Inflow event of the Tsugaru Warm Water due to the Passage of Typhoon and　Rapid Change in the Costal environment at Shizukari, located in the bay-head of Funka Bay
Funka Bay is one of the popular scallop breeding grounds in Hokkaido. Funka Bay Summer Surface water (Fs), which is transformed from the Oyashio water in early summer and higher temperature and lower salinity than the underlying Oyashio water, occupied the upper layer in the Bay. Usually during August to September, the Tugaru Warm water (TW) originated from Kuroshio and of higher temperature and salinity than the Oyashio water, enters into the bay. In 2003 summer, fishermen working near the bay-head of bay at Shizukari reported that curiously clear water appeared at the sea surface and many scallop’s juveniles were dead. We suppose that death of scallop juveniles is attributed to rapid environmental change accompanied with inflow of TW, and to investigate the environmental change in the bay accompanied with TW inflow, we carried out hydrographic observation by a ship and mooring instruments in 2004. When Typhoon 0416 passed near Hokkaido in 31 August 2004, the salinity and temperature off Shizukari locating in the head of the bay were rapidly changed and strong north-westward current flowed across the coastline was observed. In 1 September 2004, the current speed off Shizukari amounted to maximum, 50cm/sec and mean speed during 31 August to 1 September was about 20cm/s corresponding to the speed at which TW could flow form the mouth of the bay to the head of the bay. When Typhoon 0418 passed in 8 September 2004, similar rapidly environmental change could be observed. TW reached to Sizukari shore in 13 September and flowed westward across the shore at the scallop-breeding zone. At that time, vertical sections at Yakumo and Otoshibe also showed that TW flowed at the depth deeper than the scallop-breeding zone. It is inferred that such a rapid inflow of TW occur after severe weather condition like a Typhoon, and that the basin water which has a temperature-salinity characteristic similar to TW and is low in oxgen concentration, has possibility to contain harmful substances such as hydrogen sulfide.

Hatching date of Japanese common squid,Todarodes pacificus,in the Okhotsk Sea off the coast of Hokkaido in 2001 and 2002.
Japanese common squid, Todarodes pacificus, migrate to the Okhotsk Sea off the coast of Hokkaido from the Japan Sea and the Pacific Ocean. But migration of the autumn hatching group from the Japan Sea is not clear in how much it is. Then, statolith increment analysis was applied to 380 specimens of the squid in the Okhotsk Sea off the coast of Hokkaido in 2001 and 2002, in order to estimate ages and population structure. Samples were extracted so that the fishing season might be reflected, and mantle length was measured. Mantle length modes of the extracted specimens were 22cm and 23cm. The hatching month of main fishing season was presumed to be March-April. Migration of the autumn hatching group was not founded in the Okhotsk Sea off the coast of Hokkaido in 2001 and 2002. There were later hatching groups in 2002 than 2001.

Parasiticidal treatment against the fish-pathogenic protozoan Trichodina sp., an ectoparasite on the body surfaces of cultured barfin flounder, Verasper moseri. - Ⅰ Freshwater tolerance of Trichodina sp. as determined by a short-term incubation of epidermal mucous secretions from infected fish.

The purpose of this study was to develop a new and clean protocol for the control of Trichodina sp. infections on cultured barfin flounder, which could replace the use of a formalin bath. Firstly, in order to examine the environmental tolerance of Trichodina sp. in detail, short-term incubation of Trichodina sp. was established. Epidermal mucous secretions harbouring parasites were collected from the body surface of infected barfin flounder, smeared on a slide glass, and immersed in filtered seawater. Incubations were done at 3 different temperatures (5 oC, 15 oC and 20 oC), each of which yielded a high rate of live parasites (42.5-83.3 %) after 8 hours, suggesting that Trichodina sp. could readily survive under these culture conditions. Secondly, using this culture system, the effects of immersion of parasites in fresh water or in 25% or 50% sea water on vitality of Trichodina sp. were examined. The rate of surviving parasites after incubation in fresh water decreased sharply and reached 0 % by 30 minutes of incubation; immersion in partial sea water did not cause a distinct reduction in vitality of parasites. Indeed, successive observations on the morphology and vitality of parasites immersed in fresh water indicated that immersion for at least 30 minutes was essential for inducing the parasite to burst and die. Accordingly, it is suggested that a freshwater bath of infected barfin flounder for 30 minutes may prove very suitable as a new parasiticidal method against Trichodina sp. infection in an aquaculture environment.

Parasiticidal treatment against the fish-pathogenic protozoan Trichodina sp., an ectoparasite on the body surfaces of cultured barfin flounder, Verasper moseri. - Ⅱ Parasiticidal effects of fresh water on Trichodina sp. and the tolerance of juvenile barfin flounder to freshwater exposure.

Short-term incubation of Trichodina-harbouring epidermal mucous secretions from barfin flounder in fresh water for over 30 minutes was previously shown to be effective for killing of this protozoan ectoparasite. In the present study, the in situ parasiticidal effects of freshwater baths on Trichodina sp. were further investigated. Infected barfin flounder were bathed in fresh water for different durations, i.e., 0 (control), 15 and 30 min, and the parasite density on the body surface was monitored until 28 days after bathing. In groups exposed to freshwater for 15 min and over, parasite densities decreased to near-zero the following day, whereas high parasite loads were seen in control groups throughout the experimental term. In the group bathed in fresh water for only 15 min, the parasite density increased gradually from 14 days post-exposure. The density eventually reached a very similar value to that observed before bathing, because a few parasites could survive the freshwater bathing regime. In contrast, in the group bathed in fresh water for 30 min, the parasite density remained at 0 % even by 28 days after exposure, and re-establishment of Trichodina sp. never occurred. These results show that freshwater exposure should last for at least 30 minutes to ensure that all Trichodina sp. on the body surface are killed, which coincides with previous culture experiments. Such treatment was further shown to not affect the survival of juvenile barfin flounder when experimentally reared in fresh water for 6 hours, although mortality linearly increased beyond that duration. These results thus prove that freshwater baths for 30 min of duration, sufficient to eliminate on Trichodina sp., is not harmful to barfin flounder. Therefore, the use of freshwater baths for 30 min is an effective and clean method for preventing cultured barfin flounder from Trichodina sp. infection.

Studies on the quality evaluation of chum salmon Oncorhynchs keta flesh color.

Chum salmon flesh color is the most important factor in respect of quality. The present flesh color evaluation is discriminated with the subjective method. However, in order to be anxious about the incorrect discrimination by a judgment person's individual variation, it is desirable to evaluate flesh color by the objective method. It becomes important to set up the valuation basis reliable for that purpose. When a salmon processor actually discriminates flesh color grades in a disposal plant, the discrimination standard of the high accuracy adapted to visual evaluation of a fillet color is needed. Therefore, in this study, it was investigated how the difference in the form of a chum salmon sample would affect color measurement values. Based on the result, we made the objective valuation basis corresponding to subjective evaluation from CIELAB color system values in a fillet, and established the discrimination standard for chum salmon flesh color.

Quantitative evaluation of a food chain that originates from leaf litter in a river mouth

In the mouth of the Gokibiru River on the west coast of Hokkaido, Japan, we have described a food chain that extended from an amphipod Anisogammarus pugettensis to young crest-head flounder Pleuronectes schrenki and was dependent on leaf litter piled on the bottom. This study examined annual production of the animals to evaluate the food chain in the river mouth in addition to population dynamics and food habit of A. pugettensis. Population of A. pugettensis had 2-3 cohorts throughout the year and the annual production was evaluated to be 2.1g-C/m2/yr. The amphipod preferred dead leaves of maple Acer mono and alder Alnus hirsuta to macro algae of Ulva pertusa and Laminaria religiosa as foods, and derived 31% of foods from leaf litter. The annual production of P. schrenki less than 1 year in age was 0.4g-C/m2/yr and the flounder derived 25% of foods from leaf litter through A. pugettensis. Therefore, the rate of leaf litter that contributed to the production of A. pugettensis and P. schrenki were estimated to be 0.008 and 0.0004% of the annual litter accumulation, respectively.

Growth of hatchery-reared barfin flounder Verasper moseri in the Pacific coastal waters off southwestern Hokkaido. (Short Paper)