In composition of the blood cells, the Japanese common oyster, Gryphea gigas seems to be different from such allied species as Pinctada martensii and Ostrea edulis. The blood of the former consists of a single kind of blood-corpuscle and blood plasma, while in the latter tow, existence of leucocytes or lymphoid cells as well as erythrocytes has been reported previously. Therefore, the authors propose here to call the blood-corpuscle of G. gigas as it is and avoid using the term leucocyte as no erythrocytes type exist in the blood.
The materials used for the present study were made available from nursery grounds of the oyster in Shido Bay, Kagawa Prefecture, during the months from June 1959 to January 1960. The blood was collected with a syringe from the heart and the liver (digestive diverticula). In preparing glass slides in a normal procedure, blood specimens were stained by Giemsa's and May-Giemsa's methods.
Microscopic observation at 600 to 1, 500 powers have made it possible to classify, according to WINTROBE (1956), the blood under report into five types (Table 1-A to C). Type VI of the blood cell obtained from the liver is apparently the original body from which the other four types are to be developed.

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The analysis of the weight distribution of salmon caught by the drift nets was performed by use of “the theory of hatch ability concerning the fish eggs” by Dr. TAUTI.
The distribution of the weight (w) of fish is assumed to be normal distribution, where the mean value of weight is w₀. Consequently, the number of the fish, the weight of which is represented by the value between w+a/2 and w-a/2, is shown by the following formula: N_w ?? aN_oh₀/√=exp[-h²_o(w-w_o)²] where a means weight interval measured. Moreover, it is assumed that p_w (the probability of the number of fish (w) caught by the net) is expressed by the normal curve type: p_w=Cexp[-h²_i(w-w _?? )²], where w_i means the weight of the fish which are most easily caught by the gill nets with mesh size l_i. Accordingly, the number of the fish that the weight of those are occupied by the values between w+a/2 and w-a/2 may be shown by the following formula:
N_wp_w=aN_oCh²₀/√πexp[-h²₀h²_i/h²₀+h²_i(w₀-w_i)²]exp[-(h²₀+h²_i)(w-h²₀w₀+h²_iw_i/h²₀+h²_i)²]. The values of h_o² and w_o in the above equation are determined from the actual weight distribution of rainbow trout (Salmo gairdnerii irideus (GIBBONS)) in the outdoor pool (length 25m, width 5m, depth 1.0-1.5m) before the model experiment of fishing (Fig. 1). And, the value of term of (h²_o+h²_i) can be estimated from the weight of fish caught (gilled in mesh at the portion of operculum)by gill nets with different sizes of mesh. Accordingly, h²_i is obtained (Table 1, Fig. 2). According to the above results, the estimated value of h²₀ is larger than those of h²_i.
The number of fish caught by the gill net per unit time is given by the formula CN_oh_o/√h²_o+h²_iexp[-h²_oh²_i/h²_o+h²_i(w_o-w_i)²]. Assuming h²_i is independent on li as shown in Table 2, it is proportional to the term exp [-K₂(w_o-w_i)²] (Fig. 3).

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If we will assume that the results of the previous paper concerning the weight distribution of the individual fish caught by gill nets are applicable in the case of the salmon driftnets used in the region of the Northern Pacific Ocean, then it may be considered that the number of the fish caught by the drift nets (n), which have the weight (w), is proportional to the formula exp [-k₁(w-h²_ow_o+h²_iw_i/h²_o+h²_i)²]. Consequently, the mean number of the fish caught by per unit of drift nets is proportional to the formula of the exp [-k₂(w_o-w_i)²].
In this paper, from the underlying treatment we get the value of w_o with the aid of the value (h²_o+h²_i) and (h²_ow_o+h²_iw_i) computed from the data in the ocean field. The individual weight of the fish caught is measured under the consideration of the following different condition: the difference of size of mesh (12.1, 12.4, 12.7, 13.3cm), the difference of species of fish [red salmon (Oncorhynchus nerka (WALBAUM), chum salmon (Oncorhynchus keta(WALBAUM), pink salmon (Oncorhynchus gorbuscha (WALBAUM)), silver salmon (Oncorhychus kisutch (WALBAUM))], the difference of the portion of fish body which is gilled in the mesh used (operculum (II), middle portion of operculum and dorsal fin (III)). Refering to the above result, the values of (h²_o+h²_i) and (h²_ow_o+h²_iw_i) were obtained by the same treatment as the previous paper. Consequently, it was estimated that these values do not so depend on the size of mesh (l_i) (Table 1, Fig. 1, Fig.3).
Accordingly, h²₀w₀+h²_iw_i may be transformed into the following formula h²_ow_o+h²_iw_i=[h²_o+h²_i(l_i/l_o)³]w_o (l_o: shows the mesh size which is most easily to catch fish in the fishing field and value of l_o is alike to the commercial mesh size 12.1-12.4cm). Where l_i/l₀ ?? 12.1/13.3 then (l_i/l₀)³ ?? 0.75 and h²_i<h²_o (refer to the previous report). Therefore, w_o may be obtained from the known values of h²_o+h²_i and h²₀w_o+h²_iw_i (Table 2).
The mean number of the fish (per unit of drift nets) which are gilled in the mesh in a certain portion of fish body, namely N_i, may be evaluated by the following expression: N_i∝exp [-h²_oh²_i/h²_o+h²_i(w_o-w_i)²]. Accordingly, N_i has a max. value in the case w_o=w_i. Therefore, we evaluate the value of l_i given the max.

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For enlightening the efficiency of drift net operation in salmon fishery, some available data of catches of red salmon, chum salmon and pink salmon were schematized as stated below and looked at from new angles independent of the extreme divergency of their actual catches:
1. According to the number of fish individuals actually caught in every one of 12 sections constituting a stretch of drift net and differing inevitably from section to section as regards the times of laying out and hauling up, daily ranks of catches were decided for each one of these sections of net as well as for each one of said kinds of salmons. From the daily ranks the corresponding averages of daily ranks, the average daily ranks so to speak, were further calculated in proportion to the days on which the drift net was actually operated and divided into 2 groups, one higher and the other lower than the mean of ranks 12-1, viz., 6.5. These groups were marked with ?? and ??, respectively, and entered in panes of a rectangular chart on the co-ordinates of which the times of day of laying out and hauling up of net-sections were graduated. Similar types of charts were prepared for the avearge daily ranks for (i) the whole interval of fishing season from June to August, (ii) the catches in June and July, respectively, (iii) the cases in which the sum of caught individuals of red salmon and chum salmon was greater and smaller, respectively, as compared with those of pink salmon and (iv) the cases in which big catches and small catches of said three kinds of salmon were respectively experienced (Figs. 1, 2 and 3).
2. Comparing between the charts the kind of marks of said two groups, or in other words, examining whether the marks in corresponding panes are concordant or discordant with each other, efficiency of catching chum salmon may be said to be likely bound up with the times of day at which a drift net is laid out and hauled up (Figs. 2, b)-g) and Table 1), while any positive rule can hardly be found as for efficient catches of red salmon and pink salmon (Figs. 1, b)-g), 3, b)-g) and Table 1).
3. According as the average daily ranks above and below 6.5 assigned to the panes in Figs. 1-3, b)-g) were predominant at least 3 times over each other, three charts carrying the panes marked with ?? and ?? were prepared for visualizing the times of day of effective catches of chum salmon (Fig. 4, a)), red salmon (Fig. 4, b)) and pink salmon (Fig. 4. c)). On the basis of Figs. 4, a)-c), it may be said that chum salmon and pink salmon are caught most effectively by keeping the net laid out rather for a long and a short time, respectively, while any positive comment is difficult to be made upon the time of effective catch of red salmon. The fact that effective duration of drift net operation varies according to the species of salmon to be caught seems to be explained to some degree from the ecology of the fish in question, Thus pink salmon, being small in size, may perhaps be liable to get out of the net in which it became once entangled so that the apparently strange situation is met with that an effective catch of this fish is realized with a net kept laid out rather for a short time. Actually observed body portion by which the different kinds of salmons are held entrapped (Table 2) suggests that these fishes differ likely from one another also in regard to the tendency of getting out of the net.
4. From many assumed types of catch in which a fish may visit a drift net and fall entangled therein, the types indicated in Figs. 5, a) and b) were picked up as bearing closest resemblances to those in Fig. 2, a) and Fig. 1, a) respectively.

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In summer, the water-mass lacking in dissolved oxygen often covers the bottom in the central part of the Bay of Omura. This water-mass has been called “Nigashio” water by the fisher-men, and there has been an influence upon fishing conditions of the drag-net fishery in the Bay.
In this work, the author has made a study on the appearance of the “Nigashio” water in this Bay, and investigated the vertical distributions and seasonal variations of oxygen as one of the methods for analysis of its factors.
The “Nigashio” water often appears in July at first, then develops well in August to September, and it disappears in October, soon after the vertical mixing of sea water begins.
Stagnation of the water-mass of central part of the Bay, owing to the anti-clockwise eddy system, causes a well developed stratification of sea water and consequently the occurrence of the “Nigashio” water.
As one method to know a degree of development of the “Nigashio” water, the vertical gradient of water temperature is useful, and at the same time it is said that the great abundance of plankton plays an important rÔle for onset of the “Nigashio” water.
Though the “Nigashio” water occurs most frequently at the central part of the Bay, west of the Mishima Is., the area is not always fixed, and the thickness of the “Nigasho” water (oxygen lacking layer) changes by area.
The “Nigashio” water front which has an effect upon the benthic fauna acts as a cause of a temporal increase of catches of drag-nets around the “Nigashio” water area, but ultimately the productivity of fishing grounds in that area decreases very much.

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Sea-urchins, abalones and sea-hares etc. are generally known as predator of the brown seaweed, Undaria pinnatifida, which is much esteemed as an article of food in Japan. Recently, the decrease of the yield of Undaria caused by the sea-hare has been reported from the coast of Kumamoto, Mie and Aichi Prefecture. The studies had been made on the biology of the sea-hares, in connection with the damage of Undaria occured at the coast of Toyohama, Aichi Pref., in 1958-60.
This paper deals with a study on the feeding habit of the sea-hares and the results obtained are summarized as follows:
(1) Two species of the sea-hares, Aplysia juliana and A. kurodai are found on the coast of Toyohama, Aichi Pref., during the warm season especially from late April to June. This period falls on the spawning season of the animals and also at the same time on the harvesting time of the seaweed.
(2) In the laboratory experiments, A. kurodai feeds on the green and red seaweeds, while A. juliana does on the brown and green ones, having especially a preference for Undaria pinnatifida. The latter usually feeds on the blade of Undaria, but the animal may attack also the stem of the seaweed when their soft parts were exhausted.
(3) An animal of ca. 200 grams of A. juliana could consume ca. 11-12 grams of soft blade of Undaria in one day. This amount counts for a frond of young Undaria or onehalf or one-third of medial sized one.
(4) The amount of feeding remarkably decreases when the water temperature goes out of the range of 15-24°C.

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A stationary Pt electrode was studied so as to be adapted for a long continued polarographical determintion of O₂-concentration in water in the light of the following experimental data:
Steady currents were observed when the Pt electrode was polarized at -0.90, -0.95V. against Ag or at -0.85, -0.90V. against a calomel half cell.
The current was effectively protected from the disturbance caused by waterflow acr ?? ss the electrode by covering it with two sheets of filter paper soaked with phosphate buffe ?? of pH 7.
The electrodes were settled inside a cylinder of acryl resine equipped with a temperature regulating system, so as to be kept free from the effect caused by temperature changes. The cylinder was kept closed at the upper end, while opened at the lower. The content of the cylinder was accordingly left open to surrounding water at the lower end, allowing the electrodes to contact with the water. However, a gradual decrease was often observed in the current measured with the electrodes thus fixed inside the cylinder.
This decrease could be avoided by reserving an air layer in the upper part of the cylinder, though the cause of the decrease in current and the effect on it of the air layer remains yet unexplained.
Changes in pH and ion concentration in surrounding water seemed to have little effect on the current.
The current showed a good stability and also a good reproducibility in responding to O₂-concentration in water, when examined with tap water of the laboratory.

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Microscopic observation of the abnormal tissues of internal organs in three female snapping turtles, which typically showed serious illness in appearance, was made in this paper.
The abnormalities observed in each internal organ are as follows (cf. Table 1 and Plate 1):
Coelom fat is surrounded by thick membrane of connective tissue, containing a little of neutral fat and large quantity of denaturated lipid.
In respect of the muscular system, morbid degenerations such as dispersal and atrophy were seen.
As to the liver, such morbid degenerations as stagnation of sinusoid, dim swelling, disturbance of cell-cord, increase of reticulum fiber, cariopycnosis, decrease of glycogen, and numerous lipid granules were noticed.
As for the kidney, morbidities such as stagnation of glomerulus, hyalin degeneration of Bowman's capsule, renal cast, dilatation of nephritic duct, and breakdown of nephritic duct cell were recognised as serious nephrosis. But in the spleen was seen general anemia only.
From the above observations, the pathological features such as abnormal accumulation of denaturated lipid in coelom fat, dysfunction of liver and kidney, and hypoalimentary state were recognized distinctly.

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In Tanabe bay, the lift net fishery has been operating to catch Anchovy, Round herring, Mackerel and Horse mackerel with two kinds of attracting fish lamps, setting on the board and under water.
In 1952, the fishing ground was distributed in area 3miles×13miles, fishingboat had been numerated to 57 in there and the fishing season was from April to August. Each boat had been operating under the same conditions for this fishery.
In these studies, the cause for difference of the amount of catch among each boat is investigated and the results obtained are shown as follows. Swimming area of fish, which means the parts of higher density of fish, is limited to a narrow scope 1/8 area of the around and in this area a numerous boat are operating more frequently than the others.
Therefore, it is clear that the boats gained a large amount of catch have been fishing more times in this area compared with other boats. Furthermore, it is shown as the illumination power of two lamps used for this fishery is too strongly for scale of this net, many fish are gathered to out-side of net rather to inside.

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The mackerel angling (with pole and line) fishery has been operating at night with lureing lamps in the off-shore of around of Japan.
For the investigation, the following five fishing grounds were selected, surrounding of Saishu Island, off-shore of Senzaki, Tsugaru Channel, East China Sea, and southern sea of Kyushu (Satsunan Sea area).
In this studies, the difference of catches among these five fishing-grounds was discussed through two points of view of light intensity of lureing lamps and echo of fish-finder from shoals.
Consequently, it was found that the adaptability of light intensity to catch mackerel was changed by fishing-ground, the most powerfur light was neccessary in the East China Sea and other fishing-grounds were arranged in order of light intensity as follow; Saishu Island, Southern Sea of Kyushu, Senzaki and Tsugaru fishing ground and this order was given in propotion to depth of swimming layer of shoals in each fishing-ground and the degrees of sea transparency. It was also found that the use of fish-finder had brought about a remarkable effect on catches.

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The purpose of useing the lureing light in angling fishery is that not only lureing up of fish to the shallow layer where the angler is easy operated to the angling gear from deeper sea or sea bottom but also to make baiting of fish themselves is promoted by illumination light. In this studies, two angling gear types are indicated, the one is so-called tenbin, the other is for the capture of sea bream and grunt. (as showen fig. I-3). Mackerel angling in WAKAYAMA prefecture, had been carried out by two tonnage classes fishing boat; 3-7 tons class with 1.5-1.0kw candle-power lamp and over 7 tons class with 2kw. Swimming layer of mackerel was estimated as 35-50 meters in depth in there. Illumination zone of light is varied by candle power and illumination strength of about 10 lux for optimum condition of light when fish are lured up with 1.0, 1.5 and 2kw lamps was indicated 18m, 28 and 35m in depth respectively.
In Western Kyushu, sea bream and grunt are angled with hand line and then are used to lureing lamps. Fishes are lured up to about 25-30 meters from the bottom of 50 meters around by lureing light and then there are illuminated as about 10 lux. Intensity of light must be increased or decreased according to the depth of fish living layer.

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In Japan, saury has been caught by stick held dip net from September to December, in the coastal sea areas of the pacific. The process of the capture of fish with stick held dip net is divided into the following three orders according to the kinds of fishing lights. First of all, saury is gathered to around of starboard being lured by fishing lights which is equipped at starboard. Generally this light is named as gathering light and composed of 13-30 white globes of 500W.
Secondly, saury is removed to port side from starboard where fish has been grouping by the action of fish light which is set at port, usually this light is called as guiding light and composed of 3-7 white globes of 500W.
Last of all, saury is lured into the net setting in advance into the water with aid of light, usually this light is called as catching light and composed of 3-6 red colour globes of 500W. (These data concerning the composition of fishing lights were supplied from saury fishing boats in Chiba prefecture in 1955) The results of this study will be discribed as follows; Let C is the intensity of illumination in candle power the quantity of saury gathered to starboard is proportionate to C^1/2-1/4 of gathering light.
When the ratio of the candle power of guiding light to that gathering light is half and less, saury is lured most effectively to port from starboard.
The most suitable numbers of catching light to make saury lure into the net is composing 5-6 and less red colour globes.

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The relation between antimicrobial action and copolymerization of oxidized fish oils was studied.
The fact that the reversal action of nitrogenous substance on antimicrobial action of oxidized calamary oil methyl ester has a direct bearing on copolymer formation from them (Table 1), suggested that the antimicrobial action of oxidized fish oils was responsible for copolymerization of oxidized fish oils with protein. Both antimicrobial action and copolymerization of oxidized oils were accelerated by the primary oxidative product of oils, hydroperoxide (Table 2, 3), but hydroperoxide content in oxidized fish oils was not a limiting factor in the antimicrobial action. The most important reaction leading to copolymer formation from oxidized fish oils and protein seemed to involve a built-up film formation reaction which consists of a protein-lipid linkage and a lipid-lipid linkage.
Copolymerization of the antimicrobial fish oils with protein of the microbe cell wall would change the permeability of the cell wall. This effect can brought about either by blocking the entry of various nutrients into the cell or the diffusion of metabolites into the external environment, or by inactivating an enzymic system.

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Indentification of the pigments of canned red salmon was performed according approximately to the method previously reported. The chromatogram on CaCO₃ showed three bands when developed with 3% acetone in benzene (Fig. 1 and 2). It seems that the first and the second band correspond to the cis-isomers of astaxanthin derived by the processing, and the third, the main fraction, represents all-trans astaxanthin, an unchanged natural pigment (Fig. 1).
Changes in content of the pigments during the storage of canned red salmon were investigated, and it was ascertained that there were no significant changes during the storage period up to 15 months at room temperatures, although there were detected slightly higher contents of the pigment in the cans stored for 1-3 months, and the amount of the pigment in the separated oils showed an increasing tendency during the storage (Table 1).
It was found that the content of the pigment had falled to about 64% of that of fresh muscle. It seems that the heating sterilization is responsible for such a remarkable loss in the pigment.

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