INDUCED BREEDING OF ASIATIC CARPS

PERPARED BY :

DR. HIRALAL CHAUDHURI, FORMERLYPROJECT COORDINATOR,
DR. S. B. SINGH, FISH BREEDING EXPERT & OFFICER-IN-CHARGE

LAO TRANSLATION BY :

- MR. SOUTHALAT BOUTAH, DIRECTOR, LIVESTOCK
- MR. KHAMTANH VATTHANATHAM, FISHERIES SERVICE

DEPARTMENT OF LIVESTOCK - FAO / UNDP PROJECT
LAO / 82 / 014
VIENTIANE: OCTOBER, 1985

INDUCED BREEDING OF ASIATIC CARPS

The Lao people like fish and are keenly interested in fish culture. There are innumerable ponds scattered all over the country. Among the good fishes already introduced in Lao PDR for culture, the important ones are the Asiatic carps namely, rohu (Labeo rohita), mrigal (Cirrhinus mrigala), catla (Catla catla), silver carp (Hypophthalmichthys molitrix), big head (Aristichthys nobilis), grass carp (Ctenopharyngodon idella). In addition to exotic carps, the indigenous Mekong carps namely, pa phone (Cirrhinus microlepis), pa phia (Morulius chrysophekadion), pa nok khao (Osteocheilus melanopleura) etc. have a good possibility of culture in ponds.

All the above carps are good to taste, grow fast and mostly consume the natural food produced in the ponds. Also, they mature in ponds, but do not breed in the pond environment. So their pure seed is produced through the technique of “induced breeding” by injecting fish pituitary hormones (hypophysation). This technique is simple to use and LAO technicians have been trained properly in using this field method successfully in producing the pure seed of Asiatic carps.

This extension pamphlet is produced to educate many more Lao technicians and farmers in the technique of fish seed production. The method of induced breeding of carps is described in detail and the essential requirements for the fish seed production programme are listed.

A. TECHNIQUE OF INDUCED BREEDING OF ASIATIC CARPS:

1. Raising of broodfish:

A good stock of brood fishes is the primary need for a successful fish seed production programme. To raise good brood fishes of the Asiatic carps (rohu, mrigal, catla, silver carp, big head and grass carp), it is essential to select healthy fishes of 1–2 kg size of each species from the production or marketing ponds and to stock them in proper brood fish ponds at least 5–6 months in advance of the proper breeding season which generally starts with the onset of monsoon (rainy) season.

Good brood fish ponds are perennial, free from other fishes, preferably 0.5–2.0 ha in area. Unwanted fishes are removed by dewatering the pond or by thorough netting. Lime is applied at 200 kg/ha and one week after liming, manure at 5000 kg/ha (fresh animal dung) or 500 kg/ha poultry droppings is put in the pond. The pond water will then have good plankton food for the brood fishes.

The selected brood fishes of all the above named Asiatic carps can be stocked together at a total stocking density of 1500–2000 kg/ha. The ratio of stocking of various species can be kept as follows: big head 20%, silver carp 20%, catla 10%, rohu 20%, mrigal 20% (or, mrigal 10%+common carp 10%) and grass carp 10%. Provide rice bran+peanut cake at 15–20 kg/ha/day as supplementary feed. However, for grass carp supply aquatic weeds, fodder grasses, tapioca leaves and boiled tapioca, etc. regularly in adequate quantities. The feeding rate is properly adjusted so that the water does not get foul. If thick algal bloom appears, stop feeding, add more fresh water and aerate the water by using a water pump, if possible.

2. Collection and preservation of fish pituitary glands:

The pituitary glands of mature fishes are generally used for fish breeding work. Common carp is a very good fish for collecting glands (donor fish) as these are mature almost throughout the year. The pituitary glands are collected carefully and put in absolute alcohol for initial washing and later stored in a cool place or refrigerator inside air-tight glass bottles in absolute alcohol to remove water and fat from the glands. The pituitary hormones are not soluble in absolute alcohol, but highly soluble in water, so the pituitary glands when being collected should not come in touch with water.

In addition to fish pituitary glands, use of chorionic gonadotropin (CG) is made by some workers for breeding silver carp and big head. The doses used for female brood fish are generally at 3–4 mg/kg pituitary gland extract as first dose only, CG at 1200–1500 I.U./kg body weight of the female fish as second dose. Also, some workers use the synthetic LH-RH analogue and find it useful in fish breeding, but it is not so common and also more expensive. However, it has been the experience of most of the fish breeders that if the brood fish condition is maintained good, the fish pituitary glands alone are highly effective in inducing breeding of all the cultivated Asiatic carps.

In a well-managed fish seed programme, donor fishes (fishes for collection of pituitary glands) should be raised at the fish farm itself so that fresh glands are collected and preserved properly in absolute alcohol.

3. Selection of mature female and male fishes and formation of breeding sets.

When regular monsoon sets in, freshwater is accumulated in the ponds and water temperature comes down, the proper season for breeding the Asiatic carps starts. However, in colder areas like Sam Neua (Hua Phanh) and Xieng Khouang, the proper season for fish breeding is quite prolonged and it starts after the winter is over and water gets warmer and rains begin.

Now it is time to select the mature female and male fishes for breeding purposes. Good male fish are easy to select, when you run the fingers on the pectoral fin, the inner side is rough to touch, and these ooze milt when abdomen is gently pressed. Whereas, in females the pectoral fin is smooth to touch and good female fishes have a prominently bulging abdomen, soft to touch, with vent (genital region) pinkish in colour.

The individual weights of the selected female and male fishes are recorded inside hand nets. In one breeding set, one female is kept with two males inside a breeding hapa or circular breeding tank. In larger breeding tanks even two to three sets of the same species can be put for spawning. Do not fix breeding hapas in ponds with tilapias or common carp as these destroy the released eggs.

4. Dosage of hormone and preparation of fish pituitary extract.

Dosage of hormone is calculated as mg of pituitary gland per kilogram body weight of the brood fish. The female fishes are generally given two injections, the first being only a low dose and usually after 6 hours (at water temperatures between 26–30 °C) another higher dose is injected. The male fishes are injected one single low dose at the time of second injection to the female fish. The requirement of pituitary glands is calculated according to the weight of the brood fish and dose of injection. More details on dosage are given in the following account.

The pituitary hormone extract is prepared by crushing the glands inside a tissue homogenizer and adding measured quantity of distilled water to it. The gland suspension is centrifuged in a hand centrifuge and the hormone extract is poured out in a small beaker or glass phial, now ready for injection. The concentration of the extract is around 1–4 mg gland in 0.1 ml of water according to convenience of injection.

The hormone is injected intramuscularly near the tail region of the fish.

5. Induced Breeding technique

The induced fish breeding technique for the Indian carps (rohu, mrigal and catla) is slightly different from that of other Asiatic carps (grass carp, silver carp and big head). The techniques are described separately for the two groups of fishes, which are as follows:

(a) Breeding of rohu, mrigal and catla:

In the case of rohu, mrigal and catla, the female fish is given two injections; the dose of the first one generally 2–3 mg/kg body weight of the female fish and the second dose is 5–8 mg/kg body weight. The male fishes are injected at the rate of 2–3 mg/kg body weight at the time of second injection to the female. The injected female and male fishes are put back either inside breeding hapas or circular breeding tanks for spawning. Nearly 5–6 hours later, the fishes spawn, the female fish releases the eggs and the males chase the female and release milt thus the eggs are fertilized naturally in water. These eggs now start swelling up and get water-hardened within 5–6 hours and measure around 4–5 mm in diameter. The fertilized good eggs are transparent while the bad unfertilized ones turn whitish and opaque.

(b) Breeding of grass carp, silver carp and big head:

For induced breeding of these fishes also, normally two male fishes are kept with one female fish. However, sometimes in the case of silver carp the males may not have enough milt and so instead of two males even three males can be kept with one female fish. The dose of hormone used for these fishes is generally slightly higher than for the Indian carps. The first dose for the female fish is 3.5 mg/kg body weight and after 6 hours the second dose is 7.10 mg/kg body weight; the lower doses are used if the broodfish and weather conditions are good. The male fishes generally receive 3–4 mg/kg body weight dose at the time of second injection to the female. In another 5–6 hours' time the female fish is ready to realease eggs when it is gently and carefully handled and the eggs are collected in clean and dry enamel or plastic basins. Soon after this the milt from the male fishes is sprinkled over the mass of eggs and the milt and eggs are thoroughly mixed by using a feather for 3–4 minutes. Care is taken not to allow water to fall over the eggs while handling the fishes. This process is called “stripping by dry method”. The fertilized eggs are now slowly washed several times with cool, clean water from pond or stream and the excess milt and other dirty materials are washed off. Now the clean fertilized eggs start swelling and these can be put back inside the breeding hapas for water hardening for 5–6 hours, after removing the fishes and washing out the debris.

In colder areas like Sam Neua or Xieng Khouang; these fishes may often spawn naturally inside circular breeding pools and there may not be need for stripping, also the grass carp at Sam Neua have been bred two times in the Same year (Season).

6. Hatching of fertilized eggs.

Now 3–4 samples (about 25 ml each) of fully swollen eggs are collected, the good and bad eggs are counted to estimate the number of eggs per ml and the percentage of fertilization is determined. It is important to know the percentage of good eggs for hatching purposes. If percentage of good eggs is 80 or above, then about 100,000 eggs can be put inside one hatching hapa, but if the percentage is lower, then only smaller number of eggs should be put inside each hapa depending on the percentage of fertilization. This is because when bad eggs disintegrate, the water becomes foul and toxic for the good eggs. However, in a hatchery with constant flow of water, the toxic effect of disintegrating bad eggs is very much reduced.

The hatching hapas (outer and inner) are fixed in clean, deep water, and bottom of the hapa should be about 25 cm above the pond bottom and the top also about 25 cm above the water surface so that no miscellaneous fishes, etc., may get entry into the hapa. The hatching hapas thus fixed in a pond are also called an “out-door” hatchery. Remember that water temperatures above 31°C are harmful to the developing eggs.

The hatching of eggs is complete within 14–18 hours when the water temperature is between 27–30°C and it shall take more time at lower water temperatures. After hatching is complete, the inner hapas are carefully removed with broken egg shells and bad eggs. Now the hatchings remain inside the outer hapa for two more days till their mouth is formed when these are called spawn and are ready for stocking in prepared nursery ponds.

In “indoor” hatcheries, too, consisting of either hatching jars or circular tanks, spawn is similarly raised.

7. Collection and measurement of spawn.

The collection of spawn from the hatcheries (out-door or indoor) is done very carefully as the baby fish are very delicate. The water used for collection of spawn is fresh, clean, filtered and cool. The spawn is now poured over a piece of clean thin cloth put over a rectangular basin filled with clean good water. Spawn is now measured gently with perforated small aluminium or plastic cups of known volume. Generally, there are 500–600 spawn per ml and thus the total quantity of spawn produced can be estimated.

8. Stocking of spawn in prepared nurseries.

The spawn thus measured is packed either inside plastic bags under oxygen or transported in open containers in clean, well-oxygenated, cool water for stocking in well-prepared nursery ponds. The proper time for stocking spawn is either morning hours or late in the evening when it is not too hot. While stocking spawn in the pond care is necessary that the pond water is first filled into the plastic bag or open container so that the inside and outside water temperatures get gradually mixed up and the delicate spawn is not exposed to sudden change in temperature. The pond water at the place of stocking is also disturbed by hand to mix up the upper and lower layers of water. Now the spawn is poured out into the pond slowly which swim away in the nursery pond, free from predators and with plenty of natural food (the plankton).

SOME IMPORTANT POINTS TO REMEMBER :

For a successful seed production programme, the following points should be always remembered :

1. The farm should have a good stock of brood fish (females and males) of all the species in adequate numbers and these are maintained in 3–4 good ponds; not in just 1 or 2 ponds to avoid any accidental loss of stocks due to disease, escape or poaching.

2. The fish breeding centre should collect sufficient quantity of good fish pituitary glands before the breeding season, well preserved in absolute alcohol and kept in a cool place or inside a refrigerator; not glands from immature and rotten fishes and never immerse the glands in water or dilute alcohol to avoid loss of hormone which is soluble in water but not in absolute alcohol.

3. The centre should collect all essential field implements for fish breeding work (see Appendix I) much before the breeding season; not to run about collecting materials when the work is taken up.

4. Fish breeding operation on large scale should be carried out when the brood fish, water and environment conditions are most favourable; not when it is very hot and fishes not properly mature.

5. Before taking up the fish breeding programme, the centre should keep good number of nursery ponds well-prepared (free from predators, weeds, properly limed and manured and filled will good water filtered by using a suitable screen to avoid entry of unwanted fishes, etc.); not to wait and prepare nurseries after spawn is available which would otherwise result in heavy loss of valuable carp seed giving only a very poor survival and growth of spawn.

6. The seed center should collect indents of fish seed requirement of the various cooperatives, governmental farms, private fishermen of the region well in advance so that the seed production and spawn rearing programmes are suitably arranged; not to produce seed first and then wait for people to come and collect seed at their own time and will which would completely disturb the planning of fish seed production and culture programme.

7. Fish seed or fry (about 25 mm size) should be distributed from the nurseries within 2–3 weeks of rearing to utilize the nursery space profitably for raising 2–3 crops of fish fry; not to keep the fry in the nurseries for months awaiting distribution to avoid heavy mortality of seed due to overcrowding and often out-break of diseases.

8. At the time of fish seed supply to cooperative/private fish farmers, the fishery technicians/extension workers should give detailed instructions on further rearing of fry in well-prepared fingerling rearing and marketing ponds; not just to supply the seed and forget about it, because this will give only poor returns to the farmers who will gradually lose their interest in fish culture. Lastly, remember that the fish seed production programme is meaningful only if proper care and culture of the valuable fish seed to table-size fish is ensured through vigorous and efficient extension efforts.

   DO NOT PRODUCE THE FISH BABIES JUST TO DIE WITHOUT PROPER CARE : IT IS NOT ONLY WASTE OF EFFORT AND RESOURCES, BUT A CRIME. GROW THE FISH SEED PROPERLY TO BUILD THE HEALTH AND ECONOMY OF THE NATION.

Appendix I

List of some common field implements for fish seed center to produce 10 million spawn

REMARKS :

Under proper care and maintenance, the above items could last for a much longer period. Also, the quantity mentioned above is adequate to produce much more than 10 million spawn as most of the items are independent of the production targets.

Calendar for Fish Seed Production of carps for LAO PDR