| Octopus sinensis is one of the major economic species in the southern waters of China,and was often regarded as the same species with Octopus Vulgaris from the Mediterranean Sea and the Atlantic Ocean.However,owing to the differences in external characteristics and molecular biology,Octopus sinensis has been named as Octopus sinensis(O.sinensis).Octopus sinensis has short growth cycle,fast growth rate,high food conversion rate and large spawning capacity.At present,octopus is mainly cultured by cage culture after capturing wild seedlings,and artificial breeding technology is just in its infancy.In this paper,according to the problems found during the breeding of Octopus sinensis seedlings,the hatching rate of fertilized eggs is low when hatching without parental care,and the newly hatched young octopus are prone to delayed feeding.Provide scientific basis for Octopus sinensis breeding and improving seedling breeding methods.The main results are as follows:In order to investigate the artificial incubation period of fertilized eggs of Octopus sinensis,fertilized eggs in the 8 developmental stages of A,B,C,D,E,F,G and H were disposed in the sieve basin according to the following methods: each cluster of eggs was separated by 3～4 cm(control group);the cluster was separated by 3～4 cm,and washed every 1 hour by bottle-washing eggs(group 1);bunches of eggs were placed tightly in the sieve basin(group 2);bunches of eggs were placed tightly in the sieve basin,and the eggs were washed with bottle washing(group 3)at 1 hour interval every day.The fertilization hatching rate of the eggs was calculated.The juveniles hatched at the F,G and H periods of the parental care(control group)and the juveniles that were incubated separated from the parental care at the F,G,and H periods(treatment group)were reared in a 20 L bucket and fed Artemia nauplii to comparate the 7-day survival rate of larvae hatched between artificial incubation and parental octopus protection.The results showed that when the fertilized eggs developed to the E stage(16 days after incubation,the embryo began to appear about 5～8 light red pigment spot),the newly hatching larvae were obtained by artificial incubation from the female parent.When the development to G stage(maternal care incubation 20 days,fertilized egg string is gray),the best artificial incubation effect was observed in the fertilized eggs from maternal care at whose H stage(23d incubation,the fertilized egg strings were gray brown in color),99% of hatching rate was found in the fertilized eggs from maternal care.However,the membranes were early breaken when the fertilized eggs were removed due to the stimulation of external environment,with the survival rate of only 11.7% at 7 days.In the process of artificial incubation,there was significantly higher hatching rate in sparsely arranged egg strings was than that in closely arranged egg strings.Under the same density,the hatching rate was significantly increased by blowing and washing egg strings,but the effect of blowing and washing egg strings on the hatching rate was gradually decreased as the hatching date approached.In order to investigate the effects of different brine shrimp densities on the growth,development,survival rate and initial feeding rate of octopus during delayed feeding,the same batch of hatched octopus were selected.After 0 days,1 day,2 days,3 days and 4 days of starvation,the larvae were placed in the bucket with the density of 0.5ind/ m L,1 ind/ml,1.5 ind/ml,2.0 ind/ml and 3.0 ind/ml,respectively.The initial feeding rate,10-day survival rate and growth status of octopus were observed.The results showed that the initial feeding rate of octopus increased with the increase of brine shrimp density during delayed feeding,but there was no significant difference(P>0.05),the increase of brine shrimp density had no effect on the time node of PNR emergence;In the delayed feeding process,the 10-day survival rate of octopus increased with the increase of brine shrimp density.When feeding with 0d delay,the survival rate,lm and wrist length at 10 days at 0.5 ind/ml and 1 ind/ml were significantly lower than those at 3.0 ind/ml(P<0.05);After 1d delay,the survival rate,equator width,wrist length and total length at 10 days at 0.5 ind/ m L and 1 ind/ m L were significantly lower than those at 1.5 ind/ m L,2.0 ind/ml and 3.0 ind/ml(P<0.05);The 10-day survival rate of octopus was very low or 0 at all densities when feeding was delayed for 3d and 4d.Therefore,in order to ensure the survival of octopus,it is recommended to only collect octopus from the upper and middle layer of water with good clustering,and to increase the density of brine shrimp at 1.5 ind/ m L in the early feeding process.In order to explore the changes of digestive system histology and digestive enzyme activity of the newly hatched larvae of O.sinensis during the starvation process,a single-factor starvation experiment was performed on the same batch of larvae hatched with membranes.After 0d,1d,2d,3d,and 4d of starvation Samples were taken to detect enzyme activity and tissue sections were prepared.The results showed that: in the process of starvation,the activities of trypsin and pepsin showed a trend of first increasing and then decreasing.The enzyme activities reached the maximum after1 d of starvation,and reached the minimum value after 4d of starvation.There was a gradual upward trend.On the 4d,the activities of trypsin and pepsin in the satiety group were significantly higher than those in the starved group(P<0.05).Under the starvation state,the lipase activity first decreased and then increased,and the lipase activity was the highest on the 4d and was significantly higher than that in the satiety group(P<0.05);the amylase activity showed a trend of first decreasing and then increasing,decreasing to a minimum after 1d of starvation,then gradually increasing,and reaching a maximum value after 4d of starvation;The enzyme activity first increased and then decreased.After 3d,the amylase activity of the young octopus reached the maximum value,and then began to decrease.At the 4d,the amylase activity of the satiety group and the starved group were similar.In the observation of tissue sections,it was found that in the normal liver tissue of the larvae,the hepatocytes were larger,with obvious boundaries and loose arrangement.With the prolongation of the starvation time,the cell boundaries became blurred.Shrinkage and irregular arrangement of cells;with the prolongation of starvation time,the intestine and stomach of larvae will atrophy to varying degrees,and the intestinal and stomach atrophy is obvious at 2d～3d of starvation,which can indirectly explain that the irreversible point appears at 2～3d.By analyzing the change trend of enzyme activity,the change of liver size and the change of liver tissue structure,it was found that in the process of starvation,the O.sinensis mainly chooses the fat in the body for energy supply. |
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