| The objectives of this study were to establish a standard procedure for identifying fish eggs, undstand the biological characteristics of early development of walleye pollock Theragra chalcogramma, carry out ecological investigation of ichthyoplankton. First, this paper reviews the research advances at home and abrad on the dentification methods of fish eggs, the main developmental events occurred at each stages of early development, and the ecological investigation on fish eggs and larvae. Section A, identification methods of fish eggs. The fish egg information system is developed for identifying fish eggs. The software consists of three application modules. There are identifying modules, analyzing information on fish eggs species, and data of fish eggs. The software not only can identify fish eggs, but also can help to understand the biological characteristics of the eggs in the Bohai Sea and Yellow Sea. Section B, biological and experiment ecology studies of early development of walleye pollock. We focused on the main developmental event occurred on early stages of walleye pollock. Section C, ichthyoplankton surveys. The carried out in waters over the in the Huludao sea of 2009 and two artificial reef area in Laizhou bay in 2010, the preliminary analysis of environmental factors on category composition and distribution patterns of ichthyoplankton were discussed. Section A: identification methods of fish eggs-Fish egg information systemTraditional morphological method still is a commom method to identify fish eggs.The work would be time consuming; otherwise, many species of fish within a group show overlapped distributions and spawning periods, their eggs are morphologically similar so it is difficult to distinguish them. The study try to combined identifying fish eggs with mordem computer technology, developing fish egg information system.The data base of the systerm contains the species and biological characteristics of the eggs of osteichthyes in the Bohai sea and Yellow sea, 65 species, Clupeiformes have 12 species, Scopelifornes have 4 species, Anguillifornes have 1 specie, Beloniformes have 3 species, Mugiliformes have 3 species, Perciformes have 24 species, Scorpaeniformes have 7 species, Pleuronetiformes have 13 species. The system is divided into three parts. The first part is for identification. Once the egg's known characteristics, including water of emergence, season of emergence, size of egg, structure of oolemma, structure of yolk, amount of fat balls, size of fat balls, etc., are input into corresponding dialog boxes, the species could be identified. The second part analyzes the information of the egg. The characteristics of the egg, such as the attributes of egg, shape of egg, structure of oolemma, structure of yolk, etc., could be obtained through observation, thus narrowing the scale of the egg's species. The third part is a database of egg, from which the features of a few species of egg could be directly browsed; the database could also be further supplemented and perfected as information of newly-discovered species inputted. Though the database of egg needs improvement and its relevant functions need further development, the database has a high potential of development and application depending on its simple and practical method of operation.Section B: Biological and experiment ecology studies of early development of walleye Pollock.In order to know the embryonic development patternof walleye pollock Theragra chalcogramma, the morphological characteristics of fertilized eggs were observed and recorderd by Nikon SMZ1500 photomicroscope equipped with amicrometer ocular lens at the laboratory from October to December, 2008. Moreover the diameter of eggs in six development stages were measured and the egg envelop surface of 7 development stage were studied with scanning electron microscopy. Eggs of walleye pollock were pelagic, and semidemidemersal with none of oil globlule in diameter of 1.45~1.58mm. With the incubated temperature 6.3±1.24℃, salinity 34 psu, the blastoderm formed at 1 hour post fertilization(hpf); blastula stage at 24hpf; early germ ring stage at 61hpf; the segmentation period began at 134hfp. Heart begins to beat with a dosage of 161hfp, and the egg starts its incubation after the dosage rises to 319phf. During the whole development process, the diameter of Alaska pollock's egg increases gradually. The microscopic observation shows that, the micropyle of Alaska pollock falls into the category of PatterⅡ, which has flat vestibule while longer duct. When unfertilized, the fertilization tube remains open with pore diameter of 4.33±0.31μm. The oolemma contains more ruffles; cinclides of the oolemma are inconspicuous; interval of the micropyle measures 1.46±0.31μm; density of the cinclides of the oolemma is 21.1~30.6 /100μm2. During the second life span of egg, the diameter its fertilization pore measures 5.26±0.29μm; the oolemma contains less ruffles; cinclides of the oolemma become more conspicuous comparing to those in unfertilized stage; interval of the micropyle measures 2.04±0.35μm; density of the cinclides of the oolemma is 14.7~20.3 /100μm2 . After the closing phase of blastopore, the fertilization pore of egg presents the open state; a few secretion is adhered to its periphery region; the diameter its fertilization pore measures 4.48±0.15μm; interval of the cinclides measures1.70±0.23μm; density of the cinclides of the oolemma is 23.59~27.53 /100μm2. Approaching the incubation period, the fertilization pore of egg presents the open state; a few secretions are adhered to its periphery region; the pore diameter measures 4.48±0.15μm. The oolemma has a smooth surface, on which the cinclides are inconspicuous. Interval of the cinclides measures 2.56±0.22μm; density of the cinclides of the oolemma is12.38~15.97 /100μm2. The diameter of egg, the fertilization pore, as well as the dynamic change of structure of oolemma, are closed related to the embryonic development of Alaska Pollock. Also, the above indexes have impartment meaning 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's development process.Section C: Ecological investigation on egg and larvae A: Species composition and distribution of ichthyoplankton in the coastal waters of Huludao in 2009The species composition and distribution of ichthyoplankton surveys were carried out in the coastal waters of Huludao during May, August, October and December 2009. It was found that 44 eggs and 79 larvae of 13 taxa were collected during this period. Twelve taxa were as species, belonging to 11 genera, 10 families, 6 orders. Two sole fishes were only identified as family. The preponderant species were Thrissa kammalensis, Hyporhamphus sajori, Callionymus beniteguri. In spring, a total of 5 eggs and 8 larvae were captured. The occurrence frequencies of eggs and larvae were 25% and 33.33% in the horizontal tows. The average density were 24.272 ind/100m3 and 38.835 ind/100m3 in the horizontal tows. In summer, total of 36 eggs and 71 larvae were captured. In the vertical tows 31 eggs and 47 larvae were captured, and in the horizontal, 5 eggs and 24 larvae were captured. The occurrence frequencies of eggs and larvae were 100% and 66.67% respectively in the vertical tows, 20% and 73.33% in the horizontal tows. The average density of eggs and larvae were 4.463 ind/100m2 and 6.767 ind/100m2 respectively in the vertical tows, 17.934 ind/100m3 and 86.083 ind/100m3 in the horizontal tows. In autumn and winter, 2 eggs and 1 egg were captured only in the vertical tows. The occurrence frequencies of eggs were 10% and 25%, the average density of eggs were 0.259 ind/100m2 and 0.324 ind/100m2. Further analysis showed that four seasonal ecological groups could be distinguished and the warm-water species, warm-temperate species and the cold-temperate species appeared alternately in different seasons. The average community index (H′,D,J′) of the egg and larvae were low during the spring, autumn and winter, which were also lower than that in the summer. The result indicated that the community structure of ichthyoplankton was relatively stable; the diversity index of species and the uniformity of interspecific distribution in summer was relatively higher than any other seasons. The category composition and distribution patterns of ichthyoplankton in the Liaodong Bay estuary changed evidently from 1998 to 2009.B: Species composition and distribution of ichthyoplankton in the Laizhou Bay and Zhuwang aera in ZhaoYuan in 2010Five investigations were conducted at two artificial reef areas(hereinafter referred to as ZY and ZW) in the shallow waters of Laizhou Bay respectively on May, July, August, October, and November in 2011. During the investigations, the Shallow-water I Trawler Plankton Fishing Methods were applied in both horizontal and vertical directions. The investigations aim at the composition of species and quantitative distribution of egg and Larvae within this region. Results showed that, 16,115 eggs, 2,455 larvae, and no juvenile fish were collected by the five voyages of investigation (total sum of horizontal and vertical fishing).The collected is analyzed and identified to be composed of 19 species, which belongs to 7 orders, 15 families, and 19 categories. Altogether there are 6 species from Clupeiformes and Perciformes respectively, 3 species from Pleuronectiformes, 2 species from Mugiliformes, and respectively 1 species from Belonidae and Scorpaeniformes. Callionymus kitaharae occupies the dominated status among eggs of both areas during May; Thryssa kammalensis and Sphyraena pinguis jointly constitute the dominating species in the area of ZY during July. Among larvae, Sphyraena pinguis occupies the dominated status and thus solely constitutes the dominating species. Among eggs in area of ZW, Engraulis japonicus and Sphyraena pinguis jointly constitute the dominating species; Hyporhamphus sajori occupies the dominated status among larvae. During August, Thryssa kammalensis, Coilia mystus, and Sphyraena pinguis jointly constitute the dominating species; Sphyraena pinguis has the highest dominance among larvae. Engraulis japonicus and Sphyraena pinguis jointly constitute the dominating species; Hyporhamphus sojori solely occupies the status as dominance species. In respect of geographic location, the two reef areas occupy diverse positions in the same bay. The area of ZW locates at the bottom of Laizhou Bay, while the area of ZY locates at the east coast. Considering the composition of species, quantity of individuals, Margalef Richness Index (D), Shannon-Wiener Diversity Index (H′), and Pielou Evenness Index (J′), the fish plankton-type community of ZW is relatively steady. Analyzing in accordance with seasonal variation, the species, quantity, as well as the average value of Margalef Richness Index (D), Shannon-Wiener Diversity Index (H′), and Pielou Evenness Index (J′) of eggs and Larvae, of both reef areas generally stay at higher level throughout July and August, and peak in July. The analytical results indicate that, the biological diversity of eggs and larvae within the two reef areas of Laizhou Bay is, taken as a whole, of higher level. The analytical results indicate that, the biological diversity of eggs and larvae within the two reef areas of Laizhou Bay is, taken as a whole, of higher level. The analytical results indicate that, the biological diversity of eggs and larvae within the two reef areas of Laizhou Bay is, taken as a whole, of higher level. From the species of eggs and larvae within the reef areas, the ecotype of adult fish could be perceived; also, the ratio of species of upper and middle level and bottom level and nearly-bottom level is 1.2:1, thus is a close ratio. It is thus clear that artificial reef has certain attraction effect on species of both upper and middle level and bottom level and nearly-bottom level. It is a slow process to apply artificial reef on the protection of fish plankton and even the ecological environment of the whole reef area, and the potential environmental effects requires long-term investigation and research to test and verify. |
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