SEABREAM

VISHNURAJ R.SDEPT. AQUATIC BIOLOGY AND FISHERIESUNIVERSITY OF KERALA

Red seabream, Pagrus major (Temminck and Schlegel, 1843) is a demersal species that occurs in the northwest Pacific (the northeastern part of the South China Sea northward towards Japan) at depths between 10 and 50 m.

The red sea bream, Pagrus major (Chrysophrys major), is the most valuable marine fish in Japan.

A first trial to culture it has been made at a hatchery located at Seto Inland Sea coast in 1902 (KAJIYAMA, 1937). The hatchery was soon closed because of difficulty in rearing the larvae.

SHlKAMA, YMASHITA and NISHIZUKA succeeded in rearing 22 red sea bream fry from the eggs for the first time in Japan in 1962 (YAMASHITA, 1967).

These successes were achieved on an experimental scale, and therefore, further experimentation was necessary before developing mass production methods.

INTRODUCTION

1967, NOGUCHI observed natural spawning' of cultured red sea breams in a large tank at Naruto Aquarium, Tokushima, Japan+ (NOGUCHI, 1968).

Based on these successes, research has been carried out in order to find a mass rearing method for red sea bream larvae at the hatcheries belonging to Seto Inland Sea Fish Farming Association (ANONYMOUS, 1974).Most sparid species have been used in mariculture and cultivated in cages.

CLASSIFICATION AND CHARACTERSKingdom: Animalia (animals)Phylum: Chordata (chordates) Subphylum: Vertebrata (vertebrates)Superclass: Gnathostomata (jawed vertebrates) Class: Actinopterygii (ray-finned fishes) Order: PerciformesFamily: SparidaeGenus: PagrusSpecies: Pagrus major

The family Sparidae contains 35 genera and112 species, distributed mainly in tropical and temperate waters of the Atlantic, Pacific and Indian oceans (Froese and Pauly, 2005). Eighteen of these species inhabit the Adriatic continental shelf (Jardas, 1996). Two of these belong to the genus Pagrus (Cuvier, 1816): Pagrus pagrus (Linnaeus, 1758) and Pagrus coeruleostictus (Valenciennes, 1830).

DISCRIPTION Body robust, oblong, moderately compressed. Upper profile of head convex

with a bulge above eye. Lower jaw slightly shorter then upper. Head and upper body dark violet,

sides and belly silvery. Several small bright blue spots on upper sides. All spines of dorsal fin tough and not elongated. Caudal fin forked with pointed lobes. Scales moderately large, absent from

bases of soft dorsal and anal fins. Posterior margin of caudal fin black, lower margin white.

Dorsal spines (total): 12; Dorsal soft rays (total): 10; Anal spines: 3; Anal soft rays: 8.

Body with many bluish dots when fresh. Shallow body, body depth 2 or more in SL.

Transverse scales 6.5-7.5. All spines of dorsal fin are tough and not elongated. Posterior margin of caudal fin black, lower margin is white.

Occurs from 10 to 50 m depths, often on rough grounds, but also on softer bottoms.

NATURAL DISTRIBUTIONThey are mainly distributed in Northwest Pacific: northeastern part of South

China Sea (Philippines excluded) northward to Japan.

HATCHERY DESIGNThe basic considerations in establishing a fish hatchery are: (i) which site is suitable, (ii) what is the area of the site and the facilities required in relation to the goals or objectives of the hatchery, and (iii) how will the hatchery be managed.

It is of primary importance to conduct a feasibility study to determine the suitability of the site.

This should be done prior to the establishment of the hatchery. There are three factors which must be considered in designing a fish hatchery:

(i) species, (ii) production target, and (iii) level of financial input. In addition, the facility requirements will depend on the nature of organization to run the

hatchery. For government pilot projects, some laboratory support facilities are required.

Criteria in the selection of sites for seabream hatchery 1. Seawater supply The seawater used in a hatchery should be clean, clear and relatively free from

silt. The water quality should be good with minimal fluctuation in salinity all year round. Suitable sites are usually found near sandy or rocky shore. Sites which are not suitable for hatchery include areas which are heavily influenced by rain or turbulence.

An added advantage of having a site on rocky shores is that good quality seawater is relatively near the shoreline. This reduces the cost of piping installation and pumping. The hatchery site should also be free from any inland water discharges containing agricultural or industrial wastes.

2. Accessibility Ideally, a hatchery site should be selected in areas where there are active fish

farming operations so that the fish larvae produced can be easily transported and distributed to the grow-out ponds and cages. The site chosen for a hatchery must have easy access to communication and transportation channels.

3. Availability of power source A fish hatchery cannot be operated without electricity. Electricity is essential

to provide the necessary power to run the equipment and other life support systems of the hatchery.

4. Topography The ideal site should be spacious, situated on flat to gently sloping grounds,

well drained and not susceptible to floods, strong wave and tidal actions.5. Acquisition It is advisable to pay attention to land values early in the site selection

phase to ensure that the site is available for purchase or lease and at a price consistent with the project budget.

Hatchery size Hatchery design is aimed at achieving certain production targets which in

turn determine the size of the hatchery. The capacity is based on an approximate ratio between tank for production

of natural food (algae and rotifer) and larval rearing tank. The spawning tank depends on the larval requirement which is based on the

number of spawners.

SEAWATER SYSTEM Seawater can be drawn directly from the sea or from the sump pit. If the source of water is relatively clear, the water can be pumped directly

into the overhead filter tank and stored in the reservoir or storage tank. if the water is turbid and contains a high concentration of suspended solids,

it must be pumped first into a sedimentation tank where the suspended solids are allowed to settle down

Holding tanks The holding tanks in the seabream hatchery are used for various purposes

such as for brood stock conditioning and subsequent spawning, incubation, larval rearing and production of natural food.

A brood stock development/spawning tanks

An incubation tank.

A larval rearing tank.

SPAWNING AND HATCHINGMaturation The red sea breams used for spawning are kept in net cages or concrete

tanks (Dimensions: 10-20 m x 10 m x 5 m), for about a year or two depending

on their initial ages. The red sea bream becomes sexually mature when 3 years old. The spawning season extends from April to June, with a peak in early

May.Brood stock development There are two sources of seabream brood stock: wild-caught adults and

from ponds/cages (2–6 years old fishes averaging in weight from 3 to 5 kg).

It is advantageous to use pond or cage-reared brood stock as they are already used to culture conditions being easier to condition and develop them into brood fish.

1. Wild brood stock collection The fishery worker must constantly strive to minimize stress in handling

captive brood stock. Efforts to capture seabream should be confined to areas where they are

known to occur. The selection of a suitable gear or method of capture must also be

considered.2. Conditioning of wild brood stock Captured fish are placed immediately in transport tanks and taken directly to

the hatchery or holding cages. Anesthetic is not necessary if the fish are shipped in live tanks or in aerated

transport containers. Upon arrival at the hatchery, the fish are treated with antibiotic such as

oxytetracycline. 2 ppm for the dripping method for 24 hours and 20 mg per 1 kilogram of

fish for the injection method. In nature, seabream is a carnivorous and feeds voraciously on live fish.

However, in captivity, they can be conditioned to feed on dead fish.

The uneaten feed should be removed to prevent water pollution.3. Brood stock maintenance The fish, whether cultivated or wild-caught, can be maintained as brood stock

in cages and concrete tanks. (a) Cages Floating cages are usually used for brood stock development. The size of the cages varies from 10 to 100 sq.m in surface area with a depth

of 2 meters (dimension: 5 × 5 × 2m or 10 × 10 × 2m). Smaller cages are more suitable because they are easier to maintain and

manage (such as in changing of net and harvesting). The mesh size of a brood stock cage varies from 4–8 cm. Stocking density of

fish is 1 per cubic meter of water. (b) Concrete tanks The size of concrete tanks used for holding brood stock depends on the size of

the hatchery. It is advisable to use a bigger tank to allow the fish ample space for swimming.

Generally, tank volume ranges from 100–200 tons (5 × 10 × 2m and 10 × 10 × 2m). Stocking rate in brood stock tank is 1 fish for every 2 cubic meters of water.

Spawning and fertilization1. Selection of spawners The selection of spawners from the brood stock should be done months

before the beginning of natural spawning to allow ample time for the fish to be conditioned to environmental and diet controls. Spawners are normally selected based on the following criteria:

fish should be active fins and scales should be complete free from disease and parasite free from injury or wounds males and females of similar size groups are preferred spawner should be at least 4–5 kg in body weight and should not be less

than 3 years old Selected spawners are then transferred to the pre-spawning tank. The ratio of

male and female stocked in the pre-spawning tank is 1:1.

2 .Care of spawners in pre-spawning tank Immediately after stocking in the pre-spawning tank, the feeding is reduced

from 5% to 1% of the total body weight and fed once a day. This is to prevent the fish from getting fat which can result in poor gonadal

development. The feed given should be fresh marine fishes such as sardine, yellow stripe

thread fin, etc. Water in the spawning tank should be maintained in good condition. This

can be achieved by changing the water about 50–60% daily.

Spawning of seabream Presently, there are two major techniques employed in mass production of

seabream fry in Southeast Asian countries: artificial fertilization and induced spawning.

1 .Artificial fertilization. Spawners are caught in natural spawning grounds near the mouth of the

river or in salt water lakes, where the water depth is about 10–20m.

The degree of maturity of the collected spawners should be immediately checked.

If the female has ripe eggs and the male is in the running stage, stripping is done in the boat. The fertilized eggs can then be transported to the hatchery for subsequent hatching.

In cases where only the male is caught, the milt is collected by stripping into a dry glass container.

Milt is then stored in an ice box or refrigerator. The milt can maintain its viability after a week in cold storage (5–15°C).

The preserved milt should be made available for immediate use when a ripe female is caught. The dry method of fertilization is normally used in this case.

The eggs are stripped directly from the female to a dry and clean container where the milt is added.

A feather is used in mixing the milt and eggs for about 5 minutes. Filtered seawater is then added into the mixture while stirring it and then allowed to stand undisturbed for 5 minutes.

2. Induced spawning Two methods are normally used for inducing seabream to spawn in

captivity, e.g. hormonal injection and environmental manipulation. Both methods would induce the fish to spawn naturally in the tank. This results in a monthly spawning until the gonads are spent.

2.1, Induced spawning by hormone injection After stocking seabream brood stock in the pre-spawning tank for two

months, the fish are inspected twice a month during spring tide, ovarian maturity of the female is measured as follows: the eggs are sampled from the female through the use of a polyethylene cannula of 1.2 mm in diameter.

The fish is either anaesthetized or inverted gently with a black hood over the head. The cannula is inserted into the oviduct for a distance of 6–7- cm from the cloaca.

Eggs are sucked orally into the tube by the operator as the cannula is withdrawn. The eggs are then removed from the cannula and egg diameter measurement is made.

When the seabream eggs reach the tertiary yolk globule stage or have a diameter of 0.4–0.5 mm, the female is ready for hormone injection. In males, only those with running milt are chosen.

The hormones usually used to induce spawning in seabream that produce reliable results are:

Puberogen HCG + pituitary gland of Chinese carp Puberogen consists of 63% follicle stimulating hormone (FSH) and 34%

Leutinizing hormone (LH). The dosage usually applied is 50–200 IU/kg of fish.

The fish will spawn at about 36 hours after injection. If no spawning occurs, the second injection is applied 48 hours after the first injection.

The dosages of second injection should be double from that of the first injection and can also be given 24 hours after the initial injection.

The male is usually injected at the same time as the female with a dosage of 20–50 IU/kg of fish. The fish will normally spawn within 12–15 hours after the second injection.

Homogenized pituitary glands of Chinese carp are used at 2–3 mg/kg of fish mixed with Human Chorionic Gonadotropin (HCG) at 250–1,000 IU/kg of fish.

The time interval of application and spawning are the same when using puberogen .

2.2 Induced spawning by environmental manipulation Based on field observations and analysis of natural phenomena that occur

during spawning period of seabream, techniques were developed to stimulate the fish to spawn in captivity. The following steps are necessary:

changing the water salinity to simulate fish migration decreasing the water temperature to simulate the decreased water

temperature after rain lowering and subsequent addition of fresh seawater to the tank in order to

simulate the rising tide, and Follow the moon phase.

Initially, the salinity of water in pre-spawning tank is prepared at 20–25 ppt before stocking the selected spawners.

After stocking, 50–60% of water is changed daily until 30–32 ppt is reached. This will take about 2 weeks.

This will simulate the migration of fish from its growing grounds to the spawning grounds.

At the beginning of the new moon or full moon, the water temperature in the spawning tank is manipulated by reducing the water level in the tank to 30 cm deep at noon time and exposing to the sun for 2–3 hours.

This procedure increases water temperature in the spawning tank to 31–32°C.

Filtered seawater is then rapidly added to the tank to simulate the rising tide. In effect, the water temperature is drastically decreased to 27–28°C.

The fish spawn immediately the night after manipulation (1800–2000 hours) or if no spawning occurs, manipulation is repeated for 2–3 more days.

Egg collection and incubation Fertilized eggs of seabream range in size from 0.8–1 mm. They float in

the water column (pelagic) and are very transparent.Eggs in spawning tank can be collected and transferred to incubation tanks

by either of the following procedures: The spawning tanks are supplied with continuous flow of seawater. The

overflowing water carry the eggs into a small tank (2 × 0.4 × 0.3 m) containing a plankton net (200μ mesh).

Eggs are collected and transferred to larval rearing tanks the following morning.

The eggs are collected from the spawning tanks using a fine mesh (200μ) seine net the morning after spawning.

Fertilized eggs are then transferred to incubation tank at the density of 100 eggs/liter.

The eggs will hatch at about 17–18 hours at 26–28°C after spawning. Dead eggs which settled at the bottom are removed by siphoning.

Hatching rate of seabream eggs by environmental and hormonal manipulation ranges between 40–85% and 0.1–85%, respectively.

Larval rearing The rearing tanks are commonly fabricated from plastic, fiberglass, wood

or concrete. A typical larval rearing tank is rectangular in shape and located outdoor. Its volume ranges from 8–10 tons (7 × 1.2 × 1m or 10 × 1.5 × 1m).

The tanks are usually protected from strong sunshine and heavy rains by a roof tile cover

The usual stocking density for newly-hatched larvae in rearing tank is between 50–100 larvae/liter.

Egg collection

Egg collecting by seine net.

REARING THE LARVAE

Prelarval stage The newly hatched larvae are introduced into floating tanks (dimensions:

about2-4 m x 2-4 m x 1.5-2 m) made of synthetic fiber cloths. The floating tanks are hanged in a large concrete tank (water volume: 50-

200 m3). The survival rates of pre larvae are improved in tanks with abundant

propagation of uni-cellular green algae. In order to promote the propagation of uni-cellular green algae, small

amounts of inorganic and organic nutrients are added into the floating tank. The optimum density of uni-cellular green algae is about 300,000 cells/ml. Slight aeration is provided by about 8 vinyl hoses (diameter: 5 mm) per

floating tank.

The pre larvae are released into large concrete tanks after they have been reared for about 10 days in the floating tanks.

The daily rate of water renewal is set to 1/4 of the total volume several days before transferring the larvae to another rearing net cage.

Waste accumulated on the bottom is removed by siphoning. The newly hatched larvae live for the initial 3 days on their yolk sac. The actual feeding begins on the 4th day after hatching, when the yolk sac

is resorbed and the digestive organ is formed. Oyster eggs, rotifers (Braahionus pliaatilis), copepods collected by net, and

nauplius of Artemia salinaare used for feeding individuals in pre larval stage.

Copepods seem to be a better food than Artemia. Maximum initial density of pre larvae was 25000/m3 while the density at

harvest was 2000/m3. Average survival rate at pre larval stage was 10 % Pre larvae hatch at 2.0-2.3

mm total length. They grow to about 6 mm total length in 20days.

POST LARVAL STAGE Post larvae of red sea bream (about 6 mm in total length) are transferred into

net cages installed at sea. The water depth of the large concrete tanks is decreased to 1/3 (water

volume: 50 m3) before gathering the larvae in order to avoid injury due to water current.

The nets are cleaned every 2-3 days and replaced every 5 to 10 days. Post larvae are cultured to fry stage (20-30 mm total length) in the net cages for about l0-40days.

Initial density of post larvae in the net cages is about 2.000/m3. The number of fry harvested is about 400-500/m3. Survival rate during net

cage stage is about 30 %. Survival rate of fry from hatching to 20 mm total length is about 3 %. Feeding with Braohionus plieatilisand Artemia salinais preferable at the

early stage of the net cages. But the main feed used during the net cage stage is trash shrimp and fish

flesh.

The factors affecting the hatching rate

Water temperature: The fertilized eggs cease to develop at morula stage at 10° C. The hatching

rate becomes poorer and mortality increases at 25° C. The optimum incubation temperature ranges from 15.0 to 17.5° C.

Specific gravity: The fertilized eggs float at the water surface when its specific gravity is

higher than 1.023. They sink under the middle layer when the specific gravity is lower thanl.023. The hatching rate is 80-98 % for the former case and 20-50 % for the latter.

Turbidity due to mud: The effect on the hatching rates of 50 ppm silt in the water is not detectable. However a decrease in hatching rates' is noticeable at l00 ppm.Mechanical shocks: It is important to avoid mechanical shocks such as disturbance and

vibration, as much as possible, when gathering and transferring the eggs.

Red seabream, Pagrus major (Temminck and Schlegel, 1843) is a demersal species that occurs in the northwest Pacific (the northeastern part of the South China Sea northward towards Japan) at depths between 10 and 50 m.

The red sea bream, Pagrus major (Chrysophrys major), is one of the most valuable marine fish in Japan.

This is one of the fish used in aquaculture, and in India its aquaculture practice is not much developed.

The seeds producing in artificial way is to be more difficult because of its less survival capacity.

But in artificial way also seed produced, that is by induced method and environmental manipulation.

CONCLUSION

THANK YOU