to ovarian maturation, times of spawning frenquency, spawning time interval as main indicators of quality of spawns, this study aimed to explore the effects of exogenous5-HT and eyestalk ablation on the reproductive performance of the Marsupenaeus japonicus. The findings of this study would provide theoretical guidance to healthy, safe and sustainable development for aquaculture industry, and would contribute basic data to the study of shrimp reproductive ecology and shrimp genetic and breeding. The main results were as follows:1^(1) As an experimental treatment,5-HT solution was injected into domesticated M. japonicus at50ug/g body weight and15ug/g body weight. All the5-HT injection females reached the spawning condition (P<0.05), the injection of15ug/g and50ug/g of5-HT demonstrated that the amount of eggs increased by57.26%and85.22%, respectively. The increases of nauplii amount were64.02%and102.53%, respectively. The results suggests that injection of5-HT at50ug/g BW is more effective in inducing ovarian maturation and spawning in female M. japonicus broodstock, compared to the injection of5-HT-injected at15ug/g BW (P<0.05).For5-HT injection at50ug/g, with4-day intervals (day1,5and9), the neurotransmitter was applied for once, twice, third, respectively. The highest amount of eggs per spawn, fertilization rate and number of nauplii per spawn showed that3times5-HT injection was more effective than any other groups (P<0.05). Spawning occurred5times within12days in3times5-HT injection treatment. Additionally, the amount of eggs and the amount of nauplii produced per spawner also increased by104%and103%in3times5-HT injection treatment, respectively. The hatching rate of the3times5-HT injection treatment, however, declined slightly.(2)5-HT solution was ingested by domesticated M. japonicus at50ug/g body weight and15ug/g body weight.5-HT induced ovarian maturation and spawning at both dosis tested, generating more spawnings at50ug/g B W compared to that at15ug/g BW (P<0.05). The amount of eggs and the amount of nauplii produced per spawner were also increased by101.97%and188.19%in the ingestion of50ug/g of5-HT, respectively. For5-HT ingestion treatment at50ug/g, with4-day intervals (day1,5and9), the neurotransmitter was applied once, twice and3times, respectively. The result showed that the amount of eggs per spawn, hatching rate, fertilization rate and number of nauplii per spawn of the3times5-HT-ingestion treatment were higher than other treatments (P<0.05)(3)5-HT solution was permeated into domesticated M. japonicus at50ug/g body weight and15ug/g body weight and ovarian maturation and spawning were recorded. All of the5-HT permeating treatment females reached the spawning condition (P<0.05). The ovarian maturation and spawning of the5-HT permeating treatment at15ug/g BW increased insignificantly, while those of the treatment at50ug/g BW increased significantly. The amount of eggs and the amount of nauplii produced per spawner increased by107.91%and103.86%in the5-HT permeating treatment at50ug/g BW, respectively. In the case of5-HT using frequency, the amount of eggs per spawn, fertilization rate and number of nauplii per spawn of3times5-HT permeating treatment were higher than other groups (P<0.05). The hatching rate of the3times5-HT permeating treatment, however, declined insignificantly.(4) Under the same conditions, the5-HT injection,5-HT ingestion and5-HT permeating treatment groups had a comparable performance in their effects on development of ovarian maturation.5-HT induced ovarian maturation and spawning at three treatments, generating most spawnings at3times5-HT ingestion at50ug/g animals. The amount of eggs produced in each spawn was (69.49±4.12)×104, and the amount of nauplii produced was (38.96±1.16)×104, increasing by217.45%and268.31%, respectively. The finding that3times5-HT-ingestion at50ug/g treatment produced highest amount of eggs than others also suggests that the former could maintain its reproductive capability to a longer period. 2、Compared with the control group, the eyestalk ablation treatment induced a sooner and a higher rate of maturation and spawning. The number of hours to reach ovarian maturation is calculated from the beginning of treatment (eyestalk ablation) to the first spawing event. It was ahead of106hours by eyestalk ablation treatment M. japonicus.128.93hours of the spawning interval was cut down. The amount of eggs produced by eyestalk ablation treatment group increased by159.78%, the amount of nauplii increased by192.72%.3、The effects of combined5-HT ingestion and eyestalk ablation on M. japonicus maturation and spawning quality, compared to single eyestalk ablation or single5-HT-ingested (P<0.05) were evident. The amount of eggs and the amount of nauplii of5-HT ingestion treatment alone increased by202.06%and306.15%. The amount of eggs and the amount of nauplii of eyestalk ablation treatment alone increased by208.83%.On the other hand, the amount of eggs and the amount of nauplii of5-HT ingestion and eyestalk ablation combined treatment increased by259.45%and368.25%, respectively. The effects of the eyestalk ablation and the5-HT ingestion treatments differed insignificantly (P>0.05), although the effects of the latter group was higher. The amounts of eggs and the amounts of nauplii of5-HT injection and eyestalk ablation combined treatment increased by57.89%and62.10%, respectively. These results demonstrated that5-HT injection and eyestalk ablation combined treatment, in M. japonicus, stimulated ovarian maturation, spawning and the release of maturation promoting pheromones, induced a sooner and a higher rate of maturation and spawning.4、In vitro study showed that:With regard to treatment A consisted of ovary with two dosis of5-HT, the result showed that the5-HT could increased M. japonicus oocyte diameter insignificantly. Treatment B made up of ovary with single optical or brain or thoracic ganglion, no statistical differences were found. Treatment C consisting of ovary and optical with brain or thoracic ganglion also had no statistical differences, but it induced the increasing of oocyte diameter. While in treatment D, which consisted of ovary, brain and thoracic ganglion, the diameter of oocyte was the biggest (0.2665±0.047), and was bigger than any other treatment groups significantly. In female M. japonicus, in vivo study indicated that5-HT had no direct stimulation over the ovary development. By affecting the secretion of the brain and the thoracic ganglion,5-HT had stimulation over the ovary maturation. The activity in the optical was hardly affected by the5-HT used. |
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