This study examined the possibility of using underwater lamps in coastal squid jigging fishery. Fishing trials were carried out from 2009 to 2011 using coastal squid jigging boats (6.4-6.6 t) equipped with an underwater lamp apparatus with a shade to create high/low light intensity fields in the water column. The catch amounts of the squid jigging boats with the underwater lamp apparatus (experimental boats) were compared with the catch of a control boat equipped with conventional surface lamps, which simultaneously operated in the same water. The catch amounts of the experimental boats were significantly less than that of the control boat (p<0.05). However, catch amounts were expressed as functions of squid abundance, lunar phase, tide, presence of dolphins and wind direction, and the effect of using the underwater lamp apparatus was insignificant in the generalized linear modeling analysis. Thus, the underwater lamps did not increase squid catch, but were considered useful for controlling the depth of squid aggregation by changing the depth of the lamps.
The possibility of simultaneous polygamous mating in ice goby Leucopsarion petersii males was examined to estimate stock size with greater accuracy. In the field investigation, the number of males caught under the spawning nest was equal to or larger than the number of clutches attached under the nest, except one case. In the aquarium experiment, nesting males mated with only a single female at a time even when several females were available. These results suggested that ice goby males are unlikely to adopt simultaneous polygamous mating.
The effects of artificial seaweed and water depth on vulnerability of juvenile black-spot tuskfish Choerodon schoenleinii to the carnivorous crab Ashtoret lunaris were examined in the laboratory. Ten hatchery-reared tuskfish were exposed to five crabs for 24 h in replicate 400 L tanks (N=8) for each of the six treatments. The predation rate was significantly lower in the tanks with artificial seaweed than in the tanks without it. There was no significant difference in predation rate between standing artificial seaweed and lying artificial seaweed. There was no significant effect of water depth on the predation rate, either. When the behavioral pattern of the tuskfish was examined in tanks without crabs, most of the tuskfish were associated with the artificial seaweed. However, the tuskfish showed a clear diurnal activity pattern, and were distributed on the bottom of the tank during the night when the artificial seaweed was removed, implying that the predation mainly occurred at night. These results suggest that the foliage of Sargassum plants is an important nursery as a predation refuge for the tuskfish because wild black-spot tuskfish settle mainly on the thalli of Sargassum polycystum distributed in the intertidal zone, in which A. lunaris occurs simultaneously.
Two possible hybrid specimens, one from Oita fish market and the other from Nagasaki fish market, were obtained. The specimens had the characteristics of both red tilefish Branchiostegus japonicus (a silvery white triangular marking from the posterior orbital to the mid preoperculum) and yellow tilefish Branchiostegus auratus (a silvery white band from the suborbital to the upper jaw, small yellow spots on the surface of the caudal fin). In the present study, the possible hybrid specimens were evaluated in comparison with B. japonicus and B. auratus. Numerical characters of the specimens were within the range of overlapping of B. japonicus and B. auratus. By employing discriminant analysis and principal component analysis based on the morphometric indices, the results revealed that the specimens showed intermediate characteristics of morphometrics between the two species. It is confirmed that the two samples carry the genes associated with both B. japonicus and B. auratus based on nuclear DNA analyses. In conclusion, the two specimens were considered as natural hybrids among B. japonicus and B. auratus.
Reproductive traits of Japanese anchovy Engraulis japonicus were compared among the subtropical, subarctic, and inland sea areas around Japan. Adult anchovy in the subarctic areas were large in body size (standard length SL>120 mm, body weight BW>20 g) and had gonad-somatic index (GSI=GW×102/BW) greater than 7.0. Their total (per female) and specific (per 1 g BW) fecundity, estimated by the number of advanced oocytes in the ovary, were 18000 and 700, respectively. Their spawning activity was detected in June and July. In the subtropical sea areas, on the other hand, adults with advanced oocytes occurred all year round except for December and January. Their body and gonad sizes were large in spring (SL>120 mm, BW>20 g, GSI>5.0) with high total (>4500) and specific (>300) fecundities, but decreased in summer and autumn to as small as SL<60 mm and total and specific fecundity of 50 and 30, respectively. These diverse biological traits suggested that the reproductive ecology of anchovy is adaptive to local sea areas around Japan.
To identify factors affecting the somatic growth of the winter-spawning stock of Japanese common squid, the somatic growth of squid caught in the East China Sea, the Pacific Ocean and the Tsushima Strait from 2000 to 2011 was estimated using age determination from statolith microstructure analysis. The relationship between estimated age in days and dorsal mantle length was fitted using a Gompertz growth equation. The residuals of dorsal mantle length from the growth equation differed among year classes, hatch months, and sexes. Although no environmental factors correlated with the annual difference in growth, increased sea water temperature in spring in the Kuroshio-Oyashio transition region corresponded to increased growth with hatch month. Growth was smaller in males than in females during the southward migration, which suggested depressed growth in males due to earlier sexual maturation than in females.
This study was conducted in order to clarify the distribution and phenology of Undaria undarioides (Laminariales, Phaeophyceae) on the southern coast of Uchiura Bay, Shizuoka, Japan. A distribution survey carried out in late April 2008, by a scuba diving team in this area, confirmed the growth of U. undarioides in most parts of the area. The phenology survey was conducted from November 2008 to July 2009, at the depth of 5 m in the same area. U. undarioides appeared in December, grew to their maximum length in late March, and then matured in April. Afterwards, the thallus of U. undarioides started to decrease in size in May and disappeared entirely by July. The shape and size of U. undarioides were compared at their growing depths of 2, 6, 10, 14 and 18 m on March 28, 2010, revealing that thalli grown at the depth of 6 m were significantly the largest and that the size decreased as the depth increased.
Strain identification to assess the stock efficiency of ayu Plecoglossus altivelis altivelis was performed using microsatellite DNA loci, otolith Sr/Ca ratio and scale number above the lateral line at the Nariwa River, a tributary of the Takahashi River, in western Japan. The specimens collected by angling from mid-July to August represented 61.7% for the transplanted landlocked form (from Lake Biwa), 28.3% for native landlocked form (from Lake Nariwa), 1.7% for the transplanted amphidromous form, and 8.3% for hatchery-reared, while the specimens collected by gill net in September were identified as 58.6% for the transplanted landlocked form, 3.5% for the native landlocked form, and 37.9% for the hatchery-reared without transplanted amphidromous form. We discussed the effectiveness of stock separation markers for practical usage and the stock contribution status in each strain through the stocking program.
This study examined the influence of hydraulic turnover rate on apparent specific growth rate and maximum biomass of Microcystis in Lake Suwa from 1992 to 2003. The apparent specific growth rate of Microcystis decreased by flushing (>20% day−1 of the hydraulic turnover rate in a day). In addition, the apparent specific growth rate of Microcystis began to be suppressed when the turnover rate reached >2% day−1 in the exponential growth phase. The maximum biomass of Microcystis was affected by the hydraulic turnover rate from June to July. Therefore, we suggest that the short period and long-term changes of hydraulic turnover rate have large impacts on Microcystis bloom in Lake Suwa.
The selenium-containing imidazole compound selenoneine (2-selenyl-Nα, Nα, Nα-trimethyl-L-histidine) was injected into yellowtail intravenously, and a fillet was prepared 18 h after the injection. The selenoneine concentration in the red blood cells (RBCs) and red muscle were higher in the selenoneine-injected fish than in the control (water-injected) fish. A close correlation was detected between the selenoneine concentration in the RBCs and that in red muscle. In addition, a negative correlation was noted between the selenoneine concentration in the red muscle and the ROS level in the plasma. After the fish were killed, the fillets were stored on ice for 72 h, and meat slices were then prepared and stored for an additional 24 h at 4℃. The change in meat color in the selenoneine-injected fish was delayed, and the a* value of the red muscle was conserved compared with that in the control fish. Therefore, selenoneine was found to be responsible for the prevention of met-Mb formation in the red muscle of yellowtail.