The larvae of longtooth grouper Epinephelus bruneus were reared in a 150 kL tank until ten days post hatching under a natural photoperiod condition and diurnal rhythms of feeding and tryptic activity of larvae were examined. Further, effects of different photoperiods (24L: 0D, 12L: 12D, 6L: 6D: 6L: 6D, and 0L: 24D) on larval survival, growth and feeding were examined using 500 L tanks until 11 days post hatching. The longtooth grouper larvae fed on rotifers during light periods and tryptic activity was highest at 7 p.m. Larval gut contents were quite few during dark periods and larvae did not grow and survive in tanks with 0L: 24D photoperiod. The number of rotifers in larval guts was low in tanks with 24L: 0D photoperiod thought larvae fed on rotifers slightly at night. Total length and survival rates of larvae reared in tanks under 24L: 0D and 6L: 6D: 6L: 6D conditions showed similar low values, and best growth and survival rates were observed in tanks under 12L: 12D condition.
The presoaking of spat collectors in seawater containing adult Pacific oysters Crassostrea gigas is known to induce their larval settlement. In this study, we experimentally examined how presoaking conditions affect variations in success of larval oysters, using scallop Patinopecten yessoensis shell chips as spat collectors. The rate of larval settlement was enhanced by increase in water temperature, number of adult oysters, and length of presoaking period, while it was not affected by feeding to adult oysters. The ammonia-N concentration in the presoaked water was also closely related to the success of larval settlement. We herein propose a new indicator, termed condition index, which is the product, expressed in mg/L•hours, of the ammonia-N concentration multiplied by presoaked hours, and suggest that larval settlement is very successfully induced at about 20 mg/L•hours.
In the autumn of 2006, an unknown disease occurred among conchocelis of Porphyra (nori) mass-cultured using common scallop shells in Okayama Prefecture Fish Farming Center. An early symptom of the disease is tiny reddish brown spots; the color of diseased conchocelis finally turned yellowish-white. The bacterium isolated from the discolored area was confirmed to be the causative agent of this disease by artificial infection to healthy free conchocelis. When attacked by this isolate, the color of young Porphyra gametophytes turned green. The isolate was gram negative rod, strict aerobe, motile by a single flagellum, proliferated at 12-37°C , and required sea water for full growth. The bacterium is presumably a member of Pseudomonas or its closely related genus.
For the optimum design of a shrimp pot to control the catch size, experiments were carried out to study the pot stability. The pots used to catch shrimps in Hokkaido have two shapes (hemispherical and conical). To estimate the pot stability, drag and static frictional forces were measured in experiments. The drag of each pot was measured in a flume tank. The relation between the current speed and drag is presented. Static frictional forces, on a sand surface and on a rock surface, were measured for a model seabed respectively. The results showed that the drag of Usujiri shrimp pots was lower than those of Sawara and Yubetsu shrimp pots depending on the current speeds and angles. When the seabed was sand or rock, it was harder for Yubetsu shrimp pots to slide than the others. On the flat seabed, the Yubetsu shrimp pots turned over more easily than the others. In conclusion, the possibility of turning over was smaller with the hemispherical shrimp pot than the conical shrimp pot.
The sediment quality of Hiroshima Bay and the neighboring area, Suo Nada, was compared using 5 years' monitoring data. Water content (WC) and ignition loss (IL), which is an index of organic matter, were significantly higher in the Hiroshima Bay sediment than in the Suo Nada sediment. Acid-volatile sulfide (AVS) content was also higher in the Hiroshima Bay sediment in winter and spring. While WC and IL showed almost no seasonal change in both areas, AVS showed the maximum in autumn and oxidation-reduction potential (ORP) was low in summer and autumn. These differences of the sediment quality in the two areas are discussed in terms of differences in social background, area usage and oceanographic structures.
The environmental conditions of bottom sediments were estimated from the changes of the distribution and species composition of macrobenthos and meiobenthos in Hiuchi-Nada and Bingo-Nada five times from May 2002 to January 2003. The organic content of bottom sediments was as high as 20 years ago in eastern Hiuchi-Nada and Bingo-Nada. The dissolved oxygen of bottom water in summer has fallen to 2.4 mg/L in part of eastern Hiuchi-Nada and Bingo-Nada. The acid volatile sulfide of the bottom sediments was low at all stations except one. The abundance of macrobenthos decreased in September, but the species diversity of macrobenthos was not related to the dissolved oxygen at bottom water of all stations. Sigambra tentaculata (Polychaeta) occurred at all stations. The nematode/copepod ratio, a pollution indicator, was low at less than 100 during the investigation period at almost all stations. It is suggested that the environment of the bottom sediment has improved in Hiuchi-Nada and Bingo-Nada in comparison with the bottom conditions of 20 years ago.
Discrimination of stocks of ayu Plecoglossus altivelis caught by angling in the Naka River, using an assignment method with multilocus microsatellite DNA markers, was conducted to estimate the ratio of stocked fish to wild fish in the catch. Substantial differences in allele frequencies and level of genetic diversity at seven microsatellite loci observed between wild populations and released stocks enable us to classify individuals caught by angling into those originated from the wild populations and those from the released stocks. Of a total of 326 individuals sampled in the upper, middle and lower reaches of the fishing ground of the Naka River, 88.4% of the individuals were classified as originating from wild populations and the remainder from released stocks. There were significant differences in the ratio of released fish in the catch among the reaches. Taking seasonal changes of the catch rate into consideration, our data suggested that wild fish recruited into the middle and lower reaches were abundant after midsummer. Proportional stock density differed among the stocks discriminated and among the reaches. These results indicate that there is a difference in properties of fishing ground among the reaches within the river that could affect efficiency of stocking and thus appropriate stocking methods that reflect the properties are needed.
Japanese rosy bitterling Rhodeus ocellatus kurumeus is an endangered cyprinid species in Japan, due to hybridization with its subspecies R. o. ocellatus introduced from mainland China. In order to collect information for conservation, the present distribution of R. o. kurumeus in Kyushu was studied using genetic and morphological markers. Of the 46 populations examined, mitochondrial DNA (mtDNA) of R. o. kurumeus was observed in 41 populations, among which that of R. o. ocellatus was also recognized in 13 populations. Although R. o. kurumeus was widely distributed in the northern-middle part of Kyushu, it is suggested that introgression by R. o. ocellatus has been allopatrically progressing in many habitats of R. o. kurumeus. The averaged number of pored lateral line scales positively regressed with the frequency of R. o. ocellatus mtDNA. It is evident that the number of pored lateral line scales is a more efficient morphological marker than the presence of a guanine layer along the anterior margin of the pelvic fins in the identification of R. o. kurumeus.
Frozen vannamei prawn (VAN), penaeus vannamei, was stored at temperatures from 0 to 55°C after thawing, and the changes in compounds related to ATP in the muscle were examined. As a result, AMP decreased and IMP and (HxR+Hx) accumulated with almost the same ratio when stored at less than 10°C or 55°C. On the other hand, IMP accumulated more than HxR+Hx when stored at 20°C-40°C, and IMP reached up to 70%. After live VAN were killed in ice and the muscles stored at 7°C and 22°C, the accumulation of IMP at 22°C was more than that at 7°C. The umami taste of the prawn stored at 22°C was strengthened intentionally. However, the free amino acids were almost unchanged during storage.
The anti-obesity effect of salmon muscle extracts containing anserine (SEAns) was investigated in Sprague-Dawley (SD) rats. The SEAns was orally administered to six-week-old male SD rats, and the rats were free to feed on a high fat diet for two weeks. Administration of the SEAns suppressed the increase of body weight and reduced lipid droplet of hepatic tissue, serum lipid level and the adipose tissue mass around testis and kidney. These findings suggested that not only anserine but also the other components in the SEAns were likely to have an effect. The SEAns also suppressed the accumulation of lipid in adipocytes with dose dependency. Furthermore, the SEAns was not observed to cavse genetic toxicity by Rec-assay or oral acute toxicity on rats. Thus, the SEAns suppresses lipid accumulation and could be a safe functional food material which has an anti-obesity activity.