Hatchery Technology of Milkfish

(Chanos chanos)

Milkfish (Chanos chanos) is an important food fish in the Philippines, Taiwan and Indonesia. It is a popular fish for culture because it tolerates a wide variety of salinity, temperature and water quality, adapts well to high density, and reaches marketable size in

4-7 months.

Introduction

They are hardy and fast growing, and can be raised in fresh and brackish water ponds and pens. Being one of the cheapest sources of protein, milkfish are acceptable to all socioeconomic strata in the country.

Taxonomic Classification Kingdom : Animalia

Phylum : Chordata

Subphylum : Vertebrata

Class: Osteicthyes

Order : Gonorhynchiformes

Family : Chanidae

Genus: Chanos Lacepede 1803

Species: Chanos chanos Forskal 1775

English name: MilkfishScientific Name: (Chanos chanos)

Biological

Features Body fusiform, elongated, moderately

compressed, smooth and streamlined. Body colour silvery on belly and sides grading to

olive-green or blue on back. Dorsal, anal and caudal fins pale or yellowish with dark margins.

Single dorsal fin with 2 spines and 13-17 soft rays. Short anal fin with 2 spines and 8-10 soft rays, close to caudal fin. Caudal fin large and deeply forked with large scale flaps at base in adults. Pectoral fins low on body with

axillary (inner basal) scales. Pelvic fins abdominal with axillary scales and 11 or 12 rays.

Scales cycloid, small and smooth, 75-91 on lateral line. No scutes (modified pointed scales) along belly.Transparent 'adipose' tissue covers eye.Mouth small and terminal without teeth. Lower jaw with small tubercle at tip, fitting into notch in upper jaw. No bony gular plate between arms of lower jaw.Mouth small and terminal without teeth. Lower jaw with small tubercle at tip, fitting into notch in upper jaw. No bony gular plate between arms of lower jaw.

Attains typical length of 1 m but may reach maximum length of 1.8 m (male).

The behavior of milkfish is still one of the areas that has yet to be extensively studied. Large schools of milkfish have been seen in near shore waters with well-developed reefs and in coastal lagoons, suggesting that they are social.

Behavior of Milkfish

Distribution Milkfish occurs near coasts and islands in the tropical Indo-Pacific area and is largely centered around the Philippines and Indonesia.

Their distribution coincides with coral reef areas where the water is warm (more than 20°C), clear and shallow.

Milkfish do not inhabit areas of the Pacific Ocean influenced by cold currents but they do occur in seas affected by warm ocean currents.

Growth

The milkfish fry grow at a rate of 0.5 mm per day.

Using a line equation to estimate the age and growth of milkfish fry, it is estimated that shore-caught fry with a mean total length of 13.5 mm are about three weeks old from spawning while small ones of a mean total length of 10 mm are two weeks old.

Growth rates of wild and pond-reared juvenile milkfish vary from 7.0 to 8.7 mm weekly.

However, growth rates in ponds and in pens vary considerably depending on initial fish size, food, stocking density, climate, season, locality, water turnover rate, pond area and depth, pests and predators .

Reproduction There are no distinct morphological variations

between milkfish of opposite sex, especially among sexually immature adults and juveniles.

Sexually mature males possess only two openings.

Virgin females maturing for the first time may also have two distinct pores in the anal region.

milkfish reared in sea cages in the Philippines attain their first reproductive event at the age of five years.

Tank and/or pond-reared milkfish attain their first maturational event at a later age (6–9 years).

Milkfish is a highly fecund species. Mature ovaries usually comprise around 10–15% of the body weight of the spawner. Fecundity estimates of 0.3 to 1 million eggs per kg body weight have been reported.

As in other fish species, the spawning cycle of milkfish is seasonal and varies in different localities.

The length of the spawning season in various localities may be a consequence of elevated seawater surface temperatures.

Tolerance to Environmental

Condition The success of milkfish as a cultured food fish species may be attributed to its ability to tolerate extremes of environmental conditions.

These conditions include extremes of temperature, salinity, dissolved oxygen, ammonia, nitrite, crowding and starvation.

Low temperature (23°C) decreases survival, activity, food intake, and growth and development of milkfish fry and juveniles; high temperatures (up to 33°C) have the opposite effect.

Lethal temperatures for juveniles are 42.7°C and 8.5°C.

Tolerance of milkfish juveniles to low dissolved oxygen levels also varies with the size of the animal.

Symptoms of asphyxiation are discernible at 1.4 ppm oxygen among 200 to 300 g fish; 50% mortality occurs at around 0.1 to 0.4 ppm at 31 to 34°C.

Seven day old larvae are most sensitive to salinity changes and handling stress, tolerating only levels within the range of 16 to 20 ppt.

21 day old milkfish fry can tolerate salinities within the range of 0 to 70 ppt.

Milkfish can tolerate high amount of ammonia level from 2o-21 ppm.(pond reared).

Juvenile milkfish can also tolerate high levels of nitrite (freshwater: 12 ppm; brackish water: 675 ppm..

Milkfish fry and juveniles can tolerate crowded conditions.

With just enough food for body maintenance, milkfish juveniles can be kept crowded and stunted in nursery ponds for several months.

Factors affecting propagation

The age and time of sexual

maturity.

The season of propagation.

The place of propagation.

The extent of parental care.

Breeders more than five years of age are preferred.

They are expected to spawn readily one or two months after transport.

Season bound spawner.

Sexual Maturity Season of propagation

Place of propagation

Marine water system

Passive Parental Care

Parental Care

Artificial

Propagation of

Milkfish

Artificial

Propagation of

Milkfish

Site Selection

There must be ample supply of clean seawater and freshwater.

Electricity must be available to run the life support systems in the hatchery such as air blowers and water pumps.

The hatchery must be located within the convenient access to fry buyers.

a. Complete Hatchery – is a milkfish hatchery complete with spawning tanks and breeders. Egg production is an integral part of the business operation. Land area requirement may exceed one hectare. Capital outlay and operational costs are higher than satellite hatcheries. Technical and management requirement is comprehensive.

b. Satellite hatchery – is a milkfish hatchery that procures eggs from a complete hatchery, do the hatching and larval rearing until the market fry stage of 18 to 21 days. They maybe newly built facilities or old prawn hatcheries converted into milkfish hatcheries.

Types of Milkfish Hatcheries

Spawning Tanks

A milkfish hatchery needs larval rearing tanks.A Larval Rearing Tank is Circular (2-3-meter diameter) canvas or concrete tanks (3-5-ton ca-pacity) with an airstone at the center may be used. Tanks of smaller volumes are preferred for easy management. Larval rearing tanks should be placed under a shade to protect the larvae from the glare and heat of direct sunlight and to deter growth of diatoms that contribute to poor water quality. The tank is provided with a sturdy net cover to keep the breeders from jumping out

Selection of Breeders

Males are determined by the presence of milt oozing out of the urogenital pore.

Females are determined by inserting a polyethylene cannula (0.85 mm) to the urogenital pore.

Females are determined by the presence of spherical yolky oocytes.

Induced SpawningMilkfish egg maturation and ovulation do not

occur under captive condition hormonal injection is necessary.To induce spawning, use the following hormones:SPH — acetone dried pituitary gland homogenate of coho salmon prepared bythe British Columbia Research Council at Vancouver, Canada; one gramof the powder contains 17.6 mg gonadotropin.HCG — human chorionic gonadotropin, manufactured by Ayerst Laboratories,New York.

DF — Durandron Forte "250", a long-acting androgen manufactured by N.V. Organon, Holland. This is an oily solution containing 30 mg testosterone propionate, 60 mg testosterone phenylpropionate, 60 mg testosterone isocaproate and 100 mg testosterone decanoate.Preparation of the injectionDissolved HCG using its accompanying diluent. The volume of the diluent to be used is determined by the desired concentration of HCG in the 3 ml injection.

To avoid possible damage to the muscle tissue, it is recommended that not more than 3 ml of solution is used for injection.

The necessary amount of acetone dried pituitary gland is homogenized in this solution before it is finally administered.

• Intramuscular injection of gonadotropins. Injection is administered a few centimeters

below the dorsal fin.

Induced Spawning of FemaleMilkfish• Only fish with eggs having an average diameter of

at least 0.65 mm should be induced to spawn. • Usually, 2 injections are needed to induce both

captive and wild adult milkfish to spawn.• For the first injection, give the fish a combination of

10 mg SPH/kg body weight + 1,000 IU HCG/kg body weight.• For the second, 10 mg SPH/kg body weight + 2,000

IU HCG/kg body weight.• The time enterval between injections is 9-12 hours

both for wild and captive milkfish.

Male Milkfish

One of the problems in the artificial fertilization of eggs has been viscous, non-dispersing milt of milkfish caught during the natural breeding season.

This problem can be solved by injecting newly caught males that have viscous milt with 1 ml DF.

A day after the injection, the viscous milt will become more fluid and copious and will disperse easily when mixed with seawater; moreover, the percentage of motile sperms as well as sperm motility will increase

It is more advantageous to use DF rather than HCG because, aside from its long lasting effect which minimizes handling stress, it is cheaper.

Fertilization and Incubation

Between 10 and 12 hours (usually 10 hours) after the second injection, the fish will start to spawn eggs.

Spawning/stripping is done as follows: the holders, two persons with bath towels in their hands, grasp the fish, one holding at the caudal peduncle while the other handles the head region. A third person immediately covers the genital pore with a small towel to prevent further loss of eggs.

When the fish is dry, turn it upside down and hold the tail down so that the ripe eggs will flow naturally toward the genital pore. The third person holds the spawning basin beneath the genital pore. A fourth person, the spawn taker, gently presses out the eggs with the fingers, beginning pressure just in front of the genital pore.

The hand is then moved nearer the head of the fish and further gentle pressure is applied as necessary to assist the natural flow of eggs until all that will freely come out of the fish are obtained. Collect eggs in separate arbitrary batches.

As soon as one batch is collected, fertilize the eggs following the dry method with milt.

• Mix the eggs and milt gently but thoroughly using turkey or chicken feathers .After at least 3 minutes, add seawater (34 ppt salinity) to the mixture while stirring. After another 3 minutes transfer the fertilized eggs to a scoop net (mesh size, not less than 500 microns) and wash the eggs thoroughly with seawater of the same salinity (isohaline) as that in the incubation tanks.• The eggs are then transferred to the incubators.

• Six hours after the start of incubation, change 1/3 of the water in the tank with new filtered seawater.

• Fertilized eggs float in seawater with a Salinity of at least 34 ppt while unfertilized eggs sink.

Stripping the female milkfish of its eggs.

Fertilized eggs in the scoop net are washed thoroughly with filtered seawater before introducing them into the larval rearing tank.

Stocking of Larvae

1) Fill up the rearing tank with 2250 liters filtered seawater (75%of the total volume, in case different tank capacity is used). Add "green water" (use Chlorella culture at its optimum density) at a ratio of 1 liter for every 5 liters of seawater (750 liters for 2250 liters seawater, if 3-ton tank is used).

2) Compute for the number of larvae to be stocked into the rearingtank using the equation:

Desired numberof larvae to bestocked in therearing tank

= 30 larvae/liter X Total tank water volume

3) After determining number of hatched larvae, reduce water volume in the 500-liter hatching tank to 100 liters. Compute for the water volume to be transferred from the hatching tank into the rearing tank.

Example: Assuming an ELC of 180,000 in 100 liters in the hatching tank and 90,000 larvae are to be stocked in a 3-ton rearing tank, the volume of water with newly hatched larvae to be transferred (x) is computed as follows:

100 liters = 180,000 larvae x 90,000 larvae

x = 50 liters

1) Maintain mild aeration during the first week of rearing. Should water in rearing tanks turns pale, add enough Chlorella to restore the green-to-light-green color. Chlorella should be added preferably in the morning before feeding the larvae.

2) Starting on day 2 until day 14, add Brachionus at 10-15 individuals/milliliter. From day 15 to day 21, reduce Brachionus count to 0.5individual/milliliter.

3) Artemia nauplii at 0.5 individual/milliliter are fed from day 15 to

day 17. Increase feeding level to 1 individual/milliliter from day 18 until

harvest (day 21).

Larval Rearing

4) Siphon out wastes and uneaten food in the tank bottom everymorning from day 2 until day 21.

5) Change 30% of the water volume every morning from day 2 untilday 14. Change 50-70% of the water from day 15 to day 21.

The embryonic development and

hatching of milkfish a) Fertilized egg

b) 2-cellc) 4-celld) Blastulae) Late

grastulaf) Yolk plug and

embryonic streak apparent

g) C-shaped embrayo

h) Late embryonic dev’t.

i) Hatchingj) Newly hatch

Larvae

Development of Larvae

a) 1 day oldb) 2 days c) 3 days d) 4 days e) 5 daysf) 6 days g) 7 days h) 8 days i) 9 days j) 10days

a) 11 daysb) 12 days c) 13 days d) 14 days e) 15 daysf) 16 days g) 17 days h) 18 days i) 19 days j) 21 days

Harvesting

Milkfish larvae on day 21 are at about the same developmentalstage as wild-caught fry and are ready to be harvested.

Procedures for harvesting1) Drain water in the rearing tank to about one foot deep.

2) Using a small basin, scoop larvae and transfer into a big plastic basin.3)To estimate the number of harvestable larvae, count the numberof larvae in a basin of known water volume.4) Pack larvae in double-layered oxygenated plastic bags contain-ing 8-15 liters of seawater at a loading rate of 300 larvae/liter.

Spontaneous spawningSpontaneous spawning of milkfish occurs at water

temperatures of 26-34.5°C. Seawater and freshwater should have a minimum

dissolved oxygen level of 5 mg/l and low un-ionized ammonia content < 0.05 mg/L.

The optimal range for maturation appears to be 15-35 ppt. Spawning should be induced at salinities higher than 32 ppt to ensure that the eggs would float rather than sink and that the sperm will be completely activated.

Milkfish can remature from 2 to 4 times in one spawning season and have asynchronous spawning behavior in captivity.

Generally one female milkfish brood stock spawns 1 to 9 million eggs in one spawning season.

Thank you !

The End…

Questions?Questions?Questions?Questions?

Prepared by:

Rodney  PeñafielKaren Grissel OrdialezJolevie MolinaJessica MiraflorEsther Pongcol