Production of fingerlings
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60. PRODUCTION OF FINGERLINGS
The objective of the second rearing period is to grow the advanced carp fry to the fingerling size of 10-40 g. In temperate climates this period generally lasts 3-4 months from July to October. In comparison with the first rearing period the chances of good survival are much higher and the fish require less protection.
61. The following are the main environmental factors which influence carp fingerling production during this second rearing period.
(1) Warm water temperatures will accelerate growth and increase production. (3) The water-dissolved oxygen content should remain high (5-8 mg/l) for best results. (4) Predators may still cause great losses, particularly the larger ones such as frogs and birds.
(2) The importance of the quality and availability of natural food gradually decreases as the fry grow older and artificial food is introduced. (5) The weather conditions also become less vital, now that the fish have reached a larger size.
62. (1) The fingerling ponds are larger, generally ranging from 1 to 10 ha.
Their depth varies from 1 to 1.5 m. They should have a good water supply large enough to fill the pond rapidly.
(2) The outlet structure generally consists of a monk but for the larger ponds it is advisable to build outside fishing channels also. Several ponds may be drained through a common fishing channel. (3) Next to the harvesting area a working platform with road access is built where large quantities of fish may be efficiently handled for sorting, weighing, and transport loading. The banks of such large ponds should be protected against wave action by allowing the growth of emerged aquatic plants such as reeds along the wind-exposed banks.
63. The fingerling ponds are kept dry during winter. In early spring they are repaired and cleaned.
(1) The damaged banks are rebuilt. (2) The dry permanent vegetation which protects the banks is cut short so that it will produce new shoots soon. (3) The whole bottom surface is stripped of vegetation. (4) The reeds (Phragmites communis) are prepared for sale.
64. When the climate becomes warmer, it is time to prepare the ponds before filling them with water.
(1) The wet parts of the pond bottom are limed with an average
dose of 150 kg/ha.
(2) Organic fertilizers such as pig or chicken manure are spread over the entire surface (2-3 tonnes/ha), and this is followed by a very shallow loosening of the bottom soil.
(3) The most exposed banks are protected, where necessary, with woven branches.
(4) The water outlet of the pond is sealed with two rows of planks and clayey soil. The pond is then rapidly filled with water.
65. Inorganic fertilizers are applied when the pond is completely filled.
Superphosphate (100 kg/ha) and ammonium nitrate (150 kg/ha) are spread over the entire surface of the water from a boat.
66. As described earlier-see items 57, 58 and 59-the advanced fry are transported by various means in water pails, plastic bags and water tanks.
The transport takes place preferably during the coolest hours of the day.
On arrival at the pond the temperature of the water in the containers is equalized within 2-3 C with the temperature of the pond water.
A plastic chute (1) is used to transfer the fry from large lorries directly into the pond. The stocking rate of the fingerling ponds ranges from 50 000 to 100 000 inc./ha depending on the size of the pond and its productivity potential.
Smaller productive ponds are stocked at the highest density.
67. The feeding regime of the advanced fry changes as they grow larger.
When considering the amount of food consumed (1) versus time (2), large zooplankters and other kinds of natural food, especially chironomids, gain importance at first until they reach a peak after about a month (3).
It is therefore advisable to favour the development of large zooplankton and bottom fauna populations by means of fertilization to support the growth of the advanced fry at the beginning.
Later, it is the artificial food which steadily gains importance (4).
68. As the carp grow, the daily ration of artificial food pressed in percent of the weight of fish should be progressively reduced.
It should be further reduced as the water temperature drops, especially when it becomes less than 12°C. Carp stop feeding completely at around 7°C.
With a low fish density of about 50 000 inc./ha (A) the food of the advanced fry consists, in equal proportions, of artificial (1) and natural (2) feed. The artificial food contains mainly ground wheat and is distributed at the maximum daily rate of 10% of the fish biomass.
With a high fish density of at least 100 000 inc./ha (B), the food of the fish consists of little natural food (2) and, in roughly equal proportions, of two kinds of artificial feed.
Ground wheat is distributed at the maximum daily rate of 10% the fish biomass (1)
A balanced food containing about 30% protein (half of animal origin) is distributed daily at the rate of 5-10% of the fish biomass (3). This last food is supplied as 3-mm dry sinking pellets.
69. The artificial food is distributed daily from a boat, at fixed feeding stations identified by wooden poles. About 5-7 feeding stations per hectare are chosen around the fingerling pond.
70. Special feeding boats are generally used on the large ponds.
(3) There is an opening along the bottom of the boat, who
width may be regulated by the boat driver.
(2) The feed is taken out by the water current as the boat move along feeding lines (1) identified in the pond with wood poles.
71. The daily rations of artificial food are adjusted to the appetite of the fish.
The consumption of the feed is regularly checked by the fishermen, using a light scooper made of fine-mesh metal netting, for example (1).
Two to three hours after the morning food distribution, a few feeding stations are checked with the scooper. If there is food left, the daily ration will be slightly increased the following day.
If a lot of food is still present, a second check is made 5-6 hours later; if much food can still be found, the daily ration for future days will be decreased.
72. The water management of the fingerling ponds consists in keeping the level constant throughout the rearing period.
(1) The pond is filled full and fertilized.
(2) The fish are stocked. Every two weeks, the pond water is fertilized in an effort to keep the level of plankton production constant.
(3) Liquid pig manure in particular is distributed along the banks at the rate of 10 m³/ha of pond. Superphosphate (20-30 kg/ha) and ammonium nitrate (20-30 kg/ha) are spread over the entire surface from a boat.
(4) Toward the end of the rearing period when there is danger of overstocking, the water supply is increased to create a stronger flow through the pond.
73. The fish are sampled every 2-3 weeks at the feeding stations.
A few hundred fish from each fingerling pond are caught in a casting net. The average individual weight is calculated from their total weight and number. On the basis of the quantity of artificial food distributed between successive controls, the food conversion rate is calculated and the efficiency of the pond production evaluated.
If the food conversion rate does not exceed 3.5 to 4, production efficiency is good. When the food conversion rate becomes higher, the reason for the drop in efficiency should be investigated. It is usually due to the presence of disease or parasites, or to a decline in the availability of natural food. Remedial measures are then applied and the production efficiency reestablished to an acceptable level.
74. This example shows how to set about evaluating production efficiency in a fingerling pond during a specific two-week period.
At the start of this period, the average weight of the carp has already been found to be 1 g by means of the previous sampling. As the stock of advanced fry was 100 000, the standing crop was then 1 g x 100 000 = 100 kg.
At the end of the period, two weeks later, it can be determined from the sampling that the carp now average 2 g. So the standing crop is 2 g x 100 000 = 200 kg and the production during the last two weeks has been 200 kg- 100 kg = 100 kg.
An average daily ration equal to 15% of the fish biomass present at the beginning of the period has been fed and 0.15 x 100 kg = 15 kg artificial food have been distributed each day.
During the entire period under examination, 15 kg x 14 days = 210 kg have been distributed. These 210 kg of food have resulted in a 100-kg carp production and therefore the food conversion rate is 210 kg: 100 kg = 2.1.
It is concluded that the efficiency of the fish production during the last two weeks has been good in this particular fingerling pond.
75. The sampled fish are also examined to determine their feeding regime.
(1) After the distribution of artificial food the carp fry eat
(2) but later they collect natural food organisms from the water column and from the bottom.
(3) To estimate the proportion in which these two types of food are consumed by the carp fry, the fish farmer presses the fish body laterally and obtains some intestinal content.
(4) According to its colour he can tell which type of food the fish has eaten, natural food (dark) or artificial food (grayish/white). If the whole intestinal tract can be examined, the two types of food will generally be found alternating.
When the relative amount of dark areas decreases, it indicates that carp have changed their feeding regime in favour of artificial food and that the addition of some high protein pellets to the feeding ration may become necessary.
76. What is a "good" or a "bad" fingerling?
What is a "good" or a "bad" fingerling?
|(A) Good fingerling||(B) Bad fingerling|
77. The health aspects of some of the sampled fish should be examined under a binocular microscope. This is best done by a biologist or a veterinary doctor.
If necessary, therapeutic treatments are applied, such as (1) the chemical treatment of the pond water or (2) the distribution of medicated feed. (3) In simpler cases, an increased water exchange through the pond may be sufficient.
78. Most common in the fingerling ponds during the warm season are the monocellular ectoparasites such as Ichthyophthirius multifilis, the white spot disease or "ich".
(1) The pond is treated against these with malachite green at the final concentration of 0.1 ppm. Also very common are: (2) Trichodina on the fins, (3) Costia on the gills, and (4) Chilodonella on the gills and fins.
For these last three parasites the pond is treated with copper oxychloride at the final concentration of 4 ppm.
79. Other ectoparasites can also cause great damage if they become numerous and remain unchecked, as for example: (1) Argulus foliaceus, (2) Lernaea cyprinacea, (3) Ergasilus sieboldi, (4) Dactylogyrus vastator, and the leech (5) Piscicola geometra.
The pond should be treated with an agricultural insecticide- see item 34 - at the final concentration of 1 ppm, or 1 g/m³.
80. Occasionally serious fish diseases may develop in the fingerling ponds. In such cases, the advice of a veterinarian becomes necessary.
Examples are: (A) the gill rot and gill necrosis caused by the combined action of a fungus and bacteria, in adverse environments. The treatment consists in treating the pond with chlorinated lime (1 ppm) and increasing the water exchange.
(B) (1) Gill infection and (2) fin rot are bacterial diseases.
Small ponds can be treated with malachite green (0.1 ppm), but in large ponds only chlorinated lime (1 ppm) can be used. The water exchange should then be increased.
81. By the end of the second rearing period which lasts for 3-4 months, the advanced carp fry have grown into fingerlings. The average survival rate is normally 80%.
The yield ranges from 1 to 2 t/ha.
The carp fingerlings, also called "yearlings" in temperate countries, have a total length ranging from 8-12 cm and a live weight varying from 10 to 40 g.
82. At the end of the second rearing period, (A) the finger lings are harvested with large seine nets.
These nets are 20-30 m long and 2.5 m high.
(2) Their 10-15-mm mesh netting is attached on each side at regular intervals, to (1) 1.5 m wooden poles to form a baggy shape.
(3) The top of the netting is mounted on a rope with floats while (4) its bottom part is mounted on a rope with sinkers.
(5) Two corners are reinforced with steel tubing.
The seine is slowly pulled vertically along the pond bottom through two long ropes.
(6) Each of them is attached both at the top and the bottom of the wooden poles.
(B) During the harvest, double-frame dip nets (30 cm diameter) are frequently used, too.
83. The fingerlings are transferred through the outlet structure from the large rearing pond to the outside fishing channel, as the water is slowly drained from the pond.
The channel is then repeatedly fished with the seine net toward the working platform where the fish are harvested. All this should be done early in the morning before the air temperature warms up.
84. In rearing ponds not connected to a fishing channel, (1) the water is partly drained so that more than half the pond becomes dry.
(2) Water and fish are now concentrated in the deeper channels
and in the lower part of the pond.
(3) These areas are fished with the seine net toward the harvesting areas, near the access road and next to the monk.
Finally, the last part of the harvest is collected in front of the monk where a fishing pit is sometimes built. (4) The water drains out of the pond into the draining canal (4).
85. The harvested fingerlings are brought to the sorting table where they are sorted by size and, if necessary, by species.
(1) The fish are poured onto the table.
Several fishermen sort the fish rapidly, (2) pushing the various sizes through side apertures into different 50-1 water containers. The live carp are kept in these containers only for a short time. They are then immediately placed in clean water again, usually in a transport container.
All these operations usually take place in an open shed built on a working platform.
As the fingerlings have to be kept alive, it is important that they remain out of the water as little as possible and that the work proceeds with diligence and efficiency.
86. For sorting large quantities of fish, a rubber conveyor belt moving horizontally is used.
(1) The harvested fingerlings are transferred to the head of
the conveyor belt. As they are moved along, (2) they are sorted
by fishermen into water containers.
(3-4) The most abundant size/species is left on the belt to drop at the end either into a large container or into a chute and a storage basin which can be fished later.
87. The sorted fingerlings are transported from the harvesting site and stocked in either (1) storage ponds or (2) fattening ponds.
In the first case, the fish will be marketed outside the farm or they will overwinter, as discussed in the next section.
In the second case, the fingerlings will continue to grow until they reach marketable size.
88. During transportation, a chemical treatment may be applied for the elimination of ectoparasites.
In such cases, five minutes before reaching the pond where the carp will be stocked, a mixed solution of three chemicals is poured into the transport container as follows: common salt (final concentration 2 kg/m³), agricultural insecticide (200 g/m³), and malachite green (0.1 ppm).
For this last chemical, a stock solution is first prepared by mixing 20 g (1 tablespoon) of malachite green with 1001 water.
To obtain a 0.1-ppm concentration, 0.5 1 of this stock solution per cubic metre water in the fish container is used.
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