Japanese Common Squid Todarodes Pacificus Research Articles

A newly identified enzyme from Japanese common squid Todarodes pacificus has the ability to biosynthesize d-aspartate

Amino acids exist in two chiral forms, namely L and D. Although l-amino acids are predominant in vivo, certain limited circumstances have reported the usage of d-amino acids. d-aspartate (Asp), among them, plays crucial physiological roles in living organisms and is biosynthesized from L-Asp by the enzyme named aspartate racemase (AspRase). D-Asp is known to accumulate in large amounts in the nervous system of cephalopods. To understand the function of D-Asp in nervous system in more detail, it is necessary to elucidate its metabolic pathway; however, AspRase gene has not been identified in cephalopods as in the case of mammals. In this study, we successfully identified a novel gene encoding AspRase from the optic ganglion of Japanese common squid Todarodes pacificus. Our discovery of the squid AspRase challenges the prevailing assumption that AspRases across different animals share similar structures. Surprisingly, the squid AspRase is a unique enzyme that differs significantly from known AspRases, being structurally and phylogenetically related to aspartate aminotransferase (AST) and possessing both AspRase and AST activities. The optimum pH and temperature for AspRase activity using L-Asp as a substrate are approximately 7.0 and 20 °C, respectively. Moreover, we have found that AspRase activity is enhanced in the presence of 2-oxoacids. These findings have far-reaching implications for the understanding of enzymology and suggest that yet-to-be-identified mammalian AspRases may also be phylogenetically related to AST, rather than conventional AspRases. Furthermore, our results provide valuable insights into the evolution of the D-Asp biosynthetic pathway.

Climate-Related Variations in Autumn Cohort of Japanese Common Squid Todarodes pacificus

Climate-Related Variations in Autumn Cohort of Japanese Common Squid Todarodes pacificus

Structural and Phylogenetic Profiles of Muscle Actins from Cephalopods

Structural properties of cephalopod muscle actins have not been characterized in detail to date. Sequences of these actins have been determined by cDNA cloning from the arm muscles of four cephalopod species, namely, Japanese common squid Todarodes pacificus, spear squid Loligo bleekeri, common cuttlefish Sepia esculenta, and common octopus Octopus vulgaris. The sequence identities of the deduced amino acid sequences among the cephalopod actins were around 98%, and the substitutions were mostly limited to Subdomains 1 and 3. Phylogenetic analyses revealed that cephalopod actins formed one cluster and were distinguishable from the bivalve counterparts. The modeled tertiary structure of squid actin was very similar to that of rabbit counterpart, but the structures of Subdomains 1 and 3 were slightly different.

Relationship among pH, generation of free amino acids, and Maillard browning of dried Japanese common squid Todarodes pacificus meat

Relationship among pH, generation of free amino acids (FAAs), and Maillard browning was investigated in Japanese common squid during air drying at 40 °C to prevent its discoloration. In the surface color measurement, increase in the b* value which is an indicator for Maillard browning of the dried squid was mitigated at pH 4.0–6.0 and accelerated at pH 7.5–9.0. Adjusting the pH to 5.5 effectively suppressed increasing of the b* value (p < 0.05). Arginine (Arg) generation involved in the Maillard reaction, was inhibited in the dried squid at pH 5.5 (p < 0.05). Maillard reactivities between ribose and amino acids were lower at pH 4.0 than at pH 5.5 (p < 0.05). These results indicate that browning of the dried squid is significantly suppressed at pH 5.5. Moreover, suppression of Arg generation is more effective than weakening of Maillard reactivity between ribose and Arg, in mitigating Maillard browning of the dried squid at an acidic pH.

Response of winter cohort abundance of Japanese common squid Todarodes pacificus to the ENSO events

The Japanese common squid Todarodes pacificus is an economically important species with one year lifespan, which is significantly influenced by climatic and environmental variability. According to the fishery data of the winter cohort of T. pacificus from 2003 to 2012, as well as environmental data and the Oceanic Nino index (ONI, which was defined by the sea surface temperature (SST) anomaly in the Nino 3.4 region), variations in the SST, chlorophyll a (Chl a) concentration, suitable spawning area (SSA) and sea surface height anomaly (SSHA) on the spawning ground of T. pacificus were examined under the El Nino and La Nina conditions. Their influences on squid abundance (defined by catch per unit effort, CPUE) were further assessed. The results showed that seasonal changes were found in SST, Chl a and SSA on the spawning ground of T. pacificus. Correlation analysis suggested that annual CPUE was significantly positively correlated with Chl a and SSA (p 0.05). Moreover, the El Nino and La Nina events tended to dominate the changes of SSA and Chl a concentration in the key area between 25°–29°N and 122.5°–130.5°E, driving the variability of squid abundance. However, this influence varied with the intensity of each anomalous climatic event: the weak El Nino event occurred, the spawning ground was occupied by waters with enlarged SSA but with extremely low Chl a concentration, leading to low squid recruitment, the CPUE then decreased; the moderate intensity of El Nino event resulted in shrunk SSA but with high Chl a concentration on the spawning ground, the squid recruitment and CPUE increased; the moderate intensity of La Nina events yielded elevated SSA and high Chl a concentration on the spawning ground, the squid recruitment and CPUE dramatically increased. Our findings suggested that the ENSO events played crucial effects on the incubating and feeding conditions of the winter cohort of T. pacificus during the spawning season and ultimately affected its abundance.

Characterization of myosin heavy chains from the mantle muscles of cephalopods

Myosin heavy chain (MyHC) genes from the mantle muscles of three cephalopod species, namely, golden cuttlefish Sepia esculenta, Japanese common squid Todarodes pacificus, and spear squid Loligo bleekeri were subjected to synthesis of first strand cDNA by reverse transcription-PCR. As a result of sequencing of the obtained cDNA fragments, the MyHCs from S. esculenta and L. bleekeri were found to consist of 1936 amino acids, while T. pacificus MyHC consisted of 1939 residues. The sequences were found to be 73%, 55%, and 41% identical to those of the Ca2+-regulated scallop MyHCs, human skeletal MyHC, and chicken gizzard (smooth muscle) MyHC, respectively. The cephalopod MyHCs conserved ATP- and actin-binding sites as well as light chain binding sites in the head (S1) region with the clear differences in sequence homology from those of higher organisms, and typical ?-helical heptad repeats involved in the formation of coiled-coil structure in the rod region. The sequences of the two surface loops at the 25/50 kDa and 50/20 kDa junctions of the motor domain were found to be conserved among cephalopods compared to those from the other sources. In the phylogenetic tree based on the amino acid sequences, the cephalopod MyHCs formed a cluster, clearly different from the other invertebrate counterparts, in accordance with the results of tertiary structure modeling of the head regions.

Salt soluble without jelly-like component from the oviducal gland induces chorionic expansion in the ova of the Japanese common squid Todarodes pacificus

In vitro fertilization of squid requires the jelly substance found in the female oviducal gland; yet, the active component of this substance that facilitates fertilization remains unknown. Here, we used biochemical methods to separate the jelly substance of Todarodes pacificus (Oegopsida) and Sepioteuthis lessoniana (Myopsida family) into four fractions; specifically, two water soluble fractions (Molecular weight > 10,000 and < 10,000), one salt soluble fraction, and one insoluble fraction. The salt soluble fraction of T. pacificus induced chorionic expansion (perivitelline space formation), which precedes the normal embryonic development of ova. In contrast, the salt soluble fraction of S. lessoniana elicited insufficient expansion of the ova, only producing embryos with high abnormality rates. These results suggest that the salt soluble component(s) (not the jelly-like substances) in the oviducal gland induce chorionic expansion and hatching in Oegopsida, and that these components may be similar in Myopsida.

Mechanism study of high browning degree of mantle muscle meat from Japanese common squid Todarodes pacificus during air-drying

Mantle meat from the Japanese common squid (Todarodes pacificus) browns more than other squid meats during air-drying. The factors contributing to the browning of Japanese common squid, long-finned squid (Photololigo edulis) and bigfin reef squid (Sepioteuthis lessoniana) were studied in boiled and raw meat both before and after air-drying. Dried raw meat from the Japanese common squid browned more than dried boiled meat (b∗ value, from 4.7 to 28.5). The results from SDS–PAGE showed significant degradation of myosin heavy chain (MHC) suggesting that protease activity in raw Japanese common squid meat was higher than in the other two species. The concentration of arginine (1932.0mg/100g) and ribose (28.8μmol/g) in Japanese common squid meat was higher than in the other two species. These results suggest that high protease activity and high concentrations of arginine and ribose increase the browning discoloration of Japanese common squid during air-drying.

The effect of lunar cycle, tidal condition and wind direction on the catches and profitability of Japanese common squid Todarodes pacificus jigging and trap-net fishing

Jigging with artificial lights (squid jigging) and deploying of large scale trap-net (also known as a set-net in Japan), are the major methods to capture Japanese common squid Todarodes pacificus in western Japan. Squid jigging is a highly selective fishing method. However, it consumes large amount of energy for steaming to the fishing ground and for lighting. In contrast, trap-net fishing requires substantially less energy but its capture efficiency is strongly influenced by its stationary mode of capture. The primary objective of this study was to analyze how various environmental and biological factors such as the lunar cycle, tidal condition, wind direction and squid abundance affect the capture efficiency of squid jigging and trap-net fishing. We analyzed the effect of these factors on squid catch in five Fisheries Cooperative Associations located on four islands in Nagasaki Prefecture, western Japan. Our analysis shows that squid catch in jigging and trap-net fishing is mainly influenced by the lunar cycle but also tide and wind direction play a marked role. In addition, squid abundance significantly affects the catches in trap-net fishing. Recommendations are made to improve the overall profitability of squid fishing by proper choice of the capture method, location and season.

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.

Why model assumptions matter for natural resource management: interactions between model structure and life histories in fishery models

1. Bioeconomic models are increasingly used to provide benchmarks for harvest levels in wildlife and natural resource management, yet uncertainties related to model structure are underexplored. We investigate the importance of a range of uncertainties with a focus on model structure and life histories when estimating bioeconomic target reference point (TRPs) and assess the policy implications of ignoring these uncertainties. 2. We use three contrasting case studies to investigate the interactions between model, observational and process errors related to life-history parameters: the short-lived Japanese common squid Todarodes pacificus and Pacific saury Cololabis saira, and the slow-growing Patagonian toothfish Dissostichus eleginoides. We developed a simulation framework to test the harvest strategies resulting from bioeconomic TRPs under various assumptions about model structures and parameters. 3. We found the relative importance of different types of uncertainties affecting precision and accuracy of the model outputs varied according to the life-history traits. Little difference in TRP estimates was found between simple vs. complex population models for saury, while large differences were found for toothfish. The assumptions made about stock structure for squid not only resulted in different TRP estimates (generally, smaller for the multistock models), but also different economic outcomes depending on the balance of effort allocation between stocks. 4. Synthesis and applications. We use models similar to those used in the actual management of three case study species to explore the effects of interacting uncertainties on the management advice. We show that the interactions between structural elements of the models lead to very different management advice, depending on the life history of the species concerned. For the long-lived toothfish, life-history and gear selectivity parameters interacted strongly. For the short-lived squid which is managed as two stocks, spatial fishing effort allocation, correlation of environmental drivers between stocks and differential stock productivity interacted, producing very poor economic performance if assumptions about stock structure are incorrect. The key message for model-based natural resource management is that it is vital to investigate the major uncertainties related to model structure, process and estimation errors simultaneously, because they interact to produce non-intuitive results.

イカ釣り操業船周囲におけるスルメイカの行動特性

イカ釣り操業時のソナー画像と釣獲量の変化から操業船周囲におけるスルメイカの群れの動きを調べた。船上漁灯を用いた夜間操業時には，イカの群れは船体周囲を移動しながら徐々に船体に接近し，釣獲直前には船体前後に分布することが多く，船首および船尾に近い釣機ほど釣獲尾数は多かった。海中照度は船体左右に比べて船体前後で低かった。以上の結果から，イカの群れは周回しながら徐々に船体に接近し，照度の低い船体前後から船底下陰影部に入り，釣獲されると考えられる。

Feeding habits of juvenile Japanese common squid Todarodes pacificus: Relationship between dietary shift and allometric growth

In this study, ontogenetic dietary shifts in relation to morphological changes were examined in juvenile Japanese common squid Todarodes pacificus (<160mm mantle length; ML) collected in the Sea of Japan. Ten morphometric characters were measured for 147 specimens of Japanese common squid. The allometric growth pattern of each character in relation to ML was studied by using the logarithmic form of the allometric growth model with piecewise regression analysis. The allometric growth pattern indicated that the body shape of T. pacificus changed from a rounded to a more streamlined shape, and only growth of the fin base length and fin width were positively allometric. Three morphological characters had an inflection point at 53–72mm ML, indicating the transformation to an adult morphology. The digestive tract contents of 135 squids were examined for dietary shifts. T. pacificus smaller than 50mm ML fed exclusively on crustaceans such as copepods, amphipods and euphausiids, and then shifted to a mixed diet of crustaceans and fish at 50–99mm ML; after reaching 100mm ML, fish were the most important prey items and crustaceans became less important. These suggest that the swimming performance of T. pacificus changes markedly at around inflection points, the size at which T. pacificus starts to feed on fish. Therefore, the dietary shift is suggested to be closely related to the ontogenetic change in swimming performance.

Characteristics of divalent minerals extracted from liver of Japanese common squid Todarodes pacificus under various experimental conditions

In relation to the problem of how to utilize the waste from squid processing, we determined the proximate and mineral compositions of liver of the Japanese common squid Todarodes pacificus, and characterized the behavior of divalent minerals, focusing in particular on cadmium removal. The squid liver contained fat (44.0 g/100 g dry matter), protein (13.5 g/100 g dry matter), and ash (2.11 g/100 g dry matter). It also contained the macrominerals sodium, potassium, magnesium, and calcium, as well as the trace minerals iron, zinc, cadmium, and copper. Low- and high-pH treatments (pH 2 and 12) removed the cadmium entirely, but the trace minerals zinc, iron, and copper, as well as soluble protein, which are all important for proper functioning of the human organism, were also removed in large quantities. High percentages of soluble minerals and soluble protein were found in the low molecular weight (MW < 10,000) fraction. The solubility of zinc and copper were strongly related to the solubility of cadmium, but there was no relationship between the solubilities of magnesium and cadmium. On the other hand, while treatment with either 0.9 % NaCl or 100 mM phosphate buffer (pH 7.4) also removed the cadmium completely, it left some useful compounds (trace minerals and soluble protein) in the solid part, so these treatments may represent appropriate methods for removing cadmium from squid processing waste.

暗環境下の飼育水槽中におけるスルメイカの行動観察

スルメイカの対光応答特性の把握と，観察手法の構築を目的として，明暗両環境下におけるスルメイカの行動を音響カメラによって水槽内で観察した。明環境下ではスルメイカは離底して遊泳行動をとることが観察された一方，暗環境下では主に着底行動をとり，散発的に壁面に衝突する行動が観察された。このことから，スルメイカは視覚が機能しない状況では空間認識能力を失うことが示唆された。また，明暗の光条件を切換えた際には，スルメイカの行動は，切換後の光条件に対応した遊泳もしくは着底行動へと速やかに変化することが観察された。

太平洋を回遊するスルメイカ冬季発生系群の成長に及ぼす孵化時期と性差の影響

太平洋を回遊するスルメイカ冬季発生系群の成長に影響を及ぼす要因を明らかにするため，2000～2011 年に東シナ海と太平洋，対馬海峡で採集された標本の平衡石の日齢解析による成長推定を行った。日齢と外套背長の関係はゴンペルツの成長式に適合し，式からの成長差は年級，孵化月，性別により異なった。成長の年変動へ影響を及ぼす環境要因は検出されなかったが，孵化月の推移に伴う成長促進は黒潮親潮移行域の春の水温上昇と対応した。南下回遊時の雄の成長は雌より小さく，雌より早い雄の成熟に伴う成長抑制によると考えられた。

Effect of a stepwise lighting method termed “stage reduced lighting” using LED and metal halide fishing lamps in the Japanese common squid jigging fishery

Lighting systems combining light-emitting diodes (LEDs) and metal halide lamps (MHs) are expected to be energy-saving tools in Japan’s squid jigging fishery. Previous research has shown the need for light stronger than LEDs (9 kW) and 36 MHs (108 kW) to catch the Japanese common squid Todarodes pacificus. We tested a stepwise lighting method termed “stage reduced lighting” in the Tsushima Strait in January and February 2010 using nine fishing boats. LEDs (9 kW) and 50 MHs (150 kW) were lit for 3.9 h on average, and then the number of MHs was reduced to either 30 or 36 until the end of fishing (7.3 h on average). This method reduced fuel consumption by 22–25 % compared to the continuous use of all fishing lamps (159 kW). We carried out a catch analysis of nine experimental boats and 21 commercial boats during the experimental period. Generalized linear modeling analysis suggested that the squid catch can be explained by the illuminated fraction of the moon and monthly changes in squid abundance, and the lighting method. The stage reduced lighting using LEDs and MHs has the potential to reduce fuel consumption while maintaining the squid catch.

Phylogenetic relationships among the family Ommastrephidae (Mollusca: Cephalopoda) inferred from two mitochondrial DNA gene sequences

Squids of the family Ommastrephidae are distributed worldwide, and the family includes many species of commercial importance. To investigate phylogenetic relationships among squid species of the family Ommastrephidae, partial nucleotide sequences of two mitochondrial gene loci (cytochrome c oxidase subunit I [1277bp] and 16S rRNA [443bp]) of 15 ommastrephid species and two outgroup species from the families Loliginidae and Enoploteuthidae were determined and used to construct parsimony and distance based phylogenetic trees. The molecular data provided several new phylogenetic inferences. The monophyletic status of three subfamilies (Illicinae, Todarodinae and Ommastrephinae) was well supported, although phylogenetic relationships between the subfamilies were not resolved. Inclusion of a problematic species, Ornithoteuthis volatilis, to Todarodinae was indicated. Within Todarodinae, the Japanese common squid Todarodes pacificus was observed to have much closer relationship to the species of the genus Nototodarus than to its congener (Todarodes filippovae). These results indicate that re-evaluation of several morphological key characters for ommastrephid taxonomy may be necessary.

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.

Continuous monitoring of catch fluctuation of Japanese common squid Todarodes pacificus using load data of squid jigging machine

イカ釣り操業時におけるスルメイカの釣獲状況を連続的に把握するため，自動イカ釣機にかかる負荷を 1 秒毎に記録する装置を作製した。釣具ライン巻上時の平均負荷と手作業で計数して求めた釣機 1 台 1 時間当たりの釣獲尾数（CPUE）の間に高い相関が認められた。両者の関係式に基づいて負荷から CPUE を推定して実測値と比べたところ，釣具ライン 1 ストロークから操業全体まで幅広い時間スケールで推定値と実測値はほぼ一致した。以上から，負荷記録装置は釣獲状況を高い時間分解能で把握するうえで特に有用であることが分かった。