TILAPIA BREEDING: EGG COLLECTION AND INCUBATION OF EGGS IN PLASTIC JARS

Ramil Canto-Saan, Fish Hatchery Group, Nunez Street, Malakas, San Isidro, General Santos City, 9500, Philippines.

KEYWORDSTilapia Breeding • Niloticus Tilapia • Egg Collection • Incubation Jars

Tilapia species is a very profitable fish used in inland bodies of water and this fish is so hardy and easily thrives in any bodies of water. Aquaculture is not a success without tilapia because this is the easiest fish to breed and culture however present techniques employed in breeding this fish is still conventional thus the Inventor, M.J Canto-Saan, developed a system where high-breed tilapia is properly raised for 5 months in b-net hapa in earthen ponds. The breeders are then selected, and classified, sex according to gender and transferred to holding b-nets for conditioning of at least 30 days. The breeders are separated in two b-net hapas according to gender.

The selected breeders are fed twice a day with 32 percent crude protein commercial pellets for 30 days. Rows of hapa nets, 6 meters (length) and 3 meters(width) are installed in earthen ponds (20 meters in length and 40 meters in width) and greening of water is attained by fertilizing the pond with a chicken dung and synthetic fertilzer, 20-20-20. Breeders are put into these hapas at 30 females and 15 males ratio (30:15). Daily monitoring of pH, Dissolve Oxygen, Ammonia content is followed. Each hapa net with paired breeders are fed with commercial feed or rice bran twice a day for twelve (12) days. Fish technicians are task to monitor the hapa nets for surfacing newly-hatched fry. On the 12th day, the hapa nets are "crowd" with crowding bars made of wooden stick

or pvc pipes to collect fry, newly-hatched fry and fertilized eggs from each hapa net. Fry and newly-hatched fry are transferred to a nursery net for further rearing. Fry are to be fed for 30 days post hatching with a commercial fry booster made of ground fishmeal, rice bran ,soya meal,or blood meal.

Hatchery facilities

The sophistication of rearing facilities required in hatcheries will depend to a large extent on the method of management of the seed production system. If seed are harvested with 6 mm mesh seine nets, for example, only fry above 1–2 g will be harvested. On the other hand, if smaller meshed nets (e.g., mosquito netting) are used, or harvesting frequency is increased to once every one to two weeks and all broodfish are inspected, seed collected will contain eggs at various stages of development: hatchlings, pre-swim-up and swim-up fry. Harvesting at 5-day intervals will result in only egg collection. To maintain the higher yields from frequent harvesting, the eggs, hatchlings and early fry need to be incubated artificially.

Hatcheries need to be equipped with high quality water, suitable incubation systems and two to three sizes of tanks to nurture the seed to a size suitable for stocking. The efficient management of these facilities is crucial since poor care of the seed will drastically reduce overall fry production.

In addition, these facilities may also be required in some hatcheries which normally strip broodstock of their gametes to produce specific hybrids.

Technology for artificial rearing of tilapia seed

.

Egg development. As for all fishes, the rate of development of eggs and fry of tilapias is temperature-dependent (Tables 10.7 and 10.8).

Incubation of tilapia eggs. The method required to rear tilapia eggs varies between species. In mouthbrooders the most important requirement is that eggs should be kept in gentle motion, whereas Tilapia eggs develop in static conditions. All eggs, however, should be reared in well aerated, clean water of high quality.

(a) Incubation of eggs of substrate spawners

As already mentioned, the sticky eggs of Tilapia spp. are stripped onto slides. The slides are immersed in a container of well-aerated water.

(b) Incubation of eggs taken from brooders

Irrespective of the type of container used, it is preferable to use a system that is unlikely to fail, i.e., use gravity flow, minimize use of pumps, etc. Ideally, containers should be made from locally available materials. The commonly used systems are described below.

Conical or funnel up-welling jars (or “Zug” jars). These types of containers, used widely in carp propagation, are the most commonly available and therefore used in most hatcheries.

These incubators can be made from glass, plastic, perspex, fibreglass, metal or linen. Glass jars of 5–15 1 can be specially blown but, like perspex, are very expensive and may not be available. Cloth or metal incubators are cheaper to construct but it is not possible to visually inspect the egg or fry mass.

In these incubators water flows in from the bottom of the container; the flow can be adjusted to suspend the egg or fry mass in continuous motion in the water column.

J1 AQUAJARS. These containers were modified from MacDonald jars and were made of transparent plastic. They are cylindrical in shape with a round bottom. Water enters the container from a fixed pipe from above. The flow can be adjusted to gently rotate the eggs. I recommend this for commercial hatchery operators.

Table 10.6

RATE OF DEVELOPMENT OF HATCHERY REARED OREOCHROMIS SPP. EGGS

AND FRY ARTIFICIALLY INCUBATED AT 28°C

Stage of development Age

Hours degree days

2 cells 1.5–2 1.8–2.34 cells 2–3 2.3–3.58 cells 3–4 3.5–4.716 cells 4–5 4.7–5.832 cells 5–6 5.8–7.0Blastula 10–12 11.7–

14.0Embryonic shield-closure of blastopore 14–36 16.3–42

Hatching 90–102 105–119

Early fry (swim-up) 120–144 140–168

End of yolk-sac 216–432 252–504

Large range due to variation in egg size. The larger the egg the longer the time to end of yolk-sac stage.

Table 10.7

HATCHING TIMES OF ARTIFICIALLY INCUBATED O. NILOTICUSEGGS AT VARIOUS TEMPERATURES

Temperature(°C)

Time to hatching(days) (degree days)

24 5–6 120–14428 4 11230 3 9034 2 68

An alternative cheap source of either funnel or round-bottomed containers is plastic soft-drink bottles. The tops or bottoms can be easily cut off to make ideal incubators.

In both of the above systems bad eggs are automatically flushed away with the outflow.

(c) Requirements of developing eggs and fry

High water quality and husbandry standards are essential for healthy development.The J1 AQUASYSTEMS uses a specific mixed of organisms and compound mixed with the tap but filtered water to avoid fungal contamination that lead to 99 per cent hatched rate of eggs. Developing eggs and fry require oxygen-rich water, especially when large quantities of seed are being incubated. Attempts should be made to maintain oxygen levels in excess of 4–5 mg/l. To this end, plankton and algae-free water should be used. Although the plant material oxygenates the water during the day it rapidly consumes oxygen at night.

The maintenance of optimal rearing temperature is essential. Temperatures of below 24°C and above 35°C will lead to high egg mortalities, and any hatchlings may also be very weak and eventually die. Tilapia eggs and fry should be reared between 25° and 30°C, but optimal growth occurs between 28° and 30°C.

During development, large quantities of ammonia and carbon dioxide may be produced. These metabolites need to be flushed away by maintaining a continuous flow of water. If ammonia levels are allowed to exceed 5 mg/l the growth of the fry may be inhibited and the gills of developing fry may be damaged.

The maintenance of correct pH is also important to ensure healthy development, and should be kept between pH 6.5 and 7.5. A pH of below 4.5 or above 8.5 will result in high egg and fry mortalities. A high pH in combination with low water hardness may result in weakened egg shells and consequently prematurely hatched and weak fry.

It is common to treat Tilapia eggs with chemicals during incubation to control bacterial or fungal infections, using one of the following treatments:

Disinfectant Dosage (mg/l)Formalin 1 000–2 000Malachite green 1–5Acriflavin 750–1 500Buffodine 50–100

Hatching and rearing of larvae

The eggs of substrate spawners hatch within 48 h at 28°C, while mouth-brooded eggs hatch within 96 h.

The larvae of all tilapia species have bulky yolks; unable to swim, they will sink. They do not have functional mouths or gills and rely on their superficial blood vessels on the tail and body for their oxygen supply.

The larvae of mouth-brooding species should be reared in the incubators until they become free-swimming. In up-welling and down-welling incubation systems, the swim-up fry can be separated automatically if the outflow is channelled into the rearing tank thus minimizing handling.

Incubation of the sticky eggs of substrate spawners on slides helps to separate the larvae from the egg shells and from bad eggs. Prior to hatching, the slide should be turned such that eggs are on the underside of the slide. This allows the hatching larvae to fall away from the slide.

Timing of initial feeding

The correct timing of initial feeding of developing larvae is crucial for ensuring high survival and producing high quality fry. Under hatching conditions, the species of tilapia and rearing temperature are two major factors affecting the transition to exogenous feeding.

The larvae of Tilapia spp. which produce smaller eggs than mouth-brooders, develop faster and are able to ingest food by four days after hatching at 28°C and three days at 30°C.

In mouth-brooders, exogenous feeding occurs at a later age and is also temperature-dependent. At 24°C onset of feeding occurs at about eight days after hatching (12–13 days post-spawning), while at 30°C feeding initiates at four days (8–9 days post-spawning).

The onset of feeding in tilapia larvae coincides with swim-bladder inflation. Therefore it would be a prudent policy to monitor rearing temperature and to begin initial feeding of larvae just before they become early fry. It should be realized that at this stage even though the fry still possess yolk reserves these are inadequate to meet all the growth demands. Therefore if initial feeding is delayed even by a day, the growth of fry may be sub-optimal and the fry will be small for their age. These fry may also be weakened and easily become victims of disease and cannibalism.

In view of the above, the quality of seed may also be related to the seed production system. Larvae of Tilapia spp. are not orally reared and therefore the quality may not be affected by parental behaviour. Among mouth-brooders, however, larvae are capable of exogenous feeding before the time at which they are normally initially released from the buccal cavity. In addition, if the brooder delays the release of her clutch, e.g., under high stocking densities, or releases the fry for only short periods for feeding, they may begin to lose condition. Thus if naturally reared fry are collected from hapas, tanks or other confined production systems, they may be sub-optimal for their age. Under these conditions, fry from young brooders may be further disadvantaged because of their smaller yolk reserves.

Therefore one method for the fry producer to maximize the quality of fry from mouth-brooders is to remove or encourage the release of larvae from brooders prior to the early-fry stage for hatchery rearing. Larvae that approach the early-fry stage can then be fed continuously from this point onwards.

Rearing of early fry

Tanks are ideal for nurturing early fry. In these carefully controlled environments their feeding can be closely monitored, health checked, and predators kept out to ensure high survival. With proper care, survival of fry up to 2–3 g can exceed 90%.

Circular (1–2 m diameter) or rectangular (area 1–16 m2) tanks may be made of cement, fibreglass, metal or plastic. Such tanks are easily managed by one or two persons. To encourage early feeding the water depth for the initial week should be kept to about 15 cm and then gradually increased. To remove metabolic by-products, faeces and uneaten food, a good water flow is necessary. Any remaining food and faeces should be removed daily.

If complete artificial diets are fed, early fry may be stocked at up to 2 500/m2 for the first week. The advanced fry will then need to be graded and stocking density gradually decreased to about 1 500/m2. With careful management up to 30 000, 2–3 g advanced fry can be produced in a 16 m2 tank. These fry are then transferred to fingerling grow-out facilities.

Under semi-intensive conditions where green water systems are used and feeding is supplemented with low protein diets (ab. 25%), lower fry densities must be used. Under these conditions and tanks should be stocked with 100–200 early-fry/m2.

If green water systems are used, tanks sould be fertilized with chicken manure (100–150 kg/ha/day) and phosphates and nitrates (10 kg/ha/day). These rates may need to be adjusted, the main objective being to achieve visibility down to a maximum of 30 cm. Hatchery operators using green water systems should be aware of oxygen depletion due to algal respiration especially before sunrise. Dissolved oxygen levels should never be allowed to fall below 2 mg/l.

All-male seed production. A widespread problem in tilapia culture is early sexual maturation and breeding of fish in the grow-out phase. This phenomenon results in unwanted seed production and overcrowding. Under these conditions food becomes limited, resulting in the production of small fish (50–100 g) which may command a lower market price. Also, the diversion of energy from growth to egg production leads to a further decline in growth. Thus there may be large differences in the average size of males, which may be at least 50% larger.

To prevent overcrowding, and to allow for better management, all-male seed-stock may be used. These are usually produced by one of three methods: hand-sexing and mechanical grading; hybridization; androgenic sex reversal (Table 10.8).

(a) Hand-sexing and mechanical grading of fingerlings. In mouth-brooders, the sexes of mature fish may be determined by the examination of the genital papillae (Fig. 10.3). Generally, the sexes can be distinguished when fingerlings are about 30–35 g, but sexing is considerably easier in fish weighing more than 50 g. Depending on experience, about 2 000 fingerlings may be sexed in a day. Mechanical graders have also been used to separate the larger males from the females but this is less reliable than hand-sexing.

Table 10.8COMPARISON OF THE SUITABILITY OF VARIOUS METHODS

FOR ALL-MALE SEED PRODUCTION

Methods Suitability

Advantages Disadvantages

Hand sexing 

 

Requires no special equipment or facilities

Labour intensive; wastage, as females are discarded; not 100% reliable due to human error

Mechanical grading Cheap and quicker than hand sexing

Poorer sex separation than hand sexing

Hybridization

No wastage of fry as all are used Hybrid growth vigour and hardiness

Need to obtain and maintain pure species Greater management of broodstock. All-male progeny in broods not consistent. Low fry production due to species incompatability

Androgenic sex reversal

Consistent all-male seed production, if conducted correctly. No wastage of fry. No need for pure species

Availability and added cost of synthetic hormone and organic solvents. High level of technical skill and management required

(b) Hybridization. Even though various workers have shown that more than 25 different hybrid combinations produced over 80% male seed, the use of hybridization for commercial

all-male seed production is limited. Of the various hybrid combinations only a few consistently produce all-male progeny. Oreochromis hornorum is the only known species which consistently produces all-male fry when crossed with O. niloticus or O. mossambicus. The O. niloticus and O. hornorum cross is preferred because of its superior growth performance. Other crosses between O. niloticus and O. aureus which produce between 80 and 90% males are also used. This cross combines the growth vigour of O. niloticus with the cold-tolerance of O. aureus to produce a hybrid population that is largely male and is cold-tolerant.

(c) Androgenic sex reversal. It shows greatest promise and is now increasingly used. The objective of this technique is to convert genetic females into “males” by feeding sexually undifferentiated fry on diets mixed with androgenic hormones. Thus at the end of the treatment the seed will contain genetic males (normal) and genetic females sex-reversed into “males”. The success of the sex reversal treatment, however, will be dictated by factors such as quantity of hormone-treated diet ingested, dosage, age of fry used for treatment and method of diet preparation.

The most commonly used synthetic androgenic hormone is 17 methyltestosterone (17∞ MT). Various doses ranging from 30 μg/g diet to 60 μg/g diet have been used.

For most effective results, a diet containing 40 μg 17∞ MT/g diet is fed for 40 days from first-feeding. If the duration of feeding is reduced, however, or if fry older than one week are used, then the percentage of males may be reduced.

Diets and feeding routines for tilapia fry

During early development, the metabolic activity and growth of fry is very high. Therefore, to sustain optimal growth, the hatchery operator should ensure that the food available to fry contains sufficient quantities of protein for tissue construction and is nutritionally well-balanced.

Natural foods. If ponds and outdoor tanks are used to rear fry, a wide selection of natural foods may be available to the fish. Their diets consist largely of a mixture of algae, bacteria and detritus. By adding organic and inorganic fertilizers to the water, the quantity and range of food items can be increased. Addition of organic manures introduces particulate matter which is rapidly broken down by bacteria, protozoans and small invertebrates and encourages the growth of algae, phytoplankton and zooplankton all of which form an excellent source of protein and add to the balance of the diet.

Natural foods also play an important role in green water culture systems using supplementary diets. Under this management system, some natural food is available to the fry at all times, providing essential vitamins and minerals which may be deficient in the supplementary diets.

As the stocking density of fry is increased, however, the quantity of natural food available to each fry will decrease and therefore the quantity and quality of supplementary or formulated diets will become more important.

Complete diets. Correctly formulated diets containing required amounts of proteins, lipids, amino acids, fatty acids, minerals and vitamins are crucial if healthy and strong fry are to be produced in the absence of natural foods.

Protein is of primary importance for fish growth, providing the basic materials for tissue-building and energy. To sustain the high metabolic rates of the rapidly growing fry, protein requirements are very high. The quantity of protein that is ultimately included in the diet will depend on the age of the fry and the source and quality of protein.

For tilapias the protein requirement declines with age (Table 10.9). For rapidly growing tilapia fry, protein levels of between 30 and 50% have given good growth.

For fry up to 0.5 g, 50% protein is required if fed 3–4 times/day at 10–15% of body weight/day. Lower protein levels may be adequate if feeding frequency is increased to eight times/day and ration increased to 20–25% of body weight/day. Diets containing protein levels of 30–35% have proved adequate when fed at 10–15% body weight/day in semi-intensive systems where natural food supplements the artificial diet.

Table 10.9

SUMMARY OF THE MAJOR NUTRIENT REQUIREMENTS OF TILAPIAS

(in percentage of dry diet)

NutrientSize range of fish

up to 0.5 g

0.5–10 g

10–35 g

> 35 g

Crude protein 50 35–40 30–35 25–30

Crude lipid 10     10   6–10     6–8Digestible carbohydrate 25      25       25       25

Fibre   8       8   8–10    8–10

Lipids are an important sources of essential fatty acids and of energy, twice that of protein. In addition, by providing lipid in the diet the protein may be spared for tissue construction. Lipid requirements are said to decrease with the age of the fry. For fry up to 10 g, lipid levels of 10% are recommended. For fingerlings, 6% is adequate (Table 10.9).

Carbohydrates may be included in the diet as an energy source to spare protein (Table 10.9). Sources such as rice, barley, oats, millets and sorghum contain 50–60% carbohydrates. They are a cheap source of energy and are included as a bulking agent and as a binder.

Vitamins and minerals can be obtained as premixes. Vitamin premix should be used at approximately 2% of the complete dry diet. If natural food is available, the level may be reduced.

Feeding routine. Under natural conditions, tilapias are omnivorous and choose to browse on detritus, phyto- and zooplankton, algae and small invertebrates of appropriate size. They are equipped with simple stomachless guts and as such feed continuously during daylight hours.

Under hatchery conditions where formulated diets are fed, the growth and survival of tilapia fry will be influenced by factors such as particle size, feeding frequency/ration, and feeding method.

Particle size of food. The particle size acceptable to first-feeders depends on the size of the fry. Table 10.10 summarizes suggested particle sizes for tilapia fry.

Table 10.10

PARTICLE SIZE OF DIET ACCEPTABLE TO TILAPIA FRY

Feeding frequency and ration. First-feeders grow best when they are fed continuously. They are equipped with a simple gut that is designed to cope with small quantities of food.

Under hatchery conditions feeding frequency will be determined by the management of the rearing tanks. If green water systems are used, a feeding frequency of 3–4 times a day is adequate. If flow-through systems, high stocking density or clear water systems are used, first-feeders should be fed 6–8 times a day.

 

 

Fish sizeParticle

size (mm)

Weight(g)

Standard length(cm)

Tilapia spp. early fry

0.003–0.005 0.3–0.4 0.1–0.2

Mouth-brooders early fry

0.006–0.015 0.5–0.9 0.2–0.3

Fry of all species

0.05–0.25 1–2 0.25–0.5

0.25–0.5 2–3 0.5–0.75

0.5–1 3–4 0.75–11–3 4–5 1–23–30 5–9 2–3

Food intake (measured as percent body weight/day) is inversely related to fish size. The ration given to fry under hatchery conditions will also depend on the availability of natural food. In green water systems, rations of between 10 and 15% body weight/day appear adequate.

In intensive culture conditions, the rations need to be higher, generally between 25 and 30% body weight/day. As fish grow the ration should be reduced. When fry reach 1–2 g they should be fed at 10–15% body weight/day, and by 30 g at 3–5% body weight/day.

Feeding at the correct frequency and ration is important for both survival and growth. Under low rations and feeding frequencies, size variations of individual fish will increase considerably. Under these conditions, cannibalism of small fry by larger individuals may be as high as 30–35%. Under-fed tilapia fry become very aggressive. In the case of O. mossambicus it has been shown that starved 20–30 mm fry can easily kill and consume fry up to half their own size.

The feeding frequency and ration may also be related to water temperature and oxygen stress. As the oxygen level and water temperature decrease, or fish become stressed by disease, transportation, etc., food consumption will decrease. Under these conditions feeding ration will need to be reduced. Conversely, at higher temperatures, feeding should be increased. Feed may be delivered to tilapias by hand, or by use of demand or automatic feeders.