To clarify the factors contributing to the price differences of the pike-conger Muraenesox cinereus between Tokushima, Japan and Korea, we analyzed proximate and free amino acid compositions in muscle. The lipid content of the pike-conger in Korea (7.7-10.4%) was remarkably higher than that in Tokushima (1.4-3.0%). No difference was seen in the free amino acid content, which affects the taste. In the females weighing between 0.3-0.8 kg, the condition factor and hepatosomatic index of Korean fish were higher than those of Tokushima fish. Some of the fish in Tokushima matured in the spawning period, but none did so in Korea. The lower temperature of Korean waters is thought to delay maturation age and increase the lipid contents of Korean pike-conger, leading to stronger taste and higher price.
The behavior of Japanese common squid Todarodes pacificus around a squid jigging boat during night-time operation was investigated. Eighty-nine operations were conducted by R/V Hakusan-Maru (167 gross tons) equipped with 78 metal halide lamps (234 kW in total) in offshore fishing grounds in the Sea of Japan, and sonar images and squid catch were continuously recorded (logged). The positions of squid schools before they were caught were tracked from sonar image recordings using digitizer software. Squid schools moved around the boat, gradually approached the boat and then tended to locate in fore and aft areas just before they were caught. More squid were caught by jigging machines near the bow or stern than by those near the center of the boat. Underwater irradiance was lower in fore and aft areas than in port and starboard areas. These results indicate that squid schools tended to enter under the boat through fore and aft areas. Namely, fore and aft areas with low irradiance are thought to function as an entrance to the shaded area under the boat for the squid.
Nematodes are common components of marine environments. Therefore, community analysis of nematode composition is important for the characterization of marine environments. However, conventional identification based on morphological characteristics of nematodes requires highly specialized skills and is labor intensive. In this study, molecular biological techniques were examined for rapid identification of marine nematode species in intertidal sediments collected at Zigozen in Hiroshima Bay, Japan. 18S ribosomal RNA genes obtained from 89 individuals out of 96 were amplified and grouped into 22 phylotypes. Two phylotypes had over 97% similarity with species submitted to the database. The remaining 20 phylotypes showed lower similarities among the database records, suggesting that phylogenetic analysis of the 18S rRNA gene is a useful tool to clarify the diversity of nematode communities. However, more sequence data of marine nematodes needs to be accumulated to discuss the changes of nematode communities at a species level among the monitoring stations.
We determined the time of formation of incremental zones (transparent light bands) and discontinuous zones (opaque dark bands) on larval sagittal otoliths of Japanese Spanish mackerel Scomberomorus niphonius through regular samplings over a day in captivity. First, distinctive rings were observed in 5-day-old fish when the larvae started feeding. The formation of the incremental zones on sagittal otoliths started between 05:00 and 08:00, and continued from the daytime to the nighttime. On the other hand, the discontinuous zones were formed during the following nighttime period. This result is helpful to measure the width of the outermost incremental zones and count the number of daily rings precisely in otolith analysis by considering the time when the samples of larvae were caught.
Using published data for 8,683 samples obtained off the coast of Fukushima during the two-year period after the Fukushima Daiichi Nuclear Power Plant accident in 2011, the state of radioactive cesium (134Cs+137Cs) for 95 species (a total of 97 fishery items including two species that are marketed separately for the adult and immature stages) were clarified. All data available from a government website were used for this analysis. The results of cluster analysis using parameters of the annual average and standard deviation of radioactive cesium concentration indicate that the 97 items can be categorized into four groups. Group A had lower concentrations and lower variability both for the first and the second years (60 items). Group B showed a decline of concentration in the second year but it was still high (21 items). Group C had extremely high initial concentrations but levels were almost undetectable in the second year (1 item). Group D was highly contaminated throughout the two years (15 items). Almost all the items of groups A and C satisfied the government food-safety standard in the second year. On the other hand, products in groups B and D do not satisfy the standard and must be closely monitored.
The purpose of this study was to classify kelp farming management bodies based on how they operate and the products they produce. We assumed that bodies that produce similar kelp products have similar operation methods. A total of 72 bodies in Fukushima, Hokkaido during 2004-2009 were classified using three main product-production values, and nine samples were classified by process analysis. The bodies were classified into three types, and in each type, a different part of the production process was considered to be the most worker-intensive. The bodies could be classified based on the constitution of their main products associated with individual operation methods. Bodies changed their operation method depending on the product.
To assess the status of recreational trolling of the Biwa salmon Oncorhynchus masou subsp. in Lake Biwa, recreational anglers have been obliged to register with the Lake Biwa Fisheries Management Committee since December 2008. Reports for three years show that the number of anglers increased every year. The submission rate of catch reports was about 90%. Over this three-year period, the total number of fishing days and fish caught in the summer season were much larger than those in the winter season. Although about 10,000 fish were caught by anglers every year, 41.4-67.3% of them were released. The total amount of fish caught by the anglers was estimated to be 6.6-8.6 t, and the total annual commercial catch of Biwa salmon in Lake Biwa was 23.2-45.8 t.