A Rudimentary Study On The Early Life History Of Three Marine Economical Teleosts

Marine economical finfish aquaculture formed the fourth wave of Marine Aquaculture in China,acquired obvious economic value and social value,push Chinese marine aquaculture.However,during the development of marine aquaculture,there have some unresolved problems,especially the critical periods during the course of larval culture,still a obstacle hinder the stable and healthy development our Chinese marine aquaculture industries.The key element of the marine finfish aquaculture is fingerling production with good quality and high survival rate.However,due to the abundant biodiversity of fish,we must modify our protocol in order to supply relevant species with the most suitable technology. At last,the data obtained from morphological and histological observation must be used in direction of the practical works.The early life history of three important economical marine finfish in northern China (hybrid flounder,barfin flounder and Japanese parrotfish) were described the microscope observation and histological study,and further explained the emerged reasons,inner mechanism and relevant protocol of critical periods during larval early ontogeny.The concrete results are as below:1.Barfin flounder:as a cold water flatfish,the early developmental characteristics is:①The eggs were devoid of oil globule,and semi-pelagic feature;the asynchronous cleavage advanced,occurred on the third cleavage stage.The size heterogeneity between blastomeres was obvious.It had a long incubation time,under the temperature of 8±0.3℃,and salinity of 33,it took 9 d to hatch a larvae from the fertilized eggs.The different embryonic stage of barfin flounder had varied resistance to temperature and gastrula stage was sensitive to temperature.②It also had a long period from hatching to feeding,under the temperature of 8-10 ℃,and salinity of 33,the larvae began exogenous feeding on circa 8-9 dph.A dot melanin on the beak was the main feature when the larvae fed.The yolk-sac disappeared on 14 dph.The special black-brown striped bars were seen at the posterior period of post-larvae stage.③The goblet cells occurred on the posterior region of pharynx cavity and the anterior region of esophagus,and the gastric glands differentiated on 29 dph, metamorphosis began at 30 dph.During the early life stage,abundant acidophilic granules on the rectal epithelium indicated the protein-absorbing ability of the larvae intestine.④The first lymphoid organ was head kidney,then thymus and spleen,which was different to the most marine teleosts.Besides head kidney and spleen,thymus also formed the MMCs.The MMCs in spleen was most abundant.2.Hybrid flounder:as a hybrid of Japanese flounder and summer flounder-the same family,its early developmental characteristics is:①Under the temperature of 15.4～16.0℃,the embryos of hybrid flounder took 76 h to hatch,before the blastopore closure stage,the embryo first formed the optic vesicle and kuffer's vesicle,then forming somites.Before hatching,the embryoic tail and nose never touched in egg membrane.②The larvae began to feeding on 4 dph,and the yolk-sac & oil globule disappeared on 5 dph & 10 dph,respectively.The intervals of metamorphosis in hybrid flounder is longer(34-60 dph),and the emergence of the crown-like larval fins was not evident like its maternal flounder,however,the numbers of larval fins were 7-8.③Through the histological observation,the gastric glands of digestive system appeared later,and the developmental duration of the gastric glands was also slower comparison with its maternal flounder.The increment of the thyroid follicles was not evident,the pale color and fewer numbers.During the early ontogeny of the hybrid flounder,no evident indicated the differentiation of anlage of swim bladder.3.Japanese parrotfish:as a warm water species,lithophilic teleosts,the early developmental feature is: ①fertilized eggs:The yolk was segmented,and acts as a feature of fish egg classification.②The newly-hatched larve:The melanin on the larval dorsal finfold in the newly-hatched larvae,moved from to the edge of the larval dorsal finfold,and disappeared on 3 dph.This phenomenon indicated the special ontogenetic characteristics of this species.③post-larvae:The thickness of muscular tissue in intestine increased quickly during this period,and the gut evacuation rised abruptly,at the same time,the mortality rate rise up,and we resolved this problem by the means of changing the routine feeding pattern.During the juvenile stage,the jaw teeth of Japanese parrotfish fused into two whole teeth plates,which was a normal feature of Oplegnathidae.④some secreting cells were found in the thymus during the larval development, which usually were found in some lower finfish,like salmonids.Through our studies,the numbers of secreting cells in rainbow trout was fewer than Japanese parrotfish,and its arrangement was also devoid of orderliness.MMCs was also normally found in the hemopoietic organs-spleen and head kidney,also found in the parenchyma of liver, pancreas and swim bladder,which usually occurred in elasmobranch fishes and few in teleosts.