Observation on morphological structure of the early development of Theragra chalcogramma

Abstract

The embryonic development pattern of walleye pollock and the morphological characteristics of fertilized eggs were observed and recorded from October to December in 2008.The egg diameters in six stages were measured and the egg envelopes of seven stages were also studied with scanning electron microscopy.The egg of walleye pollock was pelagic,without oil globules.The diameter was 1.45-1.58 mm,the incubated temperature was(6.3±1.24) ℃ and the salinity was 34 psu.The microscopic observation showed the fertilization tube opened with(4.33±0.31) μm pore diameter;the pore canals of the egg envelope were inconspicuous;the interval of micropyle and density of the pore canals of the egg envelope were(1.46±0.31) μm and 21.1-30.6/100 μm2 respectively.The micropyle with the micropyle canal was completely plugged with material at the 2-cell stage,and the fertilization pore diameter was(5.26±0.29) μm.The egg envelope contained less ruffles and the pore canals of the egg envelope became more prominent and the interval of micropyle was(2.04±0.35) μm.The density of the pore canals of the egg envelope was 14.7-20.3/100 μm2.After the closing phase of blastopore,the fertilization pore of egg presented the open state;few secretions were adhered to its periphery region.The diameter of the fertilization pore,interval of the pore canals and density of the pore canals of the egg envelope were(4.48±0.15) μm;(1.70±0.23) μm;and 23.59-27.53/100 μm2,respectively.Approaching the incubation period,the egg envelope had a rough surface,on which the pore canals were inconspicuous with a(2.56±0.22) μm interval and the density was 12.38-15.97/100 μm2.The diameter of egg,the fertilization pore,as well as the dynamic change of structure of egg envelope,were closely related to the embryonic development of Alaska pollock.The above indexes had great importance in improving the fertility rate of egg,facilitating the normal development and spread of egg on seabed,and preventing both polyspermy and bacterial infection during the egg development process.