LENGTH FREQUENCY ANALYSIS OF PLEURAGRAMMA ANTARCTICUM,ELECTRONA ANTARCTICA,PROTOMYCTOPHUM BOLINI

British Antarctic Survey(BAS)data collected near the Antarctic Peninsula area were used in this1988/1989 study on the length frequency of three Antarctic fish species(Pleuragramma antarcticum,Electrona antarctica and Protomyctophum bolini)showing that the standard length(SL)of P.Antarcticumranged from 26.0 mm to 161.0 mm,that the 26.0 mm to 54.0 mm SL juveniles could be considered tobe the age group 1 fish,and that the SL of E.antarctica ranged from 39.4 mm to 89.7 mm for themales and 48.0 mm to 118.0 mm for the females,which may contain at least 6 age groups.This ismore than previously thought.P.Bolini had 29.2 mm to 60.2 mm SL and complicated age com-position.     

Using otolith weight to predict the age of <Emphasis Type="Italic">Pennahia macrocephalus</Emphasis> in the mouth of the Beibu Gulf

The relation between otolith weight (OW) and the age of marine fish is studied. A total of 222 individuals of bighead white croaker, Pennahia macrocephalus were sampled seasonally in the mouth of the Beibu Gulf, the South China Sea, in 2007. Since there are no significant differences in sagittal OW between otolith in pairs (P≥0.05), the undamaged left sagittal otolith is used for age determination. The highest correlations among standard length, OW and fish ages are confirmed by linear, exponential and multinomial regression. Results show that sagittal OW overlaps only occasionally among age groups, and to individuals with similar standard length, the older and slower-growing fish has a heavier otolith because of the continued otolith material deposition. There are differences in sagittal OW among different age groups and significant positive linear relationship with age (P<0.05). The age readings can be verified by plotting the sagittal OW versus the standard length for age groups, and the individuals with similar standard length but in different ages can be separated by sagittal OW frequency analysis. Mostly, the predicted ages using the regression between sagittal OW and ages are closed to the observed ages by counting annulus on scale. It indicates that the sagittal OW analysis is a useful technique for validating the accuracy of age determination by annuli counts, especially for individuals of similar size. Furthermore, the technique is applied for Pennahia macrocephalus with discussion in this paper. Supported by the National Natural Science Foundation of China (No. 30771653) and Bureau of Fisheries, Ministry of Agriculture     

Serum immunoglobulin of the mandarin fish, Siniperca chuatsi with development of polyclonal antibody

Serum immunoglobulin from the mandarin fish, or the so-called Chinese perch,Siniperca chuatsi (Basilewsky), was successfully purified using affinity chromatography. Heavy and light chains were detected on electrophoresis gel, with molecular weights being estimated at 72 and 29 kDa, respectively. The tetrameric IgM ofS. chuatsi was calculated to be 808 kDa. The rabbit polyclonal antisera against the purifed immunoglobulin were developed and tested by Western blot analysis. The antisera reacted strongly with the heavy chains ofS. chuatsi immunoglobulin. Humoral immune responses of the mandarin fish can then be examined using the developed polyclonal antibody. Project No. 30025035 supported by NSFC, State Key Laboratory of Freshwater Ecology and Biotechnology (2000FB02), and the Chinese Academy of Sciences (KZ9511-B1-111).     

ENCLOSURE EXPERIMENTS ON AND LACUSTRINE PRACTICE FOR ELIMINATING MICROCYSTIS BLOOM

Microcystis bloom, one of the most objectionable characteristics of eutrophication in tropical and subtropical waters, occurred in Donghu Lake (East lake) of Wuhan every summer from the 1970s up to 1984, but from 1985 up to now failed to occur there. The cause of its disappearance rema-ined in obscurity until recently. In situ enclosure experiments in the lake for three years showed that the stocking of the filter-feeding silver carp ( Hypophthalmichthys molitrix ) and big-head carp (Aristichthys nobilis ) played a decisive role in eliminating Microcystis bloom from the lake; but that recurrence of the bloom is possible under certain conditions. This paper presents the details and the results of enclosure ex-periments. The authors‘ analysis of fish biomass data obtained by echo-sounding and the fishery produc-tion of the lake over the years, revealed that the recurrence of Microcystis bloom can be prevented so long as the combined biomnss of silver carp and big-head carp remains at or exceeds 50 g per cubic meter of lakewater, as was the case in the lake‘s 1985 fish yield of 1015 t.     

The effects of nitrogen,phosphorus, vitamins and trace metals on the growth of the red tide organismProrocentrum Micans

Laboratory culture experiments showed that <100μ mol/L nitrate, amonium or mixture of amino acids promote the growth of the red tide organismProrocentrum micans Ehrenb, but that >100μmol/L of ammonium, or mixture of glycine and glutamate was harmful to growth, and that orthophosphate wasP. micans’ main phosphorous source in the ocean. Presence of 80μ mol/L EDTA, 0.5 to 1 μmol/L Fe³⁺, 1.0 to 20.0 μ mol/L Mn²⁺ 0.1 to 0.4 μmol/L Co²⁺ in the culture medium could improve the growth ofP. micans. Vitamin B₁ promoted growth, but vitamin B₁₂ and biotin did not. The estimated minimum cell quotas (q _o) for nitrogen and phosphorus being 0.74 pmole/cell and 0.045 pmole/cell show that phosphorus (more than nitrogen) limits the growth ofP. micans in the study area. This project was supported by the Natural Science Foundation of Zhejiang Province.     

Growth,reproduction and population growth ofCeriodaphnia cornuta sars and comparison of 7-day fecundity withCeriodaphnia dubia richard

Biology of parthenogenetic females ofCeriodaphnia cornuta Sars was studied under laboratory conditions. The mean length of neonates (first-young instars) ofCeriodaphnia cornuta was found to be 0.27 mm at 25±1°C and that of the first adult instars 0.50 mm. A maximum length of 0.69 mm was attained at the 8th adult instar. The mean longevity was found to be 19.0 days for 3 preadult and 8 adult instars. Sex maturity was reached in 4.26 days. The mean number of young per brood was 6.21. The total production for each adult reached 49.7. The maximum reproduction period occurred during the 4th adult instar. At this age, the animals were 10.25 days old, and had a body length of 0.65 mm. The innate capacity for increase (r _m) was 0.40 per female per day, the net reproduction rate (R ₀) was 33.601 per generation, the mean length of a generation (T) was 8.786 days, and the finite rate for increase (λ) was 1.492 per female per day. Comparisons using the t-test indicated that the number of eggs produced and number of broods ofC. cornuta andC. dubia were not significantly different (p>0.05) after 7 days.     

Description of the biology of Caspian vimba, Vimba vimba (Linnaeus, 1758), in Gorgan Bay-Miankaleh Wildlife Refuge (southeast Caspian Sea)

We collected Vimba vimba throughout the spawning season (mid April to mid June, 2007) in Gorgan Bay (south-western Iran) and investigated its age, growth, and reproductive traits. The maximum age was 5⁺ years. Both sexes grew allometrically (positive for males: b=3.140 9 and negative for females: b=2.791 4). The von Bertalanffy growth functions were described by the formulae L _t =32.565(1-e^{−0.184(t+0.530)}) for males and L _t =35.950(1-e^{−0.179(t+0.529)}) for females. The overall sex ratio was balanced, but males were predominant in the smaller size classes and females in the larger size classes. Based on the gonadosomatic index (GSI) values, spawning appears to occur between late April and late May in the bay. The highest mean GSI was 6.44 for males in early May and 20.36 for females in late April. Absolute fecundity varies from the minimum of 5 436 eggs for age 3⁺ fish to the maximum of 36 141 eggs for age 5⁺ fish. Fecundity was also positively correlated with fish size (length and weight). Egg diameter ranged from 1.05 to 1.70 mm in the mean of 1.42 mm. There was no correlation between female size and ova diameter.     

Simultaneous estimates ofsynechococcus spp. Growth and grazing mortality rates in the English Channel

The marine chroococooid phycoerythrin-containingSynechococcus spp. cyanobacterium has been implicated as a substantial component of the photosynthetic picoplankton in the ocean. Although its importance as food source for heterotrophic nanoplankton is now recognized, information about the cycling ofSynechococcus biomass and its diel pattern is limited and study methodology varies among authors. The selective metabolic inhibitor method was used to simultaneously estimate growth and grazing disappearance rates ofSynechococcus in the English Channel where growth rates ranged from 0.25 to 0.72/d (mean ±SD=0.51±0.17/d) and grazing mortality rates ranged from 0.19 to 0.64/d (mean ±SD=0.48±0.17/d). Size-fractionated experiments demonstrated that up to 70% ofSynechococcus disappearance could be attributed to grazers going through a 2 μm Nuclepore filter.Synechococcus grazing mortality rates (mean=0.74 ±0.25/d) during the day were always higher than that (mean=0.2±0.20/d) during the night, while growth rates showed no clear diel pattern. A positive correlation was observed between growth rates andin situ temperature ranging from 9 to 17°C, while in contrast grazing was independent of temperature. The close similatiry between average growth and grazing rates suggests a rapid recycling ofSynechococcus biomass in English Channel coastal waters.     

Molecular identification of Prorocentrum (Dinophyceae) species

A fragment of a large sub-unit ribosomal DNA (LrDNA) of 12 strains ofProrocentrum species was amplified by polymerase chain reaction (PCR). The PCR products were digested by 3 restriction endonucleases (Cfo I, Hae III, and RSA I) and then resolved in agarose gels. Results show that different species had different RFLP patterns, except forP. arcuatum (ME 131), which had the same pattern toP. micans (ME160 and 04). The same fragment of 19 strains of the genus was also amplified and subjected to denaturing gradient gel electrophoresis (DGGE). 11 different patterns were resolved. Different cultures of a same species had the same pattern. The results of RFLP and DGGE analyses showed that eight newly isolated epibenthicProrocentrum species were different from each other, and also from other cultured ones examined in this study.P arcuatum (ME132) could not be differentiated fromP. micans (ME160 and 04), it was probably mis-identified, since they are quite different morphologically.P. redfieldii (ME138) could also not be distinguished formP. triestinium (ME132), it should be regarded as a synonym ofP. triestinium. Unexpectedly, a restriction site was found inP. micans, compared with previous sequence data. Project supported by National Basic Research Priorities Program (2001CB409701, 2001CB409710) and supported by NSFC (40376040, 40025614)     

Oxygen consumption and ammonia-N excretion of Meretrix meretrix in different temperature and salinity

Effects of temperatures and salinities on oxygen consumption and ammonia-N excretion rate of clamMeretrix meretrix were studied in laboratory from Oct. 2003 to Jan. 2004. Two schemes were designed in incremented temperature at 10, 15, 20, 25°C at 31.5 salinity and in incremented salinity at 16.0, 21.0, 26.0, 31.5, 36.0, and 41.0 at 20°C, all for 8–10 days. From 10 to 25°C, both respiration and excretion rate were increased. One-way ANOVA analysis demonstrated significant difference (P<0.01) in physiological parameters in this temperature range except between 15 and 20°C. The highestQ ₁₀ thermal coefficient value (12.27) was acquired between 10 and 15°C, and about 1 between 15 and 20°C, indicatingM. meretrix could well acclimate to temperature changes in this range. Salinity also had significant effects on respiration and excretion rate (P<0.05). The highest values of respiration and excretion rate ofM. meretrix were recorded at 16.0 salinity (20°C). These two physiological parameters decreased as salinity increased until reached the minimumQ ₁₀ value at 31.5 (20°C), then again, these parameters increased with increasing salinity from 31.5 to 41.0.M. meretrix can catabolize body protein to cope with osmotic pressure stress when environmental salinity is away from its optimal range. No significant difference was observed between 26.0 and 36.0 in salinity (P>0.05), suggesting that a best metabolic salinity range for this species is between 26.0 and 36.0. This work is supported by National High-Tech R & D Program of China. (863 Program) (2002AA603014).     

Disease resistance and humoral immunomodulatory effects of vitamin C on grouper,Epinephelus awoara

The disease resistance and humoral immunomodulatory effects of vitamin C administered orally to grouper,Epinephelus awoara maintained on a frozen fish diet supplemented with vitamin C at 500, 1000, 1500 and 2000 mg/kg were investigated. After 20 weeks, the growth rates of the groups with high level of vitamin C apparently increased. The untreated fish had symptoms of vitamin C deficiency. The endogenous liver tissue vitamin C levels were found to reflect well the dietary treatments. After intraperitoneal injection or bath challenge with a virulent strain ofVibrio vulnificus, fish fed with high level vitamin C showed significantly higher survival rate compared with the normal control group. Vaccination with formalin inactivatedV. vulnificus significantly enhanced the specific antibody production in fish treated with vitamin C, and completely protected from strong bacterial challenge the groups fed on fish with vitamin C 1500 and 2000 mg/kg diet. Project 39500113 supported by NSFC and also by Guangdong Science Research Foundation (Grant No. 950711).     

Age and growth characteristics of crimson sea bream <Emphasis Type="Italic">Paragyrops edita</Emphasis> Tanaka in Beibu Gulf

Abstact  Age and growth characteristics of crimson sea bream Paragyrops edita Tanaka in Beibu Gulf were studied through bottom trawling and gillnet fleets fishing from July 2006 to December 2007. A total number of 1155 individuals, ranging from 49 to 249 mm in standard length was examined. The age of the fish was determined from sagittal otoliths. One year growth was made up of one translucent and one opaque zone. A maximum likelihood estimation procedure was used to fit the Von Bertalanffy, Logistic and Gompertz growth functions to the length-at-age data. ARSS indicated that there were no significant differences in growth between sexes in the three growth models (P>0.05), and the Von Bertalanffy growth function L _t =292.8{1−exp [−0.167(t+1.116)]} was selected as the most appropriate growth model according to Akaike’s information criterion (AIC).     

Effects of Dietary Protein Level on Growth and Utilization of Protein and Energy by Juvenile Mangrove Red Snapper （ Lutjanus argentimaculatus ）

A feeding trial was conducted in a recirculating water system to investigate the effects of dietary protein levels on growth, feed utilization, hepatosomatic index and liver lipid deposition of juvenile red snapper, Lutjanus argentimaculatus (average initial wet weight 8.0 ± 0.39 g and total length 3.14 ± 0.3 cm). In the experiment, six fishmeal-based diets were formulated to contain various protein levels (20% to 45% in 5% increments), with dietary energy ranging from 2210.7kJ lOOg to 2250.2kJlOOg dry matter. The protein to energy ratios of diets ranged from 8.58 mg protein kJ⁻¹ to 20.03 mg protein kJ⁻¹. Diets were fed for 90d to triplicate groups of fish stocked in 0.128m³ seawater tanks, 25 individuals each. The daily ration of 2% wet body weight was offered to the fish thrice a day. The fish at the end of the study had more than ten-fold (77.0g) increase in weight compared to the initial (8.0g). Fish fed diets of 40% and 45% protein produced significantly (P<0.05) higher weight gain of 77.2g and 76.5g, and specific growth rate (SGR) of 2.65% and 2.62% than those of 67.0 g and 68.3g, and 2.49% and 2.51% of the other diets. The broken-line regression of SGR against dietary protein level yielded an optimum dietary protein requirement of 42.6% (Y=−1.6295 + 0.1114 X ²,P<0.05). Survival remained 100% among groups. Feed conversion ratio decreased from 0.45 for fish fed 20% dietary protein to 0.35 for fish fed 45% dietary protein. Nitrogen intake increased with an increase in dietary protein, which in turn resulted in an increase in nitrogen gain of fish whole body. Fish fed 40% and 45% protein diets showed higher (P<0.05) nitrogen gain (0.27g and 0.26g) than those (0.23g and 025g) fed all other diets. Gross energy intake (GEI) in fish fed 45% protein was lower (600.67kJ) than that (607.97 kJ) of 40% protein diet, though the differences were not statistically significant (P>0.05); GEI ranging from 677.31 kJ to 663.20 kJ at remaining four diets (20% to 35% protein) did not appear to differ significantly (P>0.05). The highest energy gain of 518.33 kJ was obtained with fish fed 40% protein, resulting in the highest energy retention efficiency of 85.26%. The hepatosomatic index of fish fed diets of 20%, 25%, 30% and 35% protein were significantly (P<0.05) higher (2.09% to 2.57%) than those (1.44% and 1.41%) of fish fed diets containing 40% and 45% protein. Liver lipid contents decreased from 8.72% to 7.0% in fish fed dietary protein of 20% to 45% in 5% increments. Results suggest that the diet containing 40% to 42.6% protein with a P/E ratio of 17.6 mg protein kJ⁻¹ is required for good growth of L. argentimaculatus weighing between 8.0 g and 85.2 g under the culture conditions of the present study.     

Proteocephalus sinocyclocheili n. sp. (Cestoda: Proteocephalidae) in a fishSinocyclocheilus grahami tingi Fang from Yunnan, China

A new species ofProteocephalus from the fishSinocyclocheilus grahami tingi, a subspecies endemic to Fuxian Lake in Southwest China,is described. This is the first report of cestode from this host. The new species differs fromP. exiguus, P. Longicollis, P. parasiluri andP. torulosus, the only other species ofProteocephalus currently reported from China, by lacking an apical sucker, fromP. exiguus by having 45–108 rather than 24–54 testes per proglottis, and a maximum of 15 rather than 28 uterine diverticula; fromP.longicollis by having an average of 45–108 rather than 75–115 testes per proglottis and testes being in a single layer instead of 2 layers; and fromP. torulosus by having 45–108 instead of 150 testes per proglottis and testes being in 3–4 layers; and fromP. parasiluri by having 45–108 rather than 180 testes per proglottis. It resemblesP. percae, P. pollanicola, andP. thymalli in number of testes and uterine diverticula, but differs by lacking an apical sucker.Proteocephalus thymalli, like the new species, has a vagina that opens dorsally to the cirrus sac, butP. thymalli slao has postovarian testes, which the new species lacks. The possible significance of parasitological examinations of the other two subspecies ofS. grahami in two lakes close to Fuxian Lake is discussed in relation to host speciation and coevolution of the host-parasite system.     

Comparative studies of inorganic carbon utilization inEmiliania huxleyi and some non-calcifying marine microalgae

Inorganic carbon utilization in the non-calcifying marine microalgae,Nannochloropsis oculata, Phaeodactylum tricornutum andPorphyridium purpureum was compared with high- and low-calcifying strains ofEmiliania huxleyi grown in artificial seawater medium aerated with either air (0.03% V/V CO₂) or CO₂-free air. For high-calcifying strain ofE. oculata andP. tricornutem, similar growth patterns were observed in air-and CO₂-free air-grown cultures.P. purpureum showed a less final cell density in CO₂-free air than in air-grown culture. However, low-calcifying strain ofE. huxleyi was able to grow only in air-grown culture, but not in CO₂-free air-grown culture. Measurements of alkalinity, pH, concentration of dissolved inorganic carbon (DIC) and free CO₂ showed different patterns of DIC utilization. WithN. oculata, P. tricornutum andP. purpureum the pattern of DIC utilization was characterized by an increase of pH and a decrease of DIC but a constant alkalinity in the cultures aerated with air or CO₂-free air, suggesting that bicarbonate utilization was concomitant with an efflux of OH⁻. Both alkalinity and pH were maintained rather constant in air-grown culture of low-calcifying strain ofE. huxleyi, suggesting that diffusive entry of CO₂ could meet the requirement of DIC for its photosynthesis and growth. High-calcifying strain ofE. huxleyi, however, showed a pattern of decrease of alkalinity and DIC but an almost constant pH, indicating that bicarbonate was the major form of inorganic carbon utilised by this organism and bicarbonate uptake is unlikely to be accompanied by an efflux of OH⁻. The final pH values reached byN. oculata, P. tricornutum andP. purpureum in a closed system were 10.75, 10.60 and 9.85 respectively, showing that bicarbonate utilisation is concomitant with an efflux of OH⁻. While the final pH of 8.4 in high-calcifyingE. huxleyi suggests that bicarbonate utilization was not accompanied by an efflux of OH⁻. Contribution No. 3557 from the Institue of Oceanology, Chinese Academy of Sciences. This work was supported by NERC grant GRE3/7853 U. K. and partly supported by Bio-Engineering Center, SSTC 96-C01-05-01.     

Studies on color type variants from mutagenized protoplasts ofPorphyra haitanensis Chang et Zheng &P. Yezoensis ueda (rhodophycease)

Isolated protoplasts from thalli ofPorphyra haitanensis andPorphyra yezoensis were treated with colchicine or irradiated by ultraviolet (UV). Several types of color variants were observed among the protoplast offspring. After treatment with colchicine: (1) 0.04–0.09% of red type variants inP. haitanensis were obtained; (2) The rate of red type variants and the variegated chimeral thalli composed of red type and wild type of sectors were 0.31–1.11% inP. yezoensis. After irradiation with UV: (1) 3.5–10.5% of red type variants inP. yezoensis were obtained: (2) 0.5–2.0% of red type variants and the variegated chimeral thalli composed of red type and wild type of sectors were obtained inP. haitanensis. Colchicine and UV’s mutangenic effects onP. yezoensis protoplasts were stronger than those onP. haitanensis protoplasts. The most efficient concentration of colchicine was 0.05%. The optimal length of UV-radiation was 1/2 min (radiation distance 5 cm). The red type variants induced by colchicine treatment grew faster than the wild type thalli. The clones of vegetative propagation from protoplasts of red type variants were still red type thalli. The red type variants will be good materials for genetic studies and improvement ofPorphyra strains.     

Vaccination in three different ways against vibriosis of <Emphasis Type="Italic">Seriola dumerili</Emphasis> caused by <Emphasis Type="Italic">Vibrio hollisae</Emphasis>

Bacterin was prepared by formalin-inactivating the virulent strain of Vibrio hollisae isolated from diseased Seriola dumerili （amberjack） suffering from vibriosis. Healthy S. dumeriIi were vaccinated by respective procedures of intramuscular injection, immersion, and orally administration. Results of the three different vaccinations were compared. Blood was drawn from the vaccinated fish every 7 days, and the antibody titers and lysozyme activities of the sera were determined. The antibody titer of injected fish was 1：40 at 7 d, and reached its peak of 1：320 at 28 d, while the fish vaccinated by immersion and orally administration exhibited weak antibody responses, the antibody titres of 〈1：10, 1：20, 1：160 were observed at 7 d, 14 d, 35 d respectively. Compared with the control, the vaccinated fish exhibited significantly higher lysozyme activities （P〈0.05）. Upon challenge with virulent strain, the relative percent survival （RPS） of injected, immersed and oral administrated fish were 75%, 45%, and 40% respectively, and the injected fish showed significantly higher RPS than immersed and oral administrated fish. The results suggested that vaccination of S. dumerili by the injection would be the best strategy to prevent the vibriosis in S. dumerili farm.     

Assessing the germplasm of Laminaria (phaeophyceae) with random amplified polymorphic DNA (RAPD) method

Eighteen gametophytes includingL. japonica, L. ochotensis andL. longissima, were verified with random amplified polymorphic DNA (RAPD) technique. Eighteen ten-base primers were chosen from 100 primers selected for final amplification test. Among the total of 205 bands amplified, 181 (88.3%) were polymorphic. The genetic distance among different strains ranged from 0.072 to 0.391. The dendrogram constructed by unweighted pair-group method with arithmetic (UPGMA) method showed that the female and male gametophytes of the same cell lines could be grouped in pairs respectively. It indicated that RAPD analysis could be used not only to distinguish different strains ofLaminaria, but also to distinguish male and female gametophyte within the same cell lines. There is ambiguous systematic relationship if judged merely by the present data. It seems that the use of RAPD marker is limited to elucidation of the phylogenetic relationship among the species ofLaminaria. Contribution No. 4389 from the Institute of Oceanology, Chinese Academy of Sciences. This research was supported by the State's High-tech Project of China, Marine 863 project (No. 819-03-02) and (2001AA621090).     

Age groups of antarctic krill,Euphausia superba dana, in the Prydz Bay region

Age groups of Antarctic krill (Euphausia superba Dana) in the Prydz Bay region were studied by distribution mixture analysis based on length/frequency data collected by R/VJidi during the 1989/1990 and 1990/1991 austral summer. Five age groups were determined, i.e. 1⁺, 2⁺, 3⁺, 4⁺, and 5⁺, or six age groups in all, if the 0⁺ larvae were included. The mean body length of 1⁺ to 5⁺ age groups was 25.70 mm, 40.47 mm, 45.52 mm, 50.52 mm and 54.52 mm respectively. Supposing the difference in body length between successive age groups is a reflection of the early growth, the maximum growth rate occurred during the period from 1⁺ juveniles to 2⁺ subadults (14.77 mm/a). From 2⁺ subadults to 3⁺ adults the growth rate dropped steeply (5.05 mm/a) because at this stage, increase of body length was substituted, to a great extent, by the growth of sexual products. From 3⁺ onwards the growth rate was maintained at a relatively low level and decreased slowly with age. The relative abundance of age groups 1⁺ and 2⁺, in our sample must be much lower than that in the real population owing to both the large mesh size we used and the distribution difference between juveniles and adults. If we left aside 1⁺ and 2⁺ age groups and just looked at the relative abundance of adults, we found that age group 3⁺ dominated the adult population and that the relative abundance decreased sharply with increasing age. If this situation is normal, one can expect an extremely high mortality rate in adults, 82.6% from 3⁺ to 4⁺ and 94.0% from 4⁺ to 5⁺. This is reasonably expectable for the Prydz Bay region. Contribution No. 3702 from the Institute of Oceanology, Chinese Academy of Sciences. The research is an achievement of “NINE FIVE” Key Project of CAS (KZ951-A1-205) and National Key Project (98-927-01).