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Japanese oyster culture in Oyster Harbor, Ladysmith Elsey, Charles Roy 1929

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A Thesis submitted for the Degree of MASTER OF ARTS in the Department ofBIOLOGYJAPANESE OYSTER CULTURE IN OYSTER HARBOR LADYSMITHbyCharles Roy ElseyUNIVERSITY OF BRITISH COLUMBIAApril 1929* /.: >yt"p4\ KF-fi*.PiiTABLE OF CONTENTS \(1) A General Outline of the Situation. . . . Page 1(2) Experiments on Artificial Culture . . . . Page 9(3) Tables of temperature, densities, andhydrogen ion concentration............. Page 21(4) Page 24(5) Explanation of Plates ...................... Page 32(6)5.Page 33(7) Literature cited.......... ................... Page 34JAPANESE OYSTER CULTURE IN OYSTER HARBOUR A G-eneral Outline of the Situation«For many years Oysters have -been imported from the Eastern States to the Pacific Coast and planted in various places between San Francisco to the South and as far north as Ladysmith Harbour. The attention of importers has been devoted to preserving the oysters until there should be a market demand or permitting their growth in coastal waters. It has been found possible to bring them in when small by the car-load, plant them on easily accessible beds close to city markets, and to take a good profit owing to their increase in size. As a result of this practice, Eastern oysters are common at Samish, Crescent, Willipa Harbour, Oyster Bay, Washinton, and Oyster Harbour, Ladysmith. Only in Willipa Harbour are they known to have propagated, but they' are reported to have done so in at least one area at Crescent. There are records of the importation of the Japanese oyster, "G-igas,” in very small lots chiefly by Japanese fishermen in 1912. In this manner a few sacks came into Oyster Harbour, Ladysmith. In t h e 'summer of 1925 attention v/as drawn to these oysters which were found to be in excellent condition. It was reported by oystermen that there was definite evidence that they were propagating in this area. An investigation was begun in 1926 to determine to what extent they had done so, and at the same time tostudy the condition at Oyster Harbor in relation to theSince this time, the importation of the Japanese oysters to Samish and Olympia has become common. In each of these places growth is very rapid, paralleling and in some areas surpassing that in Japan. Investigations at Samish hy Kincaid have established the fact that spawning is general at Samish and Olympia. To date there has Deen no evidence of spatting at Samish but Kincaid reports i'or 1P27 a heavy set at Oyster Bay, Washington. Recently ne reports that oysters spatted at this time have grown unusually fast, practically reaching marketable size at tne age of eighteenOyster Harbor, Ladysmith is well suit*d to the culture of oysters, both because it is well protected owing to the long narrow shape (Plate 1.) and on account of the nature of the bottom. Ostrea Lurida is well established and at present leases are held by four organizations. There are however many acres which, though unsuited to the local oyster, have been shown to be it eal for growing tneof United States has said "The Pacific culturist may feelgrowth of "Ostrea Gigas."months'^¿Japanese variety "Ostrea Gigas."«  »V". Dean in (1902) referring cniefly to tne Pacific coastpsa lively interest in oysters of Japan, for not merely arecloser akin to our own in structure ana habitat and Jldtèfc:-readily acelimataDle out they are larger, betterand certainly of greater value commerciaxlyspeaking than the local product, 'Ostrea Californica’."This does not apply in Canada as regards similarity of structure but does apply to an even greater extent with reference to conditions and to commercail value as compared with "Ostrea Lurida," our native form. According to Deon (1902) the Japanese oyster thrives best in bays well- tempered by fresh water of specific gravity 1.017— 1.022.It will be noted by reference to Plate 1. that a fresh water stream of sufficient size to exercise an effect on the water flows into the Harbor; and by referring to Table 1. that this range of specific gravities prevails where records were kept.In Nikoyima, a particularily good area for spatting, the density rarely exceeds 1.017. Dean, (1902). It will be noted (Table 1.) that the highest specific gravity reported is 1.021 and this at a season long past the Normal spatting time. In Japan the breeding season usually begins in April and extends into the latter part of August (Mitsukuri 1904). During that season the water ranges between 20° and 25 Centigrade. Dean (1902) recommends importation from Hokkaida for northern regions since the temperatures there are slight­ly lower than in the more southern Japanese areas. Most of the oysters imported to Washington state have been obtained from beds about one hundred miles north of Tokio.The oysters are commonly packed for shipping in Japanese beer boxes about (4* x 2 ’ x 1') in dimmensions.Occasionally they come attached, to brush but it has been found, more economical to order them attached to shell since less space is taken up by cwitch of this kind. The cases will average five thousand first season oysters, and can be received in Vancouver for a price ranging between six and eight dollars. Under normal shipping conditions there is practically no mortality in transit and growth is hardly interrupted by the transfer. In any area at all suitable for oysters the imported Japanese form will grow rapidly and in the best areas reach a marketable size inless than two years.In the summer of 1926, approximately two thousand two and three-year old Japanese oysters were received at Oyster Harbor Ladysmith from Samish, and later in the year.twenty cases were received direct from Japan through the agency of a Japanese fish Company in Vancouver. The latter was an uneven lot, spatted on brush and averaging one year in age. They were placed in areas chosen to test their reaction to all types of environment. Plate 111. shows some of this lot exposed at low tide. Wherever the Eastern or local form will live the Japanese form may be found in a thriving condition and much more plump than the other species. In water too brackish for ,T0strea Lurida," "Gigas" has done well. Deposits placed high up in gravel and only two or three feet below extreme high tide have thrived. One hundred were placed in a shallow tidal pond at the head of.the Harbor where they were at all times covered by a minimum of ten inches of water and subjected to temperatures in mid-day up to 29° C. with a change on the incoming tide to 22° or 23° C. Table 11. shows variations over a period of one month in this section. Even in this area there was no mortality and some regular shell growth was observed.Eastern oysters used as a check, along with "Ostrea Gigas" in these unusual places; in some eases died and in every case were in poor condition and showed very little growth of. shell. Recently a high mortality has been reported among local oysters as a result of frost, but none of the Japanese species have suffered.The optimum development was recorded.by those specimens placed roughly three feet above extreme low tide; with water conditions as indicated in Tabled.. The bottom at this point was black, covered with gravel and relatively free from fixed plant growth. This is a much higher elevation than is suited to the local oyster and as suggested above makes the culture of Japanese oysters in conjunction with the native variety a practical proposition. An important consideration for the oyster farmer is the possibility of working such areas at neap tide. The late development of the Japanese oyster would be an advantage under these conditions as it. continues to be in good marketable shape long after the local species has spawned and become unfit for sale. There are undoubtedly manyj 1 J*.: i ■■• '; ■ ■. ■ ■*' :-f" -\ ■ .':í'.Jl'i-; r-'-,,l -^ . ‘ : v v, ,k y -  '■ ■ ■' • .: -. .;''^ ' ''v' ''^V' 6areas up and down the coast which would be suitable for the growing of imported Japanese oysters although unsuitable for the other species. It has already been pointed out that they may be imported at a total cost ranging from six to eight dollars for five thousand oysters and it might be mentioned that the price paid to the oyster farmer in Samish for three year old oysters is three cents each.Since the chief aim of the investigation was to enquire into reports concerning propagation; every effort was made to secure confirmatory material. Oyster men produced several oysters attached to local rock and in some cases to shells of the local oyster, Lurida. Lest any doubt regarding these oe entertained they were ready to show Japanese oysters attached to a partially submerged rocky reef in the haroor. Plate IV. shows the photograph of one apparently eight or ten years old. Three other similar attachments were noted. There could be no doubt that some reproduction had taken place and this, in consideration of the fact that only a few sacks of oysters had been' in the harbor at any time was remarkable. The oysters definitely proven to have spatted locally seemed to be of a similar age. This fact suggested a particularly long warm season as the cause.Three possible lines of investigation suggested them­selves. The most direct would have ueen to import several millions of oysters and trust to massed spawning to produce results. There was the chance of making a plankton studyduring the spawning months in hope of finding and isolating7Japanese oyster larvae among the natives. Or there was a possibility of artificial culture, using the harbor water and duplicating as nearly as possible conditions as they existed in the natural environment. In consideration of the successful experiment conducted by Prytherch (1923) and Wells (1926) with the Eastern oyster it was decided to attempt artificial culture. From the beginning it was realized that weather conditions would have much to do with the progress of the work.Nelson (1926) reports that in the case of the Eastern oyster, spawning occurs only after the temperature has been sustained at a point of 20° G. for approximately ninety-six hours. Churchill (1919) states that a temperature of 68° F. is the minimum that will permit spawning. Obviously the oysters would have to be in a well developed condition previous to this time and a gradual warming of the water must be expected. Apparently the Japanese oyster develops at- about the same rate as the Eastern species, if anything slightly earlier. Nelson (1921) says that with a cold backward spring or one in which there is much cloudy weather, the spawn may be developed as much as six to eight weeks before being thrown into the water. "In extreme cases in northern waters (referring to the Eastern coast) when as a result of long continued cool or cloudy weather during the summer the temperature never for any length of time1 attains 70 F., the spawn may not he thrown out at all hutI reabsorbed by the oyster.” Little is known of the mechanism hy which they accomplish this adjustment, hut there seems to he no other satisfactory explanation of the fate of the spawn. According to Kincaid, a high mortality among imported Eastern oysters at Willapa has been noted at the end of a season where as a result of cold water general spawning has not taken place. An interesting bio­chemical problem is suggested here; probably products of • this unnatural process have re-acted to the detriment of the oyster.On July 4th, 19£7 the Japanese oysters were found to he much further from a spawning condition than at the same date of the previous year. Considering the effect oftemperature on the spawning of the Eastern oyster, and inview of the fact that the season was unusually backward, an attempt was made to hasten development of several hundred carefully selected oysters hy placing them on the large oyster float (Plate V.) where they would he in the warm surface water at average tide and exposed directly to the sun for a few hours each day at low tide. Severalhundred were placed also in the shallow pond described inconnection with the discussion on environment.Those on the float developed rapidly and practically all were ready to spawn hy the end of July. Oysters in the shallow pond had not spawned hy September, hut this mayhave been due to sudden changes and great extremes of temperature as indicated in Table II.Oysters immediately under the float were fairly well developed but had not spawned by July 30th.. At this time several hundred were put on the float to replace the original lot which had developed sufficiently, but strangely enough this later lot could not be induced to spawn although temperature as recorded in Table II. continued to be suitable for sometime thereafter.It is interesting to note that eggs and sperms from all these non-spawning oysters whenever brought together artificially produced normal larvae right up until the endvof August when the experiment was discontinued.Experiments on Artificial Culture.Send and Ho'ri in conjunction with Kusakabe (1926) and the former two in 1927, in dealing with the reaction of the larvae of "Ostrea Gigas" have proven the development for the early stages to be very similar to that of "Ostrea Virginica." Therefore it was decided that the method outlined by Prytherch (1923) for the latter; be followed.The tanks had been previously prepared. Filtros blocks of various grades were used as filters for holding the larvae. Rearing tanks as illustrated in Plate Vll. figs. 1, 2 and 3, were used for holding the embryo forms and very young larvae. The long rearing tanks (fig. 2) for later development were similar to those used by Prytherch10(1923) except that in place of movable filtros blocks which were reported to have permitted the escape of many larvae; filtros firmly embedded in Marine glue was substituted. This made necessary a series of tanks, each with a different grade of filtros material. As the larvaereached a suitable size, the entire content of one tank would require to be siphoned into a tank with coarser filtros which would permit a great flow of water and still prevent the escape of larvae.No electrical power was at hand for running rotators.A hand pump was operated for obtaining salt water.Galvanized pipe was used as an intake and rubber hose as an outlet into the supply tank. It was found almost impossible to filter the water suitably at the rate of delivery from the pump. Finally the difficulty was partially overcome by introducing a large sand filter between the delivery pipe and the cloth filtros through which the water was admitted to the tank. A pump throwing a small continuous stream of water would have been an advantage. One of the greatest difficulties, was to obtain a steady supply of water since at low tide the water receded far beyond the reach of the intake p i p e .In addition to the above equipment, a cement tank ten feet square and six feet high was constructed on the beach in such a position that at high tide the top was just ten inches above the water level. Fine sand was placed.in thegff'bottom to serve as a filter. The tank could be filled by siphoning at high tide and the depth of the sand in it so adjusted that a drop of two or three feet through seepage would occur between tides. The intention was to keep this continually stocked with larvae from the spawning tank in the hope that they would be held for a few days or at least until they had passed through the most delicate early stages.On August 1st. one hundred oysters were transferred from the float mentioned above to a shallow.spawning tank.On August 2nd. early in the afternoon, water in this tank at a temperature of 27° C. was replaced by water at 24° C. Spawning followed immediately. It has been reported by Kincaid that oysters spawn with the incoming tide after having been exposed to the hot sun. Apparently the change in temperature, though a decrease, activates some spawning mechanism. When the tank was filled with spawn the oysters were removed and the embryos which soon developed were left until they had reached the swimming stage. After eight hours, the surface water, which contained the healthiest larvae was flooded over into containers end transferred to the rearing tank shown in Plate (Vll) Fig. 1. At the same time millions of healthy larvae were run into the harbor and a large quantity was emptied into the shallow pond at the head of the harbor; in the hope that some of them would be held there for a few days and that all of them would have several miles of tidal flats to pass over beforetemperature and specific gravities and occasional p H. determinations are reported for this area in Table II. Plankton samples taken daily did not yield any swimminglarvae however.The swimming embryos developed normally in the rearing tank, resembling exactly the early stages of the Eastern oyster as indicated by Nelson (1921.) They remained near the surface of it for twenty-four hours. After forty-eight hours none could be found in the water but samples of the sand taken with a pipette from the surface of the filtros, showed great numbers of vigorous straight-hinge larvae. . Seno, Hori, and Kusakabe (1926) report the formation of shells in tv/enty-three hours at a temperature of 23° -26° C. and in eighty-three hours at 16.3° C. The temperature in the rearing tank ranged between 20° and 23^ C. so that the rate of development appears to have been normal.No attempt was made to transfer this lot to other tanks as it was desired to determine to what extent development would take iDlace under these conditions. It was found possible to bring the larvae out of the sand and at the same time to aeriate the water by running a hose from t h e .supply tank in, at the outlet below the filtros. In this way the water was forced up through the blocks carrying with it air from the space between the block and the tank bottom.A  record of temperature, specific gravity and p H. wastaken twice each day. For ten days the temperature averaged 23.5° C. and there was no pronounced variation in specific gravity and hydrogen-ion concentration. At this time there was no mortality of larvae. Owing to imperfect filtration, referred to above, the tank was commencing to slime and it was increasingly difficult to maintain a steady flow of water.Rains and colder weather for two days caused a sudden drop in temperature to 15° C. and a change in specific gravity to 1.0165 owing to rain water admitted to the tanks. According to Kelson (1921) the larvae of the Eastern oyster is extremely sensitive to a sudden change in the temperature of the water. A drop within twenty-four hours of from 3° to 5° C. maybe followed he says' by the disappearance of a largerportion of the larvae from the water. A similar fall maynprevent the setting process completely.By the sixteenth of August many dead larvae were found, these having reached a length varying between .120’and .140 mm. Healthy larvae were still plentiful,in the water now, rather than in the sand. On August 22nd. from two gallons of water, twenty larvae averaging .175 mm. in length were found. On the twenty-seventh of August a few larvae were still alive having reached an average length of .200 mm.The left umbone was not as prominent as it should have been had growth'been normal. Hori, and Kusakobe (1926) found that larvae might live for fifty days, altaining only measurements of .220 mm. in length by .240 mm. in width.The same authors give .£80 by .£90 mm. as the normalspatting size.Spawn obtained. August 5th. was divided, between the rearing tank Plate Vll. Fig. 3 and the cement tank described above. At the end of five days the larvae in the wooden tank had reached a length of .115 mm. A heavy stream of water was now admitted from the top and the sand well stirred up. Millions of larvae came through the outlet and were caught in tarantulla cotton and transferred to the long rearing tank of finest grade filtros as described above. The same difficulty was experienced here as regards filtration and rapid temperature changes. Owing to the greater flow of water, fouling of the tanks was even more rapid and the shallower construction of the tanks was the cause of still greater temperature changes at night and during the rainy weather. Larvae in this tank did not do so well as in the tank first described. After five days there was considerable mortality. Those larvae which remained alive were only .100 mm. in length. ihe water was changed to a tank with coarser blocks and it was hoped since the difficulty with regard to filtration had now been overcome that some larvae might be saved. After five days in this tank no larvae remained alive. The largest preceding this time were .150 mm. in length.Those placed in the cement tank developed quite normally. Temperatures in it held very closely to thosein .the harbor. For ten days plankton samples from the tank showed larvae paralleling in growth that described by Hori (1926) as normal for Japan. At no time were any dead larvae found, but after ten days all live forms had apparently escaped through the sand. It is obvious that this tank though it did not hold the larvae until the spat­ting stage served a very valuable purpose in protecting the larvae through the early stages of development. There was considerable growth of brown and green algae by the tenth day adhering to the side and bottom of the tank but the water appeared to be in a healthful condition otherwise.After August 5th. when all those oysters originally placed on the float had spawned, no other spawning could be induced, although as mentioned above the o y s W r s  seemed to be in a spawning condition and practically one hundred percent development resulted from artificial fertilization.The experiment was continued in the summer of 1928.At this time the cement tank was modified to serve as a storage tank by placing in it a cement botiom and an automatic sand filter (Plate VIII). A Delco Electric plant was installed to operate a small continuously acting elect­ric pump, to run stirring apparatus, and to supply a source of heat for maintaining more constant temperatures in the rearing tanks.As on the previous year oysters were placed on the partly submerged float; this time at an earlier date into hasten development to a greater extent. Theweather for May and June was unusually cold. For thisreason little advantage in the way of higher temperatureswas derived by the use of the floats. On the first ofJuly, examination showed that eggs and sperms were even lessadvanced than at the same date in 1927. Although it willhe seen by reference to Table III. that temperatures betweenoJuly 8th and August 10th were maintained above 20 C. only an occasional oyster on opening showed development sufficient to indicate early spawning. When artificial fertilization was resorted to, late in July, seventy-five or eighty percent fertilization resulted however, so that it was decided to start two tanks with larvae obtained in this way. For two weeks oysters had been kept in the spawning tank in shallow water frequently changed but had shown no signs of spawning. Some oysters of. both sex recently opened for artificial fertilization were placed for a short time in the spawning tank, for later use. It was found on returning for them that any oysters close to these from which the spawn was exuding, were spawning vigorously.Apparently the mere presence of the spawn in the water had induced spawning although the temperature was just at 21° C. Pipettes full of eggs or sperms with sea-water were blown between the valves of feeding oysters and in practically every case spawning occurred in a few minutes.After this time whenever spawn was required for the tanks the experiment was repeated and seldom failed to produce results.In the Culture experiments the tanks used the previous year were again set up. The water this time before ad­mission to the rearing tanks was filtered through filtros, sand and tarantulla cotton. Electric light bulbs were thoroughly insulated with paraffin, painted black, and immersed in clusters in the rearing tank, in order to prevent sudden drops of temperature as recorded for the previous season. The water was stirred and aereated by simple suction aspirators attached to the water intakes.The larvae grew normally for five or six days but at this time growth appeared to be arrested. Only rarely was one found developed beyond the straight hinge stage. None exceeded .150 mm. in size and all had died by the tenth day. Repeated experiments yielded the same result. Various changes were made in the filtering devices, smaller tanks were constructed, electric light globes were placed in insulated containers, water was pumped directly from the bay rather than from the cement tank but all to no avail. There was apparently some unknown detrimental factor operating within the tanks. A possible explanation might be that filtration was too thorough, p H. was similar to that in the harbor and other organisms in the water appeared healthy.For a week spawning occurred almost daily and each time after development had proceeded to the swimming stages the whole content of the tank was run into the harbor* Probably as much fertilization resulted, in this way from the spawn of the few thousand oysters used as would normally have occurred with millions of them spawning in the harbor. Plate VI» shows ten one and two-year old Japanese oysters picked up between January and April 1929. All of these are attached to native oyster-s'nells, rocks, or barnacles and have most likely resulted from larvae liberated in this way during the two preceding years. In consideration of these cases a considerable set may be reasonably expected next year as a result of this years practice.In addition to the experiments described another was attempted with the idea of determining the re-action of the larvae to a set of constant temperatures. A tank was4constructed as outlined in Plate VIII. Fig. 2. A nevst of insulated electric light bulbs was placed at the top, and ice was admitted to a cage in the bottom through a compartment at the back. By keeping the iee-supply up and adjusting the number of lights at the top; temperatures were obtained ranging from 8° C. at the bottom flask to 20° C. at the top; each flask differing from the one immediately below it by approximately 2 degrees.Larvae were obtained and admitted to the flasks,the water being changed periodically by filtering through fine tarantulla cotton. Owing to a mechanical error in putting in the plate glass front, there were continual interruptions to the experiment through breakage. At no time was it possible to keep the tank in continuous operation for more than two days. Growth for these periods, percentage of mortality, and number of abnormal forms, agreed with results obtained by Seriô and Hori and Kusakabe (1926). There is good reason to believe that with a simple alteration in the construction of the glass panel, the tank would supply very valuable information, concerning the effect of temperature on the mid-larval stages. Its main importance at present lies in the fact that it gave a very definite range of temperatures and was relatively inexpensive and easy to operate.£0Table (1)of Maximum Development of Oysters 1 9 2 7 » Temp. In C. degrees Specific Gravity H-ionA u g . 5 P .M . 25 1 . 0 1 7 7 ----------8.4n 6 n 25 1 . 0 1 7 6 8 . 4n 7 tt 25 1 . 0 1 7 7 8 . 3 5It 8 rt 2 4 . 5 1 . 0 1 7 9 8 . 2Vf 9 n 24 1 . 0 1 8 0 ~ —it 1 0 n 22 1 . 0 1 8 4 — — —n 11 tt 2 1 . 5 1 . 0 1 8 4 8 . 3p. 1 2 tt 21 -  — —n I S tt 19 ----- ------ «• — _n 1 4 tt 18 1 . 0 1 9 0 8 . 2 5n 1 5 tt 20 1 . 0 1 8 6 8 . 1 5n 1 6 tt 2 0 . 5 1 . 0 1 8 3 8 . 5IT 17 tt 21t! 1 8 tt 20Tl 19 tt 20 1 . 0 1 8 2 8 . 2 5n 20 tt 20 1 . 0 1 8 2 8 . 2 0ft 21 tt 2 0 . 5 1 . 0 1 8 1 8 . 4II 23 tt 1 9 . 5It 24 tt 19n 26 it 1 7 . 9 1 . 0 1 9 2 8 . 2tt 28 tt 1 8 1 . 0 9 0 8 . 3it 29 tt 1 8 . 1ri 30 tt 18 1 . 0 9 1 8 . 2IT 3 1 tt 1 7 . 5 1 . 0 1 9 0 8 . 1Sep.l tt 1 7 1 . 0 2 0 0IT ■ 2 tt 17 1 . 0 2 0 8 . 2TT 3 tt 1 6 . 8 1 . 0 2 0 0 8 . 3It 4 ti 16 1 . 0 2 0n 5 tt 1 6 . 5 1 . 0 1 9II 6 rt 1 5 . 5 1 . 0 2 0It 7 tt 1 5 . 5 1 . 0 1 9IT 1 8 n 17 1 . 0 1 9II 3 0 tt 15 1 . 0 2 0Oct . 1 tt 15 1 . 0 2 011 6 tt 1 3 1 . 0 2 1II 10 tt 1 3 1 . 0 2 1n 1 8 rt 11 1 . 0 2 1Table (2)Conditions in Tidal Pond (1927)Time Temperature Specific Gravity H-ionIn Centigrade DegreesJuly 27 P.M. 2828 A.M. 22.529 P.M. 29SO A.M. 25Aug. 1 A.M. 22.53 P.M. 274 A.M. 216 P.M. 268 A.M. 2310 A.M. 2112 A.M. 19• 13 A.M. 21.514 P.M. 2515 P.M. 2516 A.M. 2017 P.M. 2718 A.M. 2525 A.M. 20.527 A.M. 21 .30 A.M. 20Concentration1.0178 8.51.0185 8.61.1580 8.71.0185 8.51.0185 8.61.0179 8.61.0182 8.71.0175 8.51.0183 8.51.0182 8.51.0190 8.11.0180 8.31.01801.0180 8.21.0184 1.01801.0179 8.41.0192 8.51.0192 8.31*0192 8.222Table"~(2)Temperature Speciflate in GraviCentigrade legreesJune 1 17 1.019TI 2 17 1.019ft 2 17 1.019TT 4 1 8 1.019fï 5 20 1.020n 6 18 . 1.020Tt 7 '• 15 1.020f! 8 15 1.017n 9 ; 22 1.017n 10 19 1.018n 11 19 1.017IT 1 2 19 1.018Tt 12 20 1.017Tt 14 18 1.018TT 15 19 1.017TI 16 17 1.018Tt 17 18 1.019TT 18 19 1.019'II 19 20 1.018TI 20 21.5 1.018n 21 20 1.017TI 22 22 1.017Tt 22 22 1.017tt 24 24 1.016Tt 25 22 1.017TI 26 21 1.017TT 27 20 1.017TI 28 20 1.017tt 29 20 1.017n 20 19 1.01bJuly 1 19 1.018It 2 19 ' 1.018TI 2 19 1.018rt 4 19 1.018ti 5 19 1.018TT 6 19 1.018tt 7 20 1.018Tt 8 20 1.018n 9 21 1.018Tt 10 22 1.018TT 11 22 1.017tt 12 22 1.017tt 12 22 1.017IT 14 22 1.017tt 15 21 1.018n 16 22 1.017TI 17 22 1.017TT 18 2 2 . 5 1.017Temperaturein SpecificCentigrade Degrees GravityEE 1.017EE.5 1.0165E4.5 1.01624 1.016E5 1.0155E5 1.0165E4 1.016522 1.0165EE 1.0165El.5 1.0165EE 1.017EE 1.017EE 1.01721 1.01720.5 1.01820 ; 1.018 21 1.016E2 1.01820 1.01919 1.01917.5 1.01917 1.02018 1.02019 1.019519 1.019519 1.020PLATEf î r p j i t o r123 117 Jismuir frW m) !sFax sp?îSS4 1. 10!26 N LADYSMITHCoff'* P- UZZ * rWATEP WKîBouldei*s>? o * ; p  j1r 'P t .PLáSJS.II.2526PLATE.IllFiiç.3.Fir.S.Explanation of Plates.32PlatePlatePlatePlatePlatePlatePlatePlateI. Oyster Harbor, Ladysmith.II. Deposit of Japanese Oysters on fairly suitable ground.III. Deposit of Japanese Oysters in most favorable area.IV. Japanese Oyster spatted on Rock Island (Hote Arrow, Plate I.)V. Oyster float used for hastening developmentof spawn.VI. Oysters spatted in the Harbor 1926 and 1927.VII. Pig.I. Best type of rearing tank for early larval stages.Pig.2. Tank used for late larval development. Pig.3. A convehient type of tank for early larval development.VIII. Pig.i. Cement tank with sand filter , from whichIto pump at low tide.Pig.2. A tank for controlling temperature, with ice at the bottom and electric globes in the surface.33SummaryI A great part of Oyster Harbour, which is of no use for Eastern or local oysters will grow Japanese oysters.II The Japanese oyster growing beside the other species in any part of the harbour is invariably in the best c o n -’ dition.III There is definite proof that spatting of Japaneseoysters has occurred in at least three separate years. Teninstances of spatting during the last three years* are re­ported. AIV Some Japanese oysters were made to develop and spawn by placing them on a partially submerged float for several weeks; in a season when none, not so treated, spawned.V n  JaPanf se oyster larvae have developed in tanks, nor­mally for ten days; and have been kept alive withoutfurthur growth, for twenty five days; but no spatting hasX*6 SIXx U0d. • ^VI Experiments to maintain constant temperatures intanks, by means of electric bulbs; were partially success­ful, but there was no improvement in larvae growth as a result. • B *VII Some increase in spatting appears to have resulted rom the release of larvae into the harbour from thespawning tank.VIII A cement tank, fitted with an automatic sand filter has proven practical for insuring a water supply at low"Cl CL6 •IX The most difficult problem in artificial culture was to prevent sudden extreme temperature changes in the tanks and at the same tim?, permit sufficient flow of water.Sufficient success was attained with a device for s udying the reaction of larval forms to a series of fixed temperatures, to warrant giving it another trial.Churchill E. PLiterature Cited1919. The oyster and the Oyster Industry of the Atlantic and Gulf Coasts.Rept. U.S.B.F., App. VIII., Doc. 890Dean Bashford1902. Japanese Oyster Culture, Bull. U.S.F.C., 1902.Hori J.1926. Notes on the Full Crown Larva and the Japanese Common Oyster (Ostrea Gigas) th.Jour. Imp. Fisheries Inst., Vol. XXII., No. 1.Hori J. and Daijiro Kusakabe1926. Preliminary Experiments on the Artificial Culture of Oyster Larvae.Jour. Imp. Fisheries Inst. Vol. XXII., No. 3Mitsukuri1904. The Cultivation of Marine and Fresh-water Animals in Japan.Bull. U.S.F.C., XXIV.Nelson T. C.1921. Aids to Successful Oyster Culture. N. J. Agr. Exp. Sta. Bull. 3511923. Attachment of Oyster Larvae.Abstr. Anat. Rec., Vol. 24, No. 6, P. 3951926. Ann. Rept. N. J. Agr. Exp. Sta.Prytherch H. S.1923. Experiments in the Artificial Propagation of Oysters. &U.S.B.F., App. XI, Doc. 961.Seno Hidemi, Hori Juzo and Kusakabe Daijiro.1926. Effects of Temperature and Salinity on the Eggs of the Common Japanese Oyster (Ostrea G i ^ a s ) Th. Jour. Imp. Fisheries Inst. Vol. XXII., No. 3 .Wells W. F.1925. A new Chapter in Shell Fish Culture. o f ^ e w ^ o r k 11 Commission* Ani1« Rept. XV., State


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