G. Tamás and L. Horvath
Warm Water Fish Hatchery, Százhalombatta, Hungary
ABSTRACT
The rearing of cyprinid fry and fingerlings is discussed. The fry rearing period takes about 1 month in nursery ponds. Fingerling rearing takes place in bigger ponds and is realized in the remainder of the growing season.
The methods are described and important facets or processes are highlighted.
RESUME
Sont exposés l'élevage larvaire et la production d'alevins de cyprinides. La première phase en frayères prend un mois, l'élevage subséquent des alevins s'étendant jusqu'à la fin de la saison en étangs plus grands.
Les méthodes pratiquées et quelques aspects importants sont décrits.
Warm water pond farming in Middle Europe has a considerable past. In this region an appropriate environment can be found for common carp, tench, wels and recently, for East Asian herbivorous fishes. In the last century, fish farming developped to an economical production branch of agriculture. Since that time the amount of land used for fish farming has gradually increased. With the development of technology, the production intensity increased as well. By consequence, the demand for fish fry for stocking has also grown.
Until a few decades ago fry was produced by the method of 'natural-like' spawning. Elaboration of the most popular method in this field was done by Dubits. According to this method breeders were put into shallow small ponds, where they spawned spontaneously. Feeding fry were harvested and introduced into bigger ponds for further rearing to the end of the season. Because of the low returns, this method is no longer practised.
Technical and scientific achievements of the last few decades have resulted in the elaboration of mass production hatchery methods. The essence of this method is, that ovulation of eggs is provoked with a hormones treatment and that the fish are in protected environment (hatchery) during the vulnerable periods of egg and larval life.
The fry period lasts to the end of the first month with warmwater fishes. It can be divided into 2 periods: non-feeding and feeding period.
The non-feeding period begins with hatching and lasts for 4–5 days, when first feeding and taking of air occurs. Non-feeding fry are kept in the hatchery, in the collector glasses (larger Zuger glasses or other devices, throughs, basins etc.). Because of great densities, water has to run through these devices. Water quality has to be excellent (almost drinking water) and should be free of tiny predatory organisms (mainly Copepods). The end of this period is marked by the first feeding of larvae. The fry have to be fed before complete resorption of the yolk sac, to secure their energy resources. Quality and size of first feed are decisive Boild egg suspension is used as first feed of Cyprinids. This nutrient can substitute feeds of full value, e.g. living feed organisms, only for a short time. If transfer of larvae to the ponds is not possible (e.g. because of weather conditions), live feed organisms have to be provided. Before stocking, temperature differences should always be eliminated.
The feeding period lasts for about 4 weeks. By this time, all organs of the fry are developed to the final stages.
Newly hached fry are kept in great densities in tanks or Zug-glasses inside the hatchery. Here they receive their first feed.
The most effective method for rearing the feeding fry is by putting them in small, protected ponds. Recent literature mentions full value starter feeds, which in the ‘future’ may result in basin rearing. The practise of pond rearing requires special conditions and very accurate management.
Requirements of nursery ponds are:
- environment protected from wind,
- excellent water quality (free of toxic matter and of organic pollution),
- ample water supply through the rearing period,
- continuous sloping of pond bottom to the drainage structure
- appropriate road system for transportation,
- protecting devices against frogs and birds.
Preparation and treatments of ponds
General remarks:
- ponds have to be kept dry, when not used
- after every turn of rearing, they should be thoroughly desinfected with lime (300–500 kg/ha).
- after inundation and treatment with lime, water of ponds has to be tested for pH (optimal values between 7–8)
- inundation of ponds has to be carried out with filtered water
- dry reed and other plants have to be cleared out of the ponds before inundation (preferably burned)
- after filling up the ponds, structures should be closed hermetically by the help of organic manure.
Tasks to be done before rearing:
- ponds have to be half filled with water
- inundation of ponds has to be started, when the fertilized eggs are put into the hatching devices. (In case of bigger ponds, - more than 1 ha - this has to be done 1 week earlier)
- simultaneous to inundation fertilization of ponds has to be carried out. Preferable dosage: organic manure 5–7 tons/hectare, artificial fertilizers: phosphorus fertilizer 100 kg/hectare, nitrogen fertilizer 150 kg/hectare.
- chemical treatment of ponds is also carried out parallel to inundation (1 ppm organic phosphoric acid ester insecticide)
- after chemical treatment, investigations on plankton stocks are necessary: required quantity of (mainly Rotatoria species) plankton biomass 3–5 ml/100 liter pond water.
- stocking density of fish larvae in bigger ponds 100–300/m2, in smaller ponds 300–600/m2.
- supplementary feeding starts on the day of stocking, for 100.000 feeding larvae 1–2 kg of supplementary feed is provided. During the first week the recommended feed composition is:
| soya meal | 25% |
| wheat meal | 25% |
| fish meal | 25% |
| blood meal | 25% |
- sanitary controll: A few fishes are investigated every 2–3 days for parasites
- if necessary, copperoxichloride treatment at the end of the rearing period should be carried out
- it has to be verified regularly that no water can flow out of the ponds
- during the second week, a fertilization (30–50 kg P/ha) has to be carried out for maintenance of zooplankton
- after appr. 4 weeks, harvesting of the rearing pond takes place. During the fishing, fry have to be handled carefully
Fry of 2–3 cm and 0.1–0.2 grammes are transferred to bigger ponds in lower densities. The fry are reared in monoculture for 1 month. After this, in the second rearing period, they are grown in polyculture to the end of the season. This way the natural protein production of ponds is utilized better.
During the second period, supplementary feeding of fish is more intensive, so the ration of artificial feeds is taken higher.
The technical and biological requirements of ponds in this period are less important than in the previous period and some concessions can be made:
Requirements of ponds for fingerling rearing are as follows:
- ponds with bigger surface (3–10 ha) are more economic
- although good quality water is important, organic pollution to a minor degree is acceptable
- easy transportation must be possible (during the season transportation of feeds and at the end of the season harvested fish)
- additional water supply during the season
- fishing pit outside or inside the pond for harvesting
- protection against predators (mainly birds)
- ponds have to be kept dry at least for a few months before rearing season
- bottom of ponds have to be tilled to a depth of some cm
- parallel to this, organic manure (3–5 kg/ha) and lime (100–200 kg/ha) have to be distributed on the pond bottom
- after this, ponds can be filled up totally. Inundation water has to be filtered to prevent wild fish from getting into the pond
The above mentioned works have to be carried out two weeks before stocking.
Ponds used for rearing of fingerlings are stocked with fry of 2–3 cm length, in polyculture. For stocking, the same age groups of different species are used. It is also important to stock all species at the same time. During the stocking, temperature differences have to be egalized and care has to be taken not to injure the fry.
To avoid feed competition, common carp should be stocked with less grass carp and bighead and more silver carp. When the water vegetation is consumed, grass carp will feed on cereals and will get ill. At the same time bighead will filter zooplankton out of the water. Carp together with a major quantity of tench is also unfavourable, as carp is a strong feed competitor to tench. Silver carp can be used in all structures of polyculture because of its favourable feeding habits.
In all polyculture structures carp serves as a basic species, as in its absence the circulation of nutrient elements is stopped and they accumulate in the mud. In practice, there is always a chosen species, which serves as basis for polyculture, and all treatments are carried out so as to promote the development of this species. According to this we speak about carp, tench, grasscarp and bighead polyculture. Predatory fishes (mainly wels and pike perch) are also useful members of polyculture. Their main role is the selection of undeveloped, invalid or diseased fish and at the same time the utilization of other protein resources. Their percentage, nevertheless, has to be low (1–2%), as otherwise, they will prey on bred species. As acceptions those cases may be mentioned, when the production of wels or pike perch is the basic aim. When using this technology, one has to count with the loss of all other fishes.
Most frequently used composition in polyculture
| 60–70% | common carp |
| 20–30% | silver carp |
| 10–15% | bighead + grasscarp |
| 1–2% | predatory fish |
In feeding of fingerlings care should be taken, that in the initial period there should be no great differences as compared to fry rearing. The first week the same feeding has to be practised. After this, with the help of appropriate zooplankton stocks, adequate protein resources are assured for the fish. Supplementary feeding can then be done using ground cereals. Depending on the temperature of the water and the apetite of the fish, 5–10 percent of their body weight can be fed. The kinds of feed used are determined by structures of polyculture. Herbivorous fishes require starch only to a minor degree. In grasscarp polycultures feeding of plants is important. Grass and leguminous plants - cut or uncut - are given depending on size and age of fish.
Protein resources of the ponds will become depleted after a certain time, when supplementary protein feeds have to be fed beside starch feeds. The protein has to be of animal (e.g. fish meal) or plant origin (soya). It often happens that in spite of the above described feeding methods, fish do not develop well. The cause for this may be found in the pollution of the environment originating from the products of metabolism, among which growth preventing matters are also present. In such cases, total or partial change of the water is recommended.
During the growing season, control fishing has to be carried out to examine the growth of the fish. As the amount of feeds given is known, the effectiveness of feeding can be stated from the average weight of a few hundred fish. During the control fishings, the sanitary state of fish is also examined. Under pond circumstances, gill diseases are the most common. These can cause serious damage. Losses can be partly eliminated by the help of liming.
By contrast to larval rearing, diseases caused by parasites are not so frequent.
Harvesting is started, when the temperature of the water decreases to 4–9°C: Fingerlings reared in polyculture are kept together during the winter or are sorted according to species and kept separately. During harvesting and transportation, fish have to be handled very carefully. In wintering ponds, malachite green treatments have to be carried out to prevent the spread of fungi.
Harvesting offers a good opportunity for controll of parasites. Flush treatments with salt solution (2–3% for 5 minutes) are used. Transportation takes place with the help of oxigen aeration. Amount of fish transported in 1m3 of water is 150–300 kg, depending on species and temperature of water.
The fish are wintered in 600–1000 m2 rather deep ponds at a rate of 5–8 ton of fish per 100 m2 with a water flow of 80–100 1/min/ton of fish. Two-weekly sanitary checks are made during the wintering.
