In Hungary, pond fish farms are generally built where the soil is unsuitable for other types of rural activities, but where water of adequate quantity and quality is available. Thus, fish farms first of all utilize land area with higher profit than irrigated crop farming could do. It is indisputable, however, that establishment of a fish farm needs high investment.
The optimum size of a fish pond is a controversial question. Experience of many years shows, on one hand, that specific yield of small ponds is generally higher than that of large ones. It is also true, on the other hand, that construction cost as well as man-labour requirement are also higher. The size and shape of fish ponds are greatly influenced by geographical conditions as well as functional factors.
In Hungarian farms, ponds serve three major functions: fry nursing, fingerling rearing and food-fish production.
The area of fry nursing ponds should be calculated on the assumption that 1 million larvae need 0.3 ha pond surface area (assuming 2.5–3 rearing cycles), regardless of whether the seed material is generated locally or purchased.
If the farm intends to rear, e.g., 50 million larvae, a pond area of 50 × 0.3 = 15 ha will be necessary for 17 million larvae per cycle (in 3 cycles), or 20 million (in 2.5 cycles). Optimum size of nursing ponds is 0.5–1 ha.
Fingerling rearing is generally done in larger, 4–8 ha ponds. One hectare of nursing pond supplies seed material for 40 ha of rearing ponds. Therefore, in the above example, 600 ha of fingerling rearing ponds will be necessary for the seed material produced in 15 ha, presuming that the farm plans to rear all the larvae it produces.
Food fish are generally produced in large ponds. Since the fingerlings reared in 1 ha will require 8 ha of pond area for food fish production, farms generally produce such fish in 90% of the total pond area. Often farms have to make compromises with these ponds. Optimum size ranges between 10 and 20 ha.
It is generally accepted that minimum water depth of fish ponds is one metre. If deeper fish ponds are constructed, their benefit will not be in higher natural production but in the higher volume of water, giving more balanced oxygen conditions and lower metabolite concentration.
Filling and drainage of fish ponds are generally from separate water systems. The aim of the traditional design (i.e., filling and drainage structures are on the opposite sides of the pond), is that flow-through water can be supplied if necessary. According to the present view, however, it can be more advantageous if filling and drainage structures are close to each other, because of the undisturbed supply of fresh water for fish collected in the inner or outer harvesting pit during harvest.
Proper size of structures is also very important. The principle is that flow-through capacity of a drainage structure should be higher than that of the feeding structure. It should be stressed, however, that a structure even of double the theoretically necessary size is not adequate if the flow rate of the drainage canal is lower than necessary, due for example to the simultaneous drainage of several ponds. The same is true for water feeding canals, where the possibility of a minimum 8–10 cm/day water level rise is of primary importance; otherwise the pond can be grown over by macrovegetation.
Fish worth producing are those which can find natural food in the pond to satisfy at least part of their food requirement. Besides biological aspects, marketing possibilities as well as economic viability of the given fish species are equally important.
In Hungary, there are five species meeting the above pre-requisites, of which those demanding supplementary feeding can be cultured in monoculture and those feeding exclusively on natural food can be reared successfully in polyculture only. It is especially important to know the feeding habits of the fish species cultured under pond conditions, as well as the interactions such as synergism and competition that might develop between these species through feeding.
The most commonly cultured fish are the following:
Common carp (Cyprinus carpio)
Common carp is the most important species farmed in Hungary. Since carp readily feeds on both natural and supplementary food (cereal grains or pellets), it can equally be cultured in mono- or polyculture. It feeds first of all on the bottom fauna; at high stocking density it will eat this out soon after the growing season begins - and will turn to feeding on zooplankton. However, not being specially adapted to this type of feed, common carp feeds mostly on Cladocera of large size (e.g., Moina). Cereal grains (such as wheat) form the supplementary food while natural food is available in the pond in adequate quality and quantity. It should be complemented with pelleted feed of higher protein content.
Silver carp (Hypophthalmichthys molitrix)
Silver carp is a commonly accepted member of the polyculture system. It is a typical filter feeding fish. Its main food source is phytoplankton, the majority of which it cannot digest under pond conditions in Hungary. This is probably compensated for by a significant zooplankton consumption. Silver carp is relatively slow growing, and has a high tolerance from the viewpoint of population density.
Bighead carp (Aristichthys nobilis)
This species is also a typical filter feeding fish, but its main food source is zooplankton. It is another potential species for polyculture. Fast growing, it is sensitive to high stocking density which reduces its growth.
Grass carp (Ctenopharynogodon idella)
Grass carp graze on macrovegetation, which in case of over-population can result in the total elimination of water weeds under natural conditions, an advantageous feature if used in irrigation canals. In fish ponds, grass carp has the option to choose among various plants, which can lead to the mass propagation of the unfavoured species (e.g., Polygonum). By the second part of the growing season, when ponds have run out of its favoured plants, grass carp generally shift to the supplementary feed supplied for common carp. This can lead to serious enteritis and massive fish kill. It can be prevented by additional feeding with grass or duck-weed. Grass carp is important in polyculture, where it may help control weed growth stimulated by fertilization. Recently grass carp has been successfully cultured in monoculture with both plant and pellet feeding.
European catfish (Silurus glanis)
European catfish, known also as sheatfish or wels, is a carnivorous species. In polyculture it feeds on wild fish introduced into the pond through filling and on diseased individuals. It can also be cultured in monoculture on moist pelleted feed.
There are three basic routes through which the fish farmer can influence fish yield in a pond: stocking, fertilization and feeding, as discussed below:
Fish stocking. Determination of stocking density (fish population) is the process of decision-making when the number, species and age groups of fishes to be stocked into a pond are determined. Stocking itself is a technical activity during which the above decision is implemented, i.e., fish are stocked in the pond.
Earlier, pond fish farming was exclusively monocultural. The first attempt to introduce polyculture was when fish of the same species but different age groups, i.e., one- and two-summer fish, were stocked in the same pond. It did not bring too much success. Real polycultural production, i.e., where fish of different species were stocked in the same pond, was first tried about 20 years ago in Eastern Europe. It proved to be a real success, resulting in lower cost and high yield, and/or costs did not change but yield was much higher. The yield-increasing potential of polyculture has not yet been fully exploited.
Optimization of fish population hence cannot be separated from the expected yield. As a general rule it can be stated that in case of low yield, a relatively small population (with the dominance of Chinese carp) is stocked. In case of high yield, however, both the stocking density and the share of fish species with supplemental feed requirement (common carp) must be increased. Table 2.1 illustrates stocking and feeding rates with different production targets.
Table 2.1
EXPECTED YIELDS OF DIFFERENT TYPES OF POLYCULTURE IN HUNGARY
| Species | 1 t/ha yield | 2 t/ha yield | 3 t/ha yield | |||
| fish/ha | percent | fish/ha | percent | fish/ha | percent | |
| Common carp | 250 | 19 | 1 200 | 50 | 2 000 | 65 |
| Silver carp | 500 | 39 | 750 | 32 | 700 | 22 |
| Bighead carp | 300 | 23 | 200 | 8 | 150 | 5 |
| Grass carp | 200 | 15 | 200 | 8 | 200 | 6 |
| Catfish | 50 | 4 | 50 | 2 | 50 | 2 |
| Total | 1 300 | 100 | 2 400 | 100 | 3 100 | 100 |
| Supplem. feed to be distributed (t/ha) | 0 –0.2 | 1.5 – 2 | 4 –5 | |||
Fertilization. The aim of fertilization is to increase the natural production of the pond. The method is indirect, since fertilizers promote the production of phytoplankton first, which then improves the nutrient supply of zooplankton. These latter organisms play a decisive role in fish feeding.
Inorganic and/or organic fertilizers are equally used in Hungarian fish farms. The advantage of the first one is that portions can be accurately defined, while the amount of nutrients taken into the pond with organic fertilizer is not precisely known.
Nitrogen (N) and phosphorus (P) are the most important nutrients for the production of algae. If the pond water does not contain enough of these two elements, fertilization can increase their concentrations so as to reach the optimum N:P ratio of 4:1.
By testing several inorganic fertilizers it was found that ammonium nitrate is the optimum source of nitrate, while that of phosphorus is ammonium phosphate. Both readily dissolve in water and have fairly high nutrient concentrations. The 4N:1P ratio is obtained by using a 3:1 ratio of ammonium-nitrate and monoammonium-phosphate.
The optimum period for fertilization in Hungary is from May to July included. Fertilization is necessary until the growth of phytoplankton and the simultaneous decrease in zooplankton become steady. At this stage, the intensive growth of the fish biomass is the limiting factor in zooplankton propagation and development. Over-production of algae (algal bloom) can also be a sign of decreasing zooplankton stock, which necessitates the increase of supplementary feeding and results in an increasing amount of inorganic matter from fish excrement in the pond.
It should also be kept in mind that fertilization will promote not only the growth of phytoplankton but also that of macrophytes in the fish pond. These can be controlled either by including grass carp in the polyculture or by mechanical cutting.
Feeding. Feeding in fish ponds is generally of a supplementary nature. The principle of pond fish farming is that 40–60% of the yield comes from natural food production. Accurate calculation of yield from this natural production is impossible but can be estimated as follows:
If the amount of feed necessary to produce 1 kg fish gain - the Food Conversion Ratio (FCR) - is approximately known (e.g., in the case of cereal grain FCR = 5 kg), dividing the amount of feed distributed by this FCR gives the approximate yield from supplementary feeds. Subtracting this from the total yield will provide the estimated natural production. These two kinds of yields are inseparable in practice, since carp feed on both natural and supplementary food simultaneously, resulting in a better utilization of cereal grains.
The food demand of fish can be expressed by their protein requirement. It is generally accepted that young fish have a higher protein demand than their elders. For 20–50 g common carp, food containing 15 mg protein/kJ (protein/ energy ratio) is the most favourable.
Fish ponds are rich in zooplankton at the time of stocking and for a while after. Later, it starts decreasing proportionally with the growth of fish in the pond. Since this growing fish stock requires increasing amounts of feed, and zooplankton in the pond is becoming scarce, feeds of a higher protein content should be fed in the last third of the growing season. This requires the use of balanced pelleted diets.
The required amount of feed with a high protein content should be assessed as a function of the expected yield. It is obvious that the less is the yield, i.e., there is less fish in the fish pond, the longer the zooplankton stock will last. In case of high yields (1.5 t/ha or more), the proportion of supplementary feeding can be as high as 50%, especially in the late months of the growing season (August and September).
It should be noted, however, that the specific feed demand of growing fish is decreasing and that the appetite of fish greatly depends also upon temperature, but as the water is cooling in September, the specific protein demand is growing, which requires feeding of pelleted feed in this month. Finally it should be stressed that over-feeding of fish can lead to excessive fattening and deterioration of meat quality, as well as extra costs.
Propagation. Fish cultured in fish farms are generally propagated artificially. Since artificial propagation is well described in detail in other FAO publications (e.g., Woynarovich and Horváth, 1984), only a summary of the most important biological and technological parameters is presented in Table 2.2. An example of the use of these figures to calculate a hatchery's requirement for equipment, water and fish is given in Table 2.3. The hypothetical hatchery has a target production of 50 million common carp larvae and 20 million silver carp larvae per year. The calculations assume an average egg production by female spawners at 0.1 kg eggs/kg body weight, and a male/female sex ratio of 1:2.
Nursing of larvae. Larvae are kept in the hatchery for only a day or two after hatching, then are transferred to small, well-prepared nursing ponds. Nursing pond preparation and management is described in detail elsewhere (e.g., Horváth, Tamás and Coche, 1985), and consequently only a summary is given here:
Pond preparation must be started about seven days before stocking, as follows:
| Days before stocking | Job description |
| 7 | The dry and vegetation-free bottom of the pond is treated with 500 kg/ha CaO and 200 kg/ha ammonium-nitrate |
| 6 | The pond is filled with 20–30 cm water |
| 4 | 3–5 t/ha organic fertilizer is applied |
| 2 | Water level is raised to 50–60 cm |
| 1 | Fast decomposing (maximum 1 week) insecticide containing phosphorous acid ester is added to the pond water in a sufficient amount to eliminate Cladocera and Copepoda zooplankton |
| 0 | Larve are stocked (about 1–1.5 million/ha) |
Feeding in the nursery ponds. The pond preparation can be regarded as successful if the filtrate of 100 l water contains at least 1 ml of zooplankton and rotifers are dominant. Feeding of larvae must be started on the third/ fourth 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 fourth/fifth day the pond must be filled to 120–150 cm. An important precondition of the success in this period is to fertilize with 200 kg/ha of organic fertilizer daily.
In Hungary, nursery ponds can be used for nursing three consecutive groups, each batch requiring 30 days (one group 7 + 23) or, altogether, 90 days. For nursing the 50 million carp and 20 million silver carp larvae cited in the above example, the following pond area is required:
and 
Table 2.2
MAIN TECHNOLOGICAL PARAMETERS OF FISH PROPAGATION IN HUNGARY
| Item | Unit | Common carp | Silver carp | Bighead carp | Grass carp | European catfish | |
| Average weight of matured female/male spawners | kg | 5/3 | 4/3 | 8/6 | 7/5 | 6/4 | |
| 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 kg dry eggs | 1 000 pc | 500 | 600 | 500 | 500 | 120 | |
| Optimal temperature for hatching and nursing | °C | 20 | 23 | 24 | 23 | 24 | |
| Incubation | degree-day | 65 | 26 | 28 | 26 | 50 | |
| Duration of larvae nursing | degree-day | 65 | 65 | 65 | 65 | 90 | |
| Number of swollen eggs in one small Zug jar (7 1) | litre | 2 | 3 | 3 | 3 | 1 | |
| 1 000 pc | 200 | 60 | 50 | 50 | 40 | ||
| Average water requirement of one small Zug jar | 1/min | 1.5 | 0.6 | 0.6 | 0.6 | 1.5 | |
| Number of larvae in one large Zug jar (200 1) | 1 000 | 500 | 300 | 300 | 300 | 201 | |
| Average water requirement of one large Zug jar | 1/min | 8 | 8 | 8 | 8 | 31 | |
| Volume of tank for spawners | 1/kg | 15 | 20 | 15 | 20 | 15 | |
| Specific water requirement: | |||||||
| with | aeration | 1/kg/min | 1.5 | 2.0 | 2.0 | 2.0 | 1.5 |
| without | 0.7 | 1.0 | 1.0 | 1.0 | 0.7 | ||
1/ Data corresponding to catfish larvae kept in hapas of 0.2–0.3 m2
Table 2.3
AN EXAMPLE OF CALCULATION OF HATCHERY EQUIPMENT,
WATER AND FISH REQUIREMENTS
| Item | Carp | Silver carp |
| Larvae needed (million), i.e., target production | 50 | 20 |
| Eggs needed: | ||
| dry (kg) | 50:0.5 = 100 | 20:0.6 = 33 |
| swollen (i) | 8 × 100 = 800 | 50 × 33 = 1 650 |
| Necessary broodstock | ||
| female (kg) | 100:0.1 = 1 000 | 33:0.1 = 330 |
| (n) | 1 000:5 = 200 | 330:4 = 83 |
| male (kg) | 300 | 125 |
| (n) | 100 | 42 |
| Zug jars needed: | ||
| small (n) | 800:2 = 400 | 1 650:3 = 550 |
| big (n) | 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 (1/min ): | ||
| spawner tank | 200 | 90 |
| small Zug jar (7 1) | 40 × 1.5 = 60 | 40 × 0.6 = 32 |
| big Zug jar (200 1) | 10 × 8 = 80 | 10 × 8 = 80 |
| Total | 340 | 202 |
During the nursing period, the fry grow very quickly. Assuming that 1 million 0.5 g/fish are harvested, the weight gain per hectare is 500 kg in 20–25 days.
This mass of fish can no longer feed sufficiently, due to the lack of zooplankton, so it should be harvested and restocked at a lower stocking density. The optimal size of fingerling ponds is 3–5 ha, with an average depth of 1.2–1.4 m. Generally 50 000–80 000 fry/ha are stocked, to be grown over the summer.
Returning to the above example, 50 million carp and 20 million silver carp larvae were produced; nursing in three groups in an 18 ha pond area resulted in recoveries of 30 million carp fry (60% survival) and 14 million silver carpfry (70% survival).
Up to this stage, the fish have been grown in monoculture. However, for growing-on over the first summer and producing fingerlings, the species are stocked together in polyculture. If the average stocking density is 62 000 fry/ha, 44 million fry need a total area of
Food fish production. Carps can be marketed in Hungary at a size of at least 1 kg. In the “conventional” system of production, this requires three years (more accurately three summers, since the fish do not grow during winter). Consequently the fish must be overwintered twice in deeper (2 m) ponds. At the end of their first summer they may average 60–80 g as in the above example; after two summers around 300 g, and after three about 1.5 kg.
More recently, however, a two-year system for market fish production has been adopted on some farms. By stocking fingerlings more lightly during their first summer, and by feeding better quality supplementary feeds, fish averaging up to 150 g can be produced in the autumn after hatching. Using the same strategy during the second year, fish averaging 800–1 200 g can be produced for the market in the second autumn.
The precise area of ponds needed for market fish production therefore differs according to the strategy adopted. Differences are further increased by variations in feeding intensity and stocking rates, and by great diversity of pond size - which in Hungarian farms can reach up to 200 ha. However, on average market fish production requires at least 8 times the pond area of fingerling production. Average stocking rate in fattening ponds is 350–400 kg/ha, and by harvest it reaches 2 600–3 200 kg/ha. Both organic and inorganic fertilizers, and both cereal feeds and pelleted diets of over 25% protein content are used.
References
Woynarovich, E. and L. Horváth. 1984. The artificial propagation of warmwater finfishes. A manual for extension. FAO Fish. Tech. Pap., (201) : 183
Horváth, L., Tamás, G. and A.G. Coche. Common Carp 2: Mass production of 1985 advanced fry and fingerlings in ponds. FAO Training Series, (9) : 85
