Production of advanced fry

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23. PRODUCTION OF ADVANCED FRY

The intensive production of advanced carp fry about 3 cm long, in well prepared earthen ponds, takes 21-30 days.

24. The chief environmental factors which influence carp fry production during this first rearing period are: (1) water temperature, as fast growth and good survival require at least 18C;

(2) quality and availability of natural food, as the early fry feed on 0.15-0.2 mm zooplankters such as rotifers; (3) dissolved oxygen content which should reach 5-8 mg/l; (4) presence of predators such as insect larvae and large copepods which may cause high losses; (5) weather conditions, changes of the atmospheric pressure, sudden temperature variations, and strong winds, often resulting in poor survival.

25. This is a summary of the technology of the production of advanced fry in fry ponds.

Its most important feature is the good preparation of the dry ponds, including fertilization (1). After half filling the ponds (2), a selective chemical treatment of the water (3) eliminates the cladoceres and the copepods which encourages the strong development of rotifers (4). Then the ponds are stocked with early fry (5). Some supplementary feed is distributed (6), and larger zooplankters are seeded (7). Advanced fry are harvested 21-30 days after the filling of the ponds, depending on environmental conditions (8). They are then transported to fingerling ponds for further rearing (9).

26. The fry rearing ponds are relatively small, generally varying from between 0.01 and 1 ha in size. Their depth averages 1 m.

(1) They should have a good water supply, a regularly sloping bottom ensuring complete drainage, and an adequate water level control structure at the outlet.

Good road access to all ponds is also essential.

27. (A) The pond outlet may be either a monk or a sluice. The monk structure may be built in front of the dike (1) or as part of it (2).

In both cases, the water is evacuated by a pipe buried beneath the dike.

The sluice structure is built across the dike and there is no need for a pipe (3).

(B) The water outlet provides the possibility of controlling the water level in the pond by using two rows of planks, the space between them being filled with compact clayey soil. In front of these planks, a screen on top of a third row of planks prevents the fish from leaving the pond.

28. The fry pond has been kept dry since the last fry production season. As the new season starts it is prepared with great care.

(1) The dry bottom is cleaned of all vegetation, which is burnt.
(2) Quicklime is spread over all the bottom of the pond at the average rate of 150 kg/ha, for sterilization and to improve the soil structure.
(3) Organic fertilizer such as pig manure is then distributed at the average rate of 5 tonnes/ha to ensure a good growth of the natural food organisms.

29. The fry pond is half filled.

Care should be taken to control the entrance of predatory fish. This can be done by filtering the water through a fine mesh material, (1) placing a filtering box or (2) a simple woven basket (2) under the inlet pipe.

With a more elaborate inlet structure such as a monk, the depth at which the water is drawn from the feeding canal can also be varied.

(3) Surface water or (4) water from the bottom can be used according to the position of the screen in the front groove of the monk.

30. (A) In small ponds (max. 400 m), inorganic fertilization is applied from the banks in two steps.

(1) During the filling of the pond, ammonium nitrate fertilizer containing 43% nitrate nitrogen is thrown in front of the water inlet which will gradually dissolve and spread through the entire water of the pond, at the rate of 150 kg/ha.
(2) When the pond is full, 100 kg/ha of superphosphate fertilizer (18% active ingredient) is spread over the water surface from the banks.
(B) In larger ponds, these two fertilizers are mixed and applied together from a boat to the whole pond surface.

31. Under the stimulus of the strong fertilization, the various groups of zooplankters develop vigorously. Their relative abundance (1) varies with time (2).

First the rotifer population develops toward its peak of abundance (3).

This is immediately followed by the small cladoceres (4) and later by the large cladoceres and the copepods (5) which successively become predominant.

This is what would happen normally in the fry ponds if they were not chemically treated for the selective elimination of certain organisms.

32. If the size of the mouth of the early carp fry is compared with the individual size of the zooplankters, it becomes evident that only the rotifers can be easily eaten by the small fish.

They are the most desirable group of food organisms for the early carp fry which feed on them eagerly.

33. In the newly filled pond, the whole range of zooplankters would normally start to develop as described above (A).

However, for the moment, it is only the rotifers which are valuable food for the growth of the early fry. Therefore, the larger zooplankters should be selectively eliminated (B). This will reduce the food competition of the cladoceres to the profit of the rotifers and it will increase the survival of the rotifers by eliminating their predators, the copepods. The largest copepods which prey on the early fry will also be eliminated.

A larger population of rotifers will be present in the pond and it will develop over a longer period of time. It is only when the early carp fry have increased in size that the cladoceres and the copepods will start to appear again and to develop normally.

34. The half-full pond is chemically treated for the selective elimination of the cladoceres and the copepods. The rotifers are not affected by this treatment.

Calculate the volume in cubic metres of the water present in the pond. Take 1 g/m water of an agricultural insecticide such as Flibol, Dipterex or Masoten (an organophosphoric acid ester or trichlorfon). (1) Dissolve the total required quantity of insecticide into 101 of water and apply this concentrated solution evenly to the pond.

(2) If it is a small pond, the solution is thrown on to the surface of the water from the banks.
(3) If the pond is large, a boat is necessary. The final concentration of the insecticide in the pond water should be 1 mg/l or I part per million.

35. To see whether the selective treatment has been effective, the zooplankton should be regularly checked.

There should be no cladocere and no copepod for the next 5 days, but the rotifer abundance should increase rapidly.

To check this, filter 1001 of pond water through a plankton net with 120-180 micron mesh. Pour the plankton sample into a graduated glass tube. Add 1-2 drops of formalin to the tube to kill the zooplankters. An hour should pass before their sedimentation at the bottom of the tube. The volume of rotifers present should then be read.

When it reaches 2-3 ml per 1001 water, the pond is ready to be stocked with the early fry. Remember that this usually takes 4-5 days.

The preparation of the ponds and the hatchery production of the early fry should therefore be planned accordingly!

36. When the rotifer population has reached its optimum level about 4-5 days after the chemical treatment, the early should be stocked as soon as possible.

They are transport from the hatchery to the ponds by various means, depending on the length of time the journey will take. Close to the hatchery, the transport can be done on foot, (1) carrying the in 301 plastic pails or (2) using a small tractor/trailer wit fibreglass water tank. For longer distances, (3) small trucks a (4) lorries are used, equipped with oxygenated water tanks During this transport, the density of early fry varies from 1 to million per cubic metre of water. Transport in plastic bags also common practice, as described in the first manual.

37. The early fry are stocked in the fry ponds at the rate of 00600 ind./m, according to the size of the pond and its potential productivity. Smaller ponds, highly productive, are socked at the highest density.

1) It is very important to ensure that the water temperature in e transport container does not differ more than 2C from that the pond.
After a long journey in a plastic bag, for example, (2) the bag should be immersed in the pond water for at least half an hour before the fry are released into the pond.
3) In a fibreglass tank the temperature is equalized by gradually adding pond water to the tank and it is only when the water temperatures are very similar that stocking is done, (4) sing the flexible canvas tube from the inclined tank.

About a week after this stocking, the half-full pond should begin to be filled, raising its water level gradually until it is completely full.

38. When stocking large fry ponds from a heavy lorry, the fish are transferred to the pond by means of a plastic chute. In such large ponds the risks of losses are very great. It is advisable to place 100-200 early fry in a small netting enclosure to control their first few weeks' survival.

39. Soon after their stocking into the pond, the early fry voraciously feed on the abundant rotifers present.

Their growth is fast and their survival rate high. But as they grow they progressively require larger preys to feed on and the individual size of the natural food organisms which are available should gradually increase.

Three main feeding phases may be defined during this firs month rearing in the fry ponds.

40. During the first 10 days after stocking, the early fry will preferably feed on rotifers.

Because of such heavy predation the abundance of the rotifer population will slowly decrease as the carp fry grow quickly By the end of this period the individual size of the rotifer becomes too small to satisfy fully the needs of the fry.

41. From about the tenth to the twentieth day the best food for carp fry consists of small cladoceres and copepods.

The populations of these zooplankters have started to develop again in the pond about 5 days after the application of the chemical treatment which had eliminated them in favour of the rotifers.

It is also then that the stocking of the early fry had taken place and, a little later, that the pond had been completely filled. It is also during this period that zooplankton is added to the pond to assist its repopulation with larger food organisms, as shown later-see item 46.

42. During the last 5-10 days of this first rearing period, the fry feed on all cladoceres and copepods.

They are also able to consume small insect larvae such as chironomids and mayflies (Cleon sp.).

43. In addition to the natural food which is so important to early fry, it is necessary to provide artificial food to ensure the best possible growth and survival during this first month of rearing.

Although both natural and artificial feed are available to the fish from the beginning of the period, the quantity of each type of food consumed (1) varies with time (2). Initially, only natural food is taken, its consumption reaching its peak about 10 days after stocking (3).

This is followed by a reduction in natural food consumption as the preference for the artificial feed gradually increases (4).

By the end of the month the fry consume relatively little natural food, and the predominance of artificial food is apparent.

It is therefore necessary to increase regularly the quantity of artificial food distributed daily during the rearing period (5).

44. The artificial food consists of a mixture of equal parts of soybean meal (1), wheat meal (2), fish meal (3) and blood (or meat) meal (4). It is in the form of a very fine dry powder made of 0.1-0.2 mm particles.

At the beginning of the period, it is distributed at the rate of 1 hire per 100 000 fry. This daily feeding ration (DFR) gradually increases during the month up to 5 litres per 100 000 fry.

Food is distributed once a day in the morning or preferably several times daily, the DFR being then divided accordingly.

Two feeding methods are used. (A) In small ponds, the artificial food is scattered over the water surface from the banks. On windy days the direction of the wind should be taken into account, as it will tend to agglomerate the floating food in one part of the pond only.

(B) In larger ponds, the powdered food is diluted with water in a bucket. The liquid mixture is then distributed from a boat at various places around the pond.

45. The water management of the fry pond is highly important, since its objective is to optimize the environmental conditions for the production of carp fry. It is carried out in five stages.

(1) After its preparation in the dry state, the fry pond is half filled with filtered water and the chemical treatment is applied. (2) About five days later, the early fry are stocked in the half full pond. (3) One week later, the filling of the pond is slowly completed, and larger zooplankton is stocked. (4) From now on, the water level is kept stable and additional water is supplied only to compensate for seepage and evaporation. (5) If by the end of the month the fry survival is good, the water supply is increased for a few days before harvesting to create an overflow.

46. About 12 days after the chemical treatment of the pond water to eliminate the larger zooplankters, it is advisable to reintroduce some of them as seeds, particularly the cladoceres Moina and Daphnia.

These are collected from other ponds with a zooplankton net and transported either in buckets (A) or in a tank (B).

In small fry ponds (100-400 m), a living biomass of 100-200 ml or about one full bucket of a dense zooplankton population is required.

In larger fry ponds, a 1-litre biomass should be sufficient. This zooplankton will rapidly reproduce in the well-fertilized pond to boost the resident population.

47. During the first rearing period, the growth, survival and health of the growing fry should be regularly controlled.

(1) The fry may be observed directly in the pond, using a white plate as a background. (2) They may also be fished easily along the banks and in grassy areas, using a fine mesh dip net. (3) Their swimming behaviour together with their general condition can be observed in a glass of water. (4) The presence of ectoparasites can be detected with a binocular microscope.

48. What is a "good" or a "bad" fry?

What is a "good" or a "bad" fry?

  Good fry (A) Bad fry (B)
Body shape: deep, plump slender,
bighead  
Colour:
belly deep yellow yellowish
back greyish green dark
tail bright, shiny dull
Tail movement: very rapid slow and
and hardly easily
visible visible

49. The growth of the fry (1) in length and (2) in weight during this first rearing period varies according to the environmental conditions.

In general, however, if these conditions meet the average standards, (1) the total length of the fry in centimetres should reach about 3 cm and (2) their live weight in milligrams should (3) be about 300 mg by the end of the four-week period.

50. By the end of the first rearing period the young carp have become advanced fry.

They measure from 2.5 to 3 cm in length, weighing from 200 to 300 mg each. The survival rate during these 25-30 days usually varies from 30 to 60%.

51. The time has come to harvest the advanced fry and transfer them to larger ponds.

If the aquatic insects such as Corixa are too abundant, the pond is first treated with a dose of 1 ppm of an agricultural insecticide. The same chemical used for eliminating the larger zooplankters can be applied, see item 34.

(1) The water level is then slowly lowered through the outlet.
(2) When the pond is half drained, fishing starts with a fine-mesh seine net. When most of the fry have been removed, the water depth is further reduced.
(3) Toward the end of the draining, a fixed trap is placed in the outlet and the remaining fry are captured as the pond is completely drained.
(4) During these operations, a long fine-mesh screen is slid into the outlet structure, in front of the two rows of wooden planks, to prevent the escape of fry.

Toward the end of the harvest this screen is replaced by the fixed trap as the last planks are being removed.

52. The fishing with the seine net is done along the pond banks.

(1) Two fishermen pull the fine-mesh net until they have collected a certain number of fry. (2) They then turn the net toward the bank where they place it horizontally, keeping the fry in the middle. (3) They slowly concentrate the fry into a small pocket, being careful always to keep them under water. (4) The fry are transferred from the net to a water container, using a dip net.

Depending on the average size of the fry the mesh size of the seine net is either 2 mm square for 2-cm fry or 4 mm square for 3-cm fry.

In both cases, the netting is generally nylon curtain material. The seine net is 10-20 m long, according to the size of the pond, and about 2 m high. Secured at each end to 1.20-m wooden poles and mounted on ropes with floats and lead sinkers, it very effectively captures the fry in its baggy central part as it is dragged along the pond bottom.

53. The fixed trap may be of two kinds.

(1) A 1 x 0.6 x 0.6 m wooden frame covered on two sides on with fine-mesh netting may be directly attached with a flexibly joint to the draining pipe.
(2) A V-shape net trap mounted on a wooden frame may slid into the outlet structure and held open by a series stretching lines.
In both cases the fry should be constantly removed from the traps with a dip net to avoid great losses caused by the strong water current flowing through them.

54. The advanced fry are transported from the ponds to storage nets to be sorted and counted before they are transported and stocked in fingerling ponds.

The nets (for example 2 x 1 x 0.8 m) are made of fine-mesh (2-4 mm) netting such as nylon curtain material. They are suspended from two sides into water-filled tanks supplied with a continuous inflow of water sprayed on the surface of each enclosure. A light frame is placed into each net to keep its bottom part down. (1) The fry are transferred into the nets on arrival from the ponds. (2) They are stored there without feeding for 24 hours maximum. (3) It is very easy to transfer them to the lorries for transport. (4) A similar system can be built in a corner of a pond, next to the water inlet, by attaching a similar storage net inside four poles.

55. The estimate of the number of advanced fry stored in the nets is obtained on the basis of the volume of a known number of fish.

(1) A 5-cm tea strainer should be filled with fish which are then counted one by one. (2) Using the same strainer, the number of such tea strainers needed to be filled with fish in order to fill a larger strainer (about 14 cm in diameter) can be obtained. The number of fish contained in the latter can be estimated by multiplying the number of fish in the small tea strainer by the number of such strainers required to fill the larger one. This larger strainer now becomes the basis for estimating numbers of this particular population of carp fry for transport. For example, 175 fry are counted in the small tea strainer and you need 10 small strainers to fill the large one. This large tea strainer holds 175 x 10 = 1750 fry.

56. Before transport and stocking, the advanced carp fry are given a quick salt bath to control ectoparasites, Trichodina in particular.

(1) A 2-3% salt solution is prepared by adding 1-1.5 kg common salt to 501 water.
(2) A piece of fine-mesh netting is placed within the container.
(3-4) Batches of fish are successively treated by being dipped for 30-40 seconds in the salt solution.
(5) The fish are then kept in clean and well-aerated water (6) until their transport.

57. Advanced fry can be transported for long distances by road or by air in plastic bags 55-60 cm in diameter and 80-90 cm high.

(1) 201 of clean water are first poured into the bag which is carefully checked for leaks.
(2) 2 000 to 5 000 advanced fry are placed in the water, depending on the duration of the transport, and the rest of the bag volume (at least 201) is filled with oxygen.
(3) The bag is tightly closed with a piece of string.
(4) It is checked again for possible leaks before it is placed in a cardboard box for transport. For additional security, the first plastic bag can be put inside a second one.

58. Advanced fry are also transported for short distances on foot in water pails (1) and by small tractor/trailer in fibreglass tanks (2).

For longer distances such tanks are fitted on to small trucks (3) or larger lorries (4), together with oxygen cylinders.

Depending on the duration of the transport, 50 000 to 100 000 advanced fry are stocked per cubic metre of water and continuous diffusion of oxygen is assured.

Remember to equalize the temperature of the water in the transport container with the storage water temperature.

59. Fibreglass water tanks of about 1 m capacity are very convenient for the transport of advanced fry.

They can be fitted to the platform of small trailers or trucks. An oxygen cylinder connected to a large diffuser made of plastic tubing mounted on a metal frame.

Such a water tank may safely transport up to 100 000 advance fry for 2-3 hours, for example, around the hatchery farm.

A flexible pipe is used to transfer the fry from the tank to the pond directly.


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