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Volume 55, Issue 4
Displaying 1-22 of 22 articles from this issue
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Masatoshi BAN2007 Volume 55 Issue 4 Pages 507-513
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe effects of alterations in growth on the incidence of precocious male maturation (PM) and seawater tolerance of sockeye salmon (Oncorhynchus nerka) were investigated. Juvenile sockeye salmon were separated into four groups (Groups A-D) and reared under different feeding regimes from November of age-0 to May of age-1. The growth regimes of groups A, B, C and D were the following: low growth throughout the duration, low from November to March and high from March to May, high from November to January and low from January to May, and high throughout the duration, respectively. The PM was determined by gonadosomatic index in May. Seawater tolerance was examined by monthly measurement of gill Na+, K+-ATPase (ATPase) activity. Proportions of PM among male fish of the groups A, B, C and D were approximately 0%, 50%, 80% and 80%, respectively. The ATPase activities of group-A remained consistently low, while that of the groups B, C and D was elevated significantly in April unrelated to differences of mean fork length and past growth. These results indicate that high growth in early winter of age-0 induces PM and consistent low growth during winter and spring hinders development of both seawater tolerance and smolt development.View full abstractDownload PDF (1138K) -
Hiromi HANZAWA, Kazunori ARAYAMA2007 Volume 55 Issue 4 Pages 515-520
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSSeasonal changes in the distribution of the channel catfish, Ictalurus punctatus, in Lake Kasumigaura were examined from December 2003 to December 2004. Nighttime sampling was conducted in three depth zones using bottom gill nets: the shallow (1m depth, 50m offshore), intermediate (4-5m depth, 600m offshore) and deep (7-12m depth, 800m offshore) zones. Fish were caught at depths deeper than 4m from October to March, except in February, when the water temperature in the shallow zone was lower than 10°C. From April to November when the temperature of the shallow water was higher than 10°C, fish were collected from all zones and were abundant in the shallow zone from April to September, when the water temperature was higher than 21°C . Mature fish only occurred in the shallow zone from May to July, during their spawning season. These results indicated that the distribution pattern of channel catfish was related to water temperature, and that the fish aggregated the deep habitat during the cold season, when the water temperature was lower than 10°C, and dispersed to all the habitats in the warm season. Especially, mature fish migrated to the shallow zone to spawn.View full abstractDownload PDF (926K) -
Daiki NOGUCHI, Nobuhiko TANIGUCHI2007 Volume 55 Issue 4 Pages 521-527
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSA large number of hatchery masu salmon, Oncorhynchus mason mason, have been released into the rivers in Japan in order to enhance the fisheries resources of this species. Unconscious genetic changes that may occur during artificial seed production should be prevented if we are to perform effective and responsible resource enhancement. In this paper, the genetic variability and population structure of masu salmon were estimated using five microsatellite DNA markers (msDNA) . Masu salmon showed a high level of genetic variability at the msDNA loci. Average allele numbers ranged between 10.40 and 15.00, average numbers of allele richness between 9.74 and 11.72, and expected heterozygosities between 0.824 and 0.874. Genetic differentiation was not observed between different year classes. Meanwhile, genetic differentiation was detected among captured locations, but distinct correlation between genetic distance and geographic distance was not observed. Finally, methods of brood stock management in artificial propagation to prevent genetic change and loss of variation for conservation of genetic diversity in wild populations are discussed.View full abstractDownload PDF (896K) -
Ryu DOIUCHI, Tomoyoshi KOKUBO, Mitsuya OGAWA2007 Volume 55 Issue 4 Pages 529-534
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSMaturation and sex ratios were examined in three-line grunt, Parapristipoma tyilineatum, occurring along the southwestern coast of Kii Peninsula, Japan. Monthly changes in gonad index (GI) demonstrated that the spawning season in this region, from April to July peaking in May and June, was slightly earlier than previously reported for other regions. GI values indicated that no females at age 1 year and all females over 2 years were mature, compared with some males at age 1 year and all males over 2 years. The sex ratio was female-biased in May and June, but male-biased in July, September and October. Because the female-biased sex ratio in May was represented by fish in the 200-239 mm fork-length class (mainly 2-3 years old) and that in June by the 200-219 mm fork-length class (mainly 2 years old), together with the fact that these samples were caught by angling and set net, there seemed to be a behavioral difference between the sexes (mainly in 2-3 year-old fish) during their spawning migration. Based on whole samples, the sex ratio was female-biased in the 190-219 mm fork-length class (and 2 year old fish) and male-biased in the greater than 300 mm fork-length class (and fish older than 7 years) .View full abstractDownload PDF (966K) -
Tatsuya YURIMOTO, Hiroshi NASU, Norihisa TOBASE, Yukio MAENO2007 Volume 55 Issue 4 Pages 535-540
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSSeasonal variations in survival, shell length, condition factor, phytopigment content in the midgut gland and glycogen content in the foot were investigated in ark shell Scapharca kagoshimensis rearing with a hung pearl-net at 1m above the bottom and a plastic cage settled on the bottom in Ariake Bay from February to October 2003. There was no or less difference in survival, condition factor, phytopigment content and glycogen content between the treatments, but growth of shell length in the plastic cage group was higher than that in the pearl-net group from June to October 2003. These results suggested that the hung culture used pearl-net offered little influence on the feeding and growth performance of ark shell.View full abstractDownload PDF (3570K) -
Kazumi NIMURA, Hiroshi TAKATSUJI, Suguru MASUDA, Junji SHIMAMOTO2007 Volume 55 Issue 4 Pages 541-546
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSA vast deforested area of approximately 8, 000 ha exists around the coast of Hainan, Shizuoka. Here we transplanted seedlings of kelpsEcklonia cavaandEisenia ayboreawere transplanted into St. 1 (ca 5m in depth) and St.2 (ca 8m in depth) in this area; we also investigated the growth and the maturation of these seedlings, and the grazing by the herbivorous fishSiganus fuscescensfrom July 2005 to February 2006. The blade length ofE. cavain St. 1 was ca 50cm in July 2005. The minimum blade length (ca 20cm) was observed from September to October 2005, and the length began to increase subsequently. During the investigation, seasonal changes in theE. cavablade length in St. 2 were similar to those observed for St. 1, and the blade length of St. 2 was always lesser than that of St.1. MatureE. cavasporophytes were observed from September 2005 to February 2006 and approximately half number of the sporophytes were matured by November 2005. Juvenile sporophytes derived from transplantedE, cavawere observed around the concrete blocks in February 2006. The grazing byS. fuscescenswas observed from August 2005 to February 2006 in both the species. Particularly, theE. ayboreasporophytes transplanted in St. 1 underwent serious grazing damage as compared to theE. cavasporophytes. The blade length ofE. ayboreawas below 10cm, and a major part of blade was grazed during the period from September 2005 to February 2006. Therefore, no juvenileE. ayboreasporophytes were observed there.View full abstractDownload PDF (2939K) -
Hideki HAMAOKA, Noboru OKUDA, Koji OMORI2007 Volume 55 Issue 4 Pages 547-555
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe effects of mixed cultivation of noble scallopChlamys nobilisand macroalgaMeyistotheca papulosaon their productivity and its potential in restoring eutrophic coastal ecosystems were examined under field and laboratory conditions. From the field, we compared the productivity among three cultivated systems, mono-culture ofC. nobilis, mono-culture ofM. papulosa, and their mixed culture, in the Uwa Sea. Field results showed the standing crop ofM. papulosawas significantly higher in the mixed cultivation than in the mono-cultivation. This result was supported by our laboratory experiments that indicatedM. papulosaeffectively assimilated ammonia excreted byC. nobilis. Under mixed cultivation in the field, we found no effects of the macroalgal covering on the growth of suspension feedingC. nobilis. Furthermore, the number of barnacles attached toC. nobiliswas fewer in the mixed culture than in the mono-culture. These results suggest that the incorporating mixed cultivation of scallops and macroalgae would be more profitable not only due to its higher algal productivity, but also due to lower labor costs in removing barnacles off the shell to improve market value. We finally discuss environmental effects of the mixed cultivation, focusing on increasing water quality and rehabilitation of macroalgal beds in the eutrophicated coastal ecosystems.View full abstractDownload PDF (1553K) -
Yasushi HIRATA, Makoto WAKANO, Danji MATSUBARA, Kazuya NAGASAWA2007 Volume 55 Issue 4 Pages 557-562
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe purpose of the present study is to assess the effects of spat collectors presoaked with seawater containing adult live diploid Pacific oysters (Crassostrea gigas) on the settlement of larval triploid Pacific oysters to develop an artificial, mass setting method. Scallop (Patinopecten yessoensis) shells used as spat collectors were presoaked for 8 days in seawater containing adult live diploid Pacific oysters before experimental setting. These presoaked scallop shells had 8-12 times as many spats as those scallop shells without pretreatment. The larval settlement on the shells completed within 24 hours of the experiment. These results show that presoaking of spat collectors in seawater containing adult live diploid oysters may be useful and efficient in mass collection of triploid oyster larvae at hatcheries.View full abstractDownload PDF (959K) -
Satoshi OHASHI, Shunsuke IWANAGA, Kazufumi OSAKO, Kazuma YOSHIKOSHI2007 Volume 55 Issue 4 Pages 563-570
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSA feeding experiment was conducted to investigate the effect of adding crushed mature ova prepared from the Pacific oysterCrassostrea gigas, to the diet forScapharca globosa ursuslarvae as a supplement to microalgae. Crushed oyster ova were high in both crude protein content and taurine concentration. Analysis of fatty acid composition showed that crushed oyster ova had lower EPA concentration thanChaetoceros calcitransbut was 6 times higher in DHA concentration thanPavlova lutheri. When crushed oyster ova was added into the diet, growth and survival rate of larvae in the experimental group were significantly higher than those in the control that were fed only with algae. During the umbo stage, the control group showed high mortality and a stagnant larval growth. In addition, significant differences in the lipid droplet contents in the gastric and digestive diverticular epithelia were observed between larvae of the two groups on 7 and 11 days post-hatch. These results suggest that giving crushed mature ova prepared from Pacific oyster as a supplementary diet toS. g. ursuslarvae prevented delayed growth that may occur following the consumption of egg yolk reserves, and effectively maintained their normal growth.View full abstractDownload PDF (7346K) -
Kenji TAKII, Manabu SEOKA, Mitsuhiko IZUMI, Hidetsuyo HOSOKAWA, Sadao ...2007 Volume 55 Issue 4 Pages 571-577
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSApparent digestibility coefficients (ADCs) and energy partition of juvenile Pacific bluefin tuna (PBT) and chub mackerel were preliminarily estimated using a moist pellet, mixing with minced sand lance and a fish meal diet. ADCs for dietary nutrients and energy in PBT at 26-28°C were ca. 5-10% lower than those of mackerel at 23-25°C. Energy partitions of PBT and mackerel were assayed under various feeding protocols at 24-25°C and 26°C, respectively, and expressed as per kg body weight/day. In PBC, energy intake (EI) was 1452 and 5173 kJ under 3-day fasting followed by 2-day feeding to satiety (3dF: 2dS) and 5-day feeding to satiety (5dS), respectively. Energy for metabolism (ME) was 481 kJ under fasting for 5-day rearing period (5dF) . Energy retention (ER) was -481, -247 and 381 kJ under 5dF, 3dF: 2dS and 5dS, respectively. In mackerel, EI was 448, 917 and 1197 kJ under 6dF: 3dS, 3dF: 6dS and 9dS, respectively, and ME was 208 kJ under 9dF. The ER was -230, 3.35, 197 and 439 kJ under 9dF, 6dF: 3dS, 3dF: 6dS and 9dS, respectively. These results indicated that lower ADCs and ER of PBT than those of mackerel were due to their insufficient digestive potency for heat damaged fish meal.View full abstractDownload PDF (1189K) -
Kenji TAKII, Manabu SEOKA, Nana OHARA, Toshiro NASU, Seiji ODA, Shiger ...2007 Volume 55 Issue 4 Pages 579-585
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSDietary utility of Chilean fish meal (FM) and pollack liver oil (PLO) for juvenile Pacific bluefin tuna Thunnus orientalis were investigated to develop their artificial diet. Diets 1, 2 and 3 were composed of 73, 63 and 53% FM and 0, 10 and 20% PLO, respectively. Control diet was raw sand lance (SL) Ammodytes personatus, with 77.6% crude protein and 6.2% crude lipid. Duplicate groups of juvenile tuna, weighing 1.68 g, were fed each diet until apparent satiety 6 times daily for 10 days. The diets and SL led low survival of tuna, due to flash collision against the tank walls. As compared with SL, diets 1-3 sustained lower daily intake and specific growth rate. Reversely, diets 1-3 led higher feed efficiency, protein efficiency ratio, apparent protein retention, final carcass crude protein content, entero-somatic index, and gastral peptic and enteral tryptic enzyme activities. Final carcass lipid and hepato-somatic index of tuna fed diets 2 and 3 were higher than those fed diet 1 and SL. These results suggest that FM in diet is a less digestible protein source for juvenile tuna, while the amino acid balance of FM sustains their requirements due to better protein retention than SL.View full abstractDownload PDF (1144K) -
Jing-Yu LI, Yoshiki MURAUCHI, Mutsuo ICHINOMIYA, Yukio AGATSUMA, Kazuy ...2007 Volume 55 Issue 4 Pages 587-597
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSHatchery-raised young sporophytes of the kelp Laminaria japonica from the coast of Osatsube, Hokkaido, were cultivated in Matsushima Bay from November 2000 to July 2001. The seasonal gross photosynthetic rate, uptake rates of NH4-N, NO3-N and PO4-P, and the carbon and nitrogen contents were examined. High photosynthetic rates were found in the middle part with maximum blade width, in contrast to low rates in the meristem. The photosynthetic rate remained stable from January to June even though the temperature ranged from 7.3 to 17.7°C, suggesting that the photosynthetic activity was adjusted to seawater temperature. Uptake of NO3-N occurred mainly in the meristem, whereas NH4-N and PO4-P uptake also occurred in other blade parts. The uptake rates of NH4-N and PO4-P increased with ambient nutrient concentrations up to 800 and 160μg/l, respectively, whereas the uptake rate of NO3-N remained stable or decreased when ambient nutrient concentration exceeded 400μg/l. Carbon and nitrogen were transported to, and stored in, the meristem, although some was consumed for growth. The erosion of the apical tissues was initiated from December and the total erosion length reached 196 cm during the cultivation period. There may be a mechanism that recycles nitrogen for sorus formation and storage for plants that persist for a second year.View full abstractDownload PDF (1773K) -
Yukio AGATSUMA, Akiko KAWASHIMA, Jing-Yu LI, Kazuya KURATA, Kazuya TAN ...2007 Volume 55 Issue 4 Pages 599-605
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe feeding-deterrent activities of acetone extracts from brown algae Padina crassa, P australis and P. japonica on abalones Haliotis discus hannai, H. discus discus and H. gigantea, and the snails Chlorostoma lischkei, Omphalius rusticus and O. pfeifferi carpenteri were tested by the bioassay using cellulose plate method. The neutral and acidic fractions of acetone extracts showed potent feeding-deterrent activity against these gastropods. The lipids, highly unsaturated and unsaturated fatty acids, were isolated from P. crassa as new feeding-deterrent metabolites. Feeding-deterrent activity of P. japonica was relatively low, possibly due to the physical defense with the accumulation of calcium carbonate. Among the three species of abalones, the mobile grazers H. discus hannai and H. discus discus are sensitive to metabolites of the algae. By contrast, the sedentary grazer H. gigantea is insensitive to those. Among the three species of snails, Chlorostoma lischkei, sympatric to Padina species, was most sensitive to the metabolites.View full abstractDownload PDF (3419K) -
Masahiro NAKAGAWA, Hiroyuki OKOUCHI2007 Volume 55 Issue 4 Pages 607-612
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSEffects of Artemia single feeding on early growth, development and survival of black rockfish Sebastes schlegeli larvae were examined under laboratory conditions. Newly born larvae of black rockfish were reared under two feeding regime. Rotifer-Artemia feeding group (control) and Anemia single feeding group from onset of feeding at 0 day after birth to 15 days after birth. There were no differences in feeding incidence, growth, developmental stage composition and survival rate between treatments. Artemia single feeding regime was proved to be feasible in newly born black rockfish larvae in a hatchery.View full abstractDownload PDF (936K) -
Toshiyuki NAKATSUBO, Masahiro KAWACHI, Nobuhiro MANO, Hitomi HIROSE2007 Volume 55 Issue 4 Pages 613-618
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe spawning period of ocean sunfish Mola mola was estimated using changes in gonad index (GI) and histological observations of gonads. GI was calculated for 183 ocean sunfish, captured from 1981 to 2006 in the waters off eastern Japan's Kanto region. GI maximum value occurred in August for both sexes of wild specimens. Gonads of 9 female specimens (total length 185-272 cm) and 4 male specimens (168-190 cm) were examined histologically. Oocytes in the ovaries revealed four distinct maturational stages. Based on the seasonal changes of GI and the gonad maturational phases, the spawning period for ocean sunfish is estimated to occur from August to October. The discovery of asynchronous oocyte development in the ovaries also suggests that ocean sunfish are multiple spawners.View full abstractDownload PDF (3044K) -
Byungsun CHIN, Masahiro NAKAGAWA, Yoh YAMASHITA2007 Volume 55 Issue 4 Pages 619-627
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSEffects of feeding and temperature on survival and growth of black rockfish larvae were studied in four rearing experiments. In the feeding regime experiment, growth and survival rates were not significantly different between the combined rotifers and Artemia feeding regime and the Artemia only regime. In the feeding level experiment, total length at 20 days after birth was significantly different by feeding level as (1.5) = (1.0) > (0.5) > (0.1), where the feeding level (1.0) is the same level as fed in the hatchery and the other values indicate ratios compared to (1.0) . In the different temperature experiments, survival rates at the intermediate temperatures of 14°C, 18°C and 22°C were significantly higher than those at 10°C and 24°C. Growth rate tended to increase as temperature increased within the examined range from 10°C to 24°C. When larvae were reared under diel temperature change (14-18°C), survival and growth rates were between 14 and 18°C of fixed temperatures showing no beneficial effects of a diel change of temperature. The most efficient rearing method for hatchery rearing was concluded to be: using (1.0) feeding level of Artemia only during the larval period at a temperature range approximately 16-20°C.View full abstractDownload PDF (1297K) -
Tsuyoshi SUGITA, Takeshi YAMAMOTO, Hirofumi FURUITA2007 Volume 55 Issue 4 Pages 629-635
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSThe effect of various dietary phosphates [mono-, di- or tri-basic calcium, sodium and potassium phosphates and calcium phytate (1P-Ca, 2P-Ca, 3P-Ca, 1P-Na, 2P-Na, 1P-K, 2P-K and Ca-phy) ] on the apparent phosphorus, protein and fat absorption was investigated in fingerling red sea bream Pagrus major. The phosphorus absorption of the 1P-Ca, 1P-Na, 2P-Na, 1P-K and 2P-K diets was higher (92-97%), but the absorption of the Ca-phy, 3P-Ca and 2P-Ca diets was lower (32, 44 and 65%, respectively) . The apparent protein absorption was significantly lower in the Ca-phy diet compared with other diets. The apparent fat absorption in the 2P-Ca and Ca-phy diets was significantly lower than that in the 1P-Na and 2P-Na diets, but the absorption in the 2P-Ca and Ca-phy diets was not different from the other diets. These results indicate that fingerling red sea bream can absorb phosphorus from 1P-Ca, 1P-Na, 2P-Na, 1P-K and 2P-K effectively, whereas they cannot absorb phosphorus from Ca-phy, 3P-Ca and 2P-Ca efficiently, and Ca-phy negatively affects apparent protein absorption.View full abstractDownload PDF (1075K) -
Masashi YOKOTA, Seiichi WATANABE2007 Volume 55 Issue 4 Pages 637-643
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSA model of infection based on individual behavior is described for an uncertain epidemic process in a closed habitat, like an aquaculture tank. We discuss differences from the traditional infection (Kermack-McKendrick) model in a homogeneous population. Each simulated fish is used as an independent participant that behaves in an ideal two-dimensional tank according to simple swimming rules with random factors. Each fish is also categorized as susceptible (S) or infective (I) in the SI compartment type. In the SIR compartment type, the recovered (R) condition is added. We assume that an infectious disease is only spread by contagion, and contacts among fish are described using a lattice model. The simulation model demonstrates more different kinds of epidemic processes than does the Kermack-McKendrick model. When a defined infection power was lowest (ρ=1) in both compartment types, negligible individual contagion occurred, and this was influenced by the fishs' behavior at the borders. Even if the infection power was sufficient (ρ=10) in the SIR compartment type, the simulation that fitted the Kermack-McKendrick model was only 31.4% in 1, 000 trials. This is attributable to random lags in the start times of exponential increases in infection. The simulation results suggest that variations in individual behavior cause uncertainty in the infection process.View full abstractDownload PDF (1111K) -
Ken-ichi Yamamoto, Takeshi Handa, Yasuaki Nakada, Hirohumi Nasu2007 Volume 55 Issue 4 Pages 645-648
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSIn the pen shell, Atrina (Servatrina) lischkeana (A. (S.) pectinata lischkeana), the effect of water temperature on the discharge of foreign substances from the mantle cavity was examined by observing sand perticles moving vertically and horizontally through the ciliated canal of the mantle. The average speed (mm/min) of sands moving was seasonally measured at the different temperature, 11 (January), 17 (April), 22 (June) and 27°C (August) which are approximate ambient temperature of the fields from which the pen shell were collected at the respective time points. The speed was also measured as the temperature was elevated 3°C every hour from each initial temperature up to a peak of 39°C . Both vertical and horizontal moving speeds increased and then decreased to zero mm/min after reaching the maximum with the rise in water temperature. However, the former speed was always smaller than the latter. The vertical movement peaked and ceased at a lower temperature than the horizontal moving. Based these findings, the pen shell will increase the discharge rate of foreign substances from the mantle cavity by increasing the activity of the cilium in the ciliated canal of the mantle, when water temperature rises over the at short term or depending on the season. However, the cessation and decrease in discharging foreign substances at an elevated temperature occurred without relation to the activity of the cilium.View full abstractDownload PDF (3659K) -
Shinsuke MORIOKA, Seiji MATSUMOTO2007 Volume 55 Issue 4 Pages 649-650
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSOtoliths of the laboratory-hatched Tilapia rendalli were investigated for 29 days after hatching. The sagitta and lapillus were observed at hatching. They were round-shaped until 10th and 3rd day and becoming oval-shaped thereafter. Increments in the sagitta and lapillus were discernible throughout their development. Increment counts for both coincided with the number of days after hatching. The asteriscus only appearing in the fish larger than 8.00 mm of standard length was oval-shaped with an ambiguous core and invisible increments. These results revealed that the sagitta and lapillus were appropriate for determining the age in days while the asteriscus was unsuitable.View full abstractDownload PDF (2847K) -
Koh HASEGAWA, Robert ADAMS, Koji MAEKAWA2007 Volume 55 Issue 4 Pages 651-652
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSIn June 2006, we found Predation on native lamprey species by a large, nonnative brown trout (600 mm in fork length) in a small stream in Hokkaido, Japan. The trout ate 15 adult lampreys and one unidenti-fied fish. Brown trout may cause decline of endangered native lamprey species.View full abstractDownload PDF (3147K) -
Koichi HARAGUCHI, Hideki KOKUBU, Hiroyuki OKUMURA, Tamiji YAMAMOTO2007 Volume 55 Issue 4 Pages 653-654
Published: December 20, 2007
Released on J-STAGE: March 09, 2010
JOURNAL FREE ACCESSFisheries are known to remove nitrogen from semi-enclosed bays. We estimated removal of nitrogen by fisheries in Ago Bay, Japan in the early 2000s to be 1.2% of the total nitrogen load in the bay. The benthic fish production in the early 2000s was markedly lower (about 1/100) than that in the late 1950s due to the develop-ment of hypoxia in the bottom water. Assuming the same amount of nitrogen is removed by fisheries now as in the late 1950s, we estimate the present nitrogen removal to be 2.1% of the load.View full abstractDownload PDF (381K)
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