Abstract:This paper describes a design for the structure of the net mouth of the two-panelbottom rope trawl, the method calculating the lengths of the headline, footrope andhanging line, and the rigging technics. According to the different working conditions between the headline and footrope,the following formulas are adopted. The headline (assuming the parabolic form): y =a₀x²; s=integral from x₁ to x²(1+y'~3)~(1/2)dx The footrope (assuming the catenary form): y=a/2(e~(x/a)+e~(-x/a)); s=a/2(e~(x/a)-e~(-x/a)) Where y-rope length; x-horizontal distance; a,a_0-parameter; s-headline orfootrope length The rigging technology for the headline, footrope and hanging line was designedin accordance with the characteristics of China's bottom trawl. It has been proved thatthe design and rigging described above are useful.

Abstract:1. The microsporidiosis was found on Priacantus tayenus from the Beibu Wan inNan Hai of China. The gonads were heavily infected by the parasites which renderthe majority of the fish lost their reproductivity. 2. The pathogenic agent of this disease is found to be a new species of the genusPlistophora and is here named Plistophora priacanthicola. The spores are ellipsoidalto shape the anterior end is narrower than the posterior end. The size of the spores: length 5.45 (4.9-60)μ, width 3.14 (3.1-3.3)μ; lenthof the polar filament 80-429μ. It resembles somewhat to P. longifillis, P. ovariae, P.oolytica and P. mirandellae, but differs from them in large size of cysts. 3. The infective rate of the parasites increases with the age of the host andthere is no variation with the sex and seasonal changes.

Abstract:"Xiang-yu" or the Ayu (Plecoglossus altivelis T. et S.) is one of the deliciousfood fishes. The present paper deals with the results on observation of the its reproduc-tive biology in Fuxi Stream, Zhejiang, during the years from 1979 to 1980. The results are summarized as follows: All individuals of one year old attain sexual maturity. The developmental processesof the gonads are quick. The ovary develops to stage Ⅱ in July, and attains to stageⅣ till middle September. The absolute fecundity varies with body length as wellas body weight, ranging from 10,659 to 65,156 eggs, average 30, 135. The relativefecundity is on an average of 730. 26. per gram. In the early September the adult fishes begin to migrate to the spawning ground.The breeding season of the Ayu in Fuxi Stream is from October to December, butthe main Spawning activity takes place between middle October to early November.The time of spawning prevails usually from sunset to early morningat about 6 a. m. The spawning grounds is situated at the brackish water region where the depth ofwater varies from 25 to 35 cm, with gravel and sand bottom and running water. Thewater-temperature is about 21-14μ, and the salinity varies from 0.5 to 8.5‰. Theeggs are adhesive and sink down to the bottom. Each female fish released eggs two or three times in a breeding season. Afterspawning most of the parents died.

Abstract:The mortality of the Pohai Sea prawns in autumn has been estimated with avariety of methods. After mating, male prawns die in large numbers. We have found that undersome assumptive conditions the mating mortality of male prawns may be estimated withsex ratio. The results are Iisted in table 2. The mating mortality is about 0.65 in lateOctober. The accumulative value of mating mortality of male prawns is about 1.05 inesrly December. The total mortality of Pohai Sea prawns have been estimated. The results are asfollows. The catch in number per month and catchpereffort as indices of abundanceare regressed against time to calculate the total mortlity. For ten-day average in 10years is about 0.25 for femals 0.34 for mals, and that in 12 ysars about 0.23 forfemals 0.34 for mals. Now we assume that the natural mortality of female prawns maybe negligible in comparison with its fishing mortality, then the total mortality of femaleprawns is approximately equal to its fishing mortality which is about 0.25 per ten-dayperiod in about 800 standard unit of fishing effort. Therefore the catchability is equalto 3.125×10^-4. After discussing the relationship between mortality and fishing effort, we confirmthat when fishing effort is less than 1000, fishing mortality varies with effort, andwhen fishing effort is greater than 1000, the increase in effort has little influence onfishing mortality. The fact shows that there is a certain limit, being about 0.3perten-day period to fishing mortality with regard to the prawn fishery in the autumnfishing season.

Abstract:The problem of rational size of "seedling" at the time of stocking is of growingimportance as lake fisheries develop. During 1973-1978,more than fifteen million fishof different sizes were stocked into lake Dong Hu, in which 86% were silver (Hypo-phthalmichthys molitrix) and bighead carps (Aristichthys nobilis). Studies have beencarried out on the growth and rate of recapture of those fish stocked in 1973. Observa-tions were also made on the characteristics and the time of formation of annuli on thescales so as to obtain scientific basis for determining the rational size of "Seedling" atthe time of stocking. The fingerlings or yearlings on which the growth estimatim are in three differentsizes, namely 11. 5-13. 0 cm (from Zhejiang province), 13. 3-16. 3 cm (fingerlings,reared locally) and 16.6-23.1 cm (yearlings, and locally). 482 individuals weresampled. Distinctions were drawn from the continuation and discontinuation of circuliand by the number of radii of apical part of the scales. The results obtained are asfollows: 1) Annuli formation on scales of silver and bighead carps fingerlings begin inApril. The main charateristics of annuli are the arrangement of circuli from dense tosparse and their continuation and discontinuation. 2) The annuli growth in body length and weight of the fingerlings take placefrom April to late October, the growing season lasts for seven months, with the peakin August. 3) Within the same length group, the growth of bighead carp is more rapid thanthat of silver carp. 4) The growth rate and recapture rate of fingerlings of the three size groups areentirely different. The larger the size at the time of stocking the higher the growthrate and recapture rate. In view of the above results, it is recommended that the rational size of fish atthe time of stocking should be raised to 16.5-23.1cm.

Abstract:The artificial rearing of mussel spats has already been employed for productivepurpose. Scale of production is steadily expanding and the yearly output and numberof crops harvested are also increasing steadily. At present, it is estimated that a smallscale productive operation would call for as many as 5×10~9 to 1×10~(10) healthy eggs.So it is imperative that the understanding on breeding habits and the techniques governing the collection of mussel eggs should be thoroughly grasped. In Qingdao we use in spring the various stimuli, including air-drying, mechanicalshaking, byssus drawing, temperature raising and by stimulating the reproductive cellsof opposite sexes, etc. to induce the mussels to ejaculate. Of these, water temperatureraising seems the most favorable and highly effectite (table 1).Usually 60% to 100%of the individuals eject. In autumn, however, this method usually worked not so well as in spring unlesssome natural prerequisites would be satisfied such as a fall of temperature and rainingduring the springtide period ect. (Table 2). Nevertheless, a better result could beattained by lowering the temperature as a stimulus. The parent mussels at first werereared in the artificially flowing sea water of low temperture (8-12℃) for 8-10hours and then put back to the sea water of normal temperature (18℃). Under suchconditions 40% of the individuals could be induced to eject. Experiment conducted on more than 9400 mussels showed that among the 1.5and 2-year-old mussesls the sex ratios of male and female in ejection were 54.4% to45. 6%. This was not perfectly agreed with the sex ratio in natural population. (10) The quantity of eggs collected from the different age groups and in differentseasons, differs greatly. The average number of eggs collected from the 2-year-oldmussels was about 8 million pieces. The ratios of eggs collected among mussels of 1-year-old, 1.5-year-old and 2-year-old were approximately as follows: 1: 4.3: 16.9(Table 5). Mussels of the same age group produced more eggs at the time shortlybefore the reproductive season than in the blooming stage of the reproductive season orin its later stage (Table 6). The 1.5-year-old autumn mussels produced more eggsthan the spring mussels, which have passed through twice the growing period of"spring-summer-winter" (Table 5,6). Based on the above findings, we were enabled tomake out a more reasonable program for theacollection of mussel eggs on a productiveseale.

Abstract:The experiment artificially gynogenetic fries of Carassius auratus auratus (redvariety) and the naturally gynogenetic ones of Carassius auratus gibelio, at the thirdday after hatching, were administered orally with methyltestosterone (MT) at fourdifferent concentrations: 25μg, 30μg, 50μg and 100μg per gram of diet. The dailyhormone diet, at about 7% as weight of the fry, was divided into two parts to feedat a. m. and p. m. This process was continued for 90 days and thereafter,the hormone-treated fry lived on a normal diet until they reached the stage at which sexingwas possible by laparotomy. The results of experiment were as follows: 1. the fries treated, with MT 25μg orMT-30μg hormone diet, developed into males except one having a gonad of ovotestis. 2.no males appeared by treating with MT-50μg or MT-100μg hormone diet. 3.60-84.6%gynogenetic fries of both kind of fish developed into males while they were daily fedwith the diet mixed with 95% crude alcohol (oneml per gram of diet) for a period of90 days. 4. the gynogenetic fry of the both sexes were fed with a normal diet onlythey all developed into females.

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Abstract:This paper presents the results of studying the life history of perinereis aibuhi-tensis Grube and the morphology of the mature maternal body for the purpose offinding an artificial cultivation method. Artificial fertilization was performed under the temperature at 27℃ in the seawater. The course of the embryomic development is summarized as follows.

Abstract:13 surveys on causal plankton of red tides were made from April to October 19T9in Dalian iTan. It revealed that the biomass of SkeLetanema castatem (Greville) Clovereached a coxicentration more than10⁴ cells/rnl in 5 surveys, while the hiornass of DactyliosoLera mediterraa Peragallo, Mesodisziwm rurxcm (Lohnzann) and Prorocen-tram micrcas Ehernberg reached more than 103 cells/ml in few surveys and morethan ten. species of common red tide causal organisms were also observed.

Abstract:this paper deals with analysis of the red tide of Triclodesrzi in Dong Hai of China.,1972. The red tide was caused by species of Cyanaphyres,eviz Trclaadsm.iwmhiTdedti Gomant, Trichodesmium thibau.ii CTomont, Trirh.octesmizm tryh.PaumEhr. The dominant species was Tricociesmium hiZdehrrrrcitiz Clvruont. Intensive redtide was found in the area of in August AfterSeptember the area of distrivutivn of red tide expanded, and the center still is locs,tedin the same place. The located area was the food base of machercis, scads and. otherfish was damaged obviously by the red tide. The hioms of zoaplankton was decreasedrapidly and the migration route of mackerels and scsds was shifted, Thonlrh death offish did not happen, the red tide caused heavy drop of catch of m;ickere.ls and scalds,and in August no fish has been caught, The uptvelling eused by stronger cyeloniv vortex in summer 1972 arid continue-ing strong typhoons were nia,jvr factors for the formation of the red tide Besides, theappearance of high temperature in water provided favourtble condition for the bloomingof these tropical algae.