The present paper gives the observations reterable to the distribution of mackerel larvae, P. tapeinocephalus, collected by larval net operated at the six layers of 0 (surface), 10, 20, 30, 40, and 50 meters in the region covering Kagoshima Bay and the Osumi channel, and some considerations, especially on the collecting method in relation to the current velocity.
The results (Tables 2 and 3) are summarized as the following lines.
1) From April to June 1960, and in March 1961 the mackerel larvae are found at all the observed layers but 50 meter one, in the fishing ground (of the adult fish) of the said region.
2) The collected larvae are of 3.1-21.0mm in total length. Most of them are small, of less than 10mm in total length (Fig. 3).
3) The collection rate from the 10m layer rises to the highest, that is of 67%.
4) The large number of samples are collected under the conditions of 18-19°C in water temperature, and 34.7-34.8% in salinity (Fig. 4).

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In an experiment to obtain bacteria-free culture of the marine diatoms, a diatom species, Melosira nummuloides was treated with antibiotics. As C. P. SPENCER (1952) states, a short exposure to the considerable doses of Penicillin and Streptomycin seems to be very effective for this purpose. Bacteria-free culture has continued. Its sterility and normal living of that diatom in such a bacteria-free circumstance were ascertained.

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It is well known that the Ayu spawn on river beds of gravel and their eggs adhere firmly to the pebbles, but little information is available on the size of gravels on which the eggs are laid and the requirements of spawners for the size composition of gravels of spawning bed.
The present study is undertaken to these problems. For this purpose, on one hand, the size of gravels sampled from natural spawning beds in two well-known spawning grounds of Sagami River in Kanagawa Prefecture were measured and the numbers of eggs attaching to the gravels of various size were counted. On the other hand, the relationships between the size of spawners and that of gravels on which they spawn were pursued in experimental ponds (Fig. 1).
The results obtained were as follows:
1) At the natural spawning grounds, most of the eggs were laid on small gravels 10mm or less in diameter (Table 1).
2) It was commonly observed in the ponds that the spawning fish measured 13.3-15.9cm in length flocked to the artificial spawning beds made of relatively small gravels, viz., 20mm or less in diameter, and spawned there. Among them the larger spawners occasionally laid their eggs on larger gravels 10-20mm in diameter, but the smaller ones exclusively spawned on smaller gravels 10mm or less in diameter (Table 2).
3) From these observations it is assumed that the Ayu tend to gather for spawning round the stream bed riched with small gravels and spawned there, and it is more clearly observed in smaller fish. The fact mentioned above seems to relate to the spawning behaviour of the fish. The Ayu have a habit of moving gravels by their movement in spawning, accordingly it is assumed that they prefer to beds of gravels which they can move compartively easily.

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Histological observations were made on the kidney of O. latipes and following results were obtained.
1) Entire kidney of this teleost has renal structure and no portion to be called head kidney consisting lymphoid tissue is observed. The renal unit in this kidney is composed, like that of other fresh-water fishes, of glomerulus, neck segment, first and second parts of the proximal convoluted segment, distal convoluted segment and initial collecting tubule. As the distal convoluted segment is demonstrated in this renal unit, this euryhaline fish is a typical fresh-water teleost.
2) Adrenal glands composing of interrenal and chromaffin cells are distributed, being adjacent to the cardinal vein and its branches, are running through the kidney or in contact with it.
The author wishes to express his cordial thanks to Dr. Mizuho OGAWA, Tokyo University of Education for the kind advice given to the present study.

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The volume of the stomach (cardiac chamber) of the Japanese spiny lobster was measured by means of a gravimetric method using emery. The method is as follows:-
V=S/S₁,
where V is volume (cc) of the stomach, S is the total weight (g) of emery put into stomach, and S₁ is the weight (g) of emery of 1 cc. The emery was let into stomach with water by a filler. The same method was used when the emery is taken out the emery from the stomach, and the emery was dried out by an evaporator for weighing. For the purpose of this study, always raw stomachs were used, as they distended well by putting emery into them (Fig. 1, A), but ones fixed by formalin or alcohol were not available for the present investigation, because they did not swell successfully by putting it into them (Fig. 1, B). The particles of the emery employed for this study measures 0.2×0.3-0.5×0.8mm in size.
The result obtained is given in the Table 1. The relationship (Fig. 2) between body-length (L), from posterior margin of orbit to distal rim of telson, and stomach volume (V) is expressed by an exponential formula, V=0.000795L^2.995, and that (Fig. 3) between V and body-weight (W) of the lobster is shown by the following formula, V=0.0184W+0.0538.

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As a link in the present studies on the green meat of albacore and yellowfin tuna, a discovery was attained of that the strength in which meat specimens can react in hot water on a redox indicator pigment thereto added makes a reliable standard for the grade judgment of meats according to their inclinations to becoming green meat, while said strength was found to have any positive connection neither with reflectance spectra nor with redox potential of the corresponding raw meat.
Among several pigments or redox indicators thus far tested, Lauth's violet was found as most suitable to be used in said reaction in hot water. Although a higher pH in reaction medium allows the reaction to take place with the more strong impression, application of a pH greater than 6.00 should be avoided because of its often causing the decolorization degree of pigment to go out of the regularity observed in a lower range of pH of its prevalence among meat specimens of different grades, thus reducing the accuracy of judgment. It was thus found desirable that pH value of the reaction system is kept at about 5.90, for example, by the use of an aqueous acetate buffer of pH 5.65.
Details in practical application of the redox indicator decolorizing reaction to predicting the latent tendency to green meat development were inquired according to the following procedure, using frozen meats of albacore and yellowfin tuna as sample: Every 5g. of ground samples was brought in a test tube into a state of suspension in 20ml. of a 0.2M acetate buffer solution of pH 5.65, which contained Lauth's violet at a concentration of 2 mg%. The test tubes were then heated after loosely plugging with glass stoppers in a boiling water bath, still kept in the bath after the completion of coagulation of the meat with occasional stirring up the coagulum for additional 30-45min. and then taken out of the bath for the degrees of decolorization of redox indicator to be observed for different grades of meat. Through arranging the degrees of decolorization thus observed in accordance with the strengths of actually observed green meat development, a conclusion was drawn that meat of such a weak reactivity as unable to strongly decolorize Lauth's violet and left colored blue or bluish green (such negative decolorization is expressed in Fig. 5 as marked with-) should be classified either into a meat destined to become “green meat” or at least into a meat of low grade.
The correlation between the grade of cooked meat and the redox indicator decolorizing power which the same meat develops on heating was confirmed of its prevalence upon the experimental results obtained with 97 and 64 individuals of albacore and yellowfin tuna, respectively. As a measure for predicting the green meat development, reliability of said decolorizing power may be considered as compatible with that of the chromatographical, yellow spot developing property⁸⁾ of meat specimens already reported from our laboratory, though these two kinds of phenomenon stand in mutual exclusion.
It was confirmed that the more strongly inclined the raw meat to green meat development, the weaker is its power of decolorizing a redox indicator, while the entity of the meat constituent that weakens the decolorizing power has not been chemically identified as yet.

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Considered from the primary use of “niboshi” (a boiled and dried product prepared mostly from anchovy) as a source of flavoring stock, the quantity and quality of the stock obtainable therefrom may of course be most significant factors that govern the grade of the product.
However, oil or fat content of “niboshi” also cannot be slighted because of its inevitably shortening the product in respect of its usableness. From such a point of view, it was examined on the one hand how the manufacturing condition for “niboshi” is reflected in the relationship between the salt content as a footpoint of processing the raw fish with aqueous common salt and the amount of nitrogenous hot water extractives as an index for flavoring ability of the product and on the other hand whether preparations of “niboshi” show any correlation between their contents of oil or fat and said kind of extractives.
The results obtained may in summary be stated as follows:
1) While no such tendency was observed for nitrogenous matters inclusive of amino nitrogen that they vary in amount according to salt content of “niboshi”, the lower content of total nitrogen was generally found the higher the salt content of the product.
2) While the amount of extractive nitrogenous matters including amino nitrogen varied somewhat in proportion to oil content of “niboshi”, any positive correlation was found between the contents of oil and salt.

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To find a technical resort to go by in preparing “niboshi” (boiled and dried products of anchovy) as completely freed as possible from the undesirable effect of the oil content of raw fish, the harm of oil was inquired of its source from two different points of view, namely, the partition of Soxhlet extractible matters among three body portions of head, viscera and muscle and the frequency of occurrence of the so-called “abura-iwashi” (a badly oily product of boiled and dried anchovy) in the products of the same season (summer) but of different sexes.
The result of inquiry indicated that:
1) As to the oil content referred to dry substance, head and viscera have values as large as two times and more of the value in muscle, while the oil contents of head and viscera vary more or less broadly according to the difference in season as well as that in sex, viscera being generally more rich in oil as compared with head.
2) While it is said that no such particular size of fish individual as selectively connected with the tendency to becoming “abura-iwashi”, in so far as the author's observation in the present inquiry is concerned, middle sized anchovy products prepared in July were found without exception to be in the state of “abura-iwashi” and large sized ones prepared in August were so to a proportion of about 46%. According to the result of examination of the possible relation between the tendency of occurrence of this undesirable phenomena and the sex of the fish subjected to processing, while no accountable difference was found between the two sexes as to the product prepared in July, the product made in August from male fish fell into said ill state more readily than that from female fish and in fact even by three times.

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Seeking a method of unequivocally determining the BHA and BHT added to the marine products, the steam-distillation method (presented by ANGLIN et al.⁴⁾) was tentatively applied to the estimation of antioxidants in the extracts obtained by Soxhlet extraction from salted-and-dried saury, the following results being obtained.
By the steam-distillation method, the separation of the antioxidants can be completed far more rapidly than by the solvent-extraction method¹⁾, and estimation of BHA is carried out without any trouble, owing to the specific reactivity of 2, 6-dichloroquinonechloroimide (2, 6-D) reagent upon BHA. This method, however, is not suitable for thereby estimating BHT, since the 2, 2'-dipyridyl (2, 2'-DP) reagent reacts on some contaminations coming in the distillates, leading often to ambiguous results just like the case of solvent extracts descrived in the preceeding paper¹⁾.

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During the last ten years, the problem of an esterase specific for acetylcholine has attracted the attention of many investigators and has got a satisfactory answer.
Cholinesterase (ChE) preparation has been made from tissue and body fluid of various vertebrates by AUGUSTINSSON in comparative enzymology. Study on the fish blood ChE, however, has not been almost made. Present work is concerned with the preparation and purification of ChE in serum or erythrocyte of fish blood, and their chemical properties.
The results obtained were as follow:
1) As shown in Table 1 and Fig. 1, serum ChE solution was highly purified from carp blood by the fractionation with ammonium sulphate; and this solution was capable of showing the activity of 2.725 (hydrolysis-ACh-mg/protein-mg/hour).
2) Erythrocyte AChE solution was purified from the carp blood by the purification shown in Fig. 2; and this solution was capable of showing the activity of 5480 hydrolysis-ACh-mg/protein-mg/hour).
3) The opitimum pH of ChE in serum or erythrocyte of carp was about 7.8, and their opitimum temperature were 27.5°C.
4) Activity-pS-curves of serum ChE were S-type; while those of erythrocytes were Bell-type with pS 2.5 of optimum substrate-concentration for ACh.

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The present studies were carried out on the effect of urethan on phosphorus compounds in muscles of mackerel.
The results are summarised as follows:
(1) The muscles of mackerels treated with 0.5% urethan for 2.0min., 1.0% urethan for 1.5min. and 2.0% urethan for 1.0min. contained 20.8-22.1mg% of 7'P in ordinary muscle and 7.0-9.7mg% of 7'P in dark muscle, respectively, more than in those of the control. But there was perceived little difference in CP content.
(2) The vigorous post-mortem degradation of 7'P and CP in the fish narcotized with urethan began a few hours later than that in the fish which were numbed with cold temperatures such as 0°C. and -20°C. and lasted longer. But there was little difference in them between the mackerel numbed with cold and the control (Table 2, Figs. 1-4).
(3) The author proposed that the narcotizing or cold-numbing method be applied to the method of catching fish from a view point of keeping the freshness of fish.

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As a first step of this sequence of studies, the author made some inquiries into the alkali digestion method which is most popularized among the methods adopted in obtaining vitamin oil from viscera of aquatic animals and carried out usually according to the scheme shown in Fig. 1.
Examining in the first place the effect of a few modifications of elementary working conditions on the amount of vitamin A reserved in raw material viscera in the digestion stage of process (see Tables 1 and 2), it was suggested that the possible decomposition of vitamin A accelerated by acidity increase of oil in raw material may surely be minimized by using highly fresh material and also that the use of alkali in the digestion is rather undesirable but for its merit of facilitating the removal of acid oil. It should also be noticed from the results shown in Tables 1 and 2 that some internal organs are possible to be higher in vitamin A content than liver at least in the case of “aburagarei”, Athresthes evermanni.
The results obtained in the examination next made into the influences of temperature, time, alkali strength and use of picking-up oil on the yield of vitamin A in alkali digestion (see Tables 3-6) indicated that these elementary conditions should be well managed according to tightness of the tissue to be digested and further that use of the more drastic conditions is connected on the one hand with a merit of enabling vitamin A to be extracted at the higher yield and concentration but, on the other hand, inevitably with the danger of the more readily causing the same not only to be washed away into drainage but also to be decomposed in thermal digestion of raw material tissue.
Further, alkali digestion being carried out on an industrial scale, it was examined how the difference in species of raw material fish can effect the partition of vitamin A among drainage, wash water and vitamin oil. As regards the result obtained in this examination (see Table 7), it should be particularly noticed that alkali digestion is possible to impose not a small loss of vitamin A on a raw material fish with a relatively high content of vitamin A and a relatively low content of oily matters as a whole perhaps owing to the situation of that, besides the stronger tendency to suffering oxidative decomposition of the more concentrated vitamin A, a great portion of oil in viscera of such raw material fish behaves in most cases as a soap-forming fraction.
In the end of the present paper, there are brought forward a result formulated from totalization of the data for 142 runs of oil extraction wherein several kinds of fishes and whales generally making the raw material in vitamin oil industry were processed by means of an industrial oil extractor (see Table 8 and Fig. 2). It will be apprehended from the result that a liver tight in the structure of tissue like that of a whale is prone to give only a low yield of vitamin A as compared with a liver loose in tissue like that of a shark or another kind of fish as a result of its requiring a rather drastic treatment in the process of alkali digestion.

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The properties of the acetone-soluble lipid contained in the ordinary meat and the red meat of “Kan-Buri” (yellowtail, Seriola quinqueradiata, caught in winter) and “Higan-Buri” (yellowtail caught in spring) were compared.
The paper chromatography indicated the presence of myristic, palmitic, stearic, arachidic, zoomaric, oleic, eicosenoic, erucic, linoleic, linolenic, acids and tri-to hexaenoic acids (C₁₈-C₂₂) in the lipid of each sample as shown in Tables 4, 5.
The unsaturation of the acetone-soluble lipid in the red meat was higher than the ordinary one. The difference in component acid between the two sample fish, may suggest that the saturated acids in yellowtail will increase towards spring while the unsaturated ones decrease slightly during the same period.

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The characteristics of lecithin (acetone-insoluble, ethanol-soluble lipid) contained in the ordinary and the red meats of “Kan-Buri” (yellowtail, Seriola quinqueradiata, caught in winter) and “Higan-Buri” (yellowtail caught in spring) were compared.
It was found in each sample fish, that the yield (%) of lecithin in the red meat was higher than in the ordinary one, and the unsaturation of conjugated fatty acids in the former than in the latter. In both cases of red and ordinary meat, the unsaturation of conjugated fatty acids in lecithin was higher in “Kan-Buri” than in “Higan-Buri”.
The paper chromatography indicated the presence of myristic, palmitic, stearic, arachidic, zoomaric, oleic, eicosenoic, erucic, linoleic and linolenic acids in the lecithin. The main constituents of the saturated fatty acids in the lecithin were palmitic and stearic acids, while those of the unsaturated acids in the lecithin were oleic and zoomaric acids.

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