Two large trawl models, at a one-quarter scale, were designed, produced and tested in a flume tank in Hirtshals (Denmark). A traditional trawl, typical for the commercially bottom fisheries in Italy, was selected as a basic design for the development of a new trawl. Characteristics of the new design should include larger meshes in the net areas, where no negative effect on catching power is foreseen, high bosom height, good bottom contact and low towing resistance. The geometry and towing resistance of both the traditional and the experimental trawl models were initially measured in the flume tank for different riggings. Based on the results from detailed flume tank tests, two full-scale trawls were designed and produced. Engineering sea trials have been made on a research vessel to measure the performance of the full-scale trawls and to verify the findings from the flume tank tests. The comparison between sea trials and flume tank tests shows that it is very difficult to accurately model, in the flume tank, trawl sections where the highly elastic Rachel netting made from polyamide is used.

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The histological changes in the ovary of sevenband grouper Epinephelus septemfasciatus were examined during vitellogenesis and final oocyte maturation. Ovaries contained oocytes at the perinucleolus stage at the start of the experiment in January. Oocytes at the primary yolk stage appeared when the gonadosomatic index (GSI) was slightly on the rise in March. After that, vitellogenesis progressed and ovaries contained oocytes at the tertiary yolk stage in May. The GSI increased drastically at the same time. These results suggest that vitellogenesis in sevenband grouper starts or is already in progress in March and is completed by May, In order to clarify the process of final oocyte maturation, luteinizing hormone-releasing hormone (LHRH) analog (des Gly¹⁰, [D-Ala⁶] LHRH ethylamide) was implanted in fish with oocytes at the tertiary yolk stage. The oocytes developed to the migratory nucleus stage in 18 h and reached the maturation stage in 42 h after implantation. This indicates that final oocyte maturation is completed within 42 h after stimulation of gonadotropin-releasing hormone.

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Polymorphism of immune-related genes has the potential to be utilized as a genetic marker to survey the disease-resistant fish population. The complement is a major factor functioning both in innate and adaptive immune systems. In the present paper it was found that C3-H1, a major isoform of the complement component C3 of carp, exhibits four genetic variants defined as electrophoretic mobility, and that the four variants have different hemolytic activity. Carp serum was electrophoresed on an agarose gel and blotted onto a nitrocellulose membrane, and C3 bands were detected by immunoblotting using monoclonal antibody specific to intact α-chain of carp C3-H1 isoform. Four C3-H1 variants, designated I, II, III and IV, with different mobility were detected, and the phenotypes II and II/IV were dominant. Each of four C3-H1 variants free of cross-contamination was purified from carp sera and examined for the hemolytic activity. It was found that C3-H1-I had the highest specific activity, which was approximately fourfold higher than that of C3-H1-II, which had the lowest activity. The results suggest the possibility that carp individuals possessing a different type of C3-H1 variants have a different level of complement activity, and that the C3-H1 polymorphism can possibly be useful to screen fish with a higher level of innate immune defense.

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The occurrence of vertebrate-type steroid hormones in the hemolymph and ovaries has been reported in several crustacean species; however, their physiological roles are not sufficiently understood. In the present study, correlations between hemolymph levels of the vertebrate-type steroid hormones and ovarian development in female kuruma prawn Marsupenaeus japonicus were examined. In the first experiment, hemolymph samples were taken in November (non-reproductive period) and June (maturing and spawning period) and the hemolymph levels of estradiol-17β, estriol, progesterone, testosterone, and 11-ketotestosterone were found not to be significantly related to the ovarian development (gonadosomatic index, 0.80-9.39). In the second experiment, ovarian development was induced by bilateral eyestalk ablation in the non-reproductive period. The hemolymph levels of estradiol-17β, estriol, and progesterone did not significantly differ between the control female prawn and the eyestalk-ablated female prawn, which underwent vitellogenesis. If the examined steroid hormones were vitellogenesis-stimulating hormones as in fish, their hemolymph levels would be expected to show significant correlations with ovarian development. However, the present study found no significant correlations between hormone levels and ovarian development. This suggests that based on the available data, the examined vertebrate-type steroid hormones do not play an important role in ovarian development in M. japonicus.

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The authors have developed a micro echo sounder operating at a frequency as high as 1 MHz, which can be attached to aquatic animals in combination with a depth and temperature sensor to obtain information on the animal's prey as well as its behavior. The performance of the sounder was evaluated in an experimental tank and its detection range was estimated to confirm its effectiveness. The beam width is 5.9° and the maximum detection distance is estimated as 34 m when the target strength of an object animal is -50 dB.

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Annual acoustic surveys were conducted using a quantitative echo sounder (frequency: 38 kHz) in the East China Sea from July to September of 1997-2001. Three groups of fish were identified from the echograms, based on school shape and swimming depth characteristics: (i) anchovy Engraulis japonicus and round herring Etrumeus teres; (ii) jack mackerel Trachurus japonicus and chub mackerel Scomber japonicus; and (iii) lantern fish Diaphus spp. and pearlside Maurolicus japonicus. The area backscattering strength (Sa) of each group was divided by the total weight of fish species caught in midwater trawls. Anchovy, round herring, jack mackerel, lantern fish and pearlside were the most abundant. The estimated biomass indices of anchovy and round herring were positively correlated with the commercial landings of these species, indicating the usefulness of acoustic surveys.

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The purpose of the present paper was to describe the dynamic behavior of gill nets using the computer-aided simulation NaLA (net shape and loading analysis), a system that was developed for determining net shape and load. The general calculation model of the system was refined after considering gill net construction and the environment during operation, such as wave motion and the boundary conditions of the water surface and bottom. This method models a gill net as a group of lumped masses interconnected by springs without mass, which are arranged as knots, mesh bars, netting lines, and other rigging components. Equations of motion are then derived for each lumped mass point. Net shape, mesh opening angle, and tension distribution are estimated at each time-step by using a PC to solve the system of equations. To examine the applicability of the refined calculation model of NaLA to gill nets, experiments were conducted with a gill net in a water channel. The experimental and calculated net shape, loading, and mesh opening angles were compared. The results agreed well, confirming that the refined calculation model of NaLA for gill nets is applicable to estimate the dynamic behavior of gill nets.

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The sequencing analysis of the mitochondrial DNA control region (mtCR DNA) was performed to assess the genetic divergence and population structure of the Chinese sucker Myxocyprinus asiaticus (Cypriniformes Catostomidae) using four sample lots from natural populations of the Yangtze River. The mtCR DNA sequences of approximately 920 base pairs were obtained. A total of 223 nucleotide positions were polymorphic, and these defined 39 haplotypes. Of the 39 haplotypes, 37 (90%) were not shared, and among the populations as a whole there was little sharing of haplotypes. The average haplotype diversity (0.958) and the average nucleotide diversity (0.052) indicated a higher level of genetic diversity of Chinese sucker through the river. Analysis of molecular variation (AMOVA) of data revealed significant partitioning of variance (P<0.001) among populations (60.29%), and within populations (39.71%). The topology according to the neighbor joining and maximum parsimony methods showed mosaic composition of the 39 haplotypes, suggesting that the populations were not completely divergent. The pairwise F statistic values, however, indicated that the population structuring existed to some extent among the geographic populations. There was a positive relationship between the aquatic distance and the genetic distance (Fst) among the populations (P<0.05). Based on our data, it is suggested that genetic drift, gene flow, and stochastic events are the possible factors influencing the population structure and genetic variation.

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In order to enhance the oxygen production in anoxic bottom water using light, the bottom water and sediment collected in different seasons from a coastal area were incubated under irradiance treatments of 7 and 15 μE/m² per s by halogen lamp provided through an optical fiber. The dissolved oxygen (DO) concentrations increased from 3.6 mg/L to 7.1 mg/L in the 15 μE/m² per s irradiance treatment, while in the dark control the DO concentrations decreased to 1.1 mg/L in June. Along with the oxygen increase, chlorophyll a concentration increased from 0.24 μg/L to 1.35 μg/L while inorganic nitrogen and phosphorus decreased. These results indicate that low-intensity light is effective in stimulating photosynthesis of coastal bottom water and for net production of DO, especially in summer. It is a promising way to improve the anoxic bottom environment.

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Feeding habits of an exotic species, the Mediterranean green crab Carcinus aestuarii, in Tokyo Bay, Japan, were studied based on the analysis of stomach contents. Monthly samples were taken from May 2000 to October 2001 at stations near the Keihin Canal along the northern shore of Tokyo Bay. Stomach contents of 367 crabs (male n=200, female n=167) were examined. Carapace width ranged from 18.50 mm to 60.67 mm. Eleven food categories were identified: Bivalvia (mostly Mytilus galloprovincialis), other Mollusca, Cirripedia, Amphipoda, Brachyura, other Crustacea, Polychaeta, Pisces, unidentified animal materials, plant materials, and unidentified materials. The results showed that C. aestuarii is an omnivorous predator and that its diet depends greatly upon the availability of local prey species, especially in intertidal areas. Moreover, the analysis found no significant differences in the feeding habits of crabs of different sizes or sexes.

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The present study examined the changes of retinoid content in larval Japanese flounder Paralichthys olivaceus and Artemia nauplii. Artemia nauplii were enriched with 100 mg all-trans retinoic acid (atRA) for 6 h in a 10-L culture tank and then starved for the next 24 h. Flounder larvae at the G stage were fed Artemia nauplii enriched with atRA and then starved for the next 24 h. They were sampled at -6 h (before enrichment), and at 0, 6, 9, 18 and 24 h after enrichment for analysis of three isomers of retinoic acid (atRA, 9 cis- and 13 cis retinoic acid), retinol, retinal, and retinyl palimitate. atRA was rapidly accumulated in Artemia without isomerization. Peaks of atRA and retinyl palmitate levels were observed at 6 and 18 h in Artemia, suggesting that Artemia excrete RA metabolites and re-uptake in the tank without water exchange. atRA levels in flounder reached a maximum level at 3 h after feeding and decrease to 50% of the maximum level within 18 h, suggesting that flounder larvae can rapidly excrete dietary atRA.

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To examine predation on larval and juvenile Pleuronectes yokohamae by Crangon uritai, the spatial distribution and feeding habits of C. uritai were studied. Crangon uritai fed on various prey, including P. yokohamae. Density-dependent predation on juvenile Crangon spp., larval and juvenile gobiid fish Chaenogobius heptacanthus, mysids, and gammarids was observed. The abundance of alternative prey might, therefore, play an important role in reducing the pressure of predation on P. yokohamae. In each year, C. uritai migrated from depths of 10 m in March to depths of 3 m in May. There was a significant negative correlation between the weighted mean depth (WMD) of C. uritai and the weighted mean bottom water temperature (WMBWT). The migration was, therefore, delayed in the cold spring, during which C. uritai occupied depths of approximately 10 m. In contrast, no significant correlation was found between the WMD of P. yokohamae and WMBWT. Settlement of P. yokohamae began at depths of 15 m, mainly during early April. The spatial distributions of these two organisms show greater overlap during the cold spring, resulting in increased opportunities for predation.

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Marine silage (MS) is a new dietary item prepared by decomposing seaweed to a cellular unit and performing lactic acid fermentation. The present paper demonstrated a large (10 L)-scale preparation and a long-term (18 months)-preservation of the MS using Undaria pinnatifida as a substrate. Furthermore, two separate feeding trials were carried out to demonstrate the dietary value of the MS to the Japanese pearl oyster Pinctada fucata martensii. In the first trial, pearl oysters grew significantly when fed the MS at 3×10⁴ cells/mL per day. Shell growth and survival (69±11 μm/day; mean ± SE and 100%, respectively, n=30) of pearl oysters were higher than for the unfed control oysters (-26±8 μm/day and 100%, n=30), while oysters fed Chaetoceros calcitrans grew 205±12 μm/day (n=29) and 96.7% survived. Proximate analysis of the MS suggested a shortage of nutritional elements such as lipid contents. The second rearing trial demonstrated remarkable shell growth when pearl oysters were fed MS supplemented with a small quantity of C. calcitrans, although this observation is based on a single rearing result and needs repeated trials. The present study is the first to demonstrate a mass preparation of MS and its positive dietary effect for a bivalve.

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Xenobiotics such as oxytetracycline and oxolinic acid need to be given orally to aquatic animals to determine their absorption, distribution and elimination. Here, we describe a method for giving xenobiotics to giant tiger prawn Penaeus monodon. A histological examination revealed serious hindgut diarrhea. This appeared to be caused by a high concentration of oxolinic acid (50 mg/kg body weight) but not oxytetracycline concentration (50 and 100 mg/kg body weight). Therefore, doses of oxolinic acid and oxytetracycline were reduced to 5-10 mg/kg to avoid the problem of hindgut diarrhea. A 1-mL syringe fitted with a feeding needle was used to inject medicated feed paste containing oxytetracycline or oxolinic acid through the mouth into the stomach. No disgorging of the medication was observed during the experiment. The maximum concentrations (Cmax) of oxytetracycline and oxolinic acid were proportional to the dose. Our method is suitable for studies of the absorption, distribution, metabolism and elimination of xenobiotics in shrimp.

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Oxytetracycline is an antibacterial agent used widely for therapy of systemic bacterial infections in farmed fish, Thailand. The pharmacokinetics of oxytetracycline after intrasinus and oral administration in giant tiger prawn was examined by using a rapid high-performance liquid chromatography (HPLC) method. The kinetics of oxytetracycline was described by a two-compartment model after intrasinus administration. The distribution half-life (T_1/2α=0.089 h) of oxytetracycline was shorter than the elimination half-life (T_1/2β=23.1 h). The kinetics of orally given oxytetracycline was fitted to a one-compartment model. The bioavailability was calculated to be 59.9%. The time required for drug absorption (TDA), defined as the time for absorption to reach 90% of the maximum level, was approximately 9 h. An apparent steady-state distribution (Vss: 0.41 L/kg) was found for oxytetracycline in the present study, which is smaller than in fish species.

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The present study was conducted to investigate the effects of dietary conjugated linoleic acid (CLA)- and conjugated docosahexaenoic acid (CDHA)-supplemented diets on the growth and body lipid composition of tilapia Oreochromis niloticus. Four dietary treatments of linoleic acid (LA), CLA, docosahexaenoic acid (DHA) and CDHA were tested in this experiment over a feeding period of 9 weeks. The initial average body weight and length of fish were 4.53±0.96 g and 5.18±0.34 cm, respectively, and temperature was maintained at 25±1°C. Two replicate groups and two control groups of fish were applied among the four dietary treatments and each group consisted of 20 juvenile fish. Growth rate, feed efficiency and tissue lipid contents were not significantly affected (P<0.05) by CLA compared to the LA control group. A higher level of hepatosomatic index and lower growth rate were obtained from the CDHA dietary group. CLA and CDHA isomers were detected mainly in non-polar lipids of muscle, liver and brain. Lower values of mono-unsaturated fatty acids and 18:2n-6 levels were found in the CLA dietary fish group and there was no effect on the 20:4n-6 level in muscle, liver and brain. Conversely, higher levels of total mono-unsaturated fatty acids were found in liver and the 20:5n-3, 22:5n-3 level of the muscle polar fraction in the CDHA dietary fish group. These results indicate that 5% of CLA in diet does not influence the growth and feed efficiency of juvenile tilapia and that CLA was observed to be incorporated into muscle, liver and brain. Lower growth and higher liver lipid contents were observed in the CDHA-supplemented dietary fish group.

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During larviculture of giant grouper, Epinephelus lanceolatus, intracohort cannibalism usually results in mass mortality. Thus, in the present study, we attempted to develop a cannibal-prey length relationship from morphometric measurements for giant grouper fry and to verify it with pairwise predation experiments. Based on measurements of morphometric characteristics (i.e. mouth width, body depth, and total length), a model of prey length (mm) to cannibal length was constructed: TL_prey=0.83 TL_cannibal-2.48. According to the equation, approximately 30% is a threshold in total length differences to use for grading giant grouper fry. The threshold was supported by our pairwise experiments using 136 pairs; we found that 33 out of 36 cannibalism incidents occurred only when the prey was of equal or smaller size than that predicted by the equation. In aquaculture practice of this species, we thus suggest that when the length of larger fry exceeded that of smaller fry by more than 30%, the potential cannibals should be removed.

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Effects of ultraviolet (UV) irradiation on genetic inactivation and ultrastructure of sperm were examined in the scallop Chlamys farreri. UV irradiation of sperm for 30 s at a UV intensity of 256 erg/mm² per s was the optimum dose to achieve haploid gynogenesis on the basis of observations on rate of cleaved eggs, chromosome constitutions and flow cytometry analysis of the larvae. The rates of cleaved eggs and development of D-shaped larvae decreased with increasing irradiation time, while the survival rate of trochophore larvae improved at UV exposure longer than 20 s, suggesting the presence of a ‘Hertwig effect’ in the gynogenesis of C. farreri. Electron microscopy showed clear destruction of the acrosome, cytoplasmic membrane, nuclear envelope, mitochondrial cristae, and flagellum in the UV-irradiated sperm. Moreover, an irradiation duration of 30 s caused decondensation of sperm chromatin. Abnormalities in these structures might affect the ability of sperm to fertilize the eggs.

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Age and growth of the yellowbelly threadfin bream Nemipterus bathybius in Kagoshima Bay, southern Japan were examined using sectioned otoliths of 1359 fishes collected from April 1998 to November 2000. Monthly changes in marginal growth increments indicated that ring marks (outer edge of opaque zone) were formed once a year between May and August. Assuming a birth date of 1 July from the monthly change of gonadosomatic index, ages ware assigned to every individual according to the number of ring marks. Length-at-age and weight-at-age data were best fitted to the von Bertalanffy among the three growth models. Equations obtained were FL_t=274.7(1-exp(-0.341(t+0.762))) for males and FL_t=231.0(1-exp(-0.161(t+4.405))) for females, where t is age (year) and FL_t is the fork length (mm) at age t, and they were significantly different (i.e. males grew faster than females). Maximum age observed was approximately 8 years for males and approximately 10 years for females.

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Marine silage (MS) is a fish hatchery diet prepared by decomposing seaweed into cellular units and performing lactic acid fermentation. MS was first developed by using a wild-type consortium composed of a lactic acid bacterium (LAB) Lactobacillus brevis and yeasts Debaryomyces hansenii var. hansenii and Candida sp. as a fermentation starter. To further examine a suitable combination of starter microorganisms, MS was prepared with different compositions of LAB and yeasts from a substrate of Undaria pinnatifida. Production efficiency of algal single cell units was not different among the trials. Inoculation of LAB significantly retarded the growth of contaminant microorganisms while a single inoculation of yeasts could not retard the growth of halophilic contaminant microorganisms. Lactobacillus brevis showed the highest predominating ability in MS among the tested, while L. acidophilus (casei-type) IAM 10074 and L. plantarum IAM12477^T also showed predominating ability with relatively inferior scores when analyzed from the results of the identification with 16S rRNA-targeted species-specific primers. The present study demonstrated that a single use of LAB, including food industry-familiar species, is suitable for preparation of MS, while the superiority of L. brevis B5201 was suggested in predominating ability in marine silage.

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