Density and sound speed contrasts of the Japanese common squid Todarodes pacificus and their influence on acoustic target strength

ABSTRACT:   In this study, density and sound speed contrasts were measured for the Japanese common squid Todarodes pacificus . Target strength (TS) data derived from an acoustic scattering model based on measurements of these two parameters were compared with TS values based on acoustic measurement data to determine whether the measured parameters are reasonable values for theoretical scattering model. Density contrast ( g ) was measured from the displacement volume and wet weight, while sound speed contrast ( h ) was measured from the acoustic measurements of travel time (time-of-flight method). The Kirchhoff ray mode model, which represents the squid body as a set of fluid-filled cylinders, was used to calculate theoretical TS. Mean g- and h -values of the squid were 1.029 and 1.041, respectively. Comparison with previous data showed that g was similar, whereas h was relatively high. The difference in the TS between the theoretical model using measured parameters and the acoustic measurement was within 3 dB. Thus, the measured g- and h -values are acceptable for theoretical models of squid.     

Purification of serine carboxypeptidase from the hepatopancreas of Japanese common squid Todarodes pacificus and its application for elimination of bitterness from bitter peptides

ABSTRACT:   An acidic serine carboxypeptidase (CPase Tpa) from the hepatopancreas of Japanese common squid Todarodes pacificus was purified. Purified CPase Tpa had a molecular mass of 36 kDa on sodium dodecylsulfate–polyacrylamide gel electrophoresis, and an isoelectric point of 6.0. The optimum pH of CPase Tpa was pH 4.0. In investigating the specificity of CPase Tpa for several peptide substances, it was found that peptides with hydrophobic or bulky amino acid residues at the P₁ position reacted well. The enzymatic activity was almost completely inhibited by p -chloromercuribenzoic acid, monoiodoacetic acid, diisopropylfluorophosphate and HgCl₂. This is the basis for its grouping in the serine carboxypeptidase family (EC 3. 4. 16. 5). The substrate specificity of CPase Tpa can be used to eliminate the bitterness of bitter peptides. In this study, the bitterness-reductive effect using bitter peptides prepared by hydrolyzing soy protein, casein and corn gluten with pepsin or trypsin was tested. The bitterness of soy peptide digested with pepsin was completely eliminated by treatment with CPase Tpa, whereas the bitterness of casein digested with trypsin and corn peptide digested with pepsin were somewhat less efficient. On the basis of these results, it is anticipated that CPase Tpa would be effective in eliminating the bitterness of some bitter peptides.     

Characterization of 38 kDa and 42 kDa chitinase isozymes from the liver of Japanese common squid Todarodes pacificus

ABSTRACT: Characterization was investigated on the 38 kDa and 42 kDa chitinase (EC3.2.1.14) isozymes from the liver of Japanese common squid Todarodes pacificus . Optimum pH toward colloidal chitin was observed at pH 3.0 for the 38 kDa chitinase, and pH 3.0 and 9.0 for the 42 kDa chitinase. K _m and k _cat of the 38 kDa and 42 kDa chitinases toward a longer substrate, glycol chitin, were 0.071 mg/mL and 1.22/s, and 0.074 mg/mL and 0.196/s, respectively. Alternatively, strong substrate inhibition of both chitinases were observed toward a short substrate, N -acetylchitopentaose (GlcNAc₅). Both chitinases decomposed not only chitin but also chitosan (D. A. 95%). The cleavage pattern and reaction rate were investigated using N -acetylchitooligosaccharides (GlcNAc_n, n  = 2–6). Both chitinases hydrolyzed GlcNAc_n ( n  = 4,5, and 6). The release of GlcNAc was not observed. The speed of the reaction was observed to be in the following order: GlcNAc₄ > GlcNAc₅ > GlcNAc₆ for the 38 kDa chitinase, and GlcNAc₆ > GlcNAc₅ > GlcNAc₄ for the 42 kDa chitinase. Both the chitinases released p -nitrophenol from p -nitrophenyl GlcNAc_n ( n  = 2, 3, and 4). N-terminal amino acid sequences of the 38 kDa and 42 kDa chitinases were YLLSXYFTNWSQYRPGAGKYFPQNI and EYRKVXYYTNWSQYREVPAKFFPEN, respectively.     

Long-term changes in zooplankton and its relationship with squid, Todarodes pacificus, catch in Japan/East Sea

Long‐term change in zooplankton biomass and composition of major zooplankton assemblages was studied with a focus on climate change and squid catch in the Japan/East Sea. This study deals with data sets of zooplankton biomass, abundance of major zooplankton assemblages, and sea surface temperature (SST) obtained during the period from 1965 to 1998, and the catch of squid, Todarodes pacificus, from 1978 to 1998. Based on its physical characteristics, the study area was divided into two subregions, a northern and southern region. The SST during the winter and spring (February and April) steadily increased after the late 1980s in the southern region. On the other hand, the northern region did not have a warm winter and had higher interannual fluctuations. Zooplankton biomass also showed an increasing trend and major zooplankton assemblages have shifted in their composition since the early 1990s. The northern region exhibited a greater increasing trend than the southern region in zooplankton biomass. Macrozooplankton such as chaethognaths, euphausiids and amphipods gradually increased after the early 1990s. In the Japan/East Sea, squid catches increased continuously after the early 1990s. The squid catch for the autumn of year n is significantly associated with the zooplankton biomass collected in October and December of year n ? 1 (r=0.864 in the northern region and r=0.818 in the southern region, P < 0.001) and macrozooplankton, especially euphausiids (r=0.578 in the northern region and r=0.840 in the southern region, P < 0.05) and amphipods (r=0.695 in the northern region and r=0.648 in the southern region, P < 0.05).     

Effect of water temperature on gonadal development and emaciation of Japanese common squid <Emphasis Type="Italic">Todarodes pacificus</Emphasis> (Ommastrephidae)

ABSTRACT:   In this study, the site of spawning ground and the relationship between oceanographic conditions and gonadal development and emaciation of the Japanese common squid Todarodes pacificus were examined based on data from research cruises. The research cruises were conducted in the south-western part of the Sea of Japan and the East China Sea in the winter of 1999. Sea surface temperature (SST) ranged 12.7–23.2°C in the survey area. Mature females concentrated on the continental shelf of the East China Sea, suggesting a major spawning ground was formed in this area. Gonadal development of the collected squid was examined using ovary somatic index (OSI) and oviduct somatic index (ODSI) in females, and emaciation was examined using mantle muscle somatic index (MI) and hepatosomatic index (HSI). Mean OSI and ODSI increased with SST at the stations where SST was greater than 15°C, particularly where SST ranged between 15 and 18°C. In contrast, mean MI and HSI decreased with increase in SST at the stations where SST was above 15°C. These results indicate that female gonads develop rapidly at SST above 15°C, and at the same time adult squids tend to be emaciated at this temperature condition.     

黄海太平洋褶柔鱼种群动态的研究

根据近年来我国主要海洋渔业公司和群众渔业单位,在黄海拖网生产专捕和兼捕太平洋褶柔鱼的统计资料,结合多年来渔业生产经验,对鱿鱼的洄游分布状况作了具体分析。同时根据2004-2006年5次对山东近海渔业资料调查中的渔获统计及生物学测定,研究近年来黄海鱿鱼资源变动规律,并利用扫海面积法估算整个黄海海域的资源量。结果表明目前黄海鱿鱼资源利用较充分,并提出资源开发保护建议。     

东海太平洋褶柔鱼的数量分布及其与环境的关系

利用1997～2000年在东海4个季节的拖网以及温盐度调查资料,分析了东海太平洋褶柔鱼的数量分布及其与环境条件的关系。结果表明：东海太平洋褶柔鱼分布水深在40～175m,集中分布水深范围在80～150m。春、夏、秋三个季节的平均资源密度最高值都出现在北部外海,冬季的平均资源密度最高值转移到南部外海。四季都有生殖群体的存在,从春季到冬季,生殖群体的重心位置由北部外海向南部外海转移。四季生活海域的表层水温为13．63～28．38℃,生物量高区的表层水温为22～26℃;表层盐度为27．72～34．72,集中分布海域的盐度为32．5～34．7。因此,东海太平洋褶柔鱼属于暖水性外海高温高盐种。     

夏季东海太平洋褶柔鱼群体结构的年际变化

依据2009―2012年连续4年在东海进行的夏季(6月)渔业资源调查资料, 分析了太平样褶柔鱼(Todarodes pacificus)的资源密度、性比、胴长结构、胴长与体质量的关系、初次性成熟胴长等基础生物学参数的年际变化, 阐述了东海太平洋褶柔鱼的群体结构动态。结果表明: (1)夏季东海太平洋褶柔鱼的出现率较高, 但资源密度分布不均。在调查的4年间, 2009年的平均资源密度最高, 2010年最低。(2)各年度的雌雄比例均符合1∶1的关系(P>0.05)。(3)夏季渔汛期的太平样褶柔鱼个体较小。相比较而言, 2012年的优势胴长组最大, 2011年最小。但各年度的优势胴长均小于200 mm。(4)雌、雄个体胴长与体质量的关系符合指数生长曲线, 年间差异极显著(P<0.001)。(5)渔获个体以性未成熟幼体为主, 性腺成熟度随胴长增加而升高。各年度雌性个体的初次性成熟胴长均大于雄性。分析认为, 2009—2012年东海太平洋褶柔鱼夏季渔汛期均以秋、冬生群的性未成熟幼体为主, 夏生群的性成熟大个体较少。各年度太平洋褶柔鱼的生长发育速度以及群体结构有所不同。本研究可为掌握该物种资源的变动规律, 实现资源的合理利用提供基础资料。

     

海洋环境因子对日本海太平洋褶柔鱼渔场时空分布的影响

根据2010—2013年11—12月日本海太平洋褶柔鱼(Todarodes pacificus)的渔获生产数据,并结合遥感获取的海洋环境数据,利用渔获量重心法、地统计插值和数理统计方法,分析了太平洋褶柔鱼的资源丰度与渔获量重心的时空变化及其与主要环境因子(海表温度、叶绿素浓度、海流)之间的关系。研究表明,渔场重心每年稍有差异,经度重心集中在132°20′E附近;纬度重心集中在36°30′N和37°30′N两个位置附近。GAM模型显示,日本海太平洋褶柔鱼渔场的最适海表温度为16~18℃;最适叶绿素a浓度为0.37~0.45 mg/m3。海洋环境与单位捕捞努力渔获量(CPUE)的回归方程的显著性检验表明,除了叶绿素a浓度呈一般显著外,海表温度和空间因子在CPUE上的回归均极显著(P0.01),符合统计意义。4年间渔场的适宜环境范围有所差异,推断主要是日本海海域对马暖流、东朝鲜暖流与里曼寒流相互交汇的强弱作用力引起的,也有不同年份季风的强弱不同以及全球气候变化的因素存在。每一年的渔场海洋环境因子稍有差别,对其资源量的影响巨大。     

盐度对海萝孢子附着、萌发和成活的影响

通过4个试验研究了盐度对海萝（Gloiopeltisfurcata）孢子附着、萌发及成活的影响。1）不同盐度（16．0—38．5）对海萝种藻所释放孢子的影响。2）不同盐度（13．5～41．0）对海萝孢子附着、萌发和成活的影响。3）不同盐度（6．0—66．0）对已附着24h、48h孢子发生体成活的影响。4）淡水浸泡不同时间（2h、4h、6h和8h）对已附着24h、48h孢子发生体成活的影响。结果表明,盐度为23．5～36．0时海萝种藻释放的孢子能正常附着和萌发;海萝孢子附着、萌发及成活的合适盐度为31．0～36．0;盐度为31．0～56．0时对已附着24h海萝孢子发生体的成活没有影响,不同时间的淡水浸泡则对其成活有影响;盐度为16．0～61．0或者2h的淡水浸泡对已附着48h孢子发生体的成活没有影响。     

东海区太平洋褶柔鱼生殖群体结构特征的季节差异

依据1997~1999年东海区春、夏、秋3个季节的底拖网资料,分析了东海区太平洋褶柔鱼生殖群体的性别组成、性腺成熟度和初次性成熟胴长等群体结构特征。结果表明:在东海区春、夏、秋三季均存在太平洋褶柔鱼的生殖群体。各季节生殖群体的雌雄比例均不符合1∶1的关系(P<0.05),雌性比例小于雄性。生殖群体中性成熟个体胴长的季节性变化较为明显,雌、雄平均胴长均以秋季最大,夏季最小。雌性个体的平均胴长均显著大于雄性。各季节太平洋褶柔鱼生殖群体中胴长与体重关系的性别差异极显著(P<0.01)。此外,不同季节雌、雄太平洋褶柔鱼的初次性成熟胴长差异较大,雌性为:春季223.4 mm、夏季170.4 mm、秋季202.3 mm;雄性为:春季174.0 mm、夏季164.3 mm、秋季165.3 mm。雄性初次性成熟胴长小于雌性,夏季雌、雄初次成熟胴长均小于春、秋季。依据春季生殖群体的胴长范围、初次性成熟胴长等群体结构特征推测,在东海区可能存在着小规模的春生群。     

太平洋褶柔鱼胃组织微塑料的积聚特性

微塑料在全球海洋环境及鱼类组织中普遍存在,越来越受到各界学者的关注。[目的]太平洋褶柔鱼是重要的头足类资源,在海洋生态系统中发挥着承上启下的重要作用,对其胃组织微塑料积聚特性的研究尚未见报道。[方法]本研究根据2018年1-3月在中国东海采集的30尾太平洋褶柔鱼样本,利用统计和相关性分析方法,对其胃组织中微塑料的积聚特性进行了研究。[结果] 结果显示,30尾测定样本中有16尾的胃组织中发现18个微塑料。微塑料丰度范围0-3个/尾,平均丰度0.6个/尾;长度范围0.332-4.337 mm,平均长度1.252 mm,其中72%的微塑料小于1 mm。微塑料颜色主要为黑(38.9%)、白(33.3%)、蓝(22.2%)和灰(5.6%)4种颜色,材质主要由棉(cotton)(44.5%)、聚酯纤维(polyester)(33.3%)和人造丝(rayon)(22.3%)3种材质组成。相关性分析表明太平洋褶柔鱼胃组织微塑料的含量与胃重、摄食等级无显著相关性,但与胴长、体重和年龄呈显著性正相关,并随着胴长、体重和年龄的增加而增加。[结论] 太平洋褶柔鱼胃组织中微塑料摄取随着其个体的生长而逐渐积聚,但这种积聚是否一直持续下去,还是在达到一定数量时保持摄入和排出的动态平衡还需进一步研究。     

低盐度对泥东风螺(Babylonia lutosa)稚螺生长与存活的影响

采用盐度渐变和突变2种方法试验低盐度对平均体重3.7 mg、平均壳高(2.24±0.24)mm的泥东风螺稚螺生长与存活的影响。结果表明:盐度28时,稚螺的生长速度最快,盐度降到24时,对稚螺的影响并不明显,摄食基本正常,但活力略有降低;变态7 d的泥东风螺稚螺能够适应高于21的低盐环境,存活基本正常,有比较高的成活率,但对其摄食和生长有一定的影响;当盐度突变至18时,泥东风螺稚螺仍能存活,突变至15时,则不能存活;而盐度渐变至15时,稚螺仍可存活;盐度逐渐降低只可扩大泥东风螺稚螺的存活盐度范围,但其对最适生长盐度范围影响有限。     

Laboratory observations on the vertical swimming behavior of Japanese common squid Todarodes pacificus paralarvae as they ascend into warm surface waters

This study examined the effect of warm temperature on the survival of paralarvae of Japanese common squid Todarodes pacificus and on their swimming behavior as they ascended to the surface. Observations were conducted on paralarvae in Petri dishes and in 85-cm-tall, cylindrical tanks that had a warmer upper layer and cooler lower layer separated by a small thermocline. Paralarvae were obtained through artificial fertilization and reared in Petri dishes at six experimental temperatures between 20.9 and 30.4 °C. Paralarvae reared at lower temperatures survived longer than those reared at warmer temperatures, and survival decreased at temperatures above 24 °C. When the mean temperatures in the upper layer of the tanks were 24.4–26.0 °C, the paralarvae ascended through the thermocline to the surface, but when the mean temperatures in the upper layer were 29.7–29.8 °C, paralarvae stopped ascending at the thermocline. These results show that paralarvae have a temperature preference but ascend to the surface in the unfavorable temperature range. The results suggest that increasing surface temperatures at spawning grounds will negatively affect both the survival and behavior of T. pacificus paralarvae.     

Distribution and migration of Japanese common squid, Todarodes pacificus, in the southwestern part of the East (Japan) Sea

Data on squid catches of Korean and Japan, water temperatures at depth of 100 m, and night-visible images of fishing boats collected in the East (Japan) Sea from 1970 to 1999 were analyzed to examine the distribution and migration of the Japanese common squid, Todarodes pacificus, in the southwestern part of the East (Japan) Sea. The main fishing grounds detected from squid catch in each grid (0.5° latitude × 0.5° longitude) by Korean squid fishery and night-visible images provided by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) were situated in the southwestern part of the East (Japan) Sea. The distribution and migration route was illustrated from squid catch in each grid and DMSP OLS image. In years of high catches, the fishing grounds were situated mainly between Ulleung Island and the eastern coastal waters of Korea, while in years of low catches they were situated between Ulleung Island and the Yamato Bank in the central East (Japan) Sea. The center of fishing activity began moving northward from around the Korea/Tsushima strait to the northern boundary of the Tsushima Warm Current in March, reaching into the Yamato Bank in September, and then returning to the strait by February. The northward and southward migration routes differed; the northward migration route occurred closer to the mainland coast of Korea than the southward migration route did. This work suggests T. pacificus begin their northward migration almost 2 months earlier than previously suggested.     

Spatial distribution of the Japanese common squid, Todarodes pacificus, during its northward migration in the western North Pacific Ocean

The spatial distribution of Todarodes pacificus in and near the Kuroshio/Oyashio Transition Zone during its northward migration was examined by comparative surveys using two types of mid‐water trawl net and supplementary squid jigging from June to July 2000. The vertical and horizontal distribution patterns varied for different body sizes in relation to the oceanographic structure. Todarodes pacificus of 1–20 cm dorsal mantle length (ML) were widely distributed from the coastal waters of Japan to near 162°E longitude, probably due to transport by the Kuroshio Extension (KE). Todarodes pacificus smaller than 10 cm ML were mainly distributed in temperate surface layers at sea surface temperatures (SSTs) >15°C near the KE meander probably because of their poor tolerance to lower temperatures and limited swimming ability. Squid of 10–15 cm ML were distributed in the offshore waters of 10–15°C SST and in the coastal waters of northern Honshu, and underwent diel vertical migrations between the sea surface at night and deeper layers during the daytime. Squid larger than 15 cm ML were distributed in the coastal feeding grounds of northern Honshu and Hokkaido until they began their southward spawning migration. They also underwent diel vertical migrations, but remained deeper at night than the squid of 10–15 cm ML; this migration pattern closely matched that of their main prey such as euphausiids. We concluded that as T. pacificus grow, they shift their distribution range from the temperate surface layer around the KE toward the colder deeper layers, above 5°C, in the Oyashio and coastal areas.     

Effects of temperature and salinity on the survival and development of mud crab, Scylla serrata (Forsskål), larvae

The combined effects of temperature and salinity on larval survival and development of the mud crab, Scylla serrata, were investigated in the laboratory. Newly hatched larvae were reared under 20 °C temperature and salinity combinations (i.e. combinations of four temperatures 25, 28, 31, 34 °C with five salinities 15, 20, 25, 30, 35 g L⁻¹). The results showed that temperature and salinity as well as the interaction of the two parameters significantly affected the survival of zoeal larvae. Salinity at 15 g L⁻¹ resulted in no larval survival to the first crab stage, suggesting that the lower salinity tolerance limit for mud crab larvae lies somewhere between salinity 15 and 20 g L⁻¹. However, within the salinity range of 20–35 g L⁻¹, no significant effects on survival of zoeal larvae were detected (P>0.05). The combined effects of temperature and salinity on larval survival were also evident as at low salinities, both high and low temperature led to mass mortality of newly hatched larvae (e.g. 34 °C/15 g L⁻¹, 34 °C/20 g L⁻¹ and 25 °C/15 g L⁻¹ combinations). In contrast, the low temperature and high salinity combination of 25 °C/35 g L⁻¹ resulted in one of the highest survival to the megalopal stage. It was also shown that at optimal 28 °C, larvae could withstand broader salinity conditions. Temperature, salinity and their interaction also significantly affected larval development. At 34 °C, the mean larval development time to megalopa under different salinity conditions ranged from 13.5 to 18.5 days. It increased to between 20.6 and 22.6 days at 25 °C. The effects of salinity on larval development were demonstrated by the fact that for all the temperatures tested, the fastest mean development to megalopa was always recorded at the salinity of 25 g L⁻¹. However, a different trend of salinity effects was shown for megalopae as their duration consistently increased with an increase in salinity from 20 to 35 g L⁻¹. In summary, S. serrata larvae tolerate a broad range of salinity and temperature conditions. Rearing temperature 25–30 °C and salinity 20–35 g L⁻¹ generally result in reasonable survival. However, from an aquaculture point of view, a higher temperature range of 28–30 °C and a salinity range of 20–30 g L⁻¹ are recommended as it shortens the culture cycle.     

Comparison of growth histories of immature Japanese common squid Todarodes pacificus between the autumn and winter spawning cohorts based on statolith and gladius analyses

Growth of the autumn and winter spawning cohorts of the Japanese common squid Todarodes pacificus was examined based on daily growth increments in the statolith and gladius. The samples were taken from three groups of young (??180 days old) squid: the autumn cohort collected in the Tsushima Current and the winter cohort collected in the Pacific near the coast and 1100?km offshore. The growth rate based on statolith analysis was highest in the winter cohort near the coast and similar in the two other groups. The daily growth based on gladius analysis during the month before capture was also highest in the winter cohort near the coast, and fluctuated more in the autumn cohort than in the winter cohort. The results suggest that gladius growth increments will be an important tool in future studies of growth in T. pacificus.