The Basic Biological Studies On The Artificial Reproduction Of Octopus Ocellatus

Octopus ocellatus′Gray,1849μis widely distributed along coastal areas of the WestPacific Ocean, with Amphioctopus fangsiao as a synonym. As one of the most importanteconomic species in the northern coast of China, it is widely favored by consumers forits delicacy and rich-nutrition, which provides a promising future for the development ofoctopus market. With the traits of short life span and extremely rapid growth, it is also aideal species for aquaculture, enhancement and releasing. However, little research hasbeen carried out on the artificial reproduction of this species now.This research mainly focuses on the basic biological aspects of the O.ocellatus,which utilize gonad development, embryo development, hatchling development andrearing as its mainstay throughout the artificial reproduction process. It provides boththeoretical basis and reference data for fishery management, artificial breeding andculture of O.ocellatus, and eventually promotes the development of cultureindustrialization. Here are the major achievements:1. A total171samples of O.ocellatus were collected monthly in Qingdao fromDecember2011to November2012. The weight, mantle length, gonad somatic index andreproductive tract parameters of samples were analyzed for both sexes. The gonaddevelopment was defined by means of histological method, nine stages of the oocytedevelopment during oogenesis were found, and ovary and testis maturity scale both withfive stages were proposed (immature, developing, maturing, mature, spent). Thematuration status and dominated germ cell types of O.ocellatus in monthly variationwere also presented. The seasonal changes showed that O.ocellatus in the coast ofQingdao had the traits of fast growth, a short life cycle, and reproducing once in its lifetime and then dying. Its reproductive cycle can be divided into four periods with thebreeding period focused in summer. Males became sexually mature at a smaller sizethan females, indicating that the mating behavior occured early and sperm storing in thefemale oviducal glands before fertilization and spawning.2. Effect of temperature and salinity on the survival and food intake status ofparents, hatching rate, egg length, survival activity index(SAI) was studied. The resultsshowed that the survival and food intake of parents O.ocellatus was a vital role for hatching. When temperature at20, the highest number of hatchlings was obtained,and the number decreased with the temperature increased; while above29, hatchingwas failed. When salinity below24, hatching was hardly accomplished; when at28, thehighest number of hatchlings was acquired; above that, the amount decreased with thesalinity increased. The growth of egg length accompanied with the hatching process,especially dramatic increase in the later stage. The SAI of O.ocellatus was mainly10.2~19.6, with the highest at35.5, which indicated the strong vitality of O.ocellatushatchlings.3. With the help of mathematical statistics method and conducting indoorincubation experiment under controlled temperature, we studied the biological zero(C),effective accumulated temperature(K) and temperature coefficient(Q10) for theembryonic development of O.ocellatus and the correlation between the embryonicstages(Ts) and effective accumulated temperature(K). We got the results that thebiological zero(C) for the embryonic development of O.ocellatus was5.15, theeffective accumulated temperature(K) at which the zygotes develop into early juvenileswas589.45d, and the optimum hatching temperature ranged from19.46to23.06. We compared the linear regression method with Single Sine method, whichwas using to simulate the accumulation of the effective accumulated temperature, theresults had no significant differences with the effective accumulated temperature hadbeen inferred. The effective accumulated temperature (K) was a fixed value for zygotesdevelop into any representative embryonic stages under different temperature conditions.There was a significant linear correlation between the embryonic stages (Ts) and theeffective accumulated temperature (K): K=26.72Ts+55.34(R2=0.996).4. The effect of temperature and salinity on the survival and growth status ofO.ocellatus hatchlings was studied. The results showed that the optimum temperature ofnewly hatchlings was18~25, the most was21and the optimum salinity was28~30.The benthic hatchlings tolerance to temperature was better than newly hatchlings, butthe maximum temperature shall not exceed25. The impact of salinity on growth wasnot significant, and the salinity should remain stable at around30.5. The effect of different ages, different food densities, different light intensities,different diets, and different time periods on the feeding behavior of O.ocellatushatchlings was studied. The results showed that2~3days newly hatchlings, in thedensity of0.1Artemia/mL, in the condition of dark or shimmer, using Artemia or shrimp as prey, in the period of evening, respectively led to the highest number of activeindividuals and feeding behavior occurrence. The impact of different prey combinationson weight and survival of hatchlings was also studied. The results showed that mixedfood (Artemia, copepods, shrimp) had the best effect on newly hatchlings, and shrimpwith fresh shellfish meat was the best for the benthic hatchlings.