Aquaculture Science
Online ISSN : 2185-0194
Print ISSN : 0371-4217
ISSN-L : 0371-4217
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Original paper
  • Yuji Mushirobira, Takuma Kawasaki, Kuniaki Nakata, Emi Takenaka, Jun N ...
    2020 Volume 68 Issue 1 Pages 1-8
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    A method for species identification of shishamo smelt (Spirinchus lanceolatus) larvae was developed using whole-mount immunohistochemistry (IHC) to estimate fish stock abundance easily and accurately. Polyclonal antibodies against extracts of shishamo smelt larvae were produced. They were preadsorbed with extracts of rainbow smelt (Osmerus mordax) larvae, purified as IgGs specific to shishamo smelt larvae extract, and labeled with alkaline phosphatase. Shishamo smelt larvae could be distinguished from rainbow smelt larvae by whole-mount IHC using the adsorbed antibody. This simplified species identification and reduced its cost. The body length of smelt larvae caught from the Shin-Kushiro River was gradually smaller during the middle-late period of sampling. Species identification of these larvae by whole-mount IHC and 16S rDNA analysis revealed that shishamo smelt was the dominant species during the early-middle period, whereas rainbow smelt was dominant during the late period. Since both methods exhibited similar abundance ratios for these two species, whole-mount IHC appears to be effective for estimating shishamo smelt stock abundance.
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  • Kazunori Shizuka, Makoto Ikenaga, Jun Murase, Natsuko Nakayama, Noriak ...
    2020 Volume 68 Issue 1 Pages 9-23
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS

    Musty odor owing to 2-methylisoborneol (2-MIB) is a worldwide concern, causing deterioration in the quality of tap water and fish catch. In lakes, a large number of 2-MIB-producing cyanobacteria have been identified to be Pseudanabaena species, but the mechanisms underlying their occurrence have not been revealed. In this study, we investigated the occurrence-related characteristics and taxonomical composition of 2-MIB-producing Pseudanabaena in Lake Ogawara, Aomori Prefecture, Japan, using molecular biology techniques in combination with microscopic observations. In molecular biological analyses, amplicon sequencing and qPCR specific for 2-MIB-producing species were performed. Musty odor-producing Pseudanabaena-like cyanobacteria (MOPPL-cyanobacteria) observed by microscopy mainly occurred during autumn–winter and, to a lesser extent, during spring–summer. There was a positive correlation between the densities of MOPPL-cyanobacteria and 2-MIB-producing strains, but the latter accounted for only 8% of the former, suggesting that a large number of non-MIB-producing strains are included in the microscopy results. At least two 2-MIB-producing Pseudanabaena strains probably exist in Lake Ogawara, and the composition of MOPPL-cyanobacteria is likely to vary at the species/strain level, which cannot be microscopically detected.

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  • Koji Matsuzaki, Moeko Kamiunten, Takashi Yanagimoto
    2020 Volume 68 Issue 1 Pages 25-32
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    In the Nemuro Strait off Shiretoko Peninsula, eastern Hokkaido, Japan, egg mass deposits of liparid snailfishes were revealed in gill cavites of 14.8% (19 out of 128) of all golden king crabs Lithodes aequispinus sampled by local fishermen using traps set on steep slopes and hard bottoms at depths of 500-750 m in 2016. We also carried out continuous sampling of liparid snailfishes and collected seven species between 2015 and 2017. (Careproctus zachirus, C. cypselurus, C. furcellus, C. rausuensis, C. rastrinus, Paraliparis grandis and Crystallichthys matsushimae). COI sequences from eggs and hatched juveniles were compared with COI sequenced from positively identified adult voucher specimens. As a result, the eggs and juveniles were identified as C. cypselurus and C. furcellus. This result and prevalence rate of the snailfish eggs in gill cavites of golden king crabs is the first report in the Nemuro Strait, southwestern part of the Sea of Okhotsk.
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  • Hiroshi Katoh, Tatsuya Oda, Atsushi Ishimatsu
    2020 Volume 68 Issue 1 Pages 33-41
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    Reactive oxygen species (ROS) are generally regarded as being involved in fish kills by the harmful microalga, Chattonella marina. We therefore hypothesized that difference in susceptibility to blooms of C. marina among aquaculture fish species relates to varying capacities of antioxidative system, which protects fish from adverse effect of ROS. We compared activities of two antioxidative enzymes, superoxide dismutase (SOD) and catalase, in gills and red blood cells (rbc) of yellowtail (YT, most susceptible), red sea bream (RSB), and Japanese flounder (JF, least susceptible). Total SOD activity of gills was not significantly different among species, while in rbc it was three times higher in JF than in YT and RSB. Catalase activities of gills and rbc were highest in JF and lowest in YT. Apparent Vmax of catalase showed a similar trend in both tissues. Apparent Km of catalase in gills was not significantly different among species, whereas in rbc it was significantly lower in RSB. Thus, SOD and catalase activities in gills and rbc are probably in part responsible for the difference in susceptibility to this microalga, although other factors such as oxygen demand and density of mucus cells in gills may also be involved.
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  • Jun Kita, Yusuke Watanabe, Masaru Shionoya, Junichi Kojima
    2020 Volume 68 Issue 1 Pages 43-50
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    We experimented with seedling production of Hapalogenys nigripinnis, using broodstock caught off Kashiwazaki, Niigata. At 31 days after hatching, 2,760 juveniles (c.a. 17 mm in standard length) could be produced in 500 l black polycarbonate tanks. The number of dead individuals increased at 8 days after hatching, which was thought to be due to the stampede swimming of the larvae responding to sudden changes in the light condition. Feeding regimes of early stages was to feed freshly spawned eggs of Sillago japonica after L-type rotifer feeding. It was thought that the feeding regime should be reexamined because of their weak preference for live eggs. Seawater temperatures of about 9°C and 29°C were continued for one month during the acclimatization period of broodstock, but the fish grew well without any weakening of feeding. They can be said to be resistant to high and low water temperatures. It is noted that they have a high resistance to abrasions. The spawning optimum temperature range is estimated to be between 23°C and 26°C. Maturation and spawning rhythms are estimated to be asynchronous type and to have multiple spawning. The early life morphology of cultured specimen is detailed in comparison with previous findings.
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  • Yuichiro Fujinami, Daisuke Shimizu, Tetsuo Yamada, Hiroyuki Okouchi
    2020 Volume 68 Issue 1 Pages 51-58
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    Body color anomaly on the blind side (hypermelanosis) is a mark of hatchery-released fish from Japanese flounder (Paralichthys olivaceus) stock enhancement programs, but little information has been reported about changing degrees of hypermelanosis after release. We compared the frequency of hypermelanosis occurrence on the blind side (hypermelanosis rate) in juveniles before release and in recaptured fish. From a survey of 14 released fish groups identified using otolith marking with alizarin complexone, no significant difference (P > 0.01) was found except for one group. For six released groups with more than 100 recaptured fish, the frequency distribution of six anomaly grades was classified by a visual observation-based pigmented area ratio on the blind side (no pigmentation, pigmented area less than 1%, 5%, 10%, 75% and more than 75%: hypermelanosis level) among juveniles. Recaptured fish at 0 or 1 year old, and 2 or more years old were also investigated. From comparison among juveniles and recaptured fish, no significant difference (P > 0.01) was found except for one group.
    These results suggest that blind side body color anomaly of Japanese flounder changed only slightly after release. We inferred that blind side body color anomaly is useful to mark hatchery-released flounder to evaluate stocking effectiveness. Additionally, results suggest that the number of recaptured flounder, as underestimated by a lack of body color anomaly on the blind side, can be corrected by dividing the number of recaptured fish with body color anomaly by the hypermelanosis rate of juveniles before their release.
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  • Masayuki Yamamoto, Atsushi Ito, Hideki Yamazaki, Masaei Kanematsu
    2020 Volume 68 Issue 1 Pages 59-64
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    The pen shell, Atrina spp., is a large and economically important bivalve. To determine an effective suspended intermediate culture for the pen shell species A. lischkeana, we examined the survival and growth rates for two initial sizes (shell lengths (SL) of approximately 5 and 10 mm) and two initial population densities (4,000 and 8,000 individuals/m2). In addition, the sand burrowing ability of spats of SL ranging from 3.2 to 23.3 mm was examined in an aquarium. Four intermediate culture experiments were conducted from summer to autumn. The mean survival rate was 57.0%, with a low value (27.8%) in the third experiment that was probably due to low salinity. In three out of four experiments, the survival rates of large spats were between 7.3% and 20.0% higher compared with those of small spats, while in the second experiment the survival rate in groups of both sizes was almost equal. The growth rate ranged from 0.37 to 0.64 mm/day (average 0.50 mm/day). The growth rates of the low-density population were 0.03–0.07 mm/day higher than those of the high-density population. Spats of SL 5–20 mm had a high sand burrowing ability.
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  • Ryoko Ueno, Tomoko Yamamoto
    2020 Volume 68 Issue 1 Pages 65-73
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    We investigated the histological and morphological processes of sexual maturation in the common estuarine polychaete Simplisetia erythraeensis (Annelida: Nereididae). Seasonal changes in their sexual maturity were also examined at Omoi River estuary in Kagoshima Bay, Japan. Histological sections of sampled individuals revealed that S. erythraeensis is gonochoristic (because specimens had only either oocytes or cell clusters of spermatogenesis) and undergoes extraovarian oogenesis at sexual maturity (because oogenesis was observed in the coelom of mature specimens). Oocytes in mature females possessed a nucleus, a yolk, and a rough-surfaced endoplasmic reticulum-like structure. Female sexual maturation occurred in two stages: F1 and F2. The female F1 stage occurred from March to August, and the F2 stage occurred from July to August when males were filled with cell clusters of spermatogenesis. In addition, the inside portion of the muscular layers of females disappeared with sexual maturity (epitokous metamorphosis) and was replaced by amoebocyte associations around the oocytes (presumably to store nutrition for the oocytes), which enabled the species to spend the majority of its energy for monotelical reproduction. No significant changes were observed in parapodia of F2 in response to epitokous metamorphosis, namely, S. erythraeensis does not seem to engage in reproductive swarming.
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Short Paper
Note
  • Shuhei Ishihara, the late Akihiro Sei, Riichi Kusuda, Tohru ...
    2020 Volume 68 Issue 1 Pages 79-88
    Published: 2020
    Released: March 20, 2021
    JOURNALS FREE ACCESS
    “FA100” of eugenol formulation is the only fish anesthetic that obtained the manufacturing approval as veterinary drugs in Japan. Since vaccines are widespread in Japan, we examined anesthetic effect and safety of “FA100” prior to vaccination for juveniles of red sea bream (Pagrus major), yellowtail (Seriola quinqueradiata), amberjack (S. dumerili), striped jack (Pseudocaranx dentex), rock bream (Oplegnathus fasciatus) and spotted knifejaw (O. punctatus). Although the test fish species and fish body weight are different, the concentration of 100 to 200 ppm of “FA100” is considered to be safe for vaccination work time of the test fish for anesthesia. However, more than 100 g in body weight of amberjack died without recovery from anesthesia. This study was recognized as a guide for the optimal anesthesia concentration and time for vaccinations in marine fishes in Japanese fish farms.
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