Reproductive biology of female Nile tilapia Oreochromis niloticus (Linnaeus) reared in monoculture and polyculture with African sharptooth catfish Clarias gariepinus (Burchell)
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This study was conducted to assess the reproductive biology and early breeding behaviour of female Oreochromis niloticus reared in monoculture and polyculture with Clarias gariepinus in earthen ponds for 8 months. Results revealed no significant difference in length at first maturity (L50) between females reared in monoculture and polyculture systems. Similarly, no significant differences were detected in absolute fecundity, relative fecundity, gonado-somatic index and condition factor between the two culture systems. The absolute fecundity was more strongly correlated with total length and body weight than with ovary weight. The study concluded that early breeding of O. niloticus in captivity is not affected by the culture systems used. Therefore, O. niloticus production in either system can be improved only through proper pond management techniques.
KeywordsEarly maturation Prolific breeding Tilapia culture systems Grow-out ponds Fecundity Ovary weight
Nile tilapia Oreochromis niloticus (Linnaeus, 1757) is a worldwide important species in aquaculture because of its fast growth, firm and tasty flesh, resistance against harsh conditions and ease production of fingerlings under captivity (Fryer and Iles 1972; Yi et al. 1996; de Graaf et al. 1999; Gómez-Márquez et al. 2003). However, early maturation and prolific breeding of O. niloticus in culture systems, especially earthen ponds is a major problem in tilapia farming (Bardach et al. 1972; McGinty 1985; Suresh and Bhujel 2012). The large numbers of fingerlings produced through reproduction during grow-out consume the feeds and dissolved oxygen intended for the stocked tilapia (de Graaf et al. 1996). Consequently, the growth rate decreases with fewer marketable-size fish. In the wild, O. niloticus starts to reproduce at a total length of 20–30 cm (150–250 g) (Lowe-McConnell 1958; Gwahaba 1973). However, under captivity O. niloticus reaches sexual maturity at a relatively smaller size of 8–13 cm (Siraj et al. 1983; de Silva and Radampola 1990; Suresh and Bhujel 2012).
Methods adopted to control overpopulation in farmed tilapias have been reviewed by Guerrero (1982) and Mair and Little (1991). These methods include monosex culture through manual sexing and hormonal sex reversal, cage culture, high stocking density, sterilization, intermittent (selective) harvesting and the use of slow maturing tilapia species or strains. However, these methods have their limitations. For example, the use of reproductive inhibitors (sterilization) such as irradiation or chemosterilants are expensive and require hatchery facilities and skilled manpower. The intervention of hormones is also expensive and sometimes difficult to obtain (Jegede 2010). On the other hand, the use of predator-control method such as African sharptooth catfish Clarias gariepinus (Burchell, 1822) through polyculture has been considered a safe biological method for controlling unwanted reproduced fingerlings in mixed-sex tilapia population in ponds without affecting the big size tilapia (Abdel-Tawwab 2005). The reproductive biology of female O. niloticus reared in monoculture system has been investigated by de Graaf et al. (1999). However, limited attempts have been made to assess the reproductive biology of female O. niloticus in polyculture system. This assessment is useful in ensuring the well-being of the cultured fish (Moreau et al. 1986), enabling protection of new recruits (King and Udo 1998).
The objective of the present study was to determine the reproductive biology of female O. niloticus with an emphasis on its early breeding behaviour under monoculture and polyculture pond systems. In order to address this objective, it was hypothesised that O. niloticus reared in monoculture system attains sexual maturity earlier and at a smaller size than those reared under polyculture system.
This study was not evaluated by an Animal Ethics Committee because there was no such committee in Tanzania during the course of the study. Nevertheless, the research methods used for fish sampling followed internationally recognised guidelines for ethical use of animals (for example, Håstein 2004; Grigorakis 2010). The fish used for determination of maturity stages were sacrificed by hypothermia through immersing them in an ice-slurry to avoid causing stress and pain before death (Sneddon 2006). By using ice water, it was possible to calm down the fish for several hours until osmoregulatory problems and exhaustion occur. It has been demonstrated that pre-chilling prior to slaughter is a minor stressor (Sneddon 2012).
The experiment was conducted in six earthen fish ponds of 150 m2 with a mean depth of 1.25 m each. The ponds received water from the source of Mori River that drains to Lake Victoria. Three ponds were stocked with O. niloticus and C. gariepinus in polyculture while the other three ponds were stocked with O. niloticus in monoculture. A stocking ratio of 1:3 for C. gariepinus and O. niloticus was adopted for polyculture treatment. Both culture systems were stocked with fingerlings of mean (±SE) initial weights of 5.01 ± 0.01 g at a stocking density of 9 fish m−2. For polyculture ponds, stocking of similar initial weights of C. gariepinus was intentionally delayed for 30 days to allow O. niloticus to grow to a size (12.26 ± 9.49 g) that C. gariepinus were unable to prey on (Shoko et al. 2014a).
Formulation and proximate composition (dry matter basis) of feed used in the study
Composition (g kg−1) dry feed
Cotton seed cake meal
Maize bran meal
Proximate composition of feed
Determination of gonad maturity stages
Description of maturity stages of female O. niloticus as adopted from Mous et al. (1995)
Stage I: Immature: Appearance like testes; sexes indistinguishable macroscopically
Stage II: Early developing: Ovaries to be recognized by small whitish dots (eggs); caudal part of the ovaries more thickened than the rostral part
Stage III: Developing or recovering: Eggs developing inside the ovaries unequal in size
Stage IV: Early ripening: Eggs equal in size but not fully grown; all coloured yellow
Stage V: Ripe: Eggs large and ovaries visible from the ventral side of the cavity
Stage VI: Spent: Eggs or juveniles in the buccal cavity; ovaries recovering, thin and reddish; eggs unequal in size, often including a few residual stage V eggs
Determination of size at first maturity (L50)
Determination of condition factor
Estimation of gonado-somatic index (GSI)
Determination of fecundity and egg diameter
The most advanced maturity stage encountered was determined by counting ovaries with GSI larger than 3% in order to determine the absolute fecundity (de Graaf et al. 1999). The egg size was determined by measuring the diameter of 40–55 randomly selected eggs per female along two axes in the counting chamber under a microscope using a calibrated eyepiece ocular micrometer at 40× magnification. At the end of the study, a comparison was made in terms of growth and yield performance between monoculture and polyculture systems as done by Shoko et al. (2011).
Data were tested for homogeneity of variances using Levene’s test. A two tailed t test was used to compare the estimates of L50, fecundity, condition factor, GSI, growth and yield between monoculture and polyculture systems. Linear regression analysis was used to test the relationship between fecundity and total length; fecundity and total weight and fecundity and oocytes diameter in monoculture and polyculture systems. Linear regression analysis was also used to test the relationship between condition factor and absolute fecundity. Fisher’s Z-test was used to compare correlation coefficients (r) between the two culture systems (Zar 2010). All statistical analyses were performed using SPSS 13 for Windows (Landau and Everit 2004). Significance of differences was judged at p < 0.05.
No significant difference was observed in GSI (t = −1.012, df = 66, p = 0.315) and condition factor (t = 0.172, df = 66, p = 0.864) between the two culture systems with no relationship between the two parameters. However, a negative relationship between condition factor and relative fecundity under both culture systems was realized.
Mean growth rates and yield parameters of O. niloticus cultured under monoculture and polyculture ponds (data are mean ± SE)
Average initial weight (g)
5.01 ± 0.05a
5.01 ± 0.05a
Rearing period (days)
Average final weight (g)
123.64 ± 2.57a
146.58 ± 3.56b
Total weight gain
118.63 ± 2.58a
141.57 ± 3.56b
Survival rate (%)
92.13 ± 1.70a
96.62 ± 3.97b
Specific growth rates (%)
1.33 ± 0.01a
1.40 ± 0.04b
Gross fish yield (tonha−1)
10.27 ± 0.55a
15.25 ± 0.64b
Net fish yield (tonha−1)
10.26 ± 0.54a
15.25 ± 0.64b
Net annual yield (tonha−1yr−1)
1797.25 ± 95.44a
2671.30 ± 111.55b
The present study was conducted to determine the reproductive biology of female O. niloticus reared in monoculture and polyculture pond systems. The results from this study negate the hypothesis that O. niloticus reared in monoculture would attain sexual maturity earlier and at a smaller size than those in polyculture. This indicates that early breeding in O. niloticus under captivity is not affected by the type of culture system used.
Findings of this study are in agreement with those reported by de Graaf et al. (1999) who suggested that pond environmental conditions are not a major cause for precocious breeding of Nile tilapia. However, Lowe-McConnell (1982) stated that early breeding in O. niloticus can be influenced by the low condition factor which is influenced by the quality of food and protein levels (Gunasekera et al. 1995). In the present study, 50.00% of females reached sexual maturity at body length of 16.38 and 16.59 cm in monoculture and polyculture, respectively. These values are comparable to those reported by Peña-Mendoza et al. (2005), but higher than those (8.00–13.00 cm TL) reported by de Silva and Radampola (1990) and Siraj et al. (1983). More importantly, it seems that O. niloticus used in the present study exhibited neoteny (early breeding). However, neoteny did not reduce somatic growth because specific growth rates in both systems are similar to 1.35 and 1.47% obtained by Abdel-Hakim et al. (2008) from monosex rearing of Nile tilapia. Specific growth rates of 1.33 and 1.40% were obtained from monoculture and polyculture systems respectively in this study.
The present study showed overlaps in the ranges of total length among the different maturity stages. This is attributed to the fact that, maturation in O. niloticus does not depend only on length but it is also controlled by other factors such as food availability and water quality (Babiker and Ibrahimu 1979; Southgate and Lucas 2012). Changes in these factors are translated as neural signals which stimulate the pituitary gland and gonads to respond to the above triggers (Southgate and Lucas 2012).
The insignificant difference in GSI between monoculture (3.86%) and polyculture (4.33%) indicates that culture system has no effect on GSI. The GSI values from the present study are comparable with the maximum GSI of 3.60, 4.00, 4.70 and 4.80% reported by Babiker and Ibrahimu (1979), Hirpo (2012), Ambali and Little (1996) and Behrends and Smitherman (1983), respectively but lower than the 7.00% reported by de Graaf et al. (1999). The difference in experimental conditions could have contributed to the differences in maximum GSI obtained from the present study.
The insignificant difference obtained in the absolute fecundity of O. niloticus raised in monoculture and polyculture systems further support the notion that culture system has no effect on the reproductive capacity of the females. In the present study, the absolute fecundity ranges of 678.00–2,086.00 and 662.00–2,096.00 recorded in monoculture and polyculture, respectively are higher than the ranges of 289.00–1,456.00 and 104.00–709.00 for O. niloticus with 10.00–23.00 cm and 12.50–20.90 cm reported by Shalloof and Salama (2008) and Gómez-Márquez et al. (2003) respectively. Furthermore, the fecundity reported in the present study is lower than the maximum absolute fecundity of 2,603.00 with a corresponding total length of 34.90 cm reported by Peterson et al. (2004). Variation in fecundity could be attributed to the differences in experimental conditions.
In the present study absolute fecundity of O. niloticus reared under both monoculture and polyculture was strongly correlated with weight and total length than with ovary weight. These results are consistent with the results obtained by Gómez-Márquez et al. (2003), Murua et al. (2003), Peterson et al. (2004) and Shalloof and Salama (2008) who found that fecundity was directly correlated with body total length and weight. No correlation existed between absolute fecundity and oocyte diameter in O. niloticus cultured under either system. This is because in fishes, the size of ripe eggs does not vary much with the size or age of the fish. This finding is in agreement with that of Shalloof and Salama (2008). The size of oocytes reported from the present study ranged from 1.36 to 2.04 mm and 1.32–2.20 mm in O. niloticus reared under monoculture and polyculture ponds, respectively. These oocyte sizes are comparable with the size of 1.00–3.00 mm reported by Gómez-Márquez et al. (2003) and 1.80–2.45 mm reported by Babiker and Ibrahimu (1979), Siraj et al. (1983), Smitherman et al. (1988), de Graaf et al. (1999) and Shalloof and Salama (2008).
The significantly higher growth and yield of O. niloticus reared in polyculture than the monoculture system can be attributed to the reduced number of O. niloticus fingerlings as a result of predation by C. gariepinus and to the less competition for food and space. This improved growth performance in polyculture is in agreement with the findings reported by de Graaf et al. (1996), El Gamal et al. (1998), Liti et al. (2002) and Offem et al. (2009).
This study showed that, female size at first maturity in O. niloticus is not affected by the culture systems used. Moreover, adding C. gariepinus to Nile tilapia population reduced the number of unwanted tilapia fingerlings and improved growth performance and yield. However, further studies are necessary to determine the size of C. gariepinus for maximum elimination of the unwanted tilapia population for maximum tilapia growth and yield.
Conceived, designed the experiments, collected and analysed data and drafted the manuscript: APS, SML and HDJM. Designed and supervised the study including data analysis: YDM. All authors read and approved the final manuscript.
This work was supported by the Inter-University Council for East Africa through Lake Victoria Research (VicRes) Initiative project and the Government of Tanzania through Commission for Science and Technology. Tanzania Fisheries Research Institute and the University of Dar es Salaam are acknowledged for granting the authors permission to participate in the study. We are also grateful to the cooperation provided by the local fish farmers in the study area.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
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