A total of 256 specimens of “Nashifugu” pufferfish Fugu vermicularis vermicularis were caught in Ariake Bay from June 1993 to May 1994, and examined for anatomical distribution of toxin by the standard mouse assay method for tetrodotoxin. The frequency of the specimens whose toxicity exceeded the quarantine limit (10MU/g) was 84% for skin, 72% for liver and 100% for ovary. The highest toxicity scores were 3120MU/g in skin, 2910MU/g in liver and 6240MU/g in ovary. In regard to muscle, only 4 specimens caused death with toxic symptoms in mice and their toxicities were calculated to be <5-7MU/g. However, they did not show any toxicity when tested on the deep part of the muscle. In further experiments, the surface part of skinned bodies of “Nashifugu” pufferfish was mostly toxic, though the deep part of the muscle did not show any toxicity. It was also shown that the surface part washed with water was nontoxic. Thus, the toxic result on the muscle was considered to be due to the contamination of tetrodotoxin from toxic skin during preparation of the samples.
The reproductive cycle and shell growth of the Manila clam Ruditapes philippinarum, transplant-ed from Lake Akkeshi to Saroma Lagoon, Hokkaido, northern Japan, were studied from April 1991 to August 1992. Histological examination revealed that the spawning season is from July to Septem-ber, with a peak in August. The shell lengths at first maturity were 25mm (2 years) and 27mm (2 or 3 years) for males and females, respectively. Disturbance rings on the shells formed upon trans-plantation were used to estimate growth, which mainly occurred in May and June. Growth is described by the von Bertalanffy growth equation for both sexes Lt=49.71 (1-exp (-0.416 t)), where Lt is the shell length (mm) at age t (year). The clams in the lagoon had a shorter spawning and growing season, were larger and older at first maturity, and had a more moderate shell length growth rate than clams from southern Japan. Finally, some reproductive and growth-related responses to various habitats were discussed.
Using a classical respiratory conditioning technique, the hearing ability of the bastard halibut Paralichthys olivaceus was measured for 7 fish at 7 frequency points between 70Hz and 500Hz. The conditioning response was measured as suppression in the respiratory activity by the piezoelectric sensor fitted on a gill cover in a quiet water tank. The bastard halibut was sensitive to sounds in the frequency range from 70Hz to 500Hz. The auditory thresholds were observed among the 7 fish with much difference (about 17dB) at 100Hz and 300Hz. But the audiogram had common characteristics that they had the lowest threshold at about 100Hz and that the threshold increased rapidly with frequency of sound between 200Hz and 400Hz. An attempt was also made examine the escape response of each of the above 7 bastard halibut by the sound stimulus, but no conditioned escape response was observed after 7 times applying training stimulus.
In order to elucidate the distribution pattern of walleye pollock Theragra chalcogramma off southwestern Hokkaido in the Japan Sea, trawling and acoustic surveys, and hydrographic observations were conducted in early April from 1989 to 1993. In 1991 and 1993, the Tsushima Warm Current Water was widely distributed in the coastal area of Aomori Prefecture, and a large number of walleye pollock were collected in the southwestern area off Hokkaido. In contrast, this water was observed only in a restricted coastal area of Aomori Prefecture in 1989 and 1990, and walleye pollock were found distributed in a coastal area 20-30 miles off Aomori Prefecture. Although an annual change in the distribution of walleye pollock was observed, they were concentrated in the area of the horizontal thermal front between the Tsushima Warm Current Water and the Japan Sea Proper Water every year. From these observations, it appears that the migration of walleye pollock in early spring is closely related to the behavior of the Tsushima Warm Current Water in the Japan Sea off Aomori Prefecture.
The effect of rearing seawater temperature on circuli formation of juvenile red sea bream Pagrus major was examined by an indoor rearing experiment. The juveniles, 119 days old after hatching, were reared under the controlled seawater temperatures at 17, 20, 23, and 26°C, and under natural seawater in different 100-1 tanks from 11 to 19, August 1994. The daily deposition rates of scale circuli increased along with seawater temperature. Correlation between seawater temperature and the rates was fitted for a parabolic curve. This correlation also agrees to that obtained from the juveniles reared in three different temperature conditions at different sea-farming stations.
A red tide of long duration (late August to mid November) of Gonyaulax polygramma Stein occurred in and around Uwajima Bay in 1994. This red tide caused mass mortalities of cultured and natural fish and shellfish stocks worth more than 8 hundred million yen. The maximum density of G. polygramma reached 6.8×104 cells/ml in Uwajima Bay. From fluorometric measurements, it is supposed that G. polygramma cells existed in the surface layer in the daytime and migrated to the bottom layers at night. During the red tide, oxygen deficient water was formed and eventually the whole water column became anoxic in the coastal waters of Uwajima Bay and Hoketsu Bay. It seems that the death of fish and shellfish was mainly attributable to the anoxic waters with high sulfide and ammonia concentrations caused by the decomposition of G. polygramma cells. The bloom of G. polygramma in Uwajima Bay was initiated in the Yoshida area, and then the bloom gradually spread to the southern areas of the bay. Analysis of this mechanism of the spread of G. polygramma cells throughout the bay will help to establish a monitoring system for future blooms. Meteorological and hydrographical data suggest that little rainfall, high water temperature and a low water exchange rate enhanced the initial occurrence and long duration of the red tide of G. polygramma.
A biological study was carried out on whelk Neptunea arthritica using samples collected from basket traps during June 1991 to March 1992. The shell height distribution of whelk has three modes and bumps. Mean shell height in each year class and age composition were obtained by analyzing the shell height distribution. The growth pattern of the mean shell height at age is a sigmoidal pattern. Two types of growth equations were estimated and the logistic growth equation gives a better fit for the data. The results indicate the growth rate of whelk is slow in the early stage of growth, however, the growth then becomes rapid, and the shell height at age four approaches 82mm. In order to manage this fishery resource, the Shiriuchi Fishing Co-Operative has set a regulation that the minimum legal size of harvested whelks is 60mm in shell height. The study showed that this current legal size is so small that most of the female whelks are caught before the first spawning, hence the legal size should be raised to 75mm.
Late summer in 1994, Microcystis bloom (dominant species: Microcystis aeruginosa) occurred for the first fime at two harbors in the north basin of Lake Biwa. The limit values of TN (total nitrogen) and TP (total phosphorus) for the occurrence of Microcystis bloom were ca 30 and 3 μg at/l, respectively. By comparing with the water quality factors of the harbors where Microcystis bloom occurred and the factors of harbors where Melosira bloom (dominant species: Melosila granulata) did, it was showed that TN, TP, DIP (dissolved inorganic phosphorus) and TN:DIN (dissolved inorganic nitrogen) tended to be higher and TN:TP and DIN:DIP ratios tended to be lower in the harbors where Microcystis bloom occurred. As the cause of the bloom of Microcystis in the north basin of the Lake Biwa, it was suggested that the suitable environment conditions for the quick growth of Microcystis was brought by the continuation of hot and clear weather in 1994. The increase of DIP exudation from bottom sediments, the intense consumption of DIN by phytoplankton, the disappearance of DIN due to nitrification and denitrification near the surface of bottom sediments might cause the increase of DIP and TN:DIN ratio. Further, the relative increase of DON (dissolved organic nitrogen) and the inorganization of DON by the symbiotic bacteria might supplied DIN to Microcystis, as many bacteria with same form were found at the middle layer of mucilage slim of colonies of Microcystis.
The effect of starvation on the individual catchability and hook-avoidance learning of the rainbow trout Oncorhynchus mykiss, was determined in angling experiments in outdoor tanks. The fish used were 215mm in mean total length and were obtained from local fish farmers and grouped into two (K and Y) separate experimental tanks. Before the angling experiments, the K group was starved for 3 days, and the Y group for 10 days. Three subgroups from the K group and five subgroups from Y group were subjected to the capture-recapture method to test the individual catchability and hook-avoidance learning. Probability analysis of the results indicated that the K group showed differences in individual catchability but did not learn to avoid hooks, whereas the Y group showed the reverse. Another subgroup from the Y group was subjected to a test with the capturerecruit method, in which angled fish were replaced with naive ones, however these still showed no difference in individual catchability. Therefore, a period of starvation does affect the individual catchability and hook-avoidance learning of rainbow trout, but the mechanism underlying this has yet to be determined.
In order to reduce fish meal in fish diets by combined addition of several alternative protein sources, fingerling yellowtail Seriola quinqueradiata were fed for 30 days on single moist pellet diets including 0-20% of defatted soybean meal (SBM) or meat meal (MM) together with a fixed amount of 20% malt protein flour (MPF). The combination with 20%SBM reduced growth and feed efficiency, probably due to both the poor amino acid profile and low digestibilities of dietary protein and carbohydrate. On the other hand, the combination with up to 20%MM or 10%SBM exhibited comparable growth to single MPF inclusion. Furthermore, there were no marked differences in the body composition, hematological characteristics, and nutrient retentions in all groups tested. These results indicate that combined additions of MPF and MM could replace half of the fish meal in yellowtail diet without any deleterious effects.
This paper describes the flow around flat plates with different aspect ratios using the method of flow visualization by hydrogen bubbles. The flow around plates was visualized over the central section and the lower tip of the plates in a circulating water tank. At an attack angle smaller than the stall, the flow on the suction side of the central section separated at the leading edge, and then reattaching at the rear part of the plates. This phenomenon disappeared at angles larger than the stall. A series of spiral wing tip vortices was formed at the lower tip of the plates, which weakened at an angle larger than the stall. The maximum lift coefficient measured by this experiment was greater than that of the linear lift derived from the potential theory. The difference was greater at lower aspect ratios. This means that the lower the aspect ratio, the higher the effects of the wing tip vortex on the lift of flat plates.
The purpose of this work is to develop a midwater trawl net to survey fish stock. A constant net mouth opening is necessary in order to measure fish stock densities accurately. For this purpose, canvas kites were attached to the midwater trawl net, instead of floats and weights. The area of canvas kites attached to the headrope and groundrope was derived from the equilibrium between the sum of vertical components of the towing force and the drag of the net. The model test were made with a scale of one-twentieth in a flume tank, in which the static characteristics of the kite-type net were compared with those of the float-type net. Further, a full-scale kite-type net was examined aboard the RV “Ushio-maru”. The kite-type model maintained a more constant form and net-mouth area than the float type net over a range of current speeds. The full-scale kite-type net maintained a constant net mouth height of 7meters, according to the plan. From these results, we conclude that the kite-type net is to be recommended for a better sampling device for fish stock assessments.
This paper discusses the efficiency of a spiral impeler mechanism, the influence of the angle of inclination of the casing, the peripheral velocity of the spiral impeller, and inner diameter of the casing for pumping up fry. It also describes the relationship between the quantity water pumped up and the clearance between the spiral impeller and inside wall of the casing. When the clearance between the spiral impeller and inside wall of the casing was less than 1.5mm, the peripheral velocity of the spiral impeller was from 0.74m/s to 1.88m/s and the inclination of the casing was less than 50°, the spiral impeller mechanism could pump up fry. The quantity of water pumped up was not affected by a clearance of less than 1.5mm between the spiral impeller and inside wall of the casing. When the volume ratio of fry and water in the fish tank was 0.30, the radius of the casing 0.25m, inclination of the casing 42°, and peripheral velocity of the spiral impeller 1.88m/s, the spiral impeller mechanism could pump up 2, 490 thousand fry per hour.
Amylase of the stomach of Tilapia nilotica was purified by ammonium sulfate precipitation, followed by affinity chromatography (α-cyclodextrin-Sepharose 6B), chromatofocusing (polyexchanger PBE 94), and gel filtration (Sephadex G-75). The amylase was found to be a single band when examined by electrophoresis. The specific activity of the purified enzyme was 54 times higher than that of the crude extract. The amylase had a molecular weight of 40, 000, showed the highest activity at pH 6.0 and 35°C, and was stable at pH 5.5-7.0 and below 45°C. The Km value of the enzyme for soluble starch was calculated to be 5.8 mg/ml. Its activity was inhibited by Hg2+, Pb2+, Cu2+, Zn2+, PCMB, and DTNB. This enzyme digested not only polysaccharides such as soluble starch, amylopectin, and amylose but also oligosaccharides such as maltotetraose, maltopentaose, and maltoheptaose.
Effect of cysteine protease inhibitor on the setting of the Alaska pollack surimi paste was studied in order to clarify the mechanism for the formation of 150kDa protein component in the paste during its setting. The addition of calpain inhibitor I and II to the paste increased the breaking force and the breaking strain of the suwari gel caused at 30°C for 5h and suppressed the formation of the 150kDa protein component. The addition of N-ethylmaleimide or iodoacetamide also suppressed the formation of this component, but remarkably lowered the breaking force and the breaking strain. The EDTA and EGTA scarcely changed the formation. From the results, it was presumed that the 150kDa component was formed by the catalysis of coexisting cysteine protease, and as a result the increment of the breaking force and the breaking strain was suppressed.
Experiments on bioconcentration and elimination of α-hexachlorocyclohexane (α-HCH) were carried out by using Sillago japonica, Rudarius ercodes, and Pagrus major at two different water temperatures of 20 and 25°C. Changes of bioconcentration factor (BCF), uptake rate constant (k1), and elimination rate constant (k2) caused by the different temperatures were studied. k2 at 25°C was larger than that at 20°C. BCF, which is expressed as k1/k2, did not change with temperature. These results suggested that k1 as well as k2 depended on temperature, and were larger at higher temperature. The present study indicated that both water temperatures of 20 and 25°C were suitable for the bioconcentration experiment using these fish species, and that the water temperature in the experiment, which determines k1 and k2, should be fixed exactly.