5.1 Artificial propagation
5.2 Rearing of fry and fingerlings
5.3 Rearing of fish to marketable size in ponds
5.4 Fish diseases and their control
5.5 Design of fish farms and its significance in management
5.6 Economics of pond culture
Although the basic fish-culture technology of China is largely based on traditional practices, a number of new innovations and improvements have been adopted. A major breakthrough in modern times is the artificial propagation of the major cultivated species of carp by the administration of hormones in 1958. Although this technique was also independently developed in India at about the same time, it is only in China that it has been possible to bring it down to the farm level on a country-wide basis and make it a common farm practice. Traditional Chinese fish culture was based on larvae and fry collected from the rivers. Hydro-electric and flood control projects implemented after liberation resulted in a drastic reduction in the availability of fry in rivers and hatchery production became a necessity. This, and effective extension work through the "three-in-one" (farmer-technician-party cadre) combination appears to have helped in the farm-level application of artificial propagation.
The method of induced breeding and hatchery and larval rearing techniques adopted in China has been described in the report of the FAO Fisheries (Aquaculture) Mission to China (FAO Fisheries Technical Paper No. 168). The study group observed some variations and improvements in the technique. The strong point of the Chinese method of induced breeding would appear to be the selection and rearing of brood fish, which do not receive the same amount of attention in other countries. In general, female silver carp and mud carp over three years old, four-year-old big head and five-year-old grass carp, are selected for breeding. Males can be about one year younger than the females. They are reared in special brood ponds, stocked at low densities of 100-150 kg/mu. They are fed at the rate of about 1-2 percent of the total body weight with wheat shoots, grain, corn or meal cake. Water quality is maintained in the ponds by periodic changes of water, at the beginning once or twice a month, but increasing to three to four times a month about a month or two before spawning. Spawned fish receive special care and are reared separately. The group saw brood fish that had been used for breeding for over 12 years. Normally five- to fifteen-year-old fish are used for breeding. It was reported that fish which have been bred a few times are more responsive to hormone administration and can be bred even by the administration of human chorionic gonadotropin (HCG) only, except for mud carp for which it is generally ineffective and for grass carp for which it is only feebly effective. The most commonly used pituitary extract is of the common carp, but the silver carp, big head and grass carp pituitaries are also used. The HCG used is the product marketed as "gonadotropin for animals".
Fig. 2 Injection of HCG to spawn a seven-year-old brood fish
A new development in induced breeding in China is the use of the LH-RH analogue as an ovulating agent. In combination with a small dose of pituitary extract, it has been found to be very effective on all species of carp, the dose required being 1-10 mg/kg of body weight, depending on the species. Its use is still not very common in China, but the group observed the breeding of all the species of Chinese carp by the administration of ampouled LRH-A and common carp pituitary extract. It was reported that the same fish can be bred twice, or, if weather conditions are favourable, even three times during a season, at intervals of 20-30 days.
The spawning and hatchery system is simple and fairly easy to maintain, but it has the disadvantage that the monitoring of fertilization, hatching, and dead and diseased eggs, is difficult. This may account for the low rate of fertilization (60-80 percent) and hatching (40-70 percent) reported from some of the centres. It will be useful to make a comparative study of this system of breeding and larval rearing with other commonly used hatchery systems and with a system based on the Chinese design but built above ground level with fibreglass or similar material which will facilitate close monitoring.
Fig. 3 Spawning and hatching pools in the Nanhai County Fish Hatchery, Guangdong Province
Fig. 6 A simpler type of hatchery used in Shi Yeh Brigade in Hubei Province
The estimated production of fry in China is over 20 thousand million.1/ Although there are some large state-owned hatcheries like the Nanhai County Fish Hatchery (in Guangdong Province) and Paitan Lake Hatchery (in Hubei Province) with a capacity of over 600 million fry per year, most of the seed production is done in individual communes and production brigades. The large central hatcheries like the one in Nanhai transport hatchlings by train or truck to different parts of the country in plastic bags filled with oxygen. Five or six-day-old larvae are sold from the Nanhai Hatchery at Yuan 3 per 10 000 and 2-3 cm fry at Yuan 19 per 10 000, plus transport charges. A critical study of the cost-efficiency of centralized hatchery operations as against farm-level seed production, has not yet been made, even though the opinion has been expressed that the former is much more economical and efficient.
1/ Although most of it is produced in hatcheries, it was learnt during a later visit by the group leader, that some quantities are collected from the rivers. Brood fish raised from larvae or fry collected from the rivers help to reduce the genetic effects of in-breeding
Monoculture is usually practised for rearing fry to fingerlings. The fry are left in the hatchery tanks for three to five days before being transported to nursery ponds of 2-3 mu. The ponds are cleared to eliminate predators and treated to control infections. They are also fertilized a few days prior to stocking, with organic manures such as "tatsao" which is a traditional Chinese combination of different kinds of herbaceous plants, with soya-bean meal or soya-bean curd, and/or rice bran or peanut cake powder. The manures stimulate the growth of planktonic organisms upon which the young fry and fingerlings will feed. The stocking density varies from one farm to another, but, in all, the practice is to have a high density at the beginning to be reduced after a few days. For example, at the Ching Po County Fish Farm, a density of 100 000/mu is maintained for one week, which is reduced to 10 000/mu for the following four weeks or until the fry reach the size for transplanting to fingerling ponds. However, at the Paitan Lake State Fish Farm, the initial stocking density of hatchlings is 70 000-80 000/mu which is reduced after ten days to 5 000/mu.
The survival rate in the stage between fry and fingerling is not very high in some of the Chinese fish farms and even the Lin Fu state-owned fish farm and hatchery, with fairly good facilities compared to commune farms, has only 30-40 percent survival rates. Hatching rates are high, reaching 80 percent, and 90 percent in many state-owned farms. However, at the Guangzhou Provincial Research Institute of Aquatic Products and Fish Breeding Farm, because of the use of poor quality river water, very low hatching rates (30-40 percent) were reported. Application of manure is carefully controlled so as not to over-fertilize as this leads to depletion of dissolved oxygen which can kill off all the fry. "Tatsao" is applied within two to three weeks of stocking of the fry of silver carp and big head at 1 300 kg/mu in ponds stocked at 10 000/mu. If the fry are weak then peanut cake is given at the rate of 0.3-1.2 kg/10 000 fry/mu, in two or four equal parts two to four times per day. For mud carp and grass carp fry less fertilization is required and 150-200 kg/mu of "tatsao" is applied every three days, together with 1.5-2.5 kg/10 000 fry/mu daily of peanut cake or rice bran. Usually the fry will grow rapidly under this management and attain fingerling size within three to four weeks.
Fingerlings may be raised in the same fry ponds but the ponds have to be cleaned out and limed to get rid of pests and prevent disease outbreaks. Great care is taken to select healthy strong fry for stocking in fingerling ponds. The usual stocking rates in monocultures are given in Table 1.
Table 1 Stocking Rates of Fingerlings in Monoculture
|
Species |
Fingerling size (cm) |
Stocking rates/mu (No.) |
Rearing period (days) |
Approximate survival (%) |
Transfer size (cm) |
|
Grass carp |
3 |
20 000 |
20 |
80 |
4.8 |
|
Grass carp |
4.8 |
4 000-5 000 |
20 |
80-90 |
6.0 |
|
Big head |
3 |
15 000 |
30 |
90 |
6.0 |
|
Big head |
6 |
4 000-6 000 |
30 |
90 |
12.0 |
|
Mud carp |
3 |
27 000 |
30 |
80 |
5.8 |
|
Mud carp |
5.8 |
9 000 |
50 |
80 |
7.5 |
|
Silver carp |
3 |
20 000 |
20-50 |
90 |
6-9.5 |
|
Silver carp |
6-9.5 |
800-1 000 |
30-40 |
90 |
12-20 |
Fingerlings may also be raised in polyculture and in this case different stocking rates are used. As shown in Table 2, the growth of the fingerlings will differ; the lower stocking rates producing bigger fingerlings.
Table 2 Stocking Rates of Finger lings in Polyculture
|
Species |
Fingerling size (cm) |
Stocking rates/mu (No.) |
Rearing period (months) |
Approximate survival (%) |
Transfer size (cm) | |
|
1 (a) Grass carp |
8 |
3 000 |
July-January |
90 |
12-16 | |
|
|
Big head |
4.5 |
15 000 |
July-January |
90 |
7.8-8.5 |
|
1 (b) Grass carp |
8 |
3 600 |
July-January |
90 |
12-16 | |
|
|
Big head |
4.5 |
2 000 |
July-January |
90 |
14-20 |
|
2 Grass carp |
4.8 |
3 000 |
July-March |
70-75 |
9-10 | |
|
|
Mud carp |
5.0 |
70 000-100 000 |
July-March |
70 |
3.9-5.8 |
|
3 (a) Grass carp |
6 |
5 000 |
July-January |
90 |
9-12 | |
|
|
Silver carp |
5 |
25 000 |
July-January |
90 |
8-9 |
|
3 (b) Grass carp |
8 |
3 600 |
July-January |
90 |
16-20 | |
|
|
Silver carp |
5 |
3 000 |
July-January |
90 |
20 |
Feeding of fingerlings is done in the same way as for fry. However, more reliance is placed on artificial feeds like rice bran, soya-bean cake, peanut cakes and wine residues. Silkworm pupae, crushed snails, and fish meal, are also used with chopped soft grass and vegetable tops being added for grass carp fingerlings.
A higher survival rate (as much as 70-90 percent) is obtained in the rearing of fingerlings about 4-5 cm. However, it is stressed that success would depend on the care and attention to details essential for the proper management of fingerling ponds. These include regular close observation and care by personnel specially assigned for the purpose, to:
(i) ensure that water colour and quality are right and if fish are surfacing, taking prompt remedial action;(ii) guarding against fish escaping owing to broken dikes or overflow of ponds after heavy rain;
(iii) adequate feeding of the fish;
(iv) cleaning of the ponds, especially the feeding places, by applying bleaching powder to sterilize the feeding areas in order to reduce the incidence of fish diseases; and
(v) preventing predation by scaring off fish-eating birds, and controlling other predatory organisms.
5.3.1 Stocking rates
5.3.2 Fertilizing, feeding and pond management
As is well known, traditional fish farming in ponds in China is based on polyculture of compatible species of Chinese carps. By judicious combinations of silver carp (Hypophthalmichthys molitrix) and big head carp (Aristichthys nobilis), which feed on plankton and generally occupy the surface area, grass carp (Ctenopharyngodon idella) and wuchan fish (Megalobrama amblycephala), which are herbivores feeding on grasses and vegetables occupying mostly the middle layers of ponds; and black carp (Mylopharyngodon piceus), crucian carp (Carassius auratus) and common carp (Cyprinus carpio) living on the bottom and feeding on detritus or benthic organisms, the Chinese farmer has been able to obtain very high rates of production.
As is only to be expected, yields vary very considerably between farms. The national average was quoted as 1 875-2 250 kg/ha (250-300 jin/mu), the production in the southern part of the country being higher. However, the more advanced communes and production brigades that the study group visited, reported much higher production. The yield data from a number of these advanced communes and state farms is summarized in Table 3. Some of the very high yields are obtained in communes that undertake fish production as the main "link" or enterprise. A very high level of inputs and constant care of stock are needed to get high production.
Fig. 8 A view of the Paitan Lake Fish Farm
The combination of species certainly contributes to high productivity. It was noticed that in some farms the number of species stocked had risen from the traditional four or five to as many as eight or nine. The new additions, although not yet widely used, are the tilapia, the white croaker and Plagiognathops microlepis. The production units appear to assume that the addition of more species would result in higher production and therefore in some places the study group was asked to suggest species that could be imported for polyculture. It is not clear that the addition of more species would contribute very substantially to increased production, as the space and resources of the ponds seem to be more or less fully utilized. It will therefore be advisable to base any further additions on more critical information on the ecology and food utilization in the ponds.
Table 3 Yields and Income from Different Types of Fish Farms visited by the Study Group
|
Name of commune |
Per caput income |
Water area |
Yield of marketable fish |
Fry production (millions) | |
|
|
|
|
Average |
Maximum |
|
|
|
(Yuan) |
(ha) |
(kg/ha) |
| |
|
A. Communes with fish as the main crop | |||||
|
Jiefang People's Commune |
242 |
66 |
3 750 |
22 500 |
- |
|
Huang Chiao People's Commune |
161.16 |
62 |
2 940 |
- |
1.5 |
|
Ho Li People's Commune |
210 |
528 |
9 855 |
15 000 |
- |
|
Sha Chiao People's Commune |
140 |
2 112 |
2 760 |
- |
- |
|
Shihu Production Brigade - Shihu People's Commune |
- |
77 |
9 030 |
13 500 |
- |
|
B. State fish farms | |||||
|
Ching Po County Fish Farm |
Fixed wages |
30 |
5 400 |
13 875 |
100+0.3 fingerlings |
|
Nanwei County Fish Farm |
Fixed wages |
29 |
6 195 |
- |
0.4 fingerlings |
|
Nanhai County Hatchery and Farm |
Fixed wages |
47 |
- |
- |
600 |
|
Lin Fu Fish Farm |
Fixed wages |
48 |
3 795 |
- |
40-50 +0.18 fingerlings |
|
Paitan Lake Fish Farm |
Fixed wages |
26 |
- |
- |
625 |
|
C. Communes with fish farming as sideline occupation | |||||
|
Chen Ling People's Commune |
363 |
119 |
1 500 |
- |
- |
|
Chang Ching People's Commune |
150 |
112 |
4 050 |
- |
- |
|
Tang Sha People's Commune |
- |
792 |
- |
- |
- |
One of the practices responsible for high productivity is multiple stocking and harvesting of ponds. Fingerlings of different sizes and species are stocked, and as the fish grow and the pond becomes crowded, the larger marketable fish are harvested and smaller fish are restocked. An example of this type of intensive polyculture was seen at the Ho Li People's Commune experimental fish farm near Wuxi. A 7.2 mu pond of 2.5-3 m depth was stocked with eight species of fish of different sizes at different times of the year. Intensive feeding was done with a mixture of crushed snails (13.2 percent), grasses (17.8 percent), rice bran and commercial feeds (1.2 percent) and fertilized water (67.8 percent), and the pond was aerated frequently. The total feed applied in the 12 months of the experiment was 827 563 jin and the total harvest of fish was 22 560.7 jin which is equivalent to a yield of 3 133.4 jin/mu or 24 850.5 kg/ha/year. In a second experimental pond of 3.3 mu under similar management, a yield of 23 175 kg/ha/year was obtained. The results of the first experiment are presented in Table 4 showing details of stocking and harvesting.
These high yields, although only experimental results, serve to highlight the potential in this culture method. The average yield from commercial production ponds in this commune is 1 314 jin/mu or 9 855 kg/ha.
In another practice, described as "multigrade conveyor culture", the ponds are stocked with different species of fish but all of the same size, and when they reach marketable size, they are all harvested together and a new stock of fingerlings planted; generally two crops are raised annually.
The frequency of harvesting and stocking depends on the species, the size of stocked fish and the acceptable market size. At the Lin Fu State Fish Farm the study group was told that it took 14 to 15 months from hatching to produce marketable size fish. Hatching was done in May and rearing of fingerlings took eight months from the end of May to January. The fingerlings were stocked in January and harvested by June/July at an average weight of 1.5-2.0 jin. Between January and June the fingerlings grow from an average weight of 5 jin/10 000 fry to 200-300 jin/10 000 fry.
In most of the fish farms visited by the study group very high stocking rates are followed, as can be seen from Table 5.
Because of the high rates of stocking, very heavy fertilization and feeding are adopted in all the farms. Fertilization is invariably with organic manures, the most important of which is pig manure. The integrated type of farming in China (see pages 29-32) facilitates easy utilization of farm manure. About 75 000 jin of pig manure is used to fertilize 1 mu of fish ponds per year. Over and above this, some 50 jin of aquatic plants or 70 jin of grasses, are applied every day to feed grass carp. The "fertilized water" which consists of residues of bean curd and other wastes from food processing industries, is also used to fertilize the water at the rate of some 200 jin for every jin of silver carp. Crushed snails are provided at the rate of 40 jin for every jin of black carp to be produced. Poultry manure may also be applied where available at the rate of about 1 t/mu of pond area per year. Besides these, many farms utilize sewage also for fertilizing ponds. Latrines are still built on ponds for direct fertilization in certain parts of Guangdong Province, but in many other areas the group visited, direct application of sewage and pig manure has been replaced by controlled fertilization with fermented excreta.
Table 4 Stocking and Harvesting Record of a 7.2 mu Experimental Fish Culture Pond in Ho Li People's Commune, Wuxi, in 1977
|
|
STOCKING |
HARVEST |
PERCENTAGE |
||||
|
Fish Species |
Month |
Number |
Weight (Jin) |
No . /mu |
Total (Jin) |
Weight stocked (%) |
Weight harvested (%) |
|
Silver carp |
Jan. |
1 275 |
547 |
177 |
|
|
|
|
Jan. |
1 292 |
984 |
179 |
|
|
|
|
|
Aug. |
3 374 |
887.5 |
468 |
|
|
|
|
|
Total |
5 941 |
2 418.5 |
824 |
|
|
|
|
|
Big head |
Jan. |
425 |
96 |
59 |
|
|
|
|
Jan. |
425 |
339 |
59 |
|
|
|
|
|
Aug. |
450 |
-* |
63 |
|
|
|
|
|
Total |
1 300 |
435 |
181 |
7 310** |
45.5 |
32.4 |
|
|
Black carp |
Jan. |
434 |
935 |
60 |
|
|
|
|
Jan. |
440 |
230 |
61 |
|
|
|
|
|
Jan. |
2 343 |
85.5 |
325 |
|
|
|
|
|
Total |
3 217 |
1 250.5 |
446 |
3 205.5 |
20.0 |
14.2 |
|
|
Grass carp |
Jan. |
450 |
850 |
63 |
|
|
|
|
Jan. |
539 |
340 |
75 |
|
|
|
|
|
Jan. |
3 060 |
42.5 |
425 |
|
|
|
|
|
Total |
4 049 |
1 232.5 |
563 |
3 218.7 |
19.6 |
14.3 |
|
|
Common carp |
Jan. |
850 |
312 |
118 |
|
|
|
|
June |
850 |
-* |
118 |
|
|
|
|
|
Total |
1 700 |
312 |
236 |
1 775 |
5.0 |
7.9 |
|
|
Wuchan fish |
Jan. |
5 000 |
464 |
694 |
|
|
|
|
Jan. |
2 000 |
67 |
278 |
|
|
|
|
|
Total |
7 000 |
531 |
972 |
2 640.3 |
8.5 |
11.7 |
|
|
Crucian carp |
May |
-* |
36 |
- |
1 481.3 |
0.6 |
6.6 |
|
Tilapia mossambica |
May |
4 250 |
35 |
590 |
|
|
|
|
July |
3 000 |
15 |
417 |
|
|
|
|
|
Total |
7 250 |
50 |
1 007 |
2 288.1 |
0.8 |
10.1 |
|
|
Others |
- |
- |
- |
- |
641 |
- |
2.8 |
|
TOTAL |
|
30 457i |
6 265.5 |
4 229 |
22 560.7 |
100.0 |
100.0 |
* The average size of these fingerlings was 2.5 cm long, but numbers not given
** Total harvest of silver carp and big head
Table 5 Stocking Ratios and Stocking Densities of some Fish Farms in China
|
Fish Species |
Lin Fu State Fish Farm |
Shihu People's Brigade Hunan Province |
Paitan Lake Fish Farm |
Ho Li People's Commune (Experimental) | |
|
Silver carp: wt (%) |
45 |
58.6 |
60 |
38.5 | |
|
|
no./mu |
250-300 |
250-300 |
- |
114 |
|
Big head: wt (%) |
20 |
17.8 |
|
7 | |
|
|
no./mu |
60-80 |
100-150 |
15 |
25 |
|
Grass carp: wt (%) |
20 |
11.3 |
20 |
19.6 | |
|
|
no. /mu |
60-80 |
80-100 |
|
78 |
|
Black carp: wt (%) |
- |
- |
- |
20 | |
|
|
no./mu |
- |
- |
- |
62 |
|
Common carp: wt (%) |
5 |
3.5 |
- |
5 | |
|
|
no./mu |
30 |
40-60 |
- |
33 |
|
Wuchan fish: wt (%) |
- |
- |
- |
8.5 | |
|
|
no. /mu |
- |
- |
- |
135 |
|
White croaker: wt (%) |
- |
8.8 |
- |
- | |
|
|
no. /mu |
- |
1 200-1 500 |
- |
- |
|
Tilapia: wt (%) |
- |
- |
- |
0.8 | |
|
|
no. /mu |
- |
- |
- |
140 |
|
Crucian carp: wt (%) |
- |
- |
- |
0.6 | |
|
Others: wt (%) |
10 |
- |
5 |
- | |
Fig. 9 Cut grass held in an enclosure for feeding grass carp
Fig. 11 Snails crushed on board a boat for feeding black carp
Fig. 12 Latrine built on a pond for direct fertilization in Nanhai, Guangdong Province
In some farms, aquatic plants and grass are ground before being introduced into the ponds, but this is not a widespread practice. Often a good percentage of the fodder decomposes and fertilizes the pond. In addition, an appreciable proportion of the grass eaten by the grass carp is excreted undigested or only partly digested, providing readily used fertilizer. With all this the pond becomes highly loaded with organic matter, giving rise to tenuous environmental conditions requiring constant attention to prevent gross pollution and consequent fish mortality, particularly under unfavourable weather conditions. Cognizant of this, many communes organize special training courses in pond management for farmers before the onset of the summer and rainy seasons, when such mortalities generally occur.
Some advanced communes, like the Ho Li People's Commune, have done preliminary work in the preparation and testing of compounded feeds. There is very little expertise in feed technology in the country at present and so the traditional methods of feeding and fertilizing are continued with only small improvements.
When water conditions deteriorate in ponds, especially when dissolved oxygen deficiency occurs, clean fresh water may be pumped in or, where aerators are installed, they are operated for extended periods. The use of aerators of various types has now become very widespread in most parts of the country, except in certain areas in the south, such as Guangdong Province. The relatively low cost of electricity for agricultural and fishery uses (Yuan 0.06/kWh) makes this feasible and economically acceptable under Chinese conditions in at least areas served by hydro-electric schemes. The majority of other developing countries may find it a major item of cost that would affect the economic viability of commercial fish farming, at least for the present.
See below different types of aerators in use in fish ponds a, b, c.
Fig. 13 Different types of aerators in use in fish ponds a.
Fig. 13 Different types of aerators in use in fish ponds b.
Fig. 13 Different types of aerators in use in fish ponds c.
As is only to be expected in such intensive systems of culture, disease is an ever-present risk. The study group found that considerable attention is devoted to disease control in research centres. Preventive measures are emphasized but local herbal, as well as chemical, products are used for treatment of diseases.
In order to prevent infection, ponds are drained and limed or treated with tea seed cake at the rate of 30 jin/mu before being filled with water. Healthy, strong and large-sized fingerlings are stocked and these are disinfected with bleaching powder solution (1 g/50 kg of water is used to disinfect 25-30 jin of fingerlings) for five minutes before stocking. The spread of disease may not occur too freely, as usually the ponds are not interconnected. Despite the direct use of sewage in ponds in some areas, there appears to be no evidence of any human diseases being transmitted, except for some reported cases of transmission of the digenetic trematode, Chlonochis sinensis, from fish to man, if raw fish is eaten. Not much critical research appears to have been done on public health hazards associated with the use of raw, or partially treated sewage in fish ponds. Human sewage constitutes almost one third of the fertilizer resources of the country and has been used in fish culture since ancient days. Detailed research on public health aspects of sewage farming will therefore be justified and important, not only for China but also for many other countries that are trying to develop productive methods of sewage disposal.
The Institute of Hydrobiology in Hubei has done considerable work on fish diseases in China and the group was briefed on the following diseases:
(i) StigmatosisThis is a bacterial disease caused by Pseudomonas sp., affecting silver carp and big head. It causes inflammation of the abdomen and also affects gonad development. Control and cure of this disease is by the application of bleaching powder and treatment with streptomycin.(ii) White spot disease
This is caused by the cilliate, Icthyophthirius multifilis and affects grass carp, causing white spots on the body of the fish.(iii) Myxosporidiasis
This is a disease affecting the goldfish, Carassius auratus, and is similar to "whirling disease" caused by Myxosoma cerebralis in Europe and the U.S.A. No cure has yet been found for this disease in China.(iv) Disease caused by trematode parasites
This includes diseases caused by Diplostomum sp., a well-known trematode parasite with a life cycle involving aquatic birds and snails. It is controlled in China by the application of copper sulphate solution at 0.7 ppm.(v) Disease caused by cestode parasites
An example of this is the infestation of grass carp fingerlings by Bothriocephalus sp., which in heavy infestations causes considerable mortality. A traditional treatment is with a 1:1 (by weight) mixture of powdered seeds of pumpkin and cucumber, which is spread over the affected pond.(vi) Other diseases
The most important of these is the infection by Lernea sp. which affects the fingerlings of silver carp and other carps, the parasite being attached to the gills or body of the fish, It is controlled by bathing the fish in 0.2-0.5 ppm solution of "Dipterex" or 80-100 ppm solution of bleaching powder. It could also be controlled by bathing in a 0.1 ppm solution of potassium permanganate. The disease is known to be most common in sewage ponds.
A fungus disease caused by Saprolegnia sp. also affects a number of species. It is controlled by the application of malachite green in a 1:150 000 solution.
As described elsewhere in this report, most of the large fish farms are built as part of communal farming systems, usually integrated with crops and livestock production; so the design of fish farms differs in many respects from that adopted in other countries. A very striking feature is the width of dikes between ponds, which is often 10 m or more wide on the crown. Similarly the sides are also very wide. These wide areas are used for the cultivation of grass and other fish fodder, vegetables, mulberry and sometimes even trees like cedar. Pigsties are also built on the dikes. This reduces the labour involved in transporting fodder or manure from long distances. Also pond silt can be applied directly to fertilize the crops.
The ponds are relatively deep, in most cases 2-3 m. This is necessary for the poly-culture of various species that inhabit distinct layers in the ponds and to enable the culture of large stocks of fish. Since draining and filling of ponds are done by pumping, the maintenance of such deep ponds is not difficult and the need for sluices and other water control structures is reduced. The study group saw pond dikes lined with concrete or bricks in some farms in Guangdong and Hunan Provinces in areas where the soil is sandy or porous.
The ideal size of production ponds was reported to be 4-5 mu. In areas where the soil is poor and porous, ponds of 10 mu are more common. Fry and fingerling ponds are generally 2-3 mu in area. There is a tendency to build rectangular or square-shaped ponds or remodel old, irregular-shaped ones into square ponds. The construction cost of square ponds is lower than that of rectangular ones and it would appear that aeration of water by wind or aerator would be more efficient in square ponds. The regular shape of the ponds facilitates the use of motorized vehicles on the farm and the mechanization of operations.
Harvesting of ponds is generally done manually with seine nets. Commune or production brigade members, both male and female, participate in fishing, but the group observed that fishing expertise, or the efficiency of gear used, was not too high. There is considerable interest in mechanization of fishing in ponds to reduce labour, but not much has been done in this direction.
Although most of the fish farming is done in earth ponds, attempts are now being made in some places to introduce indoor intensive farming in cement tanks with heating and aeration, particularly for tilapia, which cannot withstand low temperatures.
Fig. 16 Harvesting of fish from a pond in Lin Fu State Fish Farm in Hengyang
Fig. 17 A catch of Chinese carps, wuchan fish and black bream from a fish farm
Fig. 18 An experimental indoor culture of tilapia in cement tanks
Although the economics of individual operations are not of primary importance under Chinese conditions, the study group was able to obtain some useful information on the cost of production and profit made in certain communes and production brigades. As is only to be expected, there are considerable variations in investment and production cost per unit area. It ranged from Yuan 260/mu to Yuan 1 500/mu. The income from fish was quoted as Yuan 140/mu, as against Yuan 130/mu for rice in Shao Chiao People's Commune in Guangdong Province. In Shiyeh Commune in Xishui County, income from fish was reported to be Yuan 1 000/person as against Yuan 600/person from rice production. In Hengyang the cost of production of fish was Yuan 0.20-0.23/jin and it was sold to the state at Yuan 0.35/jin. In some of the communes the study group was told that the income from fish made it possible for them to buy agricultural machinery. Vegetable growing in suburban towns was said to be the only normal farming activity that provided much higher income per unit area than fish.
The percentage of the components of cost of production also varies from place to place. In one of the communes, it was reported as follows:
|
Fry: |
5 percent |
|
Labour: |
30 percent |
|
Feed and fertilizer: |
50 percent |
In some the cost of fry was said to be much higher, as much as 26.5 percent and of electricity, about 14 percent.
