Studies On Larvae Development Of Octopus Vulgaris And The Effects Of Environmental Stress On Larvae

Octopus vulgaris is widely distributed in the tropical and temperate waters of the world's oceans.It has delicious taste,rich nutrition and high edible value.due to its short life cycle and rapid growth,it has become the most concerned breeding object and research hotspot in cephalopods.However,due to environmental degradation and overfishing,the catch quantity of octopus was decreasing day by day,and the market demand for octopus was increasing,and artificial breeding and culture of Octopus vulgaris have just started.This research mainly focuses on the study of the developmental characteristics and growth patterns of Octopus vulgaris during its early development and the influence of environmental factors on its larvae,and provide technical support for octopus fishery resource conservation.In order to provide scientific basis for artificial breeding and improvement of Octopus vulgaris,the data of early growth and development were supplemented and improved.Here are the major achievements:To explore the growth and development patterns during the early period of Octopus v ulgaris,the morphological characteristics of larva,juvenile and young octopus of O.vulgari s under industrialized breeding conditions were observed and recorded.From hatching to 49-day-old,eight larvae were sampled randomly every two days,and total length,arm lengt h,mantle length,mantle width,body weight and sucker number in the longest arm were measured.In conditions of water salinity30~32 and temperature 18.6~26.0?,the average f ull length of the newly hatched larva was 3.05±0.11mm;the yolk sac of newly hatched la rvae could be absorbed by themselves before hatching or within 9 hours after hatching;th e 1-day-old larva began to feed and 17day-old larva could feed shrimp;at the age of 35days,the larvae were ready for benthonic living;the body color of 60-day-old larva chang ed from transparent to milky white;at the age of 80 days,the body color of larva is the same as adult;the organs of 100-day-old larva were mature except gonads and the morph ological characteristics were consistent with the adult.The results showed that o.vulgaris la rva(1-49 days of age)body weight exhibited a cubic function growth relationship with tota l length,the equation is y=5E-05x~3-0.0009x~2+0.0072x-0.0132;total length exhibited a linear ity growth relationship with arm length,the equation is y=-0.0012x~3+0.0492x~2+0.0243x+0.2179;total length(mm),body weight(g),arm length(mm),mantle length(mm)and mantle wi dth(mm)exhibited a cubic function growth relationship with days respectively,regression e quation:y=-0.0001x~3+0.0105x~2-0.0122x+3.0562,y=-2E-07x~3+4E-05x~2-0.0004x+0.0034,y=-0.0004x~3+0.0247x~2-0.1037x+0.8214,y=-0.0004x~3+0.0124x~2+0.0749x+1.4757 and y=-3E-05x~3+0.0025x~2+0.0354x+1.4026.We divided the early period of O.vulgaris into four development sta ges:larvae octopus,juvenile paralarvae octopus,juvenile benthonic of octopus,young octo pus.Each stage was determined by feeding style(endogenous or exogenous),morphologica l and biological characteristics and ratio between arm lengths and mantle length.The aim of the present study was to investigate the effects of different temperatures(9~33?)and salinities(12~45)on the survival and development of larva Octopus vulgaris.These experiments revealed the effects of abrupt and gradual changes of salinity on survival rate,specific growth rate,and weight gain rate.The results showed that abrupt salinity and temperature change had significant effects on larval survival rate,and after 48h,the survival of larva Octopus vulgaris exposed to salinity(27~39)were higher,more than 75%.The survival of larva at temperatures 18~27?were higher,more than 50%.Gradual change of salinity and temperature also had significant influence on survival rate,The survival of larva at temperatures 18~28?were higher,more than 50%and the survival of larva exposed to salinity(27~39)were higher,more than 75%,Surprisingly,the survival rates of larvae at 30 with different salinities were higher.Culture for 10 days at different salinity(24,27,30,33,36,39)and temperature(19?,21?,23?,25?,27?),The survival rates of larvae at salinity 27-36 and 30-33 were higher than 40%and 60%,respectively.The survival rates of larvae at 19-25 and 21-23 were higher than 30%and 50%respectively.Specific growth rate and weight gain rate were the highest at the salinity of 30 and 33.Specific growth rate and weight gain rate were the highest at the salinity of 25?and 27?,but the survival of 27?larvae were lower,about 12%.Taking the newly hatched Octopus vulgaris juveniles at test materials,this paper studied the impacts of starvation on the survival rate,behaviors,growth,and the effects of re-feeding after starvation on the survival rate and growth of the juveniles.The manipulative laboratory experiments were conducted with 0~5 days of starvation and 10 days of re-feeding to reveal the effects of re-feeding after starvation on the survival rate and growth of the juveniles.The results showed that starvation affected the survival rate,body shape,swimming behavior and digestive enzyme activities of Octopus vulgaris juveniles.On the 4th day of starvation,survival rates began to decline significantly,and juveniles experienced some abnormal behaviors,such as white body color,slow reaction and so on,and died completely on the 6th day of starvation.and so on.After the end of starvation and 10d re-feeding,the specific weight gain rate and specific growth rate of starvation 1-2d juveniles were not significantly different from the control group,but the survival rate was significantly different.The survival rate,specific growth rate and specific weight gain rate were significantly lower than those in the control group after 3 day of starvation.The point of no-return of the juveniles was the 3th day of starvation.These results could be helpful to the rational formulation of the feeding strategies for Octopus vulgaris cultivation.