Despite the great potential of tilapia culture, shortage of fry production to meet the increased global demands remains one of the main obsta- cles limiting the expansion of intensive culture of these fish. Information about egg composition, hatchability, yolk-sac absorption, and larval rear- ing is limited, inconsistent and sometimes contro- versial. Therefore, extensive efforts should be expended to face these challenges, and better understand the optimum requirements for larval rearing of tilapia.
7.9.1. Hatching systems 7.9.1.1. Earthen ponds
Spawning in earthen ponds is the oldest method used for seed production of tilapia, and is still widely used in different regions of the world, espe- cially in developing countries (Hepher and Pruginin, 1981; Macintosh and Little, 1995; Little and Hulata, 2000). Tilapia can spawn easily in ponds, regardless of pond size and depth, once the environmental requirements (temperature, salin- ity, etc.) and biological criteria (stocking density, sex ratio, etc.) are met. However, pond size, shape and depth affect harvest efficiency and seed pro- duction. Earthen ponds can be used for producing mixed-sex pure tilapia (Little et al., 1994), monosex
hybrids (Hepher and Pruginin, 1981) and first-feeding fry for sex-reversal (Verdegem and McGinty, 1987). Eggs and fry are usually har- vested, either partially or completely, at varying intervals ranging from 6 to 60 days (Fig. 7.4). It has been reported, however, that shorter harvesting intervals lead to better results. Sorting of the seeds and removal of larger fry also reduce cannibalism and result in higher production of similar-sized fry (Little, 1989). Partial harvest is carried out by dip-netting, seining or trapping, without draining the ponds, while complete harvest requires check- ing of broodfish for seed incubation, along with draining of the pond and harvesting all seed at once (Little and Hulata, 2000).
The main limitations of breeding ponds are the lack of sustainability, predation of small fry by other fish, cannibalism by older fry, asynchronous spawning and reduction of spawning frequency with overcrowding. Most of these limitations can be overcome through sound management, such as
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Species hybridized
% Females Reference
Male Female
O. mossambicus S. melanotheron 100 Peters (1963), Bauer (1968)
T. tholloni 100 Peters (1963), Bauer (1968)
O. niloticus S. melanotheron 100 Peters (1963), Bauer (1968)
T. tholloni 100 Peters (1963), Bauer (1968)
Table 7.7. Hybridization of different tilapia species to produce all-female populations.
Fig. 7.4. Harvesting tilapia fry from earthen ponds in the Philippines.
Reproduction and Seed Production 133
increasing water fertility, decreasing sediment concentration, preventing the entry of wild preda- tory fishes and regular seed harvesting (Little, 1989; Macintosh and Little, 1995).
7.9.1.2. Concrete tanks
Concrete tanks are currently among the most widely used spawning units for production of tilapia seeds (Fig. 7.3), especially for intensive cul- ture in areas where fresh water is limited. Tanks have many advantages over earthen ponds, including high yield per unit area, easy harvest and better water management through exchange and/or filtration, while their main disadvantage is the higher cost. Spawning efficiency can be affected by tank size, dimensions, shape, colour, depth and construction material. Reproductive performance of Nile tilapia was found to be better in deep tanks (1–2 m) than in shallow (0.5 m) tanks (El-Sayed et al., 1996). Courtship, spawning inten- sity and seed production of tilapia can also be related to artificial spawning shelters. Baroiller
et al. (1997) found that the seed production of Nile
tilapia was five times higher in raceways (12 m2) containing artificial shelters (three breeze blocks) than in unsheltered raceways. The authors sug- gested that artificial shelters stimulated and syn- chronized reproductive activity of the fish. On the other hand, Duponchelle and Legendre (1997) reported that absolute fecundity of Nile tilapia females reared in tanks provided with artificial reefs was lower than in naked tanks. However, this result is questionable, because the study was con- ducted for only 2 months, whereas a much longer period is required for concrete results.
7.9.1.3. Hapas
The use of hapas (Fig. 7.5) as a hatching system for tilapia has been tried in Asia (the Philippines, Thailand, Vietnam, etc.), the Americas (the USA, Brazil, Puerto Rico) and Africa (Malawi) (Little and Hulata, 2000), with varying degrees of suc- cess. Hapas have many attributes that make them an excellent hatchery system for tilapia, especially in developing countries. These include easy con- struction, easy management, easy seed harvest and low cost. Hapas can also be suspended in fer- tilized earthen ponds, deep water bodies and con- crete tanks supplied with clear water. However, they need continuous maintenance and cleaning
of fouling. Fouling leads to blocking the mesh net- ting of the hapas and deteriorating water quality inside them (Little and Hulata, 2000).
The spawning of tilapia in hapas suspended in ponds depends on broodstock density and sex ratio, broodstock exchange, wind, water turbidity and varying water level. The use of the double hapa system, where broodfish are stocked in an inner net having a larger mesh size, which allows free access of the swim-up fry produced to the outer fine-mesh hapa or directly to the surrounding water tanks/ponds has been studied. This system was found effective in reducing the disturbance of brooding fish and fry and decreasing cannibalism, but the performance was not very encouraging (Guerrero and Garcia, 1983; Costa-Pierce and Hadikusumah, 1995).
7.9.1.4. Artificial incubation
The removal of eggs and sac fry from the mouths of females and incubating them artificially is an effective method of tilapia seed production. Artifi- cial incubation is preferable to natural incubation due to: (i) elimination of cannibalism; (ii) high pro- duction of even-sized fry; (iii) increased spawning synchrony; (iv) shortened inter-spawning intervals; (v) reduction of hatching time; and (vi) facilitation of research on tilapia genetics and reproduction.
The incubation units for tilapia eggs can range from simple, inexpensive and easy-to-make units, such as soft-drink bottles and round-bottomed con- tainers, such as carboys and plastic containers (Fig. 7.6.) to commercial, more advanced, conical, upwelling jars (Fig. 7.7). The efficiency of an incu- bator depends on its type, size and shape, the
Fig. 7.5. Breeding Nile tilapia in hapas fixed in earthen ponds in the Philippines.
developmental stages of the eggs and the water quality and flow. Rana (1986) found that round-bottom incubators resulted in higher sur- vival than conical containers (85% compared to 60%), while the time to hatch was shorter in conical vessels than in round-bottom vessels (Macintosh and Little, 1995). Furthermore, Rana and Suliman (1993) found that hatching time and survival rates of tilapia fry were significantly better in downwelling round-bottomed incubators than in upwelling conical chambers.
7.9.2. Egg hatching and yolk-sac absorption
The development time that the fertilized eggs of tilapia take to hatch ranges from < 3 to> 6 days. Hatching time is affected by a number of factors, including water temperature (Rana, 1990b, c), salinity (El-Sayed et al., 2005a), water flow (Rab, 1989; El-Sayed, et al., 2005b) and broodstock nutrition (Gunasekera et al., 1996a, b; Siddiqui
et al., 1997b; El-Sayed et al., 2003). The optimum
temperature for best hatching and survival rates
134 Chapter 7
Fig. 7.6. A GenoMar tilapia hatchery in the Philippines (photo provided by K. Fitzsimmons).
Reproduction and Seed Production 135
ranges from 25 to 32°C. The decrease in water temperature below 22°C in subtropical areas can lead to a delay or decrease in seed production, as has been reported in Nile tilapia in Vietnam (Green et al., 1997) and Egypt (El-Naggar et al., 2000). Improving water temperature through heating, increasing pond depth, shading, deep hapas, etc. improves reproduction efficiency and seed production. On the other hand, high ambient water temperature (33–35°C) was found to reduce spawning efficiency, egg quality and hatchability of Nile tilapia in central Thailand during hot sea- sons (Little et al., 1997).
Water flow was also found to affect the spawn- ing efficiency and larval growth of tilapia. The time taken from yolk-sac absorption of Nile tilapia eggs to reach swim-up fry was reduced with increasing water flow (Rab, 1989; El-Sayed et al., 2005b). A flow rate of about 8 l/min in a 20 l hatching unit was found optimal for yolk-sac absorption of Nile tilapia eggs (El-Sayed et al., 2005b).
A number of studies have considered the effects of water salinity on hatchability and larval rearing of tilapia. Hatching success of O. niloticus females was comparable at 5‰ to that in fresh water, while increasing salinity to 10 and 15‰ lowered hatching success, and no hatching occurred in full seawater (Watanabe and Kuo, 1985). Al-Ahmad et al. (1988) also found that egg hatching success and fry survival of O. spilurus was twice as high in groundwater (4‰) as in seawater (40‰). On the contrary, Uchida and King (1962) found that fry production of O. mossambicus was three times higher in brackish water (8.9–15.2‰) than in fresh water.
It has also been reported that broodstock nutrition significantly affects spawning efficiency, egg hatchability and larval growth. El-Sayed et al. (2003) found that the hatchability of Nile tilapia egg hatched at different salinities (0–14‰) was linearly increased with increasing dietary protein levels from 25 to 40%. Eggs produced from broodstock fed 25% protein at 7 and 14‰ needed more time for hatching and yolk-sac absorption and resulted in poorer larval weight than those reared in fresh water. Furthermore, at high dietary protein levels (35–40%), O. niloticus eggs took about 3–4 days to hatch, while at a lower protein level (25%) hatching occurred after 4–6 days. Similar results have been reported on
O. niloticus fed 20 and 35% protein at 26°C
(Gunasekera et al., 1996a).