APPENDIX A - Fish Pond Technologies

1. POSSIBILITIES FOR FISH PRODUCTION

1.1 Fish Production of Natural Waters

The oldest way of fish production is the utilization of existing water bodies. Here the yields are generally low (20-50 kg/ha/year) and the possibilities for human intervention are rather moderate (supply of fish regularly caught).

1.2 Fish Production in Ponds

Fish ponds are constructed generally in areas with poor soil quality (sodic soils or marshes) where at the same time water in good quantity and quality is available. Thereby fish farms utilize first of all the land areas, with a relatively high production (1-5 t/ha/ year). Control of this production involves the selection of the cultured species, their size and age, feeding, fertilization of the pond, design of stocking and harvest.

1.3 Industrial, Large-Scale Fish Production

In this type of fish production first of all the potential of running water is utilized. Thus, this can be established in places where either the natural endowments are satisfactory, or effluent water from an industrial plant (e.g., power station) can be utilized. The dimensions of an industrial fish farm are always determined by the amount of water available. This type of fish farming is extremely productive (100-300 t/ha/year). Every step of a given technology here is carefully designed and controlled.

The above three types of fish production show great differences in their intensity. Though the natural waters have low production, it is 'spontaneous' (i.e., the natural reproduction is prerequisite), and the fish feed on natural feed exclusively. Naturally, the production is always a function of the natural feed available. The primary function of fish ponds is fish production, 50-70 percent of the yield is from the feed consumed during the culturing period, the rest is from fertilizer-stimulated natural feed from the pond itself.

This yield can be increased by some technical interventions, such as aeration, automatic feeders, or biologically complete, formulated feed (pellet). The yield, which is a maximum 7 t/ha, is limited however, by the amount of metabolic products of the fish, which increases along with the weight gain of the animal, until it cannot be decomposed any more by the natural circulation of the pond. In industrial fish production it is solved with a higher flow rate of the water, which eliminates the metabolic products. Here the production is limited by the specific flow rate, which is about 100 l/kg/h, with aeration of 25 I/kg. In this technology only artificial feed is given, with increased cost. If the temperature of running water is constant, the system can be operated throughout the year. If not, there should be either a break in the operation or a change in the cultured species. Since the industrial fish culturing system operates independently from the environmental, 'external' temperature, it is capable of producing market fish continuously.

One type of industrial fish producing system is the recirculation method, which ensures constant water temperature and quality. Related to the recycled water of the system, a small amount (2-5 percent daily) of water has to be supplied externally.

Table 1 shows the most important technological and technical parameters of the above system.

2. MAIN PHASES OF FISH POND CULTURE

2.1 Propagation

Fish cultured in fish farms are generally propagated artificially. Since a separate chapter is dealing with this theme, only the most important figures of design and technology are dealt with here. Some important technological features of propagation are summed up in Table 2, and illustrated through a simple example.

Table 1 Characteristic Features of Different Types of Fish Production

Management	Production		Water requirement	Fish Population	Feed		Oxygen Supply	Metabolite Elimination
	t/ha	kg/m3	(m3/kg)		Quality	kg/kg
Natural water	0.03	0.003	300	Mixed	Natural		Natural	Natural
Cage	(0.5)	50	2001/	Single species	Pellet	3-4	Natural + artificial	Natural
Fish pond (extensive)	1.0	0.1	15	Single-multispecies	Wheat	1.5-2	Natural	Natural
Fish pond (intensive)	3.0	0.3	7	Multispecies	Wheat + Pellet	2-3	Natural +	Natural
Industrial	100	10	1502/	Single species	Pellet	2	Artificial	Artificial
Recirculation	200	20	103/	Single species	Pellet	2	Artificial	Artificial

1^/ 100 m² free water surface is equivalent to 1 m² cage (still water system)
^2/ Trout, conventional concrete tanks
^3/ Calculated at 4 percent supplemental water daily

Table 2 Main Technological Parameters of Fish Propagation

Item		Unit	Common carp	Silver carp	Bighead carp	Grass carp	Sheat fish
Average weight of matured		kg	5/3	4/3	8/6	7/5	6/4
female/male spawners
Number of eggs in 1 kg:
	dry	1 000 pc	800	1 000	700	800	200
	swollen	1 000 pc	100	20	17	17	40
Larvae developing from		1 000 pc	500	600	500	500	120
1 kg dry eggs
Optimal temperature of		°C	20	23	24	23	24
hatching and nursing
Incubation		daily temperature	65	26	28	26	50
Duration of larvae nursing		daily temperature	65	65	65	65	90
Amount of swollen eggs		litre	2	3	3	3	1
in 1 small Zuger glass (7 1)		1 000 pc	200	60	50	50	40
Average water requirement		l/min	1.5	0.6	0.6	0.6	1.5
of 1 small Zuger glass
Number of larvae in 1 big Zuger glass (200 1)		1 000	500	300	300	300	201/
Average water requirement of		l/min	8	8	8	8	31/
1 big Zuger glass
Volume of tank for spawners		I/kg	15	20	15	20	15
Specific water requirement:
with aeration			1.5	2.0	2.0	2.0	1.5
without aeration		l/kg/min	0.7	1.0	1.0	1.0	0.7

1^/ Data corresponding to sheat fish larvae kept in hapa of 0.2-0.3 m²

Example:

Item		Carp (millions)	Silver Carp
Larvae needed (million)		50	20
Eggs needed:
	dry (kg)	50:0.5 = 100	20:0.6 = 33
	swollen (1)	8 × 100 = 800	50 × 33 = 1 650
Necessary brood stock:
	female (kg)	100:0.1 = 1 000	33:0.1 = 330
	(no.)	1 000:5 = 200	330:4 = 83
	male (kg)	300	125
	(no.)	100	42
Zuger glass needed:
	small (no.)	800:2 = 400	1 650:3 = 550
	big (no.)	50:0.5 = 100	20:0.3 = 67
No. of batches of eggs		400:40 = 10	550:40 = 14
Total hatching time (days)		10 × 4 = 40	14 × 2 = 28
No. of batches of larvae		100:10 = 10	67:10 = 7
Duration of larval rearing (days)		10 × 4 = 40	7 × 4 = 28
Required water flow (l/min):
	spawner tank	200	90
	small Zuger glass	40 × 1.5 = 60	40 × 0.6 = 32
	big Zuger glass	10 × 8 = 80	10 × 8 = 80
total		340	202

In the above example we have a hatchery with, 40 small and 10 big Zuger glasses, where the total volume of tanks for brood stock is 10 m³ and its water supply 300 l/min. The hatchery is to produce 50 million carp and 20 million silver carp larvae.

We calculate, by using the figures of Table 2, the number of spawners (male and female) necessary for a certain amount of larvae and the time and water flow necessary in a hatchery with the given facilities, and as a general rule consider that (1) the egg production of a mature female spawner is 0.1 kg per 1 kg body weight and (2) for two females one male is required.

2.2 Nursing of Larvae

The hatched larvae would be under endogen nutrition, thus it is necessary to keep them in the hatchery. Afterwards they are transferred to nursery ponds where natural food in sufficient amount and quality must be available. These relatively small (0.5-0.8 ha) nursery ponds, therefore, should be well prepared. This must be started about seven days before the stocking.

2.2.1 Main steps in nursery pond preparation:

Day
7	The dry and vegetation-free bottom of the pond should be treated with 500 kg/ha CaO and 200 kg/ha ammonium-nitrate (NH4NO3)
6	The pond should be filled with up to 20-30 cm water
4	3-5 t/ha organic fertilizer is applied
2	Water level should be raised to 50-60 cm
1	Fast decomposing (maximum 1 week) insecticide of phosphorous acid ester content must be added to the pond water in a sufficient amount to eliminate cladocera and copepoda zooplankton species.
0	Stocking of larvae

2.2.2 Feeding in the nurseries:

The pond preparation can be regarded successful if the filtrate of 100 1 pond water reaches 1 ml and Rotatoria are dominant in it. Feeding of larvae must be started on the 3-4th day with 2-4 kg/ha mealy feed. This period lasts 20-25 days and the feed ration of the last days must be 25-30 kg/ha. On the 4-5th day the pond must be filled up (120-150 cm) . An important precondition of the success in this period is to fertilize with 200 kg/ha of organic fertilizer daily.

2.2.3 Guideline for pre-nursing period (Cyprinidae)

Stocking	1-1.5 million larvae/ha
Harvest	0.6-1.2 million larvae/ha
Individual weight	0.3-0.8 g
Production (average)	500 kg/ha
Fertilizer necessary	4+4 t/ha
Feed necessary	200-250 kg/ha

These ponds can be used for nursing of three consecutive groups, each batch needing 30 days (one group 7 + 23) or, altogether, 90 days. For nursing the 50 million carp and 20 million silver carp larvae, cited in our example,

of nursery pond are necessary.

2.3 Nursing Period

During the prenursing period the larvae grow very fast. Presuming that 1 million 0.5 g/larvae are harvested, the weight gain per hectare is 500 kg in 20-25 days.

This mass of fish cannot feed sufficiently any more, due to the lack of zooplankton, so it should be harvested and restocked at a lower stocking density. The optimal size of a nursing pond is 3-5 ha with an average depth of 1.2-1.4 m. Generally 50-80 000 prenursed larvae are stocked.

As illustrated in our example, 50 million carp and 20 million silver carp larvae were produced, out of which prenursing in three groups in an 18 ha pond area resulted in recoveries of 30 million carp (50 × 0.6) and 14 million silver carp (20 × 0.7). So far monoculture has been used, the next part of the nursing period being carried out in polyculture, where altogether 44 million prenursed fry would need a total pond area of:

The ratio of the pond-area requirement of pre- and post-nursing period is 18:700, i.e., 1:40. If we use a culture period of 100-120 days, with the expected survival at 70 percent, recovery is 31 million fry (44 × 0.7). At an average of 60-80 g body weight the expected total weight of the whole stock is:

31 million × 70 g = 2 170 t or 3.1 t/ha

Production per hectare is 2 170:700 = 3.1 t.

In the post-nursing period the ponds should be regularly fertilized and the fry feed dispensed at 3-4 percent of body weight daily.

2.3.1 Guideline for post-nursing period

Stocking	50-80 000/ha, 25-40 kg/ha
Harvesting	35-56 000/ha, 3 000 kg/ha
Fertilizer necessary	400 kg/ha mono-ammonium phosphate or 140 kg/ha superphosphate
Feed necessary	3 000 kg/ha pellet (minimum protein content 25 percent)
	2 500 kg/ha grain

2.4 Market-size Fish Production

The 60-80 g fingerlings should reach 500-800 g body weight in 150-200 days. The stocking rate is 5-6 000/ha, the survival of which is 80 percent. Since we have altogether 31 million fry,

The ratio of the pond-area requirement for nursing and growing of market-size fish is 700:5 640, or 1:8. Considering an 80 percent survival rate, the total number of marketable fish is 25 million, with a total weight of 16 250 t if the average body weight is 650 g. Regular fertilization and feeding should also be considered.

Guideline to market size fish production:

Stocking	5-6 000/ha, 350-400 kg/ha
Harvest	4-5 000/ha, 2 600-3 200 kg/ha
Fertilizer necessary	500 kg/ha ammonium nitrate
	180 kg/ha mono-ammonium-phosphate or
	500 kg/ha superphosphate
Feed necessary	1 500 kg/ha pellet (minimum protein content 25 percent)
	3 000 kg/ha grain

3. THEORETICAL PRINCIPLES OF POND FISH CULTURE

3.1 Biological Production of Waters

Algae in the waters absorb a part of solar energy and grow (propagate) correspondingly. This is the single energy source of water biocenosis, as the algae are then consumed by fish to provide a rich source of natural feed. Metabolic products and organic materials are decomposed by bacteria.

Parallel to energy binding and consumption, biological processes are going on, the essence of which is that energy binding of algae involves oxygen release and organic material composition. While other organs utilize the energy carried by this organic material together with the released oxygen, the process results in inorganic materials which are used by algae again in binding solar energy. The schematic illustration of the process is as follows:

Figure 1. Schematic illustration of biological processes in fish pond

The figure on the left illustrates a water body without any human interference, thus the matter content of the pond is relatively constant and biological production is limited by the spontaneous speed of material-cycling. In this case the sun is the only source of energy. The scheme on the right illustrates a pond, whose matter content is continuously supplied, i.e., there are additional energy sources, in order to increase fish production. Fish production is profitable, if the fish population in the pond is a constant consumer of natural food as well as of the additionally given energy (food). Thus, it is of primary importance to have the necessary protein produced by the pond. In addition, cheap, energy-rich (i.e., protein poor), feed can be applied. This is always defined by the size of fish (protein demand of young fish is higher than that of the older ones), and the expected production.

The change of oxygen concentration is a relatively simple indicator of the intensity of energy turnover in the pond. The following figure shows the fluctuations of the oxygen concentration in two fish ponds with high and low productivity, respectively.

Figure 2. Oxygen fluctuations in fish ponds

It is clear from the above that the algal population is bigger in the pond with higher productivity (which accounts for intensive oxygen production), but the number of oxygen consuming organisms is higher as well, resulting in an early morning minimum.

3.2 Polyculture

Feeding habits and food preferences differ from species to species. This is the reason that stocking different species together gives a higher yield than monoculture because of better utilization of natural food resources. After many years of experience the following stocking ratio is given as fairly optimal:

Common carp	50-70%
Silver carp	20-30%
Bighead carp	10%
Grass carp	5-10%
Sheat fish	2-4%

As a basic rule it should be noted that in order to increase yield, the share of common carp must be increased as intensified feeding increases the yield of the common carp only.

3.3 Fertilization

As described in the section on material and energy turnover, the biological production of a pond is limited by the amount of energy bound by the algae. This, however, is defined by the quantity of 'algal-food'. Since energy-binding is a sunlight-dependent process, energy and the material release mostly take place in the dark. These two complementary processes are often asynchronic. The aim of fertilization is to overcome these gaps in turnover and maximize the energy-building properties of algae.

Both organic and inorganic (artificial) fertilizers can be applied. The effect of organic material on primary production of the pond is relatively slow, since most of the nutriments must first be decomposed by bacteria into minerals. This is of great benefit however, to zooplankton growth. Inorganic fertilizers directly promote primary production, and are optimal given in small portions daily, with, as experience has shown, a 4:1 = N:P ratio. In waters with poor buffer capacity, lime (CaCO₃) can be very useful.

3.4 Feeding

In pond fish culture, feeding is of a complementary nature, i.e., a part of production is from natural, and the rest from artificial feed. For a low production target (below 1 t/ha/year) feeding is unnecessary, but the population structure should be established accordingly (e.g., common carp: 20-30%). To attain higher production (e.g., common carp: 2 t/ha/year), however, feeding is necessary with grains. Really high production (above 3 t/ha/year) can be reached only with additional protein, vitamin and mineral premix complemented pellet, where the stocking combination is dominated by the pellet-feed consuming species (e.g., common carp: 70%).

Feeding in pond fish culture has always to be adjusted both in quantity and quality to the natural food production of the pond and to the mass of the fish. If the temperature of the fish pond markedly fluctuates in the culturing period, it should also be considered.

The feeding strategy in a properly populated and fertilized fish pond is shown in the following diagram.

The diagram demonstrates that in the first part of the culturing period, the protein requirement is met by natural food, zooplankton, thus only supplemental energy is needed (wheat). In the second half of the culturing period, the existing zooplankton stock cannot meet the requirement of the increasing mass of fish, thus the demand of the carp must be fulfilled by additional protein. The zooplankton requirement of silver carp and bighead carp is met by the small Rotatoria.

Figure 3. Feeding diagram

The body composition of carp is greatly influenced by the quantity and quality of feed given. An ad libitum strategy generally leads to the fattening of the carp. However, this impairs the food-conversion rate, as well as imparting a bad taste to the product. Therefore, in the post-nursing and market fish producing periods, the daily 5% and 3% feeding intensities respectively should not be exceeded.