Artificial hatching - jinkou fuka

Japanese: 人工孵化 - じんこうふか

Artificial hatching of eggs from poultry, silkworms, aquatic animals, etc.

[Nishida Tomoko]

poultry

Chickens and ducks kept as poultry have been deprived of broodiness, so they must be hatched artificially. Incubators are used for this purpose, and important factors that affect incubation are temperature, humidity, and the oxygen and carbon dioxide concentrations in the air. The longer the eggs are stored before being placed in the incubator, and the higher the storage temperature, the lower the hatchability becomes. If the storage period is less than one week, the temperature should be kept at 15-20°C, and for eggs stored for about two weeks, the temperature should be lowered to 10-12.5°C. For longer storage periods, the temperature should be lowered from 12.5°C to 10°C and then to 7.5°C, which will allow a hatchability rate of nearly 90% to be maintained even after three weeks. The eggs should be stored at a humidity level of 40-70%.

The incubation period is 21 days for chickens, 28 days for ducks, 28 days for turkeys, and 17 days for quails. There are flat and multi-level incubators, with multi-level incubators being more widely used. The number of eggs that can be stored varies from around 100 eggs to tens of thousands. There are two types of structures: a separate type, which separates the egg-setting chamber from the time the eggs are set until the 18th day into a chick-developing chamber for the period from egg-setting to hatching, and a combination type, which combines both. Inside the incubator, numerous egg trays (cases in which eggs are placed upright with the blunt end facing up) are arranged in a shelf-like pattern, and the heat source is an electric heater. The temperature and humidity inside the incubator are automatically and uniformly regulated by a constantly rotating stirring rod. The temperature is kept at 37-38°C, the humidity at 50-60%, the oxygen in the air at 20-30%, and the carbon dioxide concentration at less than 1%.

Eggs are turned to prevent adhesion between the chorion membrane and the shell membrane of the developing embryo inside the egg and to ensure normal development. It is said that the more times eggs are turned, the better, but in flat incubators, the position is manually turned 40 to 45 degrees back and forth several times a day. In three-dimensional incubators, eggs are turned automatically about 10 times.

Among the eggs, there are some that are infertile (unfertilized) or have stopped developing for some reason. If these eggs are not removed by candling, they will eventually rot and emit toxic gases. Egg candling is usually done twice, on the 5th to 7th day of incubation and the 15th to 16th day, but can also be done again on the 18th day. Egg candling is done in a dark room by pressing an egg candling tool against the blunt end of the egg (this is where the air cell is). The egg candling tool has a built-in lamp and is designed so that a light beam emerges from one end, and has a handle. During the 5th to 7th day of incubation, blood vessels radiate from the embryo toward the fetal membrane, making it possible to distinguish between infertile eggs, which are bright and have no embryo, and aborted eggs, which have a vascular ring visible around the edge of the fetal membrane. During the 15th to 16th day of incubation, the blood vessels become thicker and the embryo becomes larger and often moves, making it easy to distinguish from aborted eggs. For any type of poultry, a few days before hatching, the eggs are moved from the egg tray into a wire mesh cage called a brooder (a chick hatching room).The temperature in the room is kept slightly lower (37°C) because the embryos themselves are actively generating heat, and the humidity is kept slightly higher (70%) to facilitate hatching.

[Nishida Tomoko]

Silkworm

If silkworm eggs are left to their own devices, they will go into hibernation and not hatch until the following spring, but if they are given the right stimulus, they can be made to break hibernation and hatch. This is called artificial hatching of silkworms.

Univoltine species of silkworms lay hibernating eggs, while bivoltine species usually lay non-hibernating eggs (live eggs) during the univoltine period and hibernating eggs (black eggs) during the bivoltine period. Even within the same bivoltine species, the generation that lays black eggs is economically superior, so for practical purposes, the black eggs are first allowed to lay eggs and then artificially hatched for use. There are various methods for artificial hatching, but the most commonly used method at present is to immerse the eggs in heated hydrochloric acid, followed by rinsing with water, deacidification, and drying. Depending on how many days have passed since the eggs were laid and before rearing can begin, one of the following methods is used.

(1) Immediate acid immersion method: After spawning, the eggs are protected for 15 to 20 hours at an air temperature of 25°C and then immersed for 4 to 6 minutes in hydrochloric acid with a specific gravity of 1.075 and a water temperature of 46°C. The eggs hatch about 10 days after treatment. There is also a room temperature acid immersion method that uses hydrochloric acid without adjusting the temperature.

(2) Refrigerated acid soaking method After spawning, the eggs are protected at 25°C for 40-45 hours and then refrigerated at 5°C. After 40-60 days, they are taken out and treated with acid soaking (specific gravity 1.100, liquid temperature 47.5°C for 4-7 minutes) within 3 hours. The eggs hatch 11-12 days after treatment.

Artificial incubation requires technical mastery.

[Yataro Tajima]

Aquatic Animals

This refers to the artificial management of fertilized eggs of useful aquatic animals and their safe hatching. In general, it refers to the process of collecting eggs and sperm from the parents, fertilizing them, and hatching them. Fertilized eggs of aquatic animals not only differ in size and shape, but also in properties such as floating, sinking, and adhesiveness. The number of days required for hatching also differs, so hatching methods and incubators also differ.

[Kobashi Tsuguo]

Hatching facility

Planktonic eggs of species such as ark shells, abalone, prawns, and red sea bream hatch in a short time after fertilization, so they do not require special incubators. Also, because the eggs are small, the incubation tank is kept still and weakly aerated to prevent the eggs from settling and oxygen deficiency. Attached eggs of species such as carp, crucian carp, and goldfish are attached to fish nests and housed in incubation ponds to prevent oxygen deficiency. Eggs of sweetfish and smelt are attached to incubation frames made of palm bark, placed in boxes that allow free flow of water, and hung in rivers, lakes, or the sea, or set on the seabed. Eggs of swimming crabs and spiny lobsters are attached to the hairs on the female's abdominal legs, so the parents are responsible for incubating them until they hatch. Desert eggs of species such as salmon, rainbow trout, and char, which have large fertilized eggs, take a long time to hatch, so special incubators are used. The principle of an incubator is that fresh water is constantly flowing around the fertilized eggs, preventing them from dying due to lack of oxygen.

The water used for incubation must have a quality that does not adversely affect the incubation, there must be no sudden changes in temperature, and there must be sufficient dissolved oxygen. There is a certain relationship between water temperature and the number of days required for incubation, and within the optimum temperature range, the higher the temperature, the faster the eggs will hatch. Sudden changes in temperature will reduce the hatching rate. As for light, the hatching rate of most fish is not affected by normal sunlight, but salmon and trout are weak to direct sunlight and ultraviolet rays, and their hatching rate decreases, so they must be kept in a dark place. In addition, if mechanical force is applied to the eggs for transportation or disinfection, it will have a significant effect on the hatching rate. Salmon and trout eggs immediately after fertilization are very sensitive to vibration and impact, but become stronger after the eyes hatch. However, they become weaker again just before hatching, so transportation should be done when the eggs are eyed, and vibration should be avoided at other times. Vibration and impact will speed up hatching by one or two days. Carp and goldfish eggs that are just about to hatch will also hatch faster if transported. Even vibrations or shocks that do not affect the hatching rate can cause deformities in the hatched larvae.

Various aquatic bacteria that develop in dead eggs multiply and spread their hyphae, often covering live eggs and reducing the hatching rate. In the past, salmon and trout eggs were inspected every 3-5 days before hatching and dead eggs were removed, but now, once a week, malachite green diluted to 5 parts per million (5 ppm) is poured into the water for one hour to suppress the growth of aquatic bacteria. Smelt eggs are also immersed in malachite green at a concentration of 5 ppm for 10-30 minutes once a week to prevent the growth of aquatic bacteria.

[Kobashi Tsuguo]

Egg and sperm collection

There are two ways to obtain fertilized eggs: artificial insemination and natural spawning. Artificial insemination is mainly performed on salmon, trout, smelt, and sweetfish. The eggs are obtained by either the incision method, in which the abdomen is cut open to extract the eggs, or the squeezing method, in which the abdomen of the parent fish is pressed. Sperm is often obtained by squeezing, and the dry induction method, in which the eggs and sperm are mixed together and then water is added to allow fertilization, is common. In natural spawning, mature parents are placed in a spawning pond and allowed to naturally release eggs and fertilize to obtain fertilized eggs. Shellfish and other species may be stimulated by changing the temperature, adjusting the pH, drying out (exposing them to the air for a certain period of time), or exposing them to ultraviolet light. In the case of fish, the water temperature and light are often adjusted, and pituitary hormones are often administered to females to promote the maturation of the parents. When eggs are taken out of the body and placed in environmental water, they lose their fertilization ability in a short period of time, and sperm also lose their fertilization ability within one minute.

[Kobashi Tsuguo]

Rearing of hatched larvae

To raise the larvae obtained by artificial incubation in a healthy manner, the initial feed will affect the subsequent yield. Because aquatic animals have a wide variety of forms and lifestyles, newly hatched larvae differ in size and form, and they are fed different foods as well. Food given to newly hatched larvae must be large enough for the larvae to eat and easy to digest, as well as highly nutritious, able to float in the water, not degrade the water quality, and easily available. For this reason, tiny plankton organisms are mainly used as feed. Furthermore, feeding a variety of organisms as feed rather than a single species has been shown to produce better results in terms of both growth and yield.

[Kobashi Tsuguo]

[Reference] | Fish farming | Hatching | Incubators | Sericulture

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

家禽(かきん)、カイコ、水産動物などの卵を人工的に孵化させること。

［西田恂子］

家禽

家禽として飼育されているニワトリやアヒルは就巣性を除去されているので、人工的に孵化してやらねばならない。そのために孵卵器が用いられているが、孵卵を左右するたいせつな要素は温度、湿度および空気中の酸素と二酸化炭素濃度である。種卵を孵卵器に入れるまでの貯蔵日数が長いほど、また貯蔵温度が高いほどそれだけ孵化率が悪くなる。貯蔵期間が1週間以内の場合は温度を15～20℃に、2週間ほどの貯卵では10～12.5℃に下げ、それより長期保存の場合は12.5℃から10℃、7.5℃と順次温度を低下させれば、3週間でも90％近くの孵化率が維持できる。湿度は40～70％の条件下で保存する。

　孵卵日数はニワトリ21日、アヒル28日、シチメンチョウ28日、ウズラ17日である。孵卵器には平面式と立体式があるが、立体式孵卵器のほうが多く用いられている。収容卵数も100卵程度のものから数万個のものまで、さまざまである。2種の構造があり、入卵から18日までを入卵室、以降発生までをヒナ発生室とに分離するセパレート型と、両者を併設したコンビネーション型がある。器内には卵座（鈍端を上にして卵を立てて入れるケース）が多数棚状に配置され、熱源は電気ヒーターである。器内の温度と湿度は攪拌(かくはん)棒を常時回転させ、均一に自動調節されている。温度は37～38℃、湿度は50～60％、空気中の酸素は20～30％、二酸化炭素濃度は1％以下に抑える。

　卵内で発生が進んでいる胚(はい)の絨毛(じゅうもう)膜と卵殻膜の癒着を避け、正常に発育させるために転卵する。転卵回数は多いほどよいといわれるが、平面式孵卵器では1日数回、手で前後にそれぞれ40～45度ずつ位置を変える。立体式では約10回、自動的に転卵される。

　種卵のなかには無精卵（受精していない卵）や、なにかの理由で発生を中止しているものがあるので、検卵によってこれらの卵を取り除かないと、やがて腐敗して有毒ガスを発生する。検卵は普通、孵卵5～7日と15～16日の2回行うが、18日目にもう一度行うこともある。検卵は暗室内で卵の鈍端（この部分に気室がある）に検卵器を密着させて行う。検卵器はランプを内蔵し、一端から光条が出るようにくふうされ、取っ手がついている。孵卵5～7日では、胚を中心にして胎膜に向かって血管が放射されているので、胚がなくて明るい無精卵と、胎膜周縁部に血管輪が見える中止卵を区別できる。孵卵15～16日では、血管は太くなり、胚は大きくなってしばしば動くので、中止卵と容易に区別される。どの家禽でも孵化日の数日前に卵を卵座から発生座という金網籠(かご)（ヒナ発生室）の中へ移し、室内の温度は胚自身の熱発生が盛んなのでやや低く（37℃）、湿度はすこし高めにして（70％）孵化を容易にしてやる。

［西田恂子］

カイコ

カイコの越年卵は自然のままに放置すると休眠して翌春にならなければ孵化しないが、これに適当な刺激を与えれば、休眠を破って孵化させることができる。これをカイコの人工孵化という。

　カイコの一化性種は越年卵を産み、二化性種は普通、一化期には不越年卵（生種(なまだね)）を、二化期には越年卵（黒種(くろだね)）を産む。同じ二化性種でも黒種を産む世代のほうが経済的に優れているので、実用上はいったん黒種を産卵させたのち、これに人工孵化処理を行って利用する。人工孵化法には種々あるが、現在、一般に用いられているのは、加温塩酸液に浸漬(しんし)後、水洗、脱酸、乾燥する方法である。産卵後、飼育を開始するまでの日数の長短に応じ、次の方法のいずれかを用いる。

(1)即時浸酸法　産卵後、気温25℃で15～20時間保護した卵を、比重1.075、水温46℃の塩酸液に4～6分浸漬する。処理後約10日間で孵化する。温度の調節をしないで塩酸を用いる常温浸酸法もある。

(2)冷蔵浸酸法　産卵後、気温25℃に40～45時間保護した卵を5℃に冷蔵し、40～60日後に出庫して3時間以内に浸酸処理（比重1.100、液温47.5℃に4～7分）を行う。処理後11～12日で孵化する。

　人工孵化を行うには技術的な習熟が必要である。

［田島弥太郎］

水産動物

有用な水産動物の受精卵を人為的に管理し、安全に孵化させること。一般には親から卵・精子を採取して受精させ、孵化させるまでをさすことが多い。水産動物の受精卵は、大きさや形などが異なるばかりでなく、浮遊性、沈性、付着性など性質も異なり、また孵化までに要する日数も異なるので、孵化方法や孵化器も異なる。

［小橋二夫］

孵化の施設

アカガイ、アワビ、クルマエビ、マダイなどの浮遊性卵は、受精してから短時間で孵化するので、特別な孵化器を必要とせず、また卵が小さいので孵化槽は止水とし、卵の沈殿と酸素不足を防ぐために、弱い通気を施して孵化させる。コイ、フナ、キンギョなどの付着性卵は魚巣に付着させ、孵化池に収容し、酸素不足にならないようにする。また、アユやワカサギなどはシュロ皮を広げた孵化枠に卵を付着させ、水が自由に流通できる箱に収め、河・湖・海の中に垂下したり、海底に設置する。ガザミやイセエビの卵は雌の腹肢の毛に固着しているので、孵化するまで親に保育させる。受精卵の大きいサケ、ニジマス、イワナなどの沈性卵は、孵化日数も長いので特別な孵化器を使用する。孵化器の原理は、絶えず受精卵の周りを新鮮な水が流れ、酸素不足による斃死(へいし)がおこらないようにくふうされていることである。

　孵化に用いる水は、水質が孵化に悪影響を与えず、水温の急変がなく、また十分に酸素を溶存していなければならない。水温と孵化に要する日数とは一定の関係があって、適温範囲では、温度が高いほど早く孵化する。温度の急変は孵化率を低下させる。光に対しては、大部分の魚類では普通の太陽光線で孵化率は変わらないが、サケ・マス類では直射日光や紫外線に弱く孵化率が低下するので、暗所に置く必要がある。また、卵の運搬や消毒などのために、機械的な力がある程度以上加わると孵化率に大きく影響する。受精直後のサケ・マス類の卵は振動や衝撃に非常に弱く、発眼後は強くなる。しかし、孵化直前にふたたび弱くなるので、運搬などは発眼卵のときに行い、それ以外は振動を避ける。振動や衝撃を与えると、孵化が1、2日早くなる。また、コイやキンギョの孵化直前の卵も運搬すると早く孵化する。孵化率に影響しない程度の振動や衝撃でも孵化仔魚(しぎょ)に奇形が現れることがある。

　死卵に発生する各種の水生菌は繁殖して菌糸を広げ、生卵まで覆って孵化率を低下させることが多い。サケ・マス類の卵は、古くは孵化までに3～5日に1回検卵し、死卵を除去していたが、現在では1週間に1回、100万分の5（5ppm）に希釈したマラカイトグリーンを1時間流入させて、水生菌の繁殖を抑制している。また、ワカサギの卵でも5ppmの濃度のマラカイトグリーンに10～30分間浸漬することを、1週間に1回行うことで水生菌の繁殖を防除している。

［小橋二夫］

採卵・採精

受精卵を得るには、人工受精と自然産卵とがある。人工受精はおもにサケ・マス類、ワカサギ、アユで行われ、腹を切り開いて卵を取り出す切開法や、親魚の腹を圧する搾出法で卵をとる。精子は多くの場合搾出法でとり、卵と精子を混ぜ合わせたのちに水を入れ、受精させる乾導法が一般的である。自然産卵は、成熟した親を産卵池に収容し、自然に放卵・放精させて受精卵を得る。貝類などは温度の変化やpH(ペーハー)の調整、干出(かんしゅつ)（一定時間空中に露出させること）、紫外線を照射した海水などで刺激をすることもある。魚類の場合は親の成熟を促進させるために、水温や光を調節したり、また雌に脳下垂体ホルモンなどを投与することが多い。体外に出された卵は環境水中に置かれると、短時間に受精能力を失い、また精子も1分以内で受精能力を失う。

［小橋二夫］

孵化幼生の飼育

人工孵化で得られた幼生を健全に育成するには、初期の餌料(じりょう)いかんによって、その後の歩留りに影響する。水産動物の形態や生活様式がさまざまであるので、孵化幼生は大きさや形態などが異なるうえに、餌料も異なる。孵化幼生に与える餌料は、幼生が捕食できる大きさで消化しやすいもののほか、栄養価の高いもの、水中に浮遊していること、飼育水の水質を悪化させないもの、容易に入手できるものなどの条件を備えていることが必要である。したがって、餌料には微小なプランクトン生物がおもに使われている。なお、餌料生物は単一種より多種類を与えたほうが、成長・歩留りともよい結果が得られている。

［小橋二夫］

[参照項目] | 栽培漁業 | 孵化 | 孵卵器 | 養蚕

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