1. The Chinese Major Carps
This collective term comprises the following cyprinids:
grass carp (Ctenopharyngodon idellus)
silver carp (Hypophthalmichthys molitrix)
marble carp or bighead (Aristichthys nobilis)
black or snail carp (Mylopharyngodon piceus)
To this list can be added the mud carp (Cirrhinus molitorella); it does not reach the size of the above-mentioned species.
They originated in the great rivers of the People's Republic of China, Heilong Jiang (Amur River), Huang He (Yellow River), Chang Jiang (Yantze River), Xi Jiang (Pearl River). They became the object of the famous Chinese fish culture which exists since more than two thousand (exactly 2 400) years.
They were introduced for culture into Taiwan, Japan and other Southeast Asian countries. At the beginning of the sixties, when their artificial propagation was solved, they (mostly the first three species) were introduced all over the world. They are cultured with the common carp in Israel, South and Middle Europe, North Africa, in many Asian countries (India, Nepal, Pakistan, Iran, Iraq, Sri Lanka, etc.) and in the Americas (Peru, Mexico, Brazil).
2. Biology of the Chinese Major Carps
Although they are grouped together as fishes of the Far East or herbivorous fishes, or Chinese major carps or simply Chinese fishes, they differ biologically. Of course, they also have similar characteristics.
2.1 Food and Feeding Habits
Their food and feeding habits are very different; these habits are the most important for the fish culturists.
(a) The grass carp, as the name implies is a waterweed eater, and it also eats cut fresh green grass from the land. When big enough, it consumes the rough emerging vegetation of the water - reed, sedge, and such.
It inhabits the shore area of the ponds. Its preference is for certain waterweeds, and it selects first those which have a better taste. Water hyacinth, for instance, is eaten only when the carp is very hungry and no other food is available.
Grass carp is never cultured alone in monoculture (and it is not advisable to do so). An old Chinese proverb states that a well fed, big grass carp feeds three other fishes. In fact, a big grass carp eats daily a great amount of vegetal matter, 30–40% and sometimes 100% of its own weight. Naturally, most of the eaten plants leave the fish body as faeces. The vegetal matter in this partly digested form is a good organic manure for the pond on which algae, zooplankton and mostly bottom animals may grow. However, the manuring effects of the grass carps do not occur when they have not enough vegetal food in the pond.
Grass carp is a rather aggressive feeder. When the temperature in the pond is high enough (over 25°–26°C) it eats plenty. Under 18°C its appetite is low and digestion is slow; at 15°–13°C it stops feeding. When kept together with regularly fed common carp, it takes the common carp feed as well (for example grain feed) which causes sometimes inflammation of the gut (if this occurs often, it may prove fatal).
This special food requirement does not occur in its early life. Its first food contains rotifers and crustacean larvae (nauplii). Later, it feeds on zooplankton, mostly Cladocera and copepods. At 1 1/2 months (4–5 cm length), it starts to nibble filamentous algae and the tender small leaves of underwater plants. When such food is available, it soon changes its food habit. A 100 g grass carp eats a great quantity of tender waterweeds or grass cut in small pieces. As it grows it consumes more and more rough grass and weeds.
Grass carp, like all cyprinids, has no teeth in its mouth cavity, and therefore cannot bite off the leaves of the plants. It has well developed pharingeal teeth with which it chews the plant materials. It takes first a branch or leaf in its mouth and tries to tear it off. The piece of plant is then taken and pushed under the pharingeal teeth and the chewing starts. Only big fish can eat rough, strong weeds and grass. This should be kept in mind when grass carp is fed with grass. Big grass carps are even able to eradicate emerging water plants, pulling them down in the water with continuous effort.
Grass carp is usually fed with grass growing on the dikes. A 0.1-ha grass covered area is needed to feed the grass carp stock of a 1-ha pond. The grass carp increases its own production and that of other fishes by cleaning the noxious weeds, and manures the pond water. Its usefulness is multiple.
(b) Silver carp is a strainer (filterer) fish with a filtering apparatus on its gill arches so fine that it can filter out planktonic algae and organic debris as small as 0.02 mm. Silver carp feeds on planktonic algae which are plentiful in a good, fertilized pond. Silver carp is a food specialist eating mostly phytoplankton, does not take bigger food and never feeds from the bottom. It is a column-feeder filterer-fish. It is not an object of sport angling because it neither takes nor prefers any kind of bait.
Silver carp is most useful in modern fishculture because it utilizes such food which is not eaten by any other fish, and eats those foods which grow in mass in a well fertilized pond. Combatting the overpopulation of planktonic algae, it increases the biological productivity in the pond thus facilitating the better growth and production of the other fish species. Carp production is higher using silver carp rather than other species. The fish culturist has a double advantage in stocking silver carp with common carp: directly, silver carp production is considerable and indirectly, it increases common carp production. Silver carp is not used in monoculture.
Silver carp larvae begin feeding on rotifers and small crustaceans like the grass carp larvae. They start to feed on algae when over one month in age, or 4–5 cm in length.
Food habit does not change with age.
(c) Marble or bighead carp is a near relative of the silver carp. It is also a strainer (filterer) fish but its filtering apparatus is not so fine as that of silver carp. It is also a column feeder, taking food from the water column of the open parts of the pond. Its usual food contains planktonic animals (zooplankton) and larger size algae (phytoplankton). It was observed that in ponds where enough marble carp was stocked, the water bloom of blue-green algae never develops. The marble carp is an extremely useful member of the fish pond community in controlling the blue-green algae although to a minor extent it competes with common carp for zooplankton.
The marble carp larvae take the same food as the grass carp and silver carp larvae. How to distinguish young silver and marble carps: The young silver carp and marble carps are very similar in apperance. However, the silver carp has a shorter pectoral fin which does not reach the base of the abdominal fin; while the marble carp has a longer pectoral fin which surpasses the base of the abdominal fin. Although the black or snail carp and mud carp have not yet been introduced in Madagascar their food and feeding habits should be mentioned here.
(e) Black or snail carp feeds on molluscs mostly and snails living on the pond bottom and on plants. Because some snail species are the vector (intermediate host) of a disease very dangerous to the human being (bilharzia), it may offer a good means of controlling the spread of that disease. On the other hand, plenty of molluscs are growing on the pond bottom which are unexploited when snail carp is not stocked.
(f) Mud carp is a moderately-growing fish; it feeds mostly on debris accumulated on the pond bottom. It eats the bottom animals (worms, insects, larvae) as well. In this respect it competes with the common carp. It offers valuable services to the pond (and to the fish culturist) as a scavenger eating the faeces of other fishes.
2.2 Growth of the Chinese Major Carp
The growth of any fish species depends on its genetic characteristics which function satisfactorily only if qualitatively and quantitatively enough food is continuously available. Genetically the Chinese major carps are fast-growing fishes which can easily reach 5–10 kg in weight. In this respect, the mud carp is an exception as it is a moderately-growing fish and reaches only 2–3 kg.
The grass carp is the slowest-growing of the three species. But in tropical and subtropical ponds where the food is unlimited, within one year it can reach 2–2.5 kg with a stocking rate of 100–200 fish/ha. Normally they reach 0.5–0.8 kg in their first year with 400–500 fish/ha. Old fish often obtain a weight of 10–20 kg.
The silver carp also grows well. With 1 000–1 500 fish/ha and a well fertilized pond they reach nearly 1 kg weight within 8 months. Three to four-year-old silver carp can weigh 4–7 kg in rich tropical waters. Even in Europe where the production period is only 100–120 days/year, 7-year-old fish achieved 14–15 kg weight.
The fastest growing of the three species is the marble carp. In its first year it reaches 1.5–2 kg and the 3 to 4-year-old specimens can weigh 7–10 kg.
However, it is stressed that the fast growth of the Chinese major carp is realized only when they obtain enough suitable food and have sufficiently deep (at least 1–1.5 m) water.
Chinese major carps are warmwater fishes; their excellent growth evolves best in subtropical and tropical conditions.
2.3 Sexual Maturity
In Europe grass carp and silver carp reach sexual maturity in their fifth to sixth year. Males mature one year earlier. The marble carp is to the greatest extent the “warmwater fish” of the three species. It reaches sexual maturity at 7–8 years. In the tropics and subtropics sexual maturity develops earlier; a 2–3 year old specimen can be sexually ripe. Sexual maturity also depends on suitable food and water temperature. Carps mature earlier in warm water than in cold water.
3. PROPAGATION BIOLOGY
The propagation habits of the three species are the same. They are river spawners and never spawn in the confined waters of ponds. In their original habitat in summer when the rivers start to flood they migrate in great schools toward the upper reaches of the rivers where they spawn on sandy, gravelly bottom. Their eggs are non-adhesive and swell up to become semi-floating.
The marble carp has the biggest egg; unswollen it is 1–1.1 mm and swollen 3.7–5.6 mm. The egg of the marble carp is the toughest and most resistant. Next is the grass carp; its unswollen egg is 1–1.2 mm and swollen 3.5–5.3 mm.
The silver carp egg is the smallest, 0.7–1 mm and 3.5–5.3 mm unswollen and swollen respectively; and the most sensitive. A strong current in the hatching jar may cause the shell cover to be torn off from the developing embryo.
The river current moves the swollen eggs downstream and toward the shore. They develop and hatch very quickly as will be described later. The newly-hatched larvae swim upward and fall downward. In the second larval day they lie on the bottom for varying periods.
Larval development lasts 3–4 days depending on environmental temperature. As Chinese major carps never spawn sufficiently in confined water to produce a reasonable quantity of young fish, artificial propagation of this species is an unavoidable necessity.
4. HANDLING OF THE CHINESE MAJOR CARPS
4.1 SENSITIVITY
The fish culturist has to handle his cultured fish species and therefore should be well acquainted with this characteristic.
All the Chinese carps are more sensitive to handling than the common carp.
The least sensitive in this respect is the grass carp. Although it leaps a good deal, its strong scales protect it from serious injuries. The sensitivity of the Chinese carps should be respected when they are transported in water, in a hammock or in a satchel made of waterproof material. Extra care must be given to brood fish.
The bighead carp comes second. Its small scales may not protect its skin well enough. It is the most calm fish of the three; it does not jump, it is the easiest to handle.
The silver carp is the most sensitive and nervous. Its transport and handling cause great problems. When handled many fish may lose the protective mucus layer of their skin, which leads to bacterial infection and fungus attack on the skin. However, with care and experience these problems can be overcome.
4.2 OXYGEN SENSITIVITY
The silver carp is the most sensitive and the grass carp is the least sensitive in this respect. Oxygen sensitivy increases when the silver carp is injected with hormone extract. The males are even more sensitive than the females and sperm production stops if the oxygen supply is not suitable.
Marble carp is nearer to the silver carp with regard to oxygen sensitivity but does not show such extreme reactions.
The injected grass carp do not show particular sensitivity. They may spawn in a hapa (a fine net box fixed in the pond) given a suitable doses of hormone.
4.3 SENSITIVENESS OF THE SKIN, INJURIES
The Chinese major carps are far more active than common carp. When excited, they begin leaping out of the water (especially silver carp and grass carp) and this leads to handling problems. The bighead (marble carp) is an exception, it is calmer than the others. Silver carp, because of its extreme excitability and its very delicate skin, is very liable to bruising and losing its scale cover. This can often be fatal for the brood fish and successful propagation may be threatened. A breeder, bruised and with damaged scales is no longer suitable for induced propagation. If it does not die during the hormone treatment period it most likely will a few days later from ulceration (a bacteria, Proteus rettgeri, can be isolated from the ulcer).
The silver carp also suffers greatly from the effects of stress. It often happens that they lie in the water belly-up after the injection but recover within half an hour.
Grass carp, since it is also a very active fish, may lose many scales during handling which may lead to infection by Saprolegnia.
5. KEEPING THE CHINESE CARP BREEDERS IN THE NON-PROPAGATION SEASON
The preparation and keeping of the breeders to become good egg and milt producers is of utmost importance. Breeders kept in poor conditions, in shallow water, without enough suitable food, in small ponds in crowded conditions and low oxygen content, etc., will usually not respond well to the hypophysation, and even if they do respond the propagation results will be very poor.
The Chinese carps need more space, deeper water (at least 1–1.5 m deep) and ample suitable food. This latter requirement is easily satisfied as mentioned earlier.
In the non-propagation season it is best to keep the Chinese carp breeders in polyculture together (some common carp also should be stocked with them). Where two or more ponds are available for keeping the breeders, males and females can be separated for convenience.
The grass carp should be given an ample daily supply of good quality fresh green grass (Papilionatae, alfa alfa or clover have a high protein content.) In tropics suitable plants should be selected.
The silver carp and bighead receive enough phytoplankton and zooplankton food respectively when the pond is well supplied with organic manure. Other types of artificial feeding are usually not necessary for the Chinese carps.
To summarize: a deep big pond (1 000–4 000 m2) with good water supply should be chosen for the breeeders; grass carp should have ample fresh green grass daily and the other carps can be satisfied with regular organic manuring. In the tropics and subtropics 30 grass carps, with 20–25 silver carps and 10–15 bighead carps plus 20–25 common carps can be kept in a 1 000 m2 pond.
6. ARTIFICIAL PROPAGATION OF THE CHINESE MAJOR CARPS1
6.1 THE PROPAGATION PERIOD
The Chinese major carps propagate in summer (in Europe in June and July) when the water temperature is above 22°C and does not drop below 20°C. The best time for propagation is when the water is 23–26°C.
In the tropics and subtropics it is easier to fix the propagation time. Because of the egg development process, the carps are ready for propagation before the rainy season, but keeping them in high temperature for about one month, they become overripe, the egg mass starts to enter the resorption phase, at which time they are no longer suited to artificial propagation.
In Madagascar, it appears the propagation season starts in mid-September, up to mid-October in Kianjasoa and in November and December in Perinet.
Experience has shown that in the tropics and subtropics the grass carp and silver carp can be propagated at least twice a year.
6.2 THE EGG DEVELOPMENT PROCESS IN THE OVARY
The egg development in the ovary is very similar to the common carp with the difference that the Chinese major carp need warmer water for longer than the common carp.
As the egg mass builds up it reaches a stagnant (dormant, waiting) stage. The fish start to migrate toward the suitable spawning environment. During migration - which is triggered also by sexual hormones - further ripening takes place which allows immediate ovulation in the spawning area.
However, if the fish are kept in confinement too long the eggs overripen and start to be resorbed. As the eggs in overripe or resorption condition do not react to hormone treatment, the assumed local spawning season should be respected.
After resorption, the eggs start to form again and they reach the propagation stage again in the tropics after 3 to 4 months. The egg development of the Chinese carps is more uniform than in common carp and therefore off-season ovulation is very rare.
6.3 KEEPING AND HANDLING THE BREEDERS BEFORE AND DURING ARTIFICIAL PROPAGATION
Given the nervousness and susceptibility to stress of these fish species, handling differs from that of the far calmer and hardier common carp.
Generally, all handling and transport should be completed within the shortest possible time. During transport the fish should be kept in water. The satchels made of waterproof material proved very suitable for transporting the breeders one by one in water.
6.4 NETTING AND (IMMEDIATE) SORTING OF THE BREEDERS
The breeders have to be sorted and the best selected for propagation. The frequent draining and refilling of the keeping ponds is a long tiresome process and involves stress factors which should be avoided. Taking the breeders with the net is the most convenient way for the fish. This should be done as quickly as possible and in silence, avoiding the leaping of the fish. A 3–4 m deep net should be used, which is raised about 1 m above the water surface. This way the escape of many leaping fish can be prevented. The fish should be kept in the bulge of the net in the water, away from the stirred-up mud. The captured fish should not be stranded out of the water or allowed to struggle in the mud.
The suitable stock for propagation can thus be selected. It is not necessary to separate the sexes which is so important for the common carp. The male and female Chinese carps are usually kept together.
The differentiation of the sexes can be made without taking the fish out of water. The roughness of the dorsal part of the pectoral fin distinguishes the males, the smooth pectoral fin the females.
The aptitude (readiness) of the females for propagation can also be investigated in the water by turning them on their backs. The bulging of the belly, the vent, and genital opening can be observed in this position. The bulging back part of the belly, together with the redder pink protruding sexual opening and the protruding swollen anus may show the suitability of the females for hormone treatment. Well fed grass carp have a bulging belly because of the large quantities of grass eaten. The suitability of this fish can be examined when their gonads are empty and by investigating their genital opening. It is advisable not to feed the grass carps a few days prior to culling out for propagation.
The males may ooze some milt by light pressure on the belly. This testing should be made very carefully, especially on the silver carp.
The selected females and males are transferred into the concrete keeping tanks of the hatchery or better into a net box (“hapa”).
The capture of the breeders should be arranged in such a way that they can be injected immediately on capture, thus avoiding handling them twice.
The concrete tanks should have a very smooth wall. In advanced hatcheries the tanks are covered with a plastic paint. The size of the tanks depends on the capacity of the hatchery but should be approximately 3–5 m long, 1–1.5 m wide and 1 m deep. The water level is regulated by a turning pipe which allows for a quick decrease of the water level and prevents the fish from leaping out.
If such a tank is not available it is advisable to keep the breeders in a hapa in which the fish cannot hurt itself and can be taken out easily for handling. The hapa is fixed in a concrete tank or under the inflow of a small pond. Ample water must be provided in the hapa, so that the injected fish do not suffer from oxygen depletion. The size of the hapa should be 2 m long by 1 m wide and 0.7–1 m high; 2–3 breeders can be kept there at the same time.
6.5 BREEDERS RIPE FOR INDUCED PROPAGATION (RECAPITULATION)
Only those fishes which react positively to the hormone treatment (hypophysation) are ripe for propagation. The ripeness can be determined by the following signs.
Females:
bulging hind part of the abdomen (in grass carp the bulging belly can be caused by the large amounts of grass eaten); red or pink colour of the pretruding genital opening; swollen and protruding anus.
Unfortunately these signs are also shown by the females at the overripe or resorption stage of eggs.
Males:
roughness of the dorsal part of the pectoral fin, oozing milt at light pressure on the abdomen.
6.6 HYPOPHYSATION TECHNIQUES
There are many proved systems to bring about the ovulation of Chinese major carps. All such technologies have been developed according to local circumstances, experience and skills of the technicians involved.
When the Chinese major carp breeders are well fed, well treated and handled, and “ripe” for ovulation, it is easy to obtain fertilizable sexual products; however, if for any reason they are not ready for hormone treatment, nothing can be done except to wait for the suitable time.
Here is described a method which is very successful, by which many hundred millions of larvae are produced yearly in Europe and Asia. The female breeders are injected twice-first, with an introductory injection of 0.5 mg/kg body weight and after 13–15 hours they have the second, decisive injection of 4.5–5 mg/kg body weight. When the breeders show the signs of all readiness for ovulation (sometimes the old females have a fringed sexual opening), they can be injected (with hope of success) with 3.5–4 mg/kg acetone dried hypophysis.
The males are given only one injection, 1–2 hours after the females have the first injection. Thus 20–22 h may elapse between the injection and stripping of the males.
The dose is uniform for the males, 2 mg/kg of body weight.
The adequate doses and timing of the injection of the males is more important for the common carp to produce suitable quantity of milt. The optimal sex ratio is 1:1 silver and bighead or 2 female:1 male for grasscarp. For 3 silver carp females 2 males are sufficient.
The time schedule of the hypophysation can be as follows.
At 15.00 h capture and select the females and immediately administer the first injection.
At 16.00 h capture the males (if they are kept with the females they can be put into the tank or hapa at 15.00 h). They should receive their doses of hypophysis between 16.00 and 17.00 h.
The females receive the second (decisive) injection at 05.00–06.00 h in the morning. Stripping occurs after 8–10 h depending on the water temperature of the keeping tank (see below).
Where light is available at night and the water temperature in the day time is too high (as in Kianjasoa) another time schedule can be practised:
first female injection: 08.00 h
second female injection: 20.00 h
male injection: 09.00–11.00 h
The stripping should start at about 06.00–08.00 h the next day according to the night temperature of the water.
(a) Preparation of the injection
The preparation is exactly the same as for the common carp.
The best method of weighing the females is to put them in a scoopnet open top and bottom which has a hook on the end, and weigh them in that. The weight should be rounded up to the next 1/2-kg value (e.g., 3.3 kg actual weight will count 3.5; 4.6 will count 5 kg and so forth).
The hormone injection should be administered into the dorsal muscle under the dorsal fin, or peritoneum under the pectoral fin. This latter has the advantage that the solution does not flow back and no massage is needed on the injected part of the body.
(b) The ovulation
The first injection brings about the pre-ovulation stage, the second produces the ovulation. The exact time of ovulation, after the second injection, can be calculated when the temperature of the water where the fish are held is known.
In Europe where the hatcheries are supplied with heated water and have a stable temperature the calculation is simple. The ovulation occurs by 210–220 hour/grade for grass and silver carp and by 220–230 for bighead carp. In the tropics and subtropics where heating is not applied, the time of the ovulation and stripping should be determined by measuring the temperature in each hour. Adding the temperature data when it reaches the 210–215° value, the stripping can start.
Two examples
Second injection at 05.00 h -
| Temperature at | 6 = | 22°C | 23 | ||||
| 7 = | 22°C | 23 | |||||
| 8 = | 22°C | 24 | |||||
| 9 = | 23°C | 25 | |||||
| 10 = | 23°C | 26 | |||||
| 11 = | 24°C | 26 | |||||
| 12 = | 25°C | 26 | 173 | ||||
| 13 = | 25°C | = | 186 | 26 | 26 | ||
| 14 = | 25 | 25 | 199 | ||||
| 211 | |||||||
In the first case the fish should be tranquillized and stripped at 14.00 h.
In the second case 10–15 minutes after 13.00 h.
The stripping time should be adhered to punctually. The Chinese carp soon become overripe and the stripped eggs remain unfertilized due to the overripeness. When the stripping is delayed 30 min about 50% of the eggs will not be fertilized; 60 min delay may result in 100% non-fertilized eggs.
Sometimes certain females have retarded reaction to the second injection (maybe due to stress effects). In that case, ovulation may occur about 30 min later than the scheduled time.
(c) Stripping of the females
As the Chinese major carp are not stitched as the common carp, they should be taken very carefully from the water to avoid serious losses of eggs.
The readiness for stripping is examined in the water; the fish is turned on its back and a mild pressure applied on the genital opening so that some ripe eggs are released. The tail of the fish should be secured in such a way that the thumb is pressed on the genital opening. The head of the fish is then placed into the scoopnet and with that is taken out of the water. When the fish is not removed from the water in this way, it starts to lash its tail and scatters the eggs in all directions. This stripping technique without tranquillizing needs practice and is not recommended for the untrained beginner in which case it is advisable to apply tranquillizing techniques before stripping.
The fish is now put on a table, its head is covered in a towel. Before stripping, the belly and tail of the fish and the hands of the manipulator should be dried thoroughly with a soft towel. During the drying the thumb of the manipulator is on the genital opening of the fish. After this, the stripping into a dry bowl can start. The females are usually calm during this process.
When the stripping of the femsles is finished or even during that operation the males are also stripped.
(d) Stripping of the males
The Chinese carps do not provide as much milt as the common carp; therefore the milt should be collected carefully using a milt collector, or pipette, or a small glass vial.
When enough milt is collected it should be poured over the eggs without delay. It must be stressed that all of sexual products should be collected without a drop of water.
The sexual products should be mixed thoroughly by slowly shaking the pail or stirring with a feather or small plastic spoon.
One to two cm3 milt is enough for 1/2 kg of eggs. Usually the milt of two males is used for one batch of eggs to assure fertilization.
Sometimes, if there is a shortage of milt, then less is used, but in that case the mixing should be done even more carefully.
(e) Tranquillizing of the Chinese carps
As Chinese carps are very nervous and jumpy fish, it is advisable to tranquillize them before stripping, to avoid great losses of the eggs and ensure easy handling.
The sensitivity of the different Chinese carps to the dose of tranquillizers varies greatly.
The silver carp is the most sensitive in this respect. To obtain a good tranquillizing result and ensure a wakening (revival) it is recommended to use 1:100 000 solution (1 cm3 in 100 1 of water) of Chinaldin (Quinaldin) (C10H9N) and 1:12 000 MS 222 solution.
Chinaldin is generally used because of its reasonable price and easy handling.
Chinaldin is a liquid and must be thoroughly mixed with water in a bucket before pouring into the tank (hapa) where the fish are kept.
To give the correct dose a syringe or measuring cylinder is used (only for that purpose) with which the dose is measured. The dose is calculated according to the quantity of the water in which the fishes are kept.
In Analanazaotra (Perinet) the basin contained 40 cm deep water and the surface of hapa was 2 m2, i.e., the hapa held 800 1 of water. Thus for silver carp and grass carp 8 cm3 and 10 cm3 of Chinaldin is required respectively.
Before treatment the water inflow is lowered as much as possible. The Chinaldin dose is put into a bucket of water, mixed thoroughly with a stick and distributed on the surface of the hapa.
To ensure quick distribution of the dose buckets of clean water are poured over the hapa.
After 3–5 min the fish are swimming belly-up, and the stripping can start. At this point the water inflow should be partly restored so that the fish do not suffer from oxygen deficiency.
The fish are tranquil for about half an hour after which they resume their normal position.
If some fish are not ready for stripping they should be left to tranquillize further (this does not affect the ovulation process).
6.7 HANDLING THE BREEDERS AFTER STRIPPING
When the stripping is completed and the eggs have been placed in the jars or in case of failure of ovulation, the breeders have to be transferred to the breeder pond without delay. It does not matter that they are in semi-tranquillized condition but they should be upright or swimming in normal position (not belly-up).
They should be put in water in the satchel and transported without delay into the pond. They should be taken carefully from the satchel and released onto the surface of the pond. If they are thrown carelessly into the pond they may stick in the mud or entangle in the grass of the shore and die there. In Hungarian fish hatcheries 30–50% mortality of the silver carp breeders is considered normal.
6.8 FERTILIZATION OF THE EGGS
Fertilization of the eggs is very simple in clean pond water. First, a small quantity of water (10–20 cm3) is added to the mixed sexual products and after 10–20 sec more water is added in small quantities, continuously stirring.
When the water reaches the sexual products the sperms become activated and fertilization may occur. Fertilization takes place within one minute after adding the water, after which it is unnecessary to stir the egg mass for more than 2–3 min longer. The egg mass is then washed many times with clean pond water and should be put into the incubation jar. It is calculated that 100–150 g “dry” eggs fit in a middle size (50–1) jar and 300–400 g in a big (200 l) jar.
(a) Swelling of the eggs
The eggs in water start to swell immediately. The swelling is very rapid and is finished within 30–50 min.
Chinese carp eggs swell to become large, they reach 3.7–5.6 mm in diameter. The eggs are not adhesive and therefore no special chemical treatment is needed as is the case with the common carp eggs.
The swollen eggs are semi-floating; they do not roll but undulate in the incubation jar.
6.9 INCUBATION
The small (8–16 l) jars are rather unsuitable for incubation because only 30 000–50 000 (30–35 g “dry” eggs) eggs can be placed in one jar and the hatched larvae will swim out of it. Therefore a sufficiently large larvae collector has to be fixed on the end of the outflow canal.
For the incubation of the Chinese carp eggs, medium and big jars (50 l and 200 l), which are suitable also for rearing of the larvae, are best. The ready-to-hatch developed eggs should not be transferred to another jar (unlike the carp eggs where this is necessary).
The current in the jar should be very gentle as a strong current strips many eggs from the shell.
Although the eggs swell to become very large the hatched larvae are smaller than those of the common carp larvae. The smallest is the just-hatched silver carp larvae. Therefore, the screen fixture of the jar should be 300–500 μ (micron) mesh (for the common carp it is 600–800 microns).
If this requirement is not observed many larvae will escape through the mesh or be fatally injured drifting tail-forward into the holes of the screen.
(a) Egg development
The development of the fertilized Chinese carp eggs is very rapid: 18 h above 26°C, 24 h in 24–25°C. In Perinet hatching occurs 27–28 h after fertilization.
If the hatchery water is polluted it often happens that the delicate shell of the eggs will be attacked by colonies of water bacteria, and the shell loses its rigidity which causes premature hatching and very weak larvae. To avoid this, the eggs can be treated once or twice (according to the degree of bacterial infection) with 10 g tannin in 10 l water solution. The treatment is effected as with malachite green. In Perinet the present water quality is very suitable for hatching purposes and tannin treatment is not required.
When the hatchery water is clean such treatment is unnecessary. Because of the rapid development of the eggs, Saprolegnia fungus has no time to develop on the bad eggs, which - being lighter - accumulate on the surface of the good ones and can be removed by siphoning.
6.10 INDUCED SPAWNING OF THE GRASS CARP
Only the grass carp can effect air induced spawning in a small confinement such as the concrete tank or hapa.
The tank should preferably have a turning-pipe outlet. The fertilized swollen eggs can thus be removed in an appropriate egg collector. Otherwise they would have to be collected from the tank or hapa with a fine mesh scoopnet or with buckets or bowls after the removal of the breeders. The collected eggs are then placed into incubation jars.
The injection technology is the same as for induced ovulation. After the second injection, males and females are put into the same tank or hapa (2 ♀ + 2 ♂) or (1 ♀ + 2 ♂).
The timing can be arranged so that spawning takes place in the early morning.
It is important that floatable objects be placed on the surface of the tank (e.g., hard plastic objects or banana leaves). The fish will spawn readily under these objects because they offer a sense of protection.
6.11 HATCHING AND THE EARLY LARVAL STAGE
The hatching of the larvae of Chinese major carps is very rapid. Most of them hatch within 2–4 h; and all larvae hatch after 6–8 h. (The hatching of one batch of common carp eggs may last 24–30 h.) During hatching, the fine mesh fixture of the jars has to be cleaned very often with a strong feather. The empty shells of the eggs drift to the sieve cloth of the jars and clog the fine mesh screen and the water, and the larvae may overflow from the jar.
The larvae of the Chinese carps are pigmentless, white-yellowish in colour. They are so-called “swimming larvae”. They swim upward and after a certain distance they fall down without movement. This up and down process lasts for about 15–24 h after hatching. The healthy larvae repeat that movement whereas the unhealthy, defective larvae are rolled in clumps with the shells and debris to the bottom of the jar.
When the eggs are incubated in small jars a bigger jar is fixed to the end of the outflow through which it collects all the swimming larvae automatically, separating them from the debris and empty shells.
When the hatching is completed the dead eggs and egg shells and other debris should be removed from the jar without delay. If the removal of the debris is not effected quickly fungus develops on the inert organic matter. Many larvae may become entangled in the cotton-like threads of the fungus during their resting time, and die. To avoid mass mortality of the larvae the removal of the debris is essential. The water flow should be closed for a short period and when the debris settles this is removed by syphoning. Any larvae removed with the debris can be put immediately into the nursery pond.
(a) Larvae rearing
The non-feeding larval stage lasts 3–4 days depending on the temperature. During that time the organs of the larvae - mouth, gills, gut, eyes, fins, etc., - are developing.
From 10 to 20 h after hatching the swimming of the larvae slackens. More and more larvae become motionless and roll in clumps to the bottom of the jar. Formerly when flat-bottomed fine mesh boxes were used for larvae rearing, many larvae died from suffocation when drifted by the current in thick layers in the corners' of the box. This heavy loss can now be totally prevented using rearing jars (i.e., bigger jars with filter fixture).
The gentle rolling of the larvae in clumps does not harm them and provides them with ample oxygen. With this technique mortality is practically nil. Some larvae swim for a short time during that stage, and the larvae mass is never totally resting.
After about 24 h the larvae with developed organs start to swim again, and increasingly in a more “fish-like” manner. During that time they take air into the air bladder in the same way as the common carp larvae, and are now ready to take food (when feeding starts the larvae still have 25–35% of their yolk sack).
(b) The first food of the larvae
The first food of the larvae is the same as for the common carp - rotifers, single-cell animals and nauplius larvae of copepods.
In hatcheries they are fed once or twice with boiled egg yolk sieved through in a fine mesh cloth (to produce a suitable size feed which can be taken by the larvae by mouth and swallowed), or an electric mixer is used to make a fine watery suspension from the boiled egg yolk.
Kai W. Chow suggests a very useful technique to prepare “microcapsulated egg diet” for fish larvae. The preparation is the following: (1) crack the egg into a heat resistant (metal) container; (2) beat the egg vigorously with a fork or paddle to homogenize it; (3) pour rapidly (approximately 150 cc for each egg) boiling water into homogenate constantly stirring until a fine opulescent suspension is obtained; (4) make up to desired volume with cold water; (5) feed by the spoonful or scoopful directly to fish larvae.
This preparation of microcapsulated egg diet proved successful in Perinet.
After feeding with egg the larvae should be placed as soon as possible into the well prepared nursery pond.
6.12 NURSERY PRACTICE FOR THE YOUNG CHINESE CARP
(a) Preparation of the nursery ponds
The preparation of the nursery ponds for the Chinese carp larvae which have just started to feed is the same as for the common carps.
The nursery ponds should be filled and manured, possibly with chicken manure (10–20 kg/are), sheaves of dry land-grass can be fixed around the shore of the nursery pond; 3–4 days are sufficient to develop a rich rotifer plankton and single-cell animals (Paramecium) around and on the grass sheaves. This provides a suitable first food for the larvae and young fry.
The young Chinese carps up to one-month old are zooplankton feeders without exception. To maintain the rich zooplankton in the nursery ponds these should be manured at least twice weekly (5 kg chicken manure or 10 kg cow manure each time).
If vegetation is growing in the nursery pond it must be removed, otherwise the nutrients provided by the manure will be utilized and no phyto-and zooplankton development will occur.
(b) Stocking of the nursery ponds
The stocking rate of the nursery ponds is about 100/m2. Rich nursery ponds can be stocked with 200 larvae/m2.
The nursing of the Chinese major carps up to 20–30 days old should preferably be carried out in monoculture. It is not advisable to mix larvae of different age in the same nursery ponds.
The young Chinese carps reach 2.5–3 cm length (standard length) in 20–30 days and can then be transferred to another pond stocked in polyculture.
After 30 days, the young fingerlings start to feed on phytoplankton (silver carp) and filamentous algae and tender leaves of water weeds (grass carp). The bighead also changes its food, eating bigger phytoplankton and zooplankton.
The young Chinese major carps are hardier than the common carp of the same age and a better survival rate can be expected than for the common carp. However, the cropping of the young fish should be done very carfully because of the oxygen-sensitivity of their skin.
(c) Thinning the stock of young Chinese carps in the nursery ponds
The stocking rate of a well prepared nursery pond is 100–200 larvae/m2. In such density the larvae very soon exploit the natural food. Because of the good survival rate it is necessary to thin out the stock after 10 days (calculated from the time when they take their first food). Thinning of the stock is very easy because young Chinese carps live in the water column and accumulate in schools. A short net (3–4 m long) made of PVC or similar synthetic mosquito net material (mesh 1–1.5 mm) is used to capture the young fish of this age. This net is easily handled by two fishermen. The young fish should be kept in water during handling, and transported in buckets with sufficient water. The captured young fish should be conditioned before transport. They are collected in fine net boxes (made of mosquito net material) and kept there a minimum 4/maximum 24 h.
(d) Nursing Chinese major carp fry in cages
Fixed wall shallow cages 1–4 m2, e.g., like the incubation-cum-hatching cages used in Madagascar for common carp propagation, can be used. The walls and bottom of the cages are 0.8–1 mm mesh sieve cloth.
The cages should be fixed in a well manured pond rich in rotifer plankton the same day the fertilized eggs are obtained. A handfull of chicken manure is dissolved in one bucket of water and the only liquid part spread in the cage the same day. The just-feeding larvae are stocked after feeding them with egg.
About 2 000 larvae are stocked in one m2 cage. The fry are kept here only 10 days when they reach 10–15 mm length after which they can be stocked into a normal rearing pond in polyculture.
(e) Feeding of the silver carp fry
The young silver carp fry is very voracious (as are the other species). They eagerly take the fine milled flour-like food from the water surface. Usually soybean meal, maize meal or rice bran (passed through a fine mesh sieve) is used for feeding Chinese carp fry. In developed countries special feeds are prepared for fry.
6.13 TRANSPORT OF LARVAE, 10-DAY-OLD FRY, AND FINGERLINGS
Transport of Chinese carp is very important because the propagation may occur in only 1 or 2 places in a country. The transport of eggs is possible but very difficult and the technique is now under experimentation.
The 2-day-old larvae, the 10/15-day-old early fry and the 20/30-day-old fingerlings as well can be transported. However, as the Chinese carp become older and bigger, transport becomes increasingly problematic and fewer can be put in a bag or container.
(a) Transport of 2/3-day-old larvae
Transport can be without oxygen or under oxygen pressure. Large numbers of larvae of this age can be moved. For journeys lasting 8–10 h, 2 000–3 000 larvae can be transported in 15–20 l of water without oxygen. The bags should be taken in a jute sack moistened during transport to keep the water temperature low; 8 000–10 000 larvae can be transported in the same water under oxygen pressure.
Three-day-old or older larvae can be transported only under oxygen pressure because if they are prevented from filling their air-bladder, they soon die. Four-day-old larvae need plenty of suitable feed, therefore their transport over a longer period is too risky.
On reaching the destination the larvae should be stocked in a well prepared nursery pond. It is essential that the nursery pond should be without Gambusia, Tilapia or any other fish species which may consume all of the larvae. An alternative is to stock the larvae in screen boxes placed in a pond rich with rotifer fauna (2 000 larvae in one box 1.2 × 1.5 m). In the meantime the nursery should be prepared, and after 4–6 days the larvae transferred there.
(b) Transport of 10/15-day-old fry
The young fry should be collected with a very fine meshnet (1–1.5 mm mesh) without taking them out of water and collected in a bucket. They should be transported in the bucket in enough water to the packing place, and put in fine mesh net boxes with through-flowing clean water for conditioning. Depending on the transport time 3 000–5 000 fish can be put in 20 l water (4–5 h:5 000; 6–8 h:3 000 respectively). They should be transported under oxygen pressure. Here also a moistened jute sack can be used to avoid temperature increasing during transport.
If oxygen is not available they can be transported in plastic bags or containers, but stocking only 200–300 in 10 l water.
(c) Transport of older fingerlings
The transport of older fish is the same as for the common carp. It is very important to condition them for about 24 h in clean water. The gut will be emptied during that time, and the faeces will not spoil the transport water.
When the Chinese carp were transported from Hungary to Madagascar 40–50 small fish (3–4 cm standard length) were put in 3 l water under oxygen pressure. The young fish were conditioned for 6–7 days without food in a container with throughflowing water. The transport lasted 4–5 days and they arrived without mortality.
Fig. 1 Food of the Chinese major carps
(1a) big grass carp eats macrovegetation of the water; (1b) grass carp eats cut grass; (1c) readily consumes soft water weeds; (1d) young grass carp eats filamentous algae; (2a) silver carp filters algae from the water column - it can strain 0.02 mm size algae; (2b) young silver carp (up to 1 month age) is zooplankton feeder (3a) bighead or marble carp filters zooplankton and bigger phytoplankton from the water column - its filter apparatus is not so fine as of the silver carp; (3b) young bighead carp is zooplankton feeder as young silver carp
Fig. 2 Keeping and handling Chinese carp breeders during artificial propagation
mosquito net box or “hapa” convenient for keeping the breeders during artificial propagation treatments:
in one “hapa” (2 × 1 × 1 m) 2–3 breeders can be placed.
it is easy to take the breeders out of the “hapa” for manipulation - the opening end of the “hapa” is raised near the water surface in such a way that the breeders cannot jump out or struggle
this “hapa” is fixed in a pond with poles and:
Fig. 3 Changes in hour-grades according to water temperature by Chinese major carps (Horvath, 1978)
Fig. 4 Stripping and handling of the sexual products of Chinese major carps
(a) the right position to take out breeders from the water, the thumb of the manipulator is pressed on the sexual opening; (b) stripping the female on table, the head and tail covered with towel; (c) tranquillized breeders can be stripped by one man; (d) the eggs should be weighed; (e) the tranquillized male's sperm can be stripped directly over the egg mass; (f) the eggs and milt have to be mixed thoroughly without delay; (g) fertilization process: small quantity of clean water is added to the sexual products and stirred with feather for about 2 min; (h) more water is added and the eggs are stirred about 3–4 min long; (i) the already fertilized eggs are poured into a bucket of water; (j) the egg mass is washed 3–4 times with clean pond water.
Fig. 5 Incubation of the Chinese carp eggs
After washing, the egg mass is placed without delay into the incubation jars; (a) in a 50-l jar 100–150 g eggs; (b) in 200-l jars 300–350 g eggs; (c) if the incubation water is polluted by organic matter and bacteria attack the egg cells tannin solution is used to prevent premature hatching (10 g tannin in 10 l of water, of which 0.5 l is used for the 50-l jar and 1.5 l for the 200-l jar); (d) when many dead (white) eggs accumulate on the surface of the egg mass these should be removed by careful syphoning
Fig. 6.1 Tranquillizing the Chinese carps with Chinaldin
(a) measure the dose exactly using measuring cylinder or syringe, or vials of determined volume (1:100 000 for silver carp, 1:60 000 for grass and bighead carp) (1 cc in 100 l or 1 cc in 60 l water respectively); (b) pour the Chinaldin by continuous stirring in a bucket of water; (c) close up partly the inflow water; (d) pour the Chinaldin dispersion over the top of the “hapa”; (é) poúr 3–4 buckets of water over the “hapa” to disperse Chinaldin; (f) after 4–5 min the breeders are tranquil and mostly belly-up position and the stripping can start without delay
Fig. 6.2 Development of silver carp egg
(a) unswollen egg; (b) swollen egg; (c) cell division; (d) morula stage; (e) gastrula stage; (f) closing up the blastopore; (g)-(j) embryo development; (j) larva ready to hatch
Fig. 6.3 After hatching
Fig. 6.4 How to prepare microcapsulated egg diet for fish larva (K.W. Chow, 1980)
(a) crack the egg into heat resistant container; (b) beat vigorously with fork or paddle (homogenizing); (c) boil for each egg 150 cc water; (d) pour rapidly boiling water into homogenate with constant stirring; (e) make up to desired volume with cold water; (f) feed the opulescent suspension by spoonful directly to fish larvae
7.1 Hatching of Chinese carp eggs
(a) during hatching the screen inlay of the jar has to be often cleaned otherwise the empty shells clog the screen and the water may overflow: (b) when the hatching is finished the debris should be removed by syphoning; (c) the appropriate mesh size of the screen inlay in jars for Chinese carp
7.2 How to make satchel for short transport of breeders in water
(a) acquire sufficient waterproof sheeting to make a 60 × 40 × 15 cm satchel; (b) fold the sheet and fix the pleats in direction of arrows; (c) stitch the pleats to the side of the satchel and place the handle; (d) fix satchel with bamboo stick (d1) under the pleats to keep mouth of the satchel rigid
Fig. 8.1 Timetable for artificial propagation of silver carp (grass carp)
Thick arrows show the exact time of the activities
1. capturing and selecting the ready to propagate breeders; 2. first injection for the females (0.5 mg/kg); 3. injection of the males (2 mg/kg); 4. second injection of the females (4.5 mg/kg); 5. stripping of the ripe sexual products (eggs and milt); 6. placing the fertilized eggs into jars; 7. preparation (filling up and manuring) the nursery ponds; 8. matching of the larvae (27–30 h after fertilization); 9. the screens of the jars have to be cleaned very often to prevent clogging and overflow; 10. after hatching the debris should be removed from the jars; 11. the swimming larvae can be transported without oxygen pressure; 12. the swimming larvae can be transported only under oxygen pressure before taking air; 13. larva filling up air-bladder; 14. feeding the larvae with boiled egg yolk or microcapsulated egg diet; 15. stocking the larvae into the prepared nursery pond, 100–200/m2
Fig. 8.2 How to distinguish young silver carp and bighead carp
