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«EFFECTS OF AGE AND STOCKING DENSITY ON SPAWNING PERFORMANCE OF NILE TILPIA, OREOCHROMIS NILOTICUS (L.) BROODSTOCK REARED IN HAPAS TAHOUN1, A. M., M. ...»

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8th International Symposium on Tilapia in Aquaculture 2008 ٣٢٩

EFFECTS OF AGE AND STOCKING DENSITY ON SPAWNING

PERFORMANCE OF NILE TILPIA, OREOCHROMIS NILOTICUS

(L.) BROODSTOCK REARED IN HAPAS

TAHOUN1, A. M., M. A-R IBRAHIM2, Y. F. HAMMOUDA1, M. S. EID3, M.

M. A. ZAKI EL-DIN1 AND F. I.MAGOUZ2

1. Animal Production Dept., National Research Center, Cairo, Egypt.

2. Animal Production Dept., Faculty of Agriculture, Kafr El-Sheikh University, Kafr El-Sheikh, Egypt.

3. Animal Production and Fish Wealth Dept., Faculty of Agriculture, Suez Canal University.

Abstract This experiment was undertaken to investigate the effects of age and stoking density on spawning performance and growth rates of Nile tilapia Oreochromis niloticus (L.) broodstock reared in hapas. In a 2×3 factorial design, two different broodstock ages (1- year old and 3-years old) were combined with three different broodstock densities (4, 8 and 12 fish/ m2 for lower, intermediate and higher broodstock stocking density, respectively) to obtain 6 experimental treatments. Brood-fish were stocked at a sex ratio of three females to one male (3 :1 ). Nile tilapia broodstock age and stocking density significantly (P≤0.05) affected the natural spawning performance. Regardless of broodstock age, the lower stocking density had the highest seed/ female (12١3± 184.14 seeds), seed/ g female (6.93± 1.28 seeds) and seed/ day (10.99±

1.53 seeds) followed by intermediate density (1036.25± 129.35 seeds/ female, 6.08± 1.30 seeds/g female and 9.54± 1.21 seeds/ day) and higher density (745.40± 125.75 seeds/ female, 4.33±

0.80 seeds/ g female, 6.93± 1.23 seeds/ day), respectively.

Irrespective of broodstock stocking density, the broodstock age significantly (P≤0.05) influenced the female fecundity in terms of seed/ female and seed/ day. The 3-Years old female broodstock had a higher absolute fecundity than 1-years old female tilapia broodstock. At high densities, there is a competition for space which increases social interaction and in turn, causes social stress and possibly thereby affecting reproductive efficiency. The best growth performance and feed utilization was found in fry group spawned by older broodstock group (3- years old broodstock), held at the lowest (4 (3 :1 ) fish/ m2.) stocking density. The present study suggests that older broodstock (3-years old) at low stocking density 4 (3 :1 ) fish/ m2 should be used du

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Tilapia is an ideal candidate for warm-water aquaculture. They spawn easily in captivity, use a wide variety of natural foods as well as formulated feeds, tolerate poor water quality, and grow rapidly at warm temperatures. These attributes, along with relatively low input costs, have made tilapia the most widely cultured freshwater fish in tropical and subtropical countries (Biswas et al., 2005; Fasakin et al., 2005, El-Saidy

EFFECTS OF AGE AND STOCKING DENSITY ON SPAWNING PERFORMANCE OF NILE TILPIA,

٣٤٢

OREOCHROMIS NILOTICUS (L.) BROODSTOCK REARED IN HAPAS

and Gaber 2005; Peña-Mendoza et al. 2005 Borgeson et al., 2006; Tsadik and Bar, 2007 and Tahoun, 2007). For fish culture activities in Egypt as in many parts of the world, the necessity of dependable supply of Nile tilapia, Oreochromis niloticus (L.), fry is therefore imperative, but the problem of mass production is still remains. There are many possible reasons for the low production of tilapia fry. These include too low density of broodstock, inappropriate sex ratios, inadequate spawning techniques, broodstock nutrition and high fry mortality (Salama, 1996). Poor broodstock productivity, owing to low fecundity and asynchronous spawning cycles, remains one of the most significant outstanding constraints upon commercial tilapia production and its future expansion. Reproductive success in many fish species has been shown to be influenced by, among other factors, the broodstock, sex ratio, stocking density, age, size, nutrition and feeding regime (Ridha and Cruz, 1989; Smith et al., 1991; Salama, 1996; Izquierdo et al., 2001; Chong et al. 2004; Tahoun, 2007; Hammouda et al., 2008 and Ibrahim et al. 2008). Broodstock productivity clearly represents the most significant constraint on commercial tilapia production. Increased knowledge of the factors regulating broodstock productivity is therefore of great importance to the further development of tilapia culture (Coward and Bromage, 2000). Maximizing seed productivity in hatcheries is the ultimate aim of broodstock management. Traditional tilapia seed production systems suffer from productivity problems that are associated with tilapia's unique reproductive traits such as early maturity, high frequency spawning, low fecundity and high investment in parental care. Improvements in our understanding of the appropriate culture conditions and management procedure for the brood-fish are essential if we are programming reproductive development to produce reliably the numbers of eggs and fry required by grow-out farms. The aim of the present work therefore was to investigate the effects of broodstock age and stocking density on the reproductive performance of Nile tilapia broodstock and to see whether this identifies possible broodstock management strategies that may be adopted by hatcheries to improve seed production.





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Experimental fish Over-wintered male and female Nile tilapia O. niloticus broodstock were obtained from two commercial fish farms located in both Ismailia and Kafr El-Sheikh Governorates, respectively. Broodstock were netted from earthen ponds, manually selected, sexed and transferred to conditioning hapas (each measuring 6X3X1 m3), and kept separately for 25 days for adaptation to the new environment. Prior to The beginning of the experiment. The broodstock were stocked at a sex ratio of 3 females to 1 male. The average initial weights of the two ages were: 80 g for female and 77.3 g for the 1-year old fish and 307 and 273 g for female and mal, respectively, for the 3year old fish. A total number of 36 females and 14 males were counted, batch weight and stocked in each hapa at a rate of 4 (3♀:1♂), 8 (6♀:2♂) and 12 (9♀:3♂) fish/ m2.

At the beginning of experiment, random samples of approximately 10 females and 10 males from each age class were taken, individually weighed and immediately killed and kept frozen at 18 ºC until proximate analysis at the end of experiment (lasted for 108 days). Broodstock were fed a diet containing 40 % CP and 3752 Kcal ME/ Kg with a protein to energy ratio of 106 mg protein/ Kcal ME. Broodstock were fed the experimental diet at a feeding rate of 3 % of total biomass in each experimental hapa (six days/ week). Feed was introduced at 9.00 am and 4 pm with amounts adjusted at a bout 15–20 days according to new weights.

Proximate Analytical At the end of the experiment all broodstock in each hapa were netted, weighed and finally frozen for final body composition analysis. Representative samples of the experimental fish were randomly taken at the beginning and at the end of the experiments. A sample of the experimental fish diet was taken, ground and stored in a deep freezer at -18oC until proximate analysis. All of chemical analyses of diets were determined according to A.O.A.C. (1990).

Growth performance parameters The growth performance parameters were calculated according to the following equations:Average Weight Gain (AWG) = Average final weight (g) – Average initial weight (g)

EFFECTS OF AGE AND STOCKING DENSITY ON SPAWNING PERFORMANCE OF NILE TILPIA,

٣٤٢

OREOCHROMIS NILOTICUS (L.) BROODSTOCK REARED IN HAPAS

Average Daily Gain (ADG) = [Average final weight (g) – Average initial weight (g)] / time (days).

Specific Growth Rate (SGR %/day) = 100 [Ln Wt1 – Ln Wt 0 / T]

–  –  –

Wt 1: final weight (g) T: time of days.

Feed and protein utilization parameters Feed and protein utilization parameters were calculated according to the

following equations:

Feed Conversion Ratio (FCR) = Total feed consumption/ weight gain.

Protein efficiency ratio (PER) = body weight gain (g)/ protein intake (g).

Protein production value (PPV, %) = 100 [Retained protein (g)/ protein intake].

Energy utilization (EU, %) = 100 [Retained energy (Kcal)]/ energy intake (Kcal).

Spawning performance and seed output The following reproductive parameters were determined according to Mair et al.

(2004):

-Absolute fecundity:

- the number of seeds per spawning per female.

-Relative fecundity:

- the number of seeds per unit weight of female.

-Spawning frequency:

- number of spawnings per female throughout the experiment.

Statistical analysis Statistical analysis of each experiment was done using SAS Version 9 (SAS Institute, 2002) statistical package. Data were statistically analysed in a factorial design procedure. Mean of treatments were compared by Duncan (1955) multiple range test.

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Seed production There were evidences that both Nile tilapia broodstock age and stocking density significantly (P≤0.05) affected the natural spawning success in mature broodstock in hapa-in-pond hatchery system (Table 2). The results on seed production under the condition of the present work are in accordance with those of Ridha and Cruz (1999) who indicated that, seed production of Nile tilapia reared in re-circulating tank hatchery system was not different from those reported by other worker used aquaria, ponds, hapas and pools. Thus, the present results reconfirmed the earlier results that increasing the broodstock stocking density above 4 fish/ m2 led to a reduction in seed production. The use of low stocking densities would maximize production of seeds of the hatchery and lead to efficient utilization of the limited hatchery space.

333 TAHOUN, A. M. et al.

–  –  –

Means in the same column having different letters are significantly different (P≤0.05).

Data on the effect of Nile tilapia broodstock stocking density regardless of age on seed production are shown in Table (3). The results indicated that increasing broodstock density significantly (P≤0.05) reduced broodstock fecundity (seed per female). The lower stocking density had the highest seed/ female (12١3± 184.14 seeds), seed/ g female (6.93± 1.28 seeds) and seed/ day (10.99± 1.53 seeds) followed by T2 (1036.25± 129.35 seeds/ female, 6.08± 1.30 seeds/ g female and 9.54± 1.21 seeds/ day) and T3 (745.40± 125.75 seeds/ female, 4.33± 0.80 seeds/ g female, 6.93± 1.23 seeds/ day), respectively. Several researchers studied the effects of different stocking densities on the reproductive performance particularly, on Nile tilapia O. niloticus have demonstrated that increasing the level of stocking density significantly (P≤0.05) reduces spawning success and in turn mass production (Little, 1989; Ernst et al. 1991;

Ridha and Cruz, 1999 and Bhujel, 2000). In this behalf, Brummett (1995) reviewed the environmental factors which influence and regulate maturation and reproduction in tilapia brood-fish and stated that, photoperiod, temperature and population density are predictive cues which affect the onset of sexual maturation and reproduction.

–  –  –

Means in the same column having different letters are significantly different (P≤0.05).

EFFECTS OF AGE AND STOCKING DENSITY ON SPAWNING PERFORMANCE OF NILE TILPIA,

٣٤٢

OREOCHROMIS NILOTICUS (L.) BROODSTOCK REARED IN HAPAS

The effects of Nile tilapia broodstock age regardless of broodstock stocking density on seed production are presented in Table 4. Irrespective of broodstock stocking density, it was observed that, the broodstock age significantly (P≤0.05) influenced the female fecundity in terms of seed/ female, seed/ g female and seed/ day. The 3-Years old female broodstock had a higher absolute fecundity than 1-years old female tilapia broodstock.

–  –  –

Means in the same column having different letters are significantly different (P≤0.05).

The increased seed/ female, seed/ g female and seed/ day/ m2 parameters with the lower Nile tilapia broodstock density in our study is confirmed and agreed with the findings of Ridha and Cruz (1999) on Nile tilapia O. niloticus in a re-cycling tank system and the work of Behrends and Smitherman (1983) on the inter-specific spawning of O. mossambicus females with O. hornorum males in happas. The observed higher seed production at the lower stocking density compared to other stocking densities indicated more synchronous spawning activity, and increasing the density beyond 4 (3♀:1♂) fish/ m2 was not effective to improve seed production.

Comparable conclusion was drawn by Little (1989) who found that a high density such as 4.7 females/ m2 (9.5 fish/ m2) produced the lowest seed/ kg female/ day and that the maximum daily seed production was at the lowest density of 8 fish/ m2, however higher seed production could be obtained using lower stocking density. The declining 3 seed production per unit of area (1 m ) with the increase of the level of broodstock density in the present work, disagreed with the findings of Obi and Shelton (1988) who found that fry production per unit of area (m2) in tilapia, O. hornorum (Trewavas) tended to increase with the increase of broodstock stocking density. Maluwa and Costa-Pierce (1993) reported similar observations for tilapia, O. shiranus. Ridha and Cruz (1999) attributed these contrasting results to the differences in stocking densities used and added that, it must be noted that, the maximum stocking densities used by the above authors were 4 and 1.7 fish/ m2, respectively and that both two numbers were below the density used by most researchers. Therefore, the conclusion of the above authors that a high number of seed could be produced at a higher stocking density might be true as long as broodstock density did not exceed the optimum density. It can said that, there are great discrepancies among investigators even for 335 TAHOUN, A. M. et al.



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