A model experiment of the sardine “Hisago-Ami” (a kind of Japanese trap net) operated in the Tai fishing ground locating on the western coast of Wakasa Bay was done for the purpose of stud-ing the change of the configuration and total resistance of the net caused by homogeneous currents from various direction. The scale of the net was reduced to 1/350 of the full scale according to TAUTI's principle of similarity. Fig. 1 shows the detailed structure of the full scale.
This net can be divided into two parts, namely “Miami (the main net)”, and “Noboriami (the acclivity net)”, and was experimented with three different directions of currents shown in Fig. 1 (A, B and C).
The investigated velocity in terms of the full scale is changed as follows: 57cm/sec, 25cm/sec and 14cm/sec in the case of the main net and 43cm/sec, 21cm/sec and 10cm/sec in the case of the acclivity net in each direction.
The details of the net configuration in each velocity and direction, and the relation between resistance and velocity are shown in Fig. 2.
If we denote the total resistance of the net by R (kg) at the velocity of current V (cm/sec) in the full scale, then put R=kVⁿ, k and n being constants which characterize the mechanical properties of the net, these values obtained from Fig. 2 are 1.70 and 7.29 (direction A), 9-5 (direction B) for the main net, while are 1.62 and 13.8 (direction A), 11.0 (direction B) for acclivity net.

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The author conducted fundamental experiments on the effects and principles of fishing methods and gears.
Those experiments were carried out by observing the locomotion activity of fish individuals kept in a tank, set for this purpose. The locomotion activity would differ according to the influence created by the environmental condition or model of fishing gear used.
The experiments were done with 10 Goldfish Carassius auratus of an average total length of 4.0cm. They were liberated in a wooden tank of 150cm. long, 26cm. wide and 8cm. water depth. For model nets, 8 wooden frames were made and fine cotton thread was stretched vertically on each frame at intervals of 0.75, 1.00, 1.25, 1.50, 2.0, 3.0, 4.0cm except the 8th one which was wooden frame without thread as a contrast.
Two methods, namely, “Centralizing method” and “Driving to one side method” were applied here. (Fig. 1 and 2)
The first method is to drive fishes towards the center of tank from either side with two frames of different meshes, each at a driving speed of about 10cm. per minute. (Fig. 1) The number of fish which passed through each frame were counted. This was repeated for twenty times, using the same combination of frames. The total number of fish passed through the frame to either side was then found out. The same procedure was repeated using all these 8 frames, and in all combinations of two frames, each. The sum of the total values are given in Table 1. For the ratios of the number of passage of fish to either side of tank, the chi-spuare test of statistics was applied and the result is expressed in Table 1 as percentages of degrees which differ significantly.
The second method is to drive fishes to one side of tank from the other side by one frame with a speed of 10cm. per minute as the former. (Fig. 2) When the fishes are driven up to a certain position, the fishes start to turn back and locomote to the other side passing through the frame. The position of the frame from one end of the tank was observed (Fig. 2, d), and the result of 40 such experiments are given in Table 2 and Fig. 3, and the efficiency of driving is given in Table 3. The numerical values, so far got, were converted into common logarithm to get their mean values and to compare them. (Table 4) It has been found that a significant difference exists in almost all combinations when examined by the F-table of statistics. (Table 5)
Consequently, the centralizing method is so reliable as to compare directly the difference between two testings and the driving to one side method is advantageous to express sharply the peculiar quality of each testing.

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The author has done those experiments continously for the former report (Refference 1)) which was carried out “Centralizing method” and “Driving to one side method”. (Fig. 1.)
10 Goldfish Carassius auratus of an average total length of 4.0cm. were liberated in a wooden tank of 150cm. long, 26cm. wide and 8cm. water depth. For model nets of colours, 8 wooden frames were made to be stretched vinyle tube (dia. 1mm.) vertically at interval of 2.0cm. on each and the each frame had a colour of semi-transparent, yellow, white, green, pink, red, blue and except the 8th one which had fine white cotton thread.
The centralizing method was done with repeat of 40 times using all these 8 frames, and in all combinations of twoframes each. The sum of the total values were given in Table 1. and they were applied the chi-square test of statistics as expressing in the Table.
The observed values by the driving to one side method were expressed in Table 2. and Fig. 2. and the efficiency of driving was given in Table 3. and 4. Average values of them had been examined different significance by the F-table of statistics, seeing in Table 5.
As regards driving fishes on the two experiments, the frames of blue, pink and red are obviously more effective than the other frames of white, yellow, semi-transparent and white cotton thread.
As it is existing difference between the human and fishes on the senses of sight, he had examined visible distance in the water for each colour of vinyle frame taking method of as in Fig. 3. and the result is in Table 6. and Fig. 4.
Consequently, those results and quoting the result of the underwater fencing net (Refference 2)) were compared on order of effect of colours, seeing in Table 7. The orders of experiments (b) and (c) are accurate uniformity, as if the materials of model net are equal one and it had both taken method to drive fishes in. Though the (a) was done as fencing net unmoved, he had recognized few similarity between the orders of (a) and (d).

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Dealing with early stages of carp fry, we showed in previous reports that shoot carps are already recognizable among the 20 day-old fry of the same batch and that their occurence is fosterred by certain feeding conditions.
In this paper we have examined the occurrence of the shoot carp at the later stages, by culturing the modal groups of the 70-day-old fry from one batch and of one-year-old seed carp. In a modal group, which is obtained by excluding shoot individuals from among the fish having reared under the same condition, the original body length distribution is almost symmetric with a small standard deviation. When these modal groups are cultured for 3 to 12 months, their body length distribution becomes considerably skewed, evidencing that shoot carp have occured anew. And, shoot carp occur to a greater degree when the 70 day-old fry are cultured than in the case of the one-year-old carp.
Furthermore, individual carp fry of a batch are accommodated in separate vessels and reared with sufficient diet, for the purpose of examining their growth as absolutely unaffected by the mutual competition for diet. Under this rearing condition, growth of the fry is quite uniform; in other words, no shoot carp occur at all.
These results endorse our view that food competition among individual fish is a causative factor of the phenomenon of the shoot carp.

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Observing the ratio of regenerated scales to the total ones (the apparent regeneration ratio of scales), and the estimated age when the scale had been regenerated, the writer was able to make clear the following facts. The samples dealt with in the present paper were about 263 yellow sea bream caught in the East China Sea, during the term from November 1951 to October 1952.
1. The median value of the apparent regeneraton ratios of scales of each age class increases by about 6 percent per age. The maximum value observed is 76.5 percent, while the minimum one is 0.8 percent. (Table 1, Fig. 2).
2. Polya-Eggenberger type distribution is approximately applied to the frequency distribution of the apparent regeneration ratio of scales in each estimated age stage. No significant difference is observed in this ratio between the north and south areas, sexes, and among ages of samples, regarding 2 and 3 age stages.
3. The ratio of number of samples carrying no regenerated scale to the total number of those shows a relatively high value of 6.8 percent at 0 and 1 age stage, but is less than 3 percent at 2 aged one and older. (Table 2).
4. The average regeneration ratio of scales is 4.5 percent at 0 and 1 age stage, 4.9 percent at 2 aged one and more than 6 percent at 3 aged one and older. (Table 3).
5. Synthesizing above mentioned facts and other ecological and morphological knowledge on the present fish, it will be concluded that the scales of this species fall off more frequently by some physiological causes rather than the mechanical ones.

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The diurnal variation of the oxygen content of the fish-culture-pond water was observed. The oxygen content was determined by the carbon dioxide method. The density of phytoplankton was estimated by means of the transparency that was determined by N_AKAMURA's small white disk. (cf. the note of Fig. 1.).
1) Generally speaking, the dissolved oxygen content, throughout the year, was at minimum toward sun rise, after which an increase took place, reaching the maximum value at 2-3 hours before sun set, from then a decrease took place until the next morning (Fig. 1-5). But in the early morning, being short of the solar radiation, the decreasing tendency lasted for some time after sun rise. This phenomenon was remarkable at the bottom layer (Fig. 1. -B).
2) The higher the density of phytoplankton was, the wider the range of the diurnal variation of the oxygen content was (Fig. 1. -5). In the case of the pond water having a low density of phytoplankton, the level of the oxygen content was low throughout the day (Fig. 2.) As to the pond water containing an excess of phytoplankton, the level was extraordinarily high at the maximum and a rapid decrease took place during the night (Fig. 3.). In both cases, the fish presented symptoms of dyspnoea owing to the lack of the dissolved oxygen early in the morning. As for the pond water having a moderate density of phytoplankton, the level of the oxygen content was high throughout the day (Fig. 1. -A, B).
3) The larger the fish population was, so far as it was whithin a certain limit, the wider the range of the diurnal variation of the oxygen content was (Fig. 5. and Table 1. ).
4) There was a positive correlation between the oxygen increment and the amount of the solar radiation during the period (Fig. 6. and Table 2.).

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In the previous paper, the authors reported the remarkable resemblance between “perforating disease” and deformation of laver-cells caused by mechanical, chemical or osmotic action of the environments.
When a part of Porphyra-frond is injured mechanically by a tip of needle and then put into diluted sea water or fresh-water, protoplasm of operated cells coagulates very easily and the stimu-lation effect spreads gradually into the non-touched surrounding cells resulting in deformation. The aspect of deformed cell and the width of deformed area vary with the concentration of media in which the operated piece is immerced; i.e. it does not occur in hypertonic water of more than about 12‰, C1', between 10-12‰ C1' the deformation is inconsiderable, and in less than 10‰ C1' it continues for some periods with intence grade, especially under6-8‰ Cl' the deformed area decomposes into a hole. In the cultur ground the disease often occurs after vigorous rain, especially along the place near estuary.
From these, it is concluded that the so-called “perforating disease” is a non-parasitic disease. It seems to be brought about by a physiological disturbance by the plasmoptyse of cells accompanied decreased permeability in plasma-memblane and increased viscosity in plasma owing to the injure and hypotonic media.
The disease “shirogusare” reported by Arasaki (1947) also seems to have some affinity with the present disease, in the pathogenetic sence.

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With the aim of elucidating the mechanism of the sulfides production by sulfate-reducing bacteria in the estuarine region of the river receiving industrial and municipal drainages which contain organic matter in high concentration, we observed the distribution of sulfate-reducing bac-teria, sulfides, sulfates, chlorinity, organic matter, etc. in the water and in the bottom mud in the Takano River, and subsequently studied the factors which participate in the sulfides production in such a region of the river. The Takano River receives a large amount of drainages from a pulp factory and Maizuru City, and discharges itself into Maizuru Bay.
Station where the present ecological observations were carried out are shown in Fig. 1.
Results obtained are as shown in Tables 1 and 2, and in Figs. 2, 3 and 4, and may be sum-marized as follows:
1) In the river water relatively small number of sulfate-reducing bacteria were sporadically distributed regardless of the distance from the mounth of the river. It is thought that the cells of these bacteria detected in the overlying river water were brought by the water movement from the bottom mud where was the proper inhabiting place of these bacteria.
2) In the bottom mud of the river, the distribution of sulfate-reducing bacteria, in the case of anyone of marine and fresh-water types, was influenced by the chlorinity of the bottom water (Figs. 2 and 3). However, the total counts of the sulfate-reducing bacteria including both types in the mud were hardly influenced by the chlorinity of the bottom water; total aulfate reducers were almost evenly distributed in high count in the mud throughout sea-water zone, brackish zone and fresh-water zone.
3) The distribution of total sulfate-reducing bacteria in the bottom mud was also hardly influe-nced by organic content of the mud or sulfate content of the river the growth or the counts of the total sulfate-reducing bacteria in the bottom mud was not limited by organic content of the mud or sulfate content of the bottom water, viz., in these bottom muds sulfate and organic matter were sufficiectly present for the growth of the sulfate-reducing bacteria (Figs. 2, 3, 4 and Table 2). It was generally found that organic matter contained in the bottom mud of this region of the river was higher in concentration and more easily decomposable than those contained in the bottom mud of the sea.
4) On the contrary, the production of sulfides in the bottom mud by the sulfate-reduc-ing bacteria was principally influenced by the sulfate content of the bottom water and the concentra-tion of available organic matter in the mud. In the fresh-water zone where the sulfate content of the bottom water was very small, the production of sulfides in the bottom mud was mainly suppressed by the low concentration of sulfate in the bottom water; in the sea-water zone where the sulfate content of the bottom water was sufficient, the production of sulfides in the mud was

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The electric resistance of the muscles of carp, Cyprinus carpio, and crucian carp, Cyprinus carassius, was measured by a K_OHLRAUsH bridge type instrument in the course of deterioration at 17°, 20°, 25° and 30°C. The organoleptic observations and the determination of ATP and free SH group were also carried out.
It was observed, as shown in Fig. 2, that the curve of electric resistance lowered stepwise and the curve was distinguishable into six parts in total, in which the steep and the flat parts alternated. From the organoleptic observations and the determination of ATP and free SH group, the author assumed that these six parts indicate successively before rigor, full rigor, after rigor, autolysis, early spoilage, and advanced spoilage stages.

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When ice is prepared from service water containing chlorotetracyline (CTC) with which to preserve fresh fish, antibacteriolytic activity of CTC is not found so stable as expected to be. Bioassay of CTC by Koholer pad-plate method modified from Grady's has confirmed that the activity of CTC resolved in service water is lowered from 5 ppm to 1. 5 ppm in an hour, while actithat in distilled water remains almost the same in the lapse of time (Ttable 1). A possible explanation of this is that the CTC activity is likely affected by Cl₂ present in the service water as well as by the concentration of pH.
When acidified with citric acid, however, the service water has been turned out to be capable of keeping the CTC activity fairly stable. A report on the role of citric acid in this regard is under preparation.

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