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5. CHINESE CARP FRY PRODUCTION

Up until the early sixties, traditional Chinese fish culture depended totally on larvae and wild fry fished in the rivers. Not only did the numbers and species harvested vary from season to season, but the retail price for fry was relatively high. In addition, large-scale river management schemes (hydro-electric dams, flow control, irrigation) carried out after the Liberation quickly resulted in a serious reduction in the number of juveniles in rivers. The need to begin controlled spawning of reared fish became increasingly urgent and research on the subject was intensified. The first experiments conducted in 1956 on the use of pituitary hormones to control pond spawning of the silver and bighead carps were unsuccessful. Two years later, however, Professor Zhong Lin (Guangzhou, Guangdong) succeeded for the first time in obtaining the artificial spawning of these two species, hatching of 10 million eggs and producing 500 000 fry. This method was initially based on artificial fertilization of ovules obtained from mature females. It was improved in 1964 by the success of induced spawning followed by natural fertilization in fry ponds and this is the most widespread method used.

This new technology, which was quickly adapted for the induced spawning of all Chinese carps and for large-scale hatchery production of their fry, was then actively disseminated in the provinces. It was popularized even at fish farm level and soon became an integral part of the fish culture system.

Over 40 000 million fry are produced annually today, more than 95 percent of these in hatcheries (Anon., 1980). This has allowed fish culture to develop without being dependent upon the capture of larvae and wild fry. In some regions, however (e.g., middle and lower Chang Jiang and the western arm of the lower Xi Jiang), use is still made of this source of fry for stocking as a supplement to hatchery production. In 1979, in the district of Xishui (Hubei), for example, close to 100 million wild fry fished in the Chang Jiang were stocked in ponds, while 200 million fry were produced in hatcheries.

The study group had the opportunity of visiting several hatcheries and fry-rearing centres (Table 17), where the data given below were obtained.

Diagramatically, we can sub-divide the production cycle of stocking fry into three successive stages: production of larvae, production of small fry of 2–3 cm in length (nursery fry) and the production of fry of between 12 cm and 20 cm in length, for stocking (fingerling). Depending on the importance of fry as a source of income (Table 17), fry ponds usually cover 10–25 percent of the total area used for fish culture, although in some cases this percentage can reach 55 percent. The Hele people's commune (Jiangsu) was however advised to use 30 percent of their total area for fry production on a priority basis (with food-fish production taking second place), and 70 percent for the latter (with fry production taking second place), so as to utilize the water surfaces in the best possible way. When fingerlings are reared in ponds, this utilizes up to 90 percent of the fry and fingerling rearing area (Table 17). However, when fry alone are reared, up to 74 percent of the total area is used for the purpose. Fingerling rearing may be done in floating cages (Section 5.4) and in fish pens (Section 5.5).

5.1 Production of Chinese Carp Larvae 1

The first stage in the production cycle of stocking fry consists of:

  1. stocking and preparation of the brood fish
  2. spawning of the brood fish
  3. incubation and hatching of the eggs

5.1.1 Rearing brood fish

Chinese carp brood fish are either reared in ponds or caught in lakes, reservoirs or rivers.

1 Subject treated in detail by Pagán-Font and Zinet (1980)

Table 17

Features of the fry and fingerling-rearing centres visited

ProvinceGuangdongHubei
Fry-rearing centrea  1    2  34
Staff    8127 
Area (A), ha 10  22.5     23.331.6
-Incubation% A-    0.05--
-Nursery ponds    9.1  74.0-8.1
-Fingerling ponds 90.1--91.9
-Fingerling ponds A9---
-Fingerling ponds B 27---
-Fingerling ponds C 54---
-Brood fish-  19.6--
-Spawners-    0.1--
Area, % A of total    23.1100 13.6
Number of ponds (fry rearing) 45  80+38 
Production (P), fry/year140 million394 million51 million 
-8 day-old larvae  360 million
-Fry (3 cm)    34 million50 million 
-Fingerling (15–20 cm)  -  1 million
-Silver carp% P      2.9  14important
-Grass carp    12.9  18fairly important
-Bighead carp      5.7   7important
-Mud carp   71.4  61-
-Miscellaneous    7.1-fairly important
Cost of fry stocking, Y/10 000   500–600

a 1. Leliu People's Commune, Production Brigade
2. Xinhui district, Hengjiang fry-rearing centre
3. Baitanhu State Farm, district of Huanggang
4. ‘October’, Production Brigade, district of Xishui

At the Hengjiang fry-rearing centre (district of Xinhui, Guangdong), which is one of 17 hatcheries in the district, the 17 brood fish ponds cover a water surface of 4.40 ha, i.e., 19.6 percent of the total water surface of the centre. Their average surface area is 2 600 m2, and they usually vary between 1.5 m and 2 m in depth, except in the case of mud carps, which require warmer water (depth 2–3 m and protection against cold winds). Sexes are mixed (F/M ration = 1:1 or 2:3) and each brood fish is used 2–3 times per year for 6–7 years.

Each pond is stocked with a majority of one type of carp and two or three other species. In 1 ha there may be a main stock of 150–225 grass carps (i.e., 1 000–1 250 kg) or 100–150 silver carps (750–1 000 kg), or 75–100 bighead carps (750–1 000 kg), with two or three different species bringing the total to 1 500–2 250 kg.

The stocking rate for the mud carp is high and can reach 2 250–3 000 specimens/ha, i.e., 2 250–3 000 kg/ha.

When the temperature of the water exceeds 15°C, artificial feeding is considered very important. It consists of rice bran and maize chips (daily ration 1–2 percent of the ichthyomass), as well as fodder (grass carps). Regular organic fertilizing keeps the pond adequately supplied with plankton.

It is also important to maintain a good circulation of water in the pond, to renew the latter frequently and to make sure that the quality and level is adequate.

5.1.2 Selection and preparation of brood fish

For spawning purposes, brood fish are not only chosen for their individual state of health and maturity, but also in accordance with the more general criteria given below:

CarpMinimum age of femalesaIndividual weight
Bighead4 years7–12 kg
Grass5 years8–12 kg
Silver3 years3–6 kg
Black-more than 10 kg
Mud3 years0.8–1.4 kg

a Age of males: generally a year younger than the females

Spawning time for Chinese carps depends mainly on the temperature of the water: optimum 25°C, minimum 20°C, maximum 31°C. At the Hengjiang fry-rearing centre (Guangdong), the spawning season extends on average from the end of March to the end of September and reaches its maximum yearly intensity in April and May.

Preparation for spawning of selected brood fish consists of:

  1. conditioning them to future manipulation, by successively catching them and setting them free, and
  2. injecting a dose of hormone to stimulate final maturing.

The most currently used agents are fish gonadotrophin (extracted from the pituitary gland of the common carp, silver carp or bighead carp), human chorionic gonadotropin (HCG) and synthetic LH-RV analogous hormones. Pituitary collection from fish weighing more than 0.6 kg is done in the centres where food-fish are bought and sold (price: Y 0.05/pituitary in the district of Xinhui, Guangdong). They are treated and then preserved either in alcohol or dry, until they are used. The pituitary extract is prepared by grinding the gland in a normal saline solution (7.8 gm NaCl/litre). A brood fish usually requires 5–10 ml of solution, depending on its live weight (Figure 12). A few examples of different types of injections were cited; the dosages are given per kilogram of female brood fish:

  1. grass, silver, bighead carps: 4 mg of dehydrated common carp pituitary (HDCC);
  2. bighead and silver carps: 1 100 international units HCG;
  3. mud carps: 3.5 mg HDCC, and
  4. grass carps: 0.01 mg LRH-A

At the Hengjiang fry-rearing centre (Guangdong), preparation of mud carp brood fish was demonstrated. After the brood fish had been chosen (maturity, health, sex ratio 1:1), a first injection is given to the females and the brood fish are stored in a net in a transit pond. Eight hours later, a second injection is given to the females and the first to the males. The brood fish prepared in this way are then placed in the spawning pond (Figure 13).

Figure 11

Figure 11 A silver carp brood fish is selected from the storage pond and placed in a canvas bag in which it will be transferred to the spawning pond (Photo F. Botts)

Figure 12Figure 13
Figure 12The brood fish is weighed to determine the dose of hormone necessary for it to reach final maturity (Photo F. Botts)Figure 13Spawning pond and round incubation ponds (background), comprising an automatic transfer system for eggs. API, Zhu Jiang, Guangzhou, Guangdong (Photo F. Botts)

5.1.3 Spawning of the brood fish

Until 1963, fertilized eggs were produced only by means of artificial fertilization of ova extracted manually by stripping the females (Figures 14 and 15). This method is still used, e.g., at the hatchery of Baitan Hu State Farm. Since 1964, however, natural fertilization in spawning ponds is preferred (Figure 13).

This method was demonstrated at the Hengjiang fry-rearing centre (Guangdong) with the mud carp. The spawning pond was an oval-shaped cement pond which contained 69 m3 of water and 230 brood fish of both sexes. Approximately 6 h after the second injection, the females spawn (preferably at dawn) and the ova are fertilized simultaneously by the males present. Approximately 30 min after egg-laying, the eggs (pelagic) were collected in a fine-meshed dragnet (Figure 16), while the brood fish were removed and transferred to their stocking pond. The quantity of swollen eggs collected amounted to 32.9-litre buckets, i.e., 288 litres of eggs. For the mud carp, the number of swollen eggs per litre is on average 63 000. More than 18 million eggs were therefore collected.

In other hatcheries, transfer of fertilized eggs can be carried out automatically from the spawning pond to the incubation pond by means of a system of valves and pipes, either before or after swelling (Figure 13).

Chinese carps show a relatively high rate of fertility (Table 18). The average is approximately 50 000 ovules/kg of female, except for the mud carp (100 000/kg) and the black carp (25 000–30 000/kg). Fertilization rate is generally in the region of 80 percent.

Figure 14

Figure 14 Stripping a mature female in order to carry out artificial fertilization (Photo F. Botts)

Figure 15

Figure 15 Milt is taken from the male with a syringe and is then used for artificial fertilization of female ova (Photo F. Botts)

Figure 16

Figure 16 Collecting eggs after spawning and fertilization in the spawning pond. Hengjiang fry-rearing centre, Guangdong

Table 18

Potential and actual fertility of Chinese carps
(Adapted from Anon., 1980, page 22)

SpeciesOvocytes average No./kgGonadosomatic ratioa (%)Ovules obtained with artificial propagationSize of eggs before swelling
Average No./kgMaximum No./kgNo./gNo./ml
Grass carp120 00017.147 700103 000700–750650–700
Bighead carp124 00017.858 800  77 600650–700600–650
Silver carp141 00020.151 800  75 400700–750650–700
Mud carp240 00016.0100 000+ 1 500 
Black carp  65 00010.825 000–30 000   

a GSP = (weight of ovaries × 100): body weight

5.1.4 Incubation and hatching of fertilized eggs

Incubation of the eggs takes place either in round cement ponds (Figures 13, 17 and 21), or in jars (Figures 18 and 19), provided with a flow of water which allows them to remain in suspension. The period of incubation varies depending mainly on the temperature of the water. A relatively high temperature speeds up the development of the embryo. The silver carp would require 61 h incubation at 18°C, 35 h at 22°C and 18 h at 28°C. The temperature of the water must be relatively stable and between 18°C and 31°C. Optimum temperature for Chinese carps in general is between 22°C and 28°C.

At Hengjiang (Figure 17), the study group was able to observe egg incubation in a round pond (diameter 2.90 m; depth of water 0.8 m; volume 4.6 m3), in which there was a flow of 3 rpm. This type of incubator, which is built of bricks, stone and cement, allows 700 000–800 000 eggs/m3 to develop. The average hatching rate is 80 percent.

At the Baitan Hu State Farm hatchery on the other hand, incubation may also be carried out in clay jars. The capacity of each jar is 150 litres and they contain 150 000–200 000 eggs, which are kept in movement by means of a vertical flow. A strainer fixed to the upper part prevents the eggs from being carried away. This method is used for larvae production on a smaller scale. The ‘October’ Production Brigade (district of Xishui, Hubei) has this type of hatchery (15 jars, 200 litres each) and produces 8 million larvae per year in this way (Figure 18).

After hatching, the larvae are usually kept in the incubator until their sac has been formed and even until their yolk sacs have been resorbed. They then swim freely and are collected and transferred to the nursery ponds. At 26°C, for the grass carp, this period may last 110 h, i.e., 4–5 days.

However, when the larvae are to be sold outside the farm, as happens at the Hengjiang fry-rearing centre (Guangdong), the larvae may be kept for several days in a net cage hung in the pond (Figure 20), in which some natural food is available. Eight-day old fry (6+ mm) are produced in this way and distributed (Section 13.1.1).

5.2 Nursery Rearing of Chinese Carps 1

Nursery rearing consists of producing fry 2–3 cm in length (average 0.5 g), from larvae a few days old. Monoculture in small ponds of approximately 200 m2 and with a water depth of 1–1.5 m2 is used.

1 Subject dealt with in detail - Pagán-Font and Zinet (1980)
2 See also multigrade farming method

Figure 17

Figure 17 Round ponds for incubation and hatching of eggs. Hengjiang fry-rearing centre, Guangdong

Figure 18Figure 18

Figure 18 Rustic hatchery with terracotta incubation jars. Details of the upper strainer and water supply. ‘October’ Production Brigade. District of Xishui, Hubei

Figure 19

Figure 19 Cement incubation jar. Capacity 500 litres and 800 000–1 million eggs. Fish Culture Centre of the district of Qingpu, Shanghai

Figure 20

Figure 20 Cage for stocking young fry prior to transport. Hengjiang fry-rearing centre, Guangdong

Figure 21

Figure 21 Examining eggs which are being incubated in a two-compartment round pond (Photo F. Botts)

Prior to stocking, the pond is cleaned, disinfected (Section 6.6.4) and fertilized. Fertilization is considered very important for the future success of the rearing operation. It combines an application of ‘tatsao’ (a mixture of several tender and easily decayed herbaceous plants), compost (1:1 mixture of vegetable matter and organic fertilizer with 1 percent quicklime, used after decay), and mineral fertilizer (ammonium sulphate or urea and calcium super-phosphate). The purpose of fertilizing is to promote adequate development of the planktonic organisms preferred by the young fry of the Chinese carp species, reared in ponds. Indeed, this feed preference varies depending on the species and changes gradually during the nursery stage (Table 6).

The colour of the water indicates the degree of fertility of the pond. It must preferably be a brownish-green to greenish brown. Young bighead carps are also used for this purpose (2 250–3 000 specimens, 20 cm long/ha). Fertilization is adequate when the carps do not surface too often early in the morning. These bighead carps also feed on macrozooplankton (e.g., cladocera), which are not favourable to the growth of the young fry. They are removed from the pond before stocking of nursery fry takes place.

The stocking rate of a nursery fry pond depends on its fertility, depth and local climatic conditions, feeding, etc. Generally speaking, the rate for grass carps, bighead and silver carps is 150–225 fry/m2, and for mud carps, 450–600 fry/m2.

Feeding during rearing varies according to the species and the region. It may be based on regular applications of tatsao, with or without supplementary feeding. This may consist of groundnut cakes, maize flour or rice bran (Guangdong) and a soya cake or coconut based paste. The daily ration varies between 1 and 4 percent of the biomass present.

During the nursery stage, average fry growth is between 0.01 and 0.02 g/day. It varies according to age and species. For fry under 6–8 days old, the daily rate of growth is highest for the grass carp. It is slightly less for the bighead and silver carps. However, over the age of 6–8 days, the species are classified from this point of view in reverse order (silver carp > bighead carp > grass carp) until the age of about 30 days.

The fry reach 2–3 cm in less than a month. At the Leliu People's Commune, nursery rearing takes 25–30 days; at the Baitan Hu State Farm, only 15 days are required (feeding with soy bean milk), and in the Shanghai area, it is 20–25 days. Mortality reaches 20–40 percent during this period. It is relatively lower for the grass carp.

Prior to the young fry being transferred to other ponds, they are strengthened physically. This is done by raising the net two or three times and by getting them used to high densities in cage nets (Figures 22 and 23). Finally, they are collected, sorted according to size and stocked to await their transfer (Figures 24, 25 and 26).

5.3 Fingerling-Rearing in Ponds 1

This consists of producing stocking fry which will become food-fish. The young 2–3 cm-long fry grow to a size of between 12 and 30 cm, except for the mud carp (6–8 cm)2. This second stage of the rearing process varies from region to region, depending on the final size to be reached. At the Leliu People's Commune (Guangdong), it is broken down into three distinct periods:

However, at the Baitan Hu State Farm (Hubei), 16 cm-long fingerlings are produced in 150 days.

1 See Pagán-Font and Zinet (1980)
2 Also see the multigrade rearing method (Section 6.1.4)

Figure 22

Figure 22 Catching and holding pen placed in fry-rearing pond (Photo F. Botts)

Figure 23

Figure 23 The fry are gathered in the holding pen with a seine net. They are ‘trained’ either before being transferred at the end of the first rearing stage, or monthly during the second stage (Photo F. Botts)

Figure 24

Figure 24 The fry are sorted according to size, by using bamboo woven baskets (Photo F. Botts)

Figure 25

Figure 25 When they have been sorted and counted, the fry are transferred to the fingerling ponds (Photo F. Botts)

Figure 26

Figure 26 Fry being tipped into the fingerling pond (Photo F. Botts)

Fingerling ponds resemble fry ponds. After draining, the latter are often used to produce fingerlings. Before being stocked, the ponds selected are cleaned, disinfected and fertilized as are nursery ponds (Section 5.2).

Either the monoculture system or polyculture of two or three species may be used. Monoculture is usually preferred to produce 6 cm fry. Over and above that size, however, higher stocking rates and shorter rearing periods are possible with monoculture. It is therefore preferred to polyculture if the rate of utilization of the available ponds has to be increased, i.e., to meet increased demand for stocking fry. With polyculture, on the other hand, more complete use is made of natural food. Since it is a longer process, it can also be used to retard production of large fingerling until the suitable season (i.e., until the following spring for fingerling stocked after July). Depending on the circumstances, a combination of both types of culture is successfully practised in fish farms in China.

Stocking rates vary considerably for similar reasons. By way of example, Tables 19 and 20 show some possibilities using monoculture and polyculture, respectively (Anon., 1980). As regards polyculture, the different species (maximum three) are chosen on the basis of their dietary requirements (Table 6). The grass carp can be reared in combination with either silver, bighead or mud carps or with bighead and mud carps, because their diets complement each other. Bighead and silver carps are not often reared together, because there would be a certain degree of competition for the natural food in the pond.

During rearing, there must be regular distributions of supplementary feed. Depending on local conditions, this may include aquatic plants (e.g., Wolffia sp., Lemna minor, Vallisneria sp., Hydrilla sp., Potamogeton sp.), and young land plants (for grass carps), as well as the by-products of plant crops (e.g., cakes and various brans, wine, sugar and soya dregs) and animals (e.g., silkworm pupae, molluscs, mussels, fish meal). A high density of planktonic organisms is maintained by means of regular applications of organic fertilizer (e.g., tatsao and compost). Daily feed rations vary in accordance with the temperature of the water. They are larger with optimum temperatures (25°–32°C) and proportionally smaller when conditions are not as good (cooler temperatures, dissolved oxygen deficiency).

During rearing, management tasks consist of supervising the ponds and the quality of water, feeding and fertilizing, sterilizing the troughs, disease prevention/treatment and predator control. In addition, every month, the fry are gathered in a seine net. This strengthens them physically and at the same time, they are sorted and the weaker among them transferred to another pond (Figures 22 to 26). Special attention is paid to the wintering of mud carps, which are more vulnerable to low temperatures.

Table 19

Monocultural fingerling-rearing in ponds, Guangdong province
(Adapted from Anon., 1980, page 63)

Species of Chinese carpStockingDuration of rearing process daysSize at harvesting (cm)
Size (cm)Rate individual/m2
Grass3.030  204.8
4.8206.0
4.87.5–9.0120–150
(Sept.-Jan.)
9–12
Silver3.030  20–506–9.5
6–9.51.2–1.530–4012–20
3.045  120–180
(July-Nov. or Jan.)
8–8.5
Bighead3  22–30306
6  6–93012
3  24  120–180
(July-Nov. or Jan.)
9
Mud3.041  305.8
5.813.5507.5
3.067.5260–280
(July-April)
7–7.5
3.0180      280–300
(May-March)
4–6

The mortality rate in fingerling ponds is fairly high, although it declines as the fingerlings grow. For the grass carp, it may be 20% (3–4.8 cm), 15–20% (4.8–8 cm) and 10% (8–16 cm), i.e., a total mortality of 45–50% (3–16 cm). It may even be slightly higher when the young fry have to winter through to spring stocking.

Rate of growth varies depending on the species considered. Average rates are as follows (in g/day): bighead carp 6.3; grass carp 6.2; silver carp 4.2; mud carp 0.1 (Anon., 1980).

An original method for producing bighead and silver carp stocking fry was developed at the Baitan Hu State Farm (Hubei). Every year before May, a long-stemmed, early variety of rice is planted out in the ponds, which will be used for raising fingerlings of these two species (Figure 27). Around 10 July, the rice is about 1 m high and the grains, which are well formed, still have a milky consistency. The wild fish are got rid of with insecticide and the rice is immersed. The pond is fertilized and stocked with fry of an average length of 6 cm. Until 15 September, these fry feed on plankton and grains of rice and some supplementary feed is distributed until harvest time. This takes place in mid-November, after approximately four months of rearing and when the fingerling have reached 17 cm. This method results in a saving of 200 kg of soy bean cake per 10 000 fry, the cost price of which is thus cut by almost 50%. The only danger lies in a possible dissolved oxygen deficiency caused by rotting rice culms. A close watch must therefore be kept on the water of the ponds and if necessary, paddle aerators must be used during critical periods.

Table 20

Fingerling-rearing by polyculture in ponds, Guangdong province
(Adapted from Anon., 1980, page 64)

Species of Chinese carpStockingDuration of rearing process (days)Size at harvesting (cm)
Size (cm)Rate individual/m2
Grass8.04.5190–210
(early July to Jan.)
12–16
Bighead4.522.5   7.8–8.5
Grass8.05.4175–195
(mid July to Jan.)
12–16
Bighead4.53    14–20
Grass6  7.5190–210
(early July to Jan.)
9–12
Silver5  37.5   8–9
Grass8  5.4175–195
(mid July to Jan.)
16–20
Silver5  4.5 20
Grass4.84.5250–270
(early July to March)
9–10
Mud3.0105–150 3.9–5.8

Figure 27

Figure 27 Intermediate rice cultivation on the bed of the fingerling pond. Baitan Hu State Farm (Hubei)

5.4 Fingerling-Rearing in Floating Cages

The study group had the opportunity of observing stocking fry production in floating cages placed either in reservoirs (Bailianhe, Hubei and Qingshan, Zhejiang - Table 35), or in the navigable channels of the Shaoxing district, Zhejiang. The three methods are compared in Table 21 which gives the main features of each.

In the reservoirs (Figure 28), stocking fry are produced either for other floating cages (10–13 cm, 20–25 g), or for extensive fish culture in the reservoir itself (200 g). The fry produced in the channels are also relatively large (150 g) and are used for stocking the sections of the navigable channels that have been prepared for the purpose (Section 8.2). This system which was successfully experimented in 1978 (10 cages, i.e., 660 m2) and in 1979 (222 cages, i.e., 14 652 m2), was to reach pilot scale in 1980 with the use of higher stocking rates.

5.5 Fingerling-Rearing in Pens

Fry for stocking the Qingshan Reservoir (Zhejiang) are produced in a fish pen (Figure 30). This consists of a bay of approximately 1.6 ha, closed by a net barrier. The lower part of the net is held against the bottom by means of a chain and blocks of concrete. The upper part is attached to floating pontoons and emerges from the water to a height of 0.8 m. This net has a 7.5 mm mesh. The depth of the water varies with the season and can reach a maximum of 6 m.

In spring each year, the pen is stocked with bighead and silver carp fingerlings of an average size of 13 cm/20–25 g, at a rate of 150 000–225 000/ha. After 250 days of rearing, including a winter season, the pen contains a per hectare average of 125 000–190 000 fingerlings, each weighing 200–250 g. The barrier is then opened and these fish escape to the reservoir itself.

Management in this case consists of maintaining the barrier (adjusting height, cleaning the first metre under water once a week), organic fertilization and supplementary feeding (rice bran and soy bean cake).

Starting with a stock of 3 750 kg/ha, the yield was 35 500 kg/ha, which represents a production of approximately 31 800 kg/ha. This is a very productive method which deserves to be more widely used.

Figure 28

Figure 28 Series of floating cages for the production of stocking fry. Qingshan Reservoir, Zhejiang

Table 21

Some examples of polyculture-rearing of fingerlings in floating cages

PlaceBailianhe Reservoir, HubeiQingshan Hangzhou Reservoir, ZhejiangNavigable channels; district of Shaoxing, Zhejiang
1.Rearing cages-floating cages-floating cages-fixed cages
  -28–32 m2 x 2 m = 56–64 m3-100–169 m2 x 2 m = 200–338 m3-66 m2 x 2 m = 132 m3
2.Stocking       
 Size/unit weight3 cm/0.5 g10–13 cm/20–25 g10–15 cm/15 g
 Density, indiv./m2300–45012025–40
 Rate, kg/m30.075–0.1151.50.18–0.30
 Species used for polyculturesilver carp85%silver carpsilver carp70%
 bighead carp10%bighead carpbighead carp  5%
 grass and black carp  4%grass carp (few)grass carp10%
 Wuchang bream  1% Wuchang bream15%
3.Feedingnaturalnatural (+ supplement if plankton insufficient)wine dregs, cakes, soy beans, rice bran 
4.Mortality25–35% (escape, injuries)10% for silver and bighead carps; 30–40% for grass carpmaximum 20% for silver and bighead carps; enteritis in the grass carp
5.Rearing time2 monthsabout 8 months7–8 months
6.Yield   
 Size/unit weight13 cm/25 g25 cm/200 g25 cm/200 g 
 Density, indiv./m2225–30090–10020–35 
 Rate, kg/m32.8–3.89–102.0–3.5
7.Production   
 Total kg/m32.7–3.77.5–8.51.8–3.2
 Monthly average kg/m31.35–1.850.94–1.060.26–0.46

Figure 29

Figure 29 Series of fixed cages for the production of stocking fry. Navigable channels of the Shaoxing district, Zhejiang

Figure 30

Figure 30 Fingerling-rearing in pens, in a bay of the Qingshan Reservoir, Zhejiang. View of the bay and the fence


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