ARTIFICIAL PROPAGATION

Advantages of Artificial Propagation

1.Better rates of fertilization and hatching

2. Protection against enemies and unfavourable environmental conditions

3. Breaking of the parasite chain

4. Better conditions for growth and survival

5. Out of season supply of fry and fingerlings

6. Production of superior strains of fry

The artificial intervention in this procedure consists of:

(a) collection of eggs, larvae or fry (b) their protection from natural enemies and unfavourable environmental factors (c) raising the larvae up to the fingerling stage(d) distributing them for stocking in different water bodies.

Steps in artificial propagation

1. capture of wild brood fish from spawning grounds, 2. selection of breeders from wild stock for natural spawning or for hormone treatment, 3. rearing of brood fishes,

4. inducement of natural spawning with or without hormone treatment, 5. procurement of ripe sexual products by stripping with or without hormone treatment, 6. artificial fertilization, 7. incubation and hatching of eggs, and 8. rearing of larvae, fry, and fingerlings.

Brood fish are sexually ripe fish they can either be : - collected from natural waters just prior to the spawning season - collected from spawning grounds - raised on farms

Farm rearing of brood stock

-Widely practised all over the world-It enables the building-up and selection of healthy breeders for eventual stock improvement).

Factors affecting broodstock rearing1.Temperature 2. Light3. Oxygen content 4. Tranquility5. Stocking density 6. Size and depth of the pond 7. Food

1.Temperature

it is advisable to rear the brood stock in a pond where extreme fluctuations of temperature do not occur

Generally, warmer environment accelerates gonadal maturation

2. Light

The requirement for illumination varies with different species. Many fishes are irritated in illuminated environments

3. Oxygen

Frequent fluctuations and low levels of oxygen content in pond water tend to inhibit gonadal development

Fresh, oxygen-rich water, is an important requirement during the rearing of brood stock.

4. Tranquillity

It is believed that frequent disturbances interfere with normal gonadal development

5. Stocking density

Although most cultivated fishes are able to tolerate crowded pond conditions, the effects of crowded conditions on gonadal development is often deleterious

In general it is not advisable to stock would-be breeders along with market-destined fish, especially if the latter are fed an unbalanced diet.

Young prospective breeders can be reared in restricted numbers along with ripe breeders.

6. Size and depth of pond

The rearing pond for larger brood fish (2–10 kg or above) should be about 2 000–4 000 m2. Smaller brood fish can be raised in smaller ponds.

The depth of brood fish ponds generally varies from 1 to 2 m.

7. Food

A suitable and adequate food supply is of foremost importance to brood fish.

If the fish are left hungry or starving, the vitellogenesis phase of egg development is affected.

If the food is deficient in essential nutrients, particularly the amino-acids, vitamins, and minerals, the egg development is adversely affected, ultimately leading to the failure in ovulation.

Breeders reared on ample natural food or on a protein-rich artificial diet yield satisfactory results.

It is better to breed a smaller number of brood fish on qualitatively and quantitatively satisfactory diet (or natural food) than to keep a huge stock under half-starved conditions.

Age and weight of the breeders.

The “first spawners” or “virgins” are usually used for artificial propagation.

Larger fish produce more eggs, but the handling of “giants” weighing over 10–15 kg is rather difficult and tiresome.

The fecundity of medium size fish (2–6 kg) is generally higher than that of giant fish. Spawners of 0.5–2 kg weight are very easy to handle and strip.

Before releasing the breeders in special spawning ponds for spontaneous spawning, or before they are prepared for induced spawning, the fish culturist should make sure that they are in a “ready-for-spawning” condition. Unless their gonads have developed up to the resting or dormant stage, they will not respond to any propagation technique. Therefore, sorting out of the right breeders is very important for successful artificial propagation.

Selection of breeders for ready spawning or for hormone treatment

The symptoms indicative of the ready-to-spawn conditionFemales:

Well-rounded and soft abdomen, the fullness of which extends posteriorly past the pelvis to the genital opening.

The genital opening is swollen, protruding, and reddish or rose in colour; its edge is uneven or fringed.

The anus (vent) may also be swollen and reddish.

In some column-living fishes, the abdomen becomes red coloured.

Some fishes develop a nuptial colour before ovulation.

Males:

The male releases a few drops of thick milt when its abdomen is pressed slightly.

In some male fishes (Chinese carps and Indian major carps) the dorsal surface of the pectoral fin becomes rough.

Some male fishes of the Orinoco and Amazon basins produce a sound when taken out of the water.

Methods of Inducing ovulation and/or spawning

1.Simulation of suitable environmental factors

2. Administration of gonadotropic hormones

3. Combination of the two methods

Some pond spawners can be stimulated to spawn by providing:1. nests2. artificial spawning surface (Kakabans-mat-like structures measuring a few m2 in area)

3.spawning receptacle

4.conditions simulating the decisive natural environmental conditions

Decisive natural conditions to bring about spawning in common carp:•suitable water temperature (18°–22°C),•grass-bottomed spawning ground•water saturated with dissolved oxygen•slowly rising water level•presence of the other sex•absence of other fishes

Hypophysation - “short cut” of the natural process

- gonadotropic hormone extracted from the pituitary of some other fish (donor) is injected into the breeder and brings about final ovulation 

Limitations of Hypophysation

1.Some of the sensitive fish cannot tolerate the treatment2.Other fish may ovulate only irregularly3.Breeders whose ovaries have not yet reached the adequately ripe stage fail to respond to hypophysation4.Varying contents of gonadotropin hormone in the pituitary gland

Dosage

• it is generally difficult to fix the exact dosage, with the result that generally more hormone than required is injected into the breeders•hormone dosage required can vary significantly from fish to fish of the same species and from technique to technique•dosage actually depends on the “readiness” of the females; their age, size, sensitivity and many other factors

Total dose

2.5 – 3 mg (1gland) – hypophysis required per kg weight in the case of large breeders weighing over 5 kg

1.5 mg (0.5 gland) - hypophysis required per kg weight for medium sized fishes (2–5 kg)

0.75 mg (0.25 gland) - hypophysis required per kg weight for small fishes (0.5–2 kg)

•It is advisable to avoid overdose in preparatory injection, since it may lead to partial ovulation, thereby upsetting the normal schedule

1. Single, full (100 percent) or knock-out dose - is given when the breeder has been in the resting phase for a long time

2. Multiple doses

2.1 preparatory dose - is about 10 percent of the total dose.

2.2 decisive dose

The males, as a rule, are only given one dose of hormone, usually at the time when the females are given the last decisive dose.

It is important that the males are not administered the hormone earlier, since that may result in releasing the sperm before the females are ready to ovulate.

The dosage of gonadotropin hormone extract is expressed:

1.in milligrammes

2.as a number of acetone-dried hypophysis glands – gland unit

The acetone-dried pituitary gland of a 1.5–2 kg common carp weighs 2.5–3 mg.

This size of hypophysis is taken as a unit, when the dosage is expressed in terms of number of glands.

Solvent

The solvent used for gonadotropic hormone is 0.6–0.9 percent NaCl (common salt) solution

The solvent is prepared by dissolving 7 g (.7%)of clean common salt, free of iodine, in 1 l of boiled and already cooled drinking water

Preparation of pituitary gland solution

1. Counting /weighing of the pituitary glands

2. Pulverization

3. Addition of a measured quantity of solvent to dissolve the pituitary gland (10-30 mins)

Choice of body part to inject

1.Intramuscular2.Intraperitoneal3.Intracraneal

•The fish becomes more quiet if its head is covered with a piece of cloth. It is advisable to use towels while handling breeders and not to touch them with bare hands.

•While injecting scaly fishes, it is necessary to take the precaution of not pricking them through the scales, but to insert the needle beneath the scale and prick through the underlying muscle

Requirements for full ovulation(after injection)

1.Suitable temperature2.High oxygen content3.Calmness

•If temperature is too low, ovulation takes a very long time, or in most cases becomes inhibited. High temperature not only causes higher oxygen demand and rapid metabolism, but also has its own inhibitory effect.

•The pituitary treated fish needs about 50 percent more oxygen than before the treatment. The excitement caused by handling and treatment also results in enhanced oxygen consumption. It is, therefore, essential to keep the treated breeders in a well aerated environment or in clean, oxygen-rich flowing water.

•Disturbed fish become agitated, swim rapidly and jump against the wall of the tank, thereby exposing themselves to injury. Their tranquillity can be secured by putting dark floating objects on the surface of the tank where the treated breeders are kept.

“Hour-grade”The temperature of water in the tank in which the breeders are held is measured every hour after the last decisive injection up to full ovulation. The readings are added to arrive at the hour-grade.

•A knowledge of hour-grade value would help the fish farmer to know exactly when to expect ovulation after the last injection.

The hour grade value depends on:

1.the fish species treated2.the type of treatment3.the size of the female4.whether the fish starts spawning immediately after ovulation or not.

(a)Hour-grade in relation to fish species

At a temperature of 21°–22°C, the hour-grade of common carp is 240–260, while that of grass carp, silver carp, and bighead is 200–220.

(b) Hour-grade in relation to the type of treatment•The hour-grade is 340–360 in the case of common carp, when only one decisive dose is administered.

•It will be only 240–260 if a preparatory dose is given 24 hours prior to the decisive dose.

•The hour-grade value would go down further to 200–220 in cases where two decisive injections are given with an interval of 6–8 hours.

•The pattern may hold good for other species as well.

(c) Hour-grade in relation to size of the females•It is well known that the smaller females ovulate earlier than larger females.

•This is particularly conspicuous when the females differ greatly in size; e.g., 1–2 kg and 7–10 kg.

• In common carp, the hour-grade value is usually about 130–150 only when the breeders are of small size (1.0–2.0 kg).

d. whether the fish starts spawning immediately after ovulation or not

•When released with ripe active males, most of the injected females begin spawning in the “ward basin” or “ward tank”.

•Failure to spawn would mean that the species is not responsive, the males are inactive or already spent, the females are injured or suffering from an overdose of hormone, or some of the environmental factors are unfavourable.

“Induced spawning” or“hormone induced spawning” –spawning of fishes that are treated by gonadotropic hormone in the presence of active males after normal ovulation

Induced spawning has both advantages and disadvantages

Advantages:

1. There is no need to calculate the exact time of ovulation, or watch the females to determine whether they are ready for stripping.

2. It is not necessary to catch the breeders for stripping, thereby avoiding possible injuries to the breeders.

3. There is no need to strip the breeders and fertilize the eggs artificially, which process is not only time-consuming but would also require more working hands.

4. The danger of over-ripening of eggs in the ovary would not arise, since the fish would start to spawn as soon as ovulation is completed.

Stocking density and Sex RatioTo achieve successful induced spawning, it is advisable to put together one female and two-three males, two females and three males, or a maximum of three females and four males, depending on the size of the ward tank.

In the case of breeders weighing 2–3 kg each, a maximum of two females and three males can be put in a ward tank of 2 m2.

As many as three-five females and four-six males can be put in the same tank if they weigh only 0.5–1 kg each.

If the breeders weigh 4–5 kg each, the putting together of only one female and two smaller males is advised. Still larger fishes would require a larger ward tank to obtain satisfactory results.

Fertilization

1.Natural

2.Artificial / Dry– requires collection of eggs and sperm

Fertilizing Solution

The fertilizing solution is prepared by dissolving 30 g carbamide (urea) and 40 g common salt (NaCl) in 10 litres of clean (preferably filtered) pond water.

The quantity of the solution to be poured on to the eggs in the beginning is about 10–20 percent of the volume of the eggs to be handled.

The mixture is then stirred with a plastic spoon or a feather for about three-five minutes continuously, during which time one sperm enters an egg through the micropyle and completes the process of fertilization.

Tannin Solution

is prepared by dissolving 5–8 g of tannin in 10 litres of water

About 2–4 litres of tannin solution is placed in a plastic bucket and a maximum of 2–3 litres of swollen eggs may be added to it all at once.

After stirring for 3–5 seconds, clean water should be poured into the bucket. Once the eggs have settled down, the water is drained out, preferably by using a strainer.

Incubation and Hatching of eggs

•Fertilized eggs should be placed in the incubators not more than 1 minute after fertilization in the case of untreated sticky eggs

•Hatching normally occurs starting 24 hours from fertilization and is highly influenced by temperatued re and dissolved oxygen

Larval Rearing and Fry Nursing

Major Requirements:

1.Larval Rearing Facilities

2.Food

3.Water Quality