Fisheries science Vol. 70(2004) No. 6

This study explored the fundamental process that controls interannual change in plankton biomass on the Pacific coast of Japan, focusing on the spring period of shirasu fishery. A 1-D model of primary production revealed that the strength of horizontal advection induced by warm water intrusion from the Kuroshio into the Pacific coast is the most critical for plankton biomass compared with other factors such as diffusion and production. This conclusion was also confirmed by a sensitivity analysis of the model.

The size selectivity of a trammel net for herded oval squid Sepioteuthis lessoniana in Tateyama Bay, Chiba Prefecture, was estimated by comparison between the mantle length frequency distributions of oval squid caught by a trammel net and by a set net. The measured mesh sizes of the inner net of the trammel net and of the final section of the set net were 85.3 and 11.3 mm, respectively. In the trammel net fishery where oval squid are herded into the net, most of the oval squid are caught in the bag-shaped inner net. Hence, the logistic function was employed for the size selectivity curve of the trammel net. The ‘share each length's catch total’ (SELECT) model was implemented for the estimation of the selectivity curve. The size selectivity r(l) of the trammel net for the oval squid was expressed as a logistic function of the mantle length l: r(l)=exp (-18.57+0.88 l)/[1+exp (-18.57+0.88 l)]. From these logistic parameter estimates, the 50% selection mantle length and selection range (L₇₅-L₂₅) were calculated as 21.07 and 2.49 cm, respectively. The selection probability of oval squid whose mantle girth was equivalent to the mesh perimeter of the inner net was 0.09. Accordingly, oval squid of a girth smaller than the mesh perimeter were likely to pass through the mesh to escape from the net.

The hydrodynamic resistance of small pot traps has been conducted in order to establish some basic information. The specific objectives of the study was to measure the hydrodynamic force and estimate the critical setting condition for traps. Five types of traps with different materials were used in the experiment: a netted semi-cylinder shape, a wire semi-cylinder shape, a heart shape, a box shape, and a cylinder shape. The hydrodynamic force of each trap was measured in a flume tank. Flow speeds in the flume tank were 0.1, 0.2, 0.3, 0.4, and 0.5 m/s. Attack angles for this study were 0, 15, 30, 45, 60, 75, and 90 degrees. At an attack angle of 0 degrees the main axis of the trap was parallel to the water flow and at 90 degrees it was vertical. The values of the hydrodynamic drag coefficient varied with traps: netted semi-cylinder shape, 2.75-5.96; wire semi-cylinder shape, 2.81-4.49; heart shape, 2.77-3.66; box shape, 2.39-2.97; and for cylinder shape, 3.57-3.67. The flow speed (0.5 m/s) was effective to set the netted semi-cylinder, wire semi-cylinder, box, and cylinder shaped traps. The same flow speed applied to the heart-shaped trap was only effective to a maximum of 30 degrees attack angles and below.

Estrogen receptor (ER) cDNA was cloned from the liver of common Japanese conger Conger myriaster. Common Japanese conger ER cDNA contains 2543 nucleotides including an open reading frame that encodes 596 amino acids, with a molecular weight of 66.1 kDa. The deduced amino-acid sequence of the common Japanese conger ER shares 85% identity with that of eel Anguilla japonica ER-β, and 39-46% and 53-59% identity with the deduced sequences of ER-α and ER-β of other species, respectively. In a phylogenetic analysis, the common Japanese conger ER was found to cluster with the ER-β of other species. The common Japanese conger ER-β also has six domains (A-F), which are conserved in the nuclear receptor superfamily. The amino-acid sequences in the C and E domains were highly conserved between common Japanese conger ER-β and other ER. However, the other domains showed low homology. In the female common Japanese conger, ER-β mRNA was highly expressed in the liver and pituitary gland. The expression levels of the ER-β gene increased from the oil droplet stage to the primary yolk globule stage and were maintained until the migratory nucleus stage.

Baited traps were used over 24 h to reveal the diel activity and vertical distribution of three dominant lysianassoid amphipods (Scopelocheirus onagawae, Anonyx omorii, Anonyx abei) in Onagawa Bay, north-eastern Japan. The three species were the most dominant small crustacean scavengers in the bay. Most individuals were caught by traps deployed 0.3 m above the bottom, showing that they were active in the layers close to the sea bottom. No habitat segregation was found among species or developmental stages, suggesting that these scavengers rely on the food supply from bottom deposits. The three species increased remarkably in numbers of collected individuals at night, showing a rise in feeding activity. The two Anonyx species were collected only during the night, and S. onagawae was collected mostly during the night. The nocturnal activity appears to be an adaptation to reduce predation risks. However, juveniles of S. onagawae appeared even during the day, suggesting that feeding might take precedence over avoiding predation. Baited traps collected ovigerous females of S. onagawae but not of Anonyx species; the reason for the difference could not be determined.

To clarify the feeding habits of tidal mudflat fishes, the gut contents of 29 fish species, collected from unvegetated tidal mudflats in Tokyo Bay, central Honshu, Japan, were examined. Ontogenetic changes in food preference were recognized in 21 species, including several of commercial importance (e.g. Acanthogobius flavimanus, Konosirus punctatus, Mugil cephalus cephalus, Plecoglossus altivelis altivelis, and Sardinella zunasi). In general, larvae and/or juveniles of these species fed mainly on small zooplankton or benthic harpacticoid copepods, later switching to other prey items with growth (e.g. gammaridean amphipods, mysids, polychaetes, detritus, bivalves, and juvenile fishes). A cluster analysis based on dietary overlaps showed that the tidal mudflat fish assemblage comprised six feeding guilds (small benthic and epiphytic crustacean, zooplankton, detritus, mollusc, polychaete, and fish feeders). Of these, small benthic and epiphytic crustacean feeders were the most abundantly represented in the number of species.

Females of the swimming crab Portunus trituberculatus were cultured under natural temperature and high temperature (21°C) conditions to examine ovarian development and oviposition from autumn (October) to the beginning of breeding season in the following spring (May). Ovaries developed because of vitellogenesis of oocytes from October to December and their developmental state did not change during the overwintering period from December to March. In spring, from late March to mid May, some ovaries reached prematuration and maturation stages and ovipositions began from mid-late April under natural temperature conditions. Females reared in tanks of high temperature regimes oviposited earlier than those reared in tanks of natural temperatures. The number of days to oviposition tended to decrease with advancement of the beginning times (early February to late April) of culture of females under high temperature regimes; induced ovipositions were achieved more easily with increasing photoperiod from c. 12 h in early February to c. 14 h in late April. Therefore, it is inferred that the temperature and photoperiod are important environmental factors controlling ovarian development and oviposition.

Two experiments were conducted to determine the capability of the giant gouramy Osphronemus gouramy to assimilate dietary carbohydrate. In experiment 1, fingerlings with an initial body weight of 29-32 g were fed diets containing 20.8, 35.6, 49.8 and 57.0% carbohydrate three times daily, to satiation, for 40 days. In experiment 2, subadults with an initial body weight of 78.7-79.5 g were fed diets containing 21.2, 30.1, 38.6 and 47.5% carbohydrate three times daily, to satiation, for 60 days. The diets had the same amount of protein and the same energy content. The results of experiment 1 showed that the blood glucose levels of fish fed high carbohydrate diets (49.8 and 57.0%) in the 18 h postprandial were lower than those of fish fed low carbohydrate diets (20.8 and 35.6%). The peak of the blood glucose levels in all treatments was found 5 h postprandial. Experiment 2 showed that the blood glucose level of fish was the same among treatments; and the peak of the blood glucose levels was found 9 h postprandially. It was also found that the protein retention, daily growth rate and feed efficiency of the dietary 20.8% carbohydrate levels in experiment 1 were all significantly higher than in other treatments; whereas those in experiment 2 showed no significant difference among the treatments (P>0.05). In both experiments 1 and 2, lipid retention increased significantly as the dietary carbohydrate level was elevated (P<0.05). It was concluded that fingerlings of giant gouramy have a lower capability for utilizing dietary carbohydrate, and of the treatments, the 20.8% diet was optimal, whereas subadults could utilize diets with higher carbohydrate levels, as high as 47.5%.

The stock size estimates from adaptive framework virtual population analysis are sometimes very sensitive to the model's assumptions. The uniqueness and precision of stock size estimates from adaptive framework virtual population analysis are examined analytically and numerically. The results indicate that (i) when the fishing mortalities remain constant for all years, the stock size estimates are not determined uniquely without additional assumptions, and (ii) when the cumulative fishing mortalities are similar among cohorts, the precision of stock size estimates will be poor, even if the abundance indices are precise and informative. For the precise estimation of stock size, it is necessary that fishing mortalities vary among years, that cumulative fishing mortalities vary among cohorts and that auxiliary information such as selectivity is available in addition to precise abundance indices.

This study investigated the effect of conjugated linolenic acid (CLNA) on the growth and lipid composition of fingerling rainbow trout Oncorhynchus mykiss. Thirty individuals in each tank with three dietary treatments and duplicate groups were subjected to three dietary levels (0:4, 2:2, 4:0) of CLNA and linolenic acid (LNA) at 16°C in the laboratory for a period of 9 weeks. Punicic acid (cis-9, trans-11, cis-13-18:3) and linseed oil were used as sources of CLNA and LNA, respectively. The hepatosomatic index and body lipid content of the 2% CLNA dietary treatment increased significantly (P<0.05) with respect to the control (LNA treatment). But the specific growth rate and percent gain did not improve significantly. After 6 weeks' observation, the 4% CLNA dietary treatment exhibited higher mortality and liver weight but lower weight gains (1.1-1.9 g). No significant differences were observed in the results of the feed efficiency and moisture as well as the protein content of the whole body among the treatments. Incorporation of CLNA into fish tissues was at a distinctly higher level in neutral lipids than in polar lipids. Increased levels of 22:6n-3 were found in the 4% CLNA treatment but decreased levels were found in the 2% CLNA treatment in both neutral and polar fractions. In the CLNA treatments, saturated fatty acid was relatively unaffected, the level of 18:1 was increased and the level of 18:2n-6 was decreased. These results indicate that the lower level (2%) of CLNA had no significant effect on the growth and the higher level (4%) of CLNA caused higher mortality as well as attenuating the growth of the fish. Dietary CLNA accumulated in a greater amount in the neutral lipids and modulated the fatty acid composition in the whole body of rainbow trout fingerlings.

The food habits of 595 houndsharks of four species, Triakis scyllium (n=179, 42-148 cm total in length), Hemitriakis japanica (n=57, 42-102 cm), Mustelus griseus (n=193, 39-100 cm), and Mustelus manazo (n=166, 43-120 cm), found in the central Seto Inland Sea, Japan, from March 1997 to October 1999 and May 2000 to July 2002, were studied. T. scyllium changed their main food items from shrimps to echiuran worms then to cephalopods with their growth. Comparing food habits by the value of similarity (maximum=1), the small-sized T. scyllium had a low value (0.17) compared to larger sharks. T. scyllium gradually increased the diversity of food until it reached 700 mm long in total length, however, after that it decreased. H. japanica appeared mainly in summer and autumn and ate cephalopods and fishes. M. griseus preyed on various crustaceans and decreased the diversity of food with growth. M. manazo preferred crustaceans and polychaetes. There was no certain tendency in the diversity of the food habit for M. manazo.

Myxobolus buri Egusa, 1985, is a well-documented myxosporean parasite that causes the scoliosis of cultured yellowtail Seriola quinqueradiata. A similar parasite has been described as Myxobolus acanthogobii Hoshina, 1952, from the brain of the yellowfin goby Acanthogobius flavimanus, although this parasite is not associated with skeletal abnormalities in host fish. The present study aimed to re-examine the identification of these two parasites by morphological and molecular analyses. Morphological characteristics (e.g. presence of the intercapsular processes and several folds on the sutural ridges) and spore dimensions were not distinguishable between the two species and were consistent with those in the original descriptions. Molecular analysis indicated that small subunit rRNA gene sequences shared 100% identity between the two parasites. Consequently, it can be concluded that M. buri is synonymous with M. acanthogobii, and thus this parasite can be reassigned as M. acanthogobii.

In order to establish genetic signatures for intraspecific identification, parts of the genes rbcL, rbcS and psbA and their intergenic spacer (IGS) regions were amplified by polymerase chain reaction (PCR) from the chloroplast genomes of Heterosigma akashiwo strains isolated from Japan. A transfer RNA-Leu gene trnL and a hypothetical gene cfxQ, which is related to ribulose bisphosphate carboxylase/oxygenase expression, were found in the upstream region of the rbcL gene and in the rbcS-psbA IGS region, respectively. All the gene-coding regions and the IGS regions between rbcL and rbcS showed the same sequences among the strains tested. In contrast, the rbcL upstream regions and the rbcS-cfxQ IGS regions showed some differences such as nucleotide substitutions, duplications and inversions between NIES-5 and the other strains. Based on these sequence data, five genetic signatures were established and their simple and rapid detection by means of strain-specific PCR primers and PCR-restriction fragment length polymorphism techniques was examined. The results suggested the usefulness of these genetic signatures and techniques for the discrimination of H. akashiwo populations.

An application of the acoustic Doppler current profiler (ADCP, 153.6 kHz) in combination with a scientific echo sounder (EK60, 38 and 200 kHz) was investigated to estimate the density of krill Euphausia pacifica. The acoustic backscattering strength from sound scattering layers was compared with biomass estimates from midwater trawls. Euphausia pacifica was targeted among mixed species populations in the sound scattering layer in the offshore Funka Bay area of Hokkaido, Japan. The frequency characteristics of acoustic backscattering by krill were calculated using a distorted wave Born approximation scattering model at three frequencies. Krill aggregations identified from the EK60 data were extracted as the mean volume backscattering strength difference between two frequencies. They were then used to identify similar aggregations in the ADCP data by matching observation times and depths for the two methods, which were applied simultaneously. Results from the comparison of the mean volume backscattering strength and the density calculated from the ADCP and EK60 showed that ADCP can be used to measure density and spatial-temporal distribution of krill aggregations. Current speed and direction at the study site were found to be 16.1 cm/s and 187.0°, respectively, and krill speed and direction (including the current component) were found to be 19.8 cm/s and 172.2°, respectively. Based on the ADCP data, the net speed and direction of the krill aggregations were found to be 5.9 cm/s and 128.0°, respectively.

A histological examination was made of the ontogenetic development of the digestive and immune systems of the larval and juvenile kelp grouper Epinephelus bruneus reared in the laboratory. The liver, gall bladder, pancreas and the demarcating region between the intestines and rectum were formed within 3 days post-hatch (dph). During the preflexion phase (within 16 dph), revolution of the intestine concluded, and pharyngeal teeth and the mucous cells of the esophagus were differentiated. In the transitional period to the juvenile stage (25 dph), the blind sac of the stomach, gastric glands and pyloric caeca began to form. From the viewpoint of the differentiation phase of the adult-type digestive system, the kelp grouper is similar to Heterosomata, hitherto reported. The primordial thymus, kidney and spleen were present at 12, 1 and 6 dph, and the small lymphocytes in these lymphoid organs appeared at 21, 30 and 33 dph, respectively. The developmental sequence of the lymphoid organs and the appearance ages of the lymphoid organs and small lymphocytes in the lymphoid organs in the kelp grouper are similar to those of other marine fish previously reported, except for the Pacific bluefin tuna Thunnus orientalis.

A new abalone postlarval culture system, Stott's abalone postlarval production system (SAPPS), is being developed as an alternative method for settling larvae and on-growing postlarval abalone. SAPPS was tested in trial 1 using two commercially available artificial diets, Adam and Amos (Adam; supplied by Adam and Amos, Mt Barker, SA, Australia) and Cosmo (Cos; supplied by Cosmo, Matsuyama, Japan), against the diatom biofilm method (Diatom). In trial 2, SAPPS was tested against the previous production system (PPS, used by Stott et al. 2002). Larvae were induced to metamorphose and the resulting postlarvae were on-grown in 10-L flow-through tanks for 28 days in their respective treatments. The final survival of postlarvae was significantly higher (P<0.05) in the SAPPS-Cos group (56.7±11.15%) than in the Diatom (9.4±2.7%) and SAPPS-Adam groups (8.5±1.1%). The final length of postlarvae in SAPPS-Cos (1065±73 μm) was significantly higher (P<0.05) than those in the other two treatments (average of 841-883 μm). In trial 2 the metamorphosis rate was improved by using Spirulina platensis. The final length of postlarvae in SAPPS (1449-1471 μm) was significantly higher (P<0.05) than PPS (1065-1075 μm) and Diatom (993 μm). There is potential for SAPPS to be used as an alternative to the current diatom method in the culture of postlarval abalone.

A feeding trial was conducted to investigate the effect of dietary lipid and phosphorus levels on nitrogen and phosphorus excretion of young yellowtail under on-site conditions for 4 months. Three levels of dietary lipid (200, 250 and 300 g/kg) and four levels of supplemental phosphorus (0, 2, 4 and 7 g/kg) were tested in a complete randomized design with a 3×4 factorial arrangement. Each net cage of 170 yellowtail were fed the experimental diets for 4 months and the fish grew from approximately 346-912 g, at water temperatures between 18 and 23°C. Dietary phosphorus levels did not cause any difference in weight gain, specific growth rate, feed conversion ratio and nitrogen retention. However, its increasing supplemental levels reduced phosphorus retention, consequently increasing its excretion, whereas nitrogen excretion remained uninfluenced. In contrast, increasing the dietary lipid level resulted in its greater deposition in the whole body of young fish leading to a reduction in nitrogen excretion. This study has shown that phosphorus levels need not necessarily be high in the diets of young yellowtail. In addition, dietary lipid can be manipulated favorably to produce environmentally suitable diets.

The occurrence and distribution of larval and juvenile Japanese flounder Paralichthys olivaceus and major demersal fish from May to September were examined at seven sandy beaches at the central Seto Inland Sea. The flounder appeared from late May to August and were mainly collected at a depth of 2-5 m. Settlement of larval flounder was seen from late May to late June. A total of 6412 individuals of 17 species representing 12 families were collected in the study area. The dominant fish species were Favonigobius gymnauchen (56.0%), Tarphops oligolepis (8.1%), Rudarius ercodes (7.8%), P. olivaceus (7.3%), Repomucenus spp. (7.0%) and Heteromycteris japonica (3.3%). The catches of flounder differed among beaches and months. The number of flounder in June at Ohama Beach, where the most flounder were collected, was 22.6 individuals per haul (400 m²). The density of the flounder correlated negatively to that of F. gymnauchen.

The abundance of food organisms and feeding habits of larval and juvenile Japanese flounder were examined during the period from May to August in 1999, 2000 and 2001 at the sandy Ohama beach, the central Seto Inland Sea. The food organisms collected with a sledge net consisted of 40 families from 18 orders, dominated by mysids, crangonids and gammarids. The mean densities of mysids, crangonid shrimp (Crangon spp.), gammarids and fish were 2.74, 6.74, 2.91 and 0.15 individuals/m², respectively. The main prey of the flounder (n=202; range of total length 9.80-75.95 mm) was mysids and small crangonid shrimp (<14 mm in body length). Prey fish availability was low, as the density of fish was low. The small crangonid shrimp was abundant, and the large crangonid shrimp, which could prey on larval flounder, was not abundant. The crangonid shrimp was important not as a predator for the flounder but as prey. The flounder preferred epifaunal mysids, Nipponomysis ornata and Anisomysis ijimai, to sand-burrowing mysids, Iiella oshimai, and avoided crangonid shrimp.

The attracting effect of a small dose of tetrodotoxin (TTX) on eight toxic snail species (Polinices didyma, Natica lineata, Natica vitellus, Zeuxis sufflatus, Niotha clathrata, Oliva miniacea, Oliva mustelina and Oliva hirasei) and two non-toxic species (Pomacea canaliculata and Satsuma bairdi) was investigated. Each toxic snail species was determined to contain TTX. The minimum lethal dose of TTX for most toxic snails was estimated to be >44.5 μg TTX/20 g body weight, but for non-toxic snails it was <3.6 μg TTX/20 g body weight. After the attracting test, it was found that for all toxic snails there was a significantly positive relationship between the comparative attracting variation and the toxicity reported, and this relationship was linear (y=5.895x+3.443, r=0.806). The relationship between TTX resistance ability and toxicity also had a positive correlation (y=0.113x+52.447, r=0.814). However, non-toxic species showed a negative response. The more toxic snails appeared to prefer TTX, indicating that TTX is an attractant for toxic snails.

Samples of colloidal chitin and chitosans with deacetylation degrees (DD) of 50, 65, 75 and 95% (DD50, DD65, DD75 and DD95, respectively) were prepared from shrimp chitin. The hydrolytic activity of cellulase on these samples increased with the increasing DD of chitosan, with DD95 being the most easily hydrolyzed. Colloidal chitin was hardly hydrolyzed. The optimal reaction temperature and pH for cellulase digestion of chitosan were 55°C and pH 5.2, respectively. During cellulase digestion of chitosan, the 9-h hydrolysate had the highest enhancing effect on the proliferation of a human hybridoma cell, HB4C5. This hydrolysate is composed of low-molecular-weight chitosan (LMWC), with a molecular mass of 20.0 kDa, and chitooligosaccharides, which are composed of sugars with a degree of polymerization of 1-6. In vitro, the 9-h hydrolysate increased both cell proliferation and immunoglobulin (Ig) M secretion of HB4C5 because of the presence of chitooligosaccharides for the former activity and LMWC for the latter activity. In vivo, samples of the chitosan hydrolysate, chitooligosaccharide mixture and LMWC significantly increased the levels of serum IgG and IgM, and enhanced concanavalin A- and lipopolysaccharide-induced proliferation of mouse lymphocytes.

During the processing of heshiko, a fermented mackerel product, a rapid increase in peptide content in the extract and a remarkable decrease in the IC₅₀ (the inhibitor concentration to inhibit 50% of enzyme activity) as an index of the angiotensin l-converting enzyme (ACE) inhibitory activity were observed. Systolic blood pressure (SBP) in spontaneously hypertensive rats (SHR) decreased between 2 and 4 h after single oral administration of heshiko extract at a dose of 10 mg/kg as a peptide, and SBP recovered its initial level by 8 h. For single doses of extract at three different levels (5, 10 and 50 mg/kg), SBP similarly decreased after between 2 and 4 h. The decreased SBP at 50 mg/kg was almost equal to that at 10 mg/kg, indicating a low dose dependency for heshiko extract. Through successive administration of heshiko extract or its desalted extract at 1 mg/kg for 10 days, SBP decreased 7 days after the start of administration and it recovered its initial level 5 days after stopping administration. During these periods, the change in ACE activity in blood plasma from SHR administered the extract roughly corresponded to that of SBP, suggesting that ACE inhibition was related to a decrease in SBP. For long-term administration of the extract to 5-week-old SHR for 70 days, SBP decreased 28 days after the start of administration. The decreased SBP remained low for 28 days after stopping administration, whereas the decreased ACE activity recovered its initial level. These results suggest that heshiko extract influences not only ACE inhibition, but also other systems that regulate blood pressure.

The aim of this study was to develop a practical preventive method for color deterioration of sliced or filleted yellowtail muscle, especially of dark muscle, during frozen storage and post thawing. When the sliced meats were packaged in a vacuum with low oxygen permeable flexible films and then stored frozen below -40°C, no significant discoloration or browning of dark muscle was observed for 9 months or more. For higher temperature storage at -20°C or -30°C, nitrogen gas substituted packaging was a useful practical method for storing sliced meats for 6 weeks. In order to prevent color deterioration of sliced meats after thawing and subsequent storage at 0°C, the efficacy of materials of packaging was investigated. The most desirable result was obtained by using a film with oxygen permeability of 50-90 cm³/m² per 24 h.

Parvalbumin, a calcium-binding sarcoplasmic protein of approximately 12 kDa, represents the cross-reactive, major allergen in fish. In consideration of the fact that parvalbumin is contained at high levels not only in fish muscle but also in frog muscle, the present study was undertaken to clarify whether fish-allergic patients react to two parvalbumins (α- and β-parvalbumins) purified from the bullfrog Rana catesbeiana, which is sometimes consumed as a delicacy in Japan. In enzyme-linked immunosorbent assays (ELISA), sera from 12 of the 14 patients tested reacted equally to both parvalbumins purified from the Pacific mackerel Scomber japonicus and the bigeye tuna Thunnus obesus. Of the 12 sera positive to fish parvalbumins, eight sera also reacted to α- and β-parvalbumins of the bullfrog with different spectra: one serum reacted strongly to α-parvalbumin, six sera reacted strongly to β-parvalbumin and one serum reacted equally to both α- and β-parvalbumins. In addition, inhibition ELISA experiments revealed cross-reactivity between fish and bullfrog parvalbumins. Based on these results, it is proposed that fish-allergic patients should avoid the consumption of frog meat unless they are accurately diagnosed as lacking immunoglobulin E against frog.

The glass transition behavior of processed fish muscles (bonito, tuna, mackerel, sea bream, cod) and its muscle protein fractions (sarcoplasmic and myofibrillar proteins) were studied using differential scanning calorimetry. Each dried processed fish muscle and the extracted protein fractions showed clear glass transition phenomenon. The T_g values of muscles and myofibrillar proteins from red muscle fishes tended to be lower than those from white muscle fishes though there was no difference on T_g of sarcoplasmic proteins. The T_g value of whole muscle was considerably lower than that of extracted protein fractions because of the plasticizing effects of low molecular weight materials contained in the muscle.

The depletion of ascorbic acid derivatives in fish feed during the feed processing (extrusion cooking and drying) was studied at five extrusion cooking temperatures and at 85°C for 2 h dryer processing temperature. Three ascorbic acid derivatives were used: L-ascorbyl-2-mono-phosphate Mg (APM), L-ascorbic acid sodium (AAS) and L-ascorbic acid palmitic acid ester (AAP). Samples were collected after drying and ascorbic acid derivatives losses evaluated. APM was found to be quiet stable with an average retention of 88%, but AAS and AAP were unstable and the depletion was very high.

The microstructure of extruded pellets (EP) for fish under various extrusion cooking temperatures was studied by using a twin-shaft extruder. As the extrusion cooking temperature increased, the expansion rate increased and the bulk density of EP decreased. The liquefaction of the material started because of the increase in inner material temperature, the decrease in inner material pressure, and the decrease in main motor amperage. Thus, the microstructure of EP changed depending on the extrusion cooking conditions, that is, the extrusion cooking temperature effected greatly the liquefaction of the material. Generally, when the extrusion cooking temperature increased, the expansion rate increased, but a suitable temperature was found for a maximum expansion rate. The microstructure of the EP was caused by the liquefaction of the material and the microstructure effects on the function of EP. For example, the water holding capacity was affected by the inner bubble structure of an EP. These functions affect the character of the feed. EP produced under suitable conditions can have additional functions for feed.

Algal-oligosaccharide-lysates (AOL), derived from six agars and four algal polysaccharide extracts (APE), were treated with 100-500 activity units (AU) of MA103-agarases or MAEF108-agarases, and their antioxidative properties evaluated. Soluble total polyphenols (TP) were between 462.2±1.6 gallic acid equivalents (GAE, μg/mL) and 70.6±17.4 GAE. The DPPH radical scavenging capacity of all AOL went from 68.3±0.7% to 0.5±0.1%. The ferrous ion chelating capacity of all AOL went from 93.1±0.2% to 21.7±0.9%. Evaluation of the H₂O₂ scavenging capacity of all AOL was between 35.9±5.4% and 0.1±0.2%. The reducing power of all AOL went from 51.3±2.6 to 3.2±6.8 expressed as μg/mL ascorbic acid. In DPPH radical scavenging capacity, ferrous ion chelating capacity and reducing power etc., the AOL derived from the APE of Porphyra dentate (digested by 500 AU of MAEF108-agarases) were highest, in all test sets. However, the AOL derived from the APE of Monostroma nitidum (digested by 500 AU of MAEF108-agarases) had the highest H₂O₂ scavenging capacity in all test sets. The order of antioxidative activity performance of all AOL treated in this experiment, by these four antioxidative methods, is as follows: ferrous ion chelating capacity>DPPH radical scavenging capacity>H₂O₂ scavenging capacity>reducing power; this may be related to their polyphenols, small molecular weight polysaccharides or simple sugar constituents. In this study, it is demonstrated that various agarases derived from algal oligosaccharide mixtures possess good potential for use as a health food, due to their antioxidative capacity.