Aquaculture Science
Online ISSN : 2185-0194
Print ISSN : 0371-4217
ISSN-L : 0371-4217
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Original paper
  • Kazunori Kumon, Yosuke Tanaka, Chisako Ishimaru, Yoshitaka Sakakura, T ...
    2018 Volume 66 Issue 3 Pages 177-184
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    One of the major problems in the larviculture of Pacific bluefin tuna (PBT) Thunnus orientalis is sinking syndrome; larvae die by sinking to the bottom of rearing tanks during nighttime. We evaluated the effects of different photoperiods on survival, growth and feeding of PBT larvae in small tanks and mass-culture tanks. First, larvae were reared until 8 days after hatching in 500 l tanks under 2 different photoperiods; 14L:10D and 24L:0D (2,000 lux). Larval survival was 9-times higher under 24L:0D (15.5±7.6%) than 14L:10D (1.8±0.6%). Larvae at 24L:0D was significantly larger than those at 14L:10D. The number of larval gut content was the highest before light-out in 14L:10D group and was few during dark period. Larvae in 24L:0D continuously fed on rotifers, while the lowest larval gut contents was observed at 3 a.m. Secondly, we reared PBT larvae until 10 days after hatching in 2 rearing tanks (40 kl) under 2 different photoperiods; 24L:0D and 14L:10D. Survival of larvae under 24L:0D (29.3%) was about 10-times higher than 14L:10D (3.1%), while there was no significant difference in growth between treatments. These results indicate that 24L:0D condition improved survival of PBT larvae.
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  • Shizuo Aino, Taiga Yodo, Motoi Yoshioka
    2018 Volume 66 Issue 3 Pages 185-192
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    To clarify the influence of a weir located in the lower-reach of the Shonai River on the upward migration of ayu Plecoglossus altivelis altivelis, we conducted frequent sampling, otolith analysis by EPMA method, and combined analysis of abundance, size, and age at habitat change. Under the weir, ayu were first caught on April 5 and CPUE showed a maximum in mid-June. At the fishways in the weir, until mid-May, few fish were caught by set net. But in late May, CPUE increased and showed a maximum. Throughout the study period, larger individuals as caught under the weir were not observed in the fishways. Furthermore, ayu which spent approximately 80 days after entering into the river were caught in late May under the weir. From otolith analysis, individuals sampled at middle reach of the river, under the weir and in the fishways, peak time of entering the river was early April, late April and mid-May, respectively. Individuals that passed the fishways soon after arrival at the weir early in the upward migration season could go up to the middle reach of the river, while those which failed to continue the upward migration remained under the weir which was an unsuitable habitat.
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  • Kenji Takii, Toshifumi Kai, Tadanobu Fukawa, Ayumi Katoh, Fumiaki Taka ...
    2018 Volume 66 Issue 3 Pages 193-198
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    A noninvasive assay for estimating stomach evacuation velocity and daily meal frequency for a commercially available artificial diet was evaluated using Pacific bluefin tuna fingerlings. This was attributed to the hypothesis that fish could consume a diet until filling up a gap of the stomach after a feeding until satiation. Consecutive feeding frequencies of 4, 11 and 3 meals daily from 7:00 to 17:00 for 5 days each, were conducted on a single group of 1,200 fingerlings, weighing 70-190 g in a net cage. The daily feed intake linearly increased with passing the feeding protocols. For each daily feeding event, % daily feed intake of a first meal was higher than those of second meals onward in a day. The stomach evacuation velocity expressed as a slope, subtracting accumulative % daily feed intake of a second meal onward from that of a first meal, was y = -6.94x + 29.6, y = -7.08x + 31.2 and y = -7.07x + 44.4 for 4, 11 and 3 meals daily, respectively. These results indicate that the stomach evacuation velocity of the fingerlings was estimated to be around 7% daily feed intake per hour, and daily meal frequency was 3 or 4 until apparent satiety was achieved with the artificial diet.
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  • Yuta Ota, Yoshimi Ishihara, Hiroshi Saitho, Nobuhiko Akiyama
    2018 Volume 66 Issue 3 Pages 199-208
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    A. melanogaster were taken from an outdoor tank once a month from March 2013 to August 2014. From March to July both years, the GSI value stayed high and individuals with developed gonads were observed. However, in August both years, the GSI suddenly dropped, and individuals with regressed gonads were observed. These results indicate that the spawning season of A. melanogaster reared in outdoor tanks was from the end of March to the end of July. In order to investigate the factors which affected the end of the spawning season, in August both years, A. melanogaster were reared in different combinations of water temperatures and daylight lengths on May 10 and the summer solstice (June 21). The spawning of A. melanogaster was terminated for all daylight lengths at 28°C. However, the spawning continued in the case of the all daylight lengths at 20°C. The spawning was terminated under the conditions of 22°C 12L12D and 24°C 12L12D in the summer solstice. One of the main factors for the end of the spawning season seems to be the influence of high water temperature. However, it was revealed that short day treatment under the low water temperature conditions also helped end the spawning season.
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  • Natsumi Sano, Natsuki Hasegawa, Kazuhiro Hanyu, Dai Miyawaki, Akira Ko ...
    2018 Volume 66 Issue 3 Pages 209-216
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    For improved resource management, we estimated the genetic structure of the asari clam Ruditapes philippinarum to reveal the local population network formed by transportation of pelagic larvae in Ise Bay, Japan. We sampled juvenile clams (shell length < 20 mm) at six locations in Ise Bay and one location in the adjacent Mikawa Bay in May and November in 2013 and 2014. We analyzed 24 or 25 individuals from each sampling location at each sampling period and performed microsatellite analysis with 4 loci (Asari16, Asari62, Asari64 and KTp8). Analysis of molecular variance (AMOVA) revealed significant genetic differentiation between the sampling periods (FCT = 0.00590, P = 0.00000) but no genetic differentiation between the sampling locations (FCT = -0.00142, P = 0.83773). This indicates that the genetic characteristics of settlements are nearly homogeneous for different sampling periods but not so for different locations. It is thus possible that pelagic larvae originate from multiple sites in the bays and are intermingled, which suggests a metapopulation may have formed by transportation of pelagic larvae in Ise Bay.
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  • Soichiro Yamamoto, Ryusei Ito, Masaaki Sato
    2018 Volume 66 Issue 3 Pages 217-226
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    We investigated spawning ground habitats and maturation status of marbled flounder Pseudopleuronectes yokohamae in the southern part of Suo Nada, the Seto Inland Sea, in an area where mature fish were caught, in winter of 2016. Eggs spawned by marbled flounder were found on the surface sediments layer in the survey area a maximum density of 340 eggs per square meter. Therefore, we concluded that this area was a spawning ground of marbled flounder. In this area, marbled flounder started maturation when the bottom water temperature was below at ca. 16°C. In both sexes, larger and older fish approached the spawning ground earlier than smaller and younger individuals. The sex ratio {female/total (except immature individual)} for the specimens caught by a set-net near the survey area was significantly higher than 0.5 (P < 0.05) in the pre-spawning period, but lower than 0.5 (P < 0.01) in the early part of spawning period, and constant at approximately 0.5 from middle to the last part of spawning period. These results suggest that the migration pattern around spawning season differs between males and females.
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  • Masato Sato, Jun-ichi Tsuboi
    2018 Volume 66 Issue 3 Pages 227-233
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    Tomozuri angling is a method of catching ayu Plecoglossus altivelis that takes advantage of the territorial behaviour to monopolize benthic algae attached to substrates. To investigate the relationship between the timing of stocking (i.e., a trade-off with body size) and recapture rate, growth rate, and cost-benefit ratio of ayu caught by tomozuri angling, hatchery-reared juveniles were stocked into a tributary of the Yoneshiro River basin, in 2015 and 2016. After stocking in May (early stocking group; daily minimum temperatures at stocking were 8.9°C and 12.3°C, respectively) and June (normal stocking group; daily minimum temperatures at stocking were 13.0°C and 13.4°C, respectively), recapture experiments were conducted using tomozuri angling and casting net in August of each year. Recapture rates (an index of survival rate) did not differ between stocking groups. Growth rate of the early stocking group was higher than that of the normal stocking group. Moreover, the cost-benefit ratio of the early stocking group was over 2.7 times higher than that of the normal stocking group. These results suggest that early stocking serves as a useful method for stock enhancement of ayu, thus improving the cost-benefit ratio of tomozuri angling.
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  • Yasuyuki Tsukamasa, Hiroshi Yamashita, Akinori Takashima, Ryohei Matsu ...
    2018 Volume 66 Issue 3 Pages 235-242
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    Japanese eel-flavored Amur catfish, Silurus asotus (JEC), is produced as an alternative to the endangered Japanese eel Anguilla japonica (JE). In this study, the quality of JEC was evaluated and compared with that of JE, wild Amur catfish (WC), and cultured Amur catfish fed pellets usually given to carp or red seabream. Among the griddle-cooked fish filet, the lipid content was the highest in JE (31.8%), followed by JEC (5.5%) and WC (2.2%). The glutamate and inosine monophosphate (IMP) concentrations were the highest in cooked JEC (0.96 and 8.8 µmol/g, respectively) and the lowest in cooked JE (0.42 and 4.4 µmol/g, respectively). Docosahexaenoic acid components of the lipid of JEC were the highest at 7.67%, whereas that of JE was 3.3%. In the sensory evaluation, the fatty taste score for JE was significantly higher than that for all Amur catfish groups, the latter among which showed no significant difference in fatty taste scores. The overall sensory evaluation score for WC was significantly lower than that for the other catfish. JEC had a reduced foul smell compared to WC meat, and it countered its low lipid content compared to JE with its high levels of glutamate and IMP.
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  • Tadashi Imai, Kazuya Dehama, Tomoko Sakami, Toshinori Takashi, Tetsuo ...
    2018 Volume 66 Issue 3 Pages 243-250
    Published: 2018
    Released: September 20, 2019
    JOURNALS FREE ACCESS
    Effects of ammonium supply deprivation on ammonia oxidation activity and nitrifying microorganism communities in filter materials were examined to present appropriate management methods for bioreactors after the termination of rearing. Ammonia oxidation activities were measured using ceramic filter materials kept in artificial seawater without any ammonium additions for 24 weeks at 25°C. The nitrifying activities decreased to 97.8% and 78.2% of the initial after 1 and 2 weeks respectively. Subsequently, the activities gradually decreased to 5.4% after 24 weeks of incubation. The relative abundance of archaeal amoA gene in the filter materials kept in ammonia deprivation for 24 weeks was similar to that of the initial one. On the other hand, the relative abundance of bacterial amoA gene reduced to ca. half of the initial one. These results lead to the following management method for biological filters after the termination of rearing: 1) To maintain a high activity level of filter materials, an ammonium supply is necessary in every week. 2) If the bioreactor is maintained without an ammonium supply, prior to the next use an additional ammonium supply as booster is necessary for re-activation of the filter materials.
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