Assessment of African Clariid Catfishes for Tilapia
Population Control in Ponds
O. A. Fagbenro
Department of Fisheries and Wildlife
Federal University of Technology,
P.M.B. 704 Akure, Nigeria
ABSTRACT
Quantitative evaluation of predation efficiency of two hybrid clariid catfishes (Heterobranchus longifilis x Clarias gariepinus and H. bidorsalis x C. gariepinus) in controlling recruitment and while producing adult (market-size) Oreochromis niloticus was conducted in small earthen ponds (200 m2) using three tilapia: hybrid catfish stocking combinations (5:1, 10:1, 20:1). After 180 days of combined stocking, the tilapia: hybrid catfish combinations that gave effective control of tilapia recruitment were 5:1 and 10:1 and produced tilapia AT values (total weight of market-size tilapia (150 g) expressed as % of total weight of the whole tilapia population) 90. Differences in tilapia AT value, mean final weight of O. niloticus between 5:1 and 10:1 treatments were not significant (P > 0.05). Mean final weight and total yield of market-size O. niloticus in the mixed culture treatments were superior (P < 0.05) to that attained in the tilapia monoculture (control) treatment. Estimated annual production of market-size O. niloticus at 5:1, 10:1 and 20:1 were high and similar (P > 0.05), ranging from 5.2 to 5.7 kg/ha/yr. Results indicated that both hybrid catfishes are suitable predators for controlling tilapia stunting and overpopulation in pond culture. This paper also presents the results from the predator-prey ratios tested for different African clariid catfishes in controlling tilapia recruitment in ponds.
INTRODUCTION
A general problem associated with the culture of tilapia (Oreochromis, Sarotherodon, Tilapia spp.) is the intensive reproduction which often produces large populations of small-sized (stunted) tilapia recruits; which are of low value to consumers. In order to produce adult tilapia (150 g market size), special culture techniques may be required. Several effective methods have been used to control such undesirable tilapia populations. These include monosex culture (monosex hybrids, manual sexing or grading, sex reversal), cage culture, tank culture, the use of predators, stock manipulation, the use of irradiation, chemosterilants and other reproduction inhibitors, stock manipulation/selective harvesting, the use of slow maturing tilapia species. Of all these methods, the use of local predatory fish species to control such unwanted/undesirable tilapia recruitment in ponds is one of the most effective methods recommended for Africa (Guerrero 1982).
Density control of tilapia populations by predators is not thoroughly researched in Africa as only few indigenous predators have been tested, namely Lates niloticus (Bedawi 1985; Ofori 1988), Notopteris affer (Iscandari 1986), Parachanna obscurus (De Graaf et al. 1996), Hemichromis fasciatus (Fagbenro & Sydenham 1997). These predators have some drawbacks, for example, there is a difficulty in obtaining fingerlings of N. affer due to non-availability in natural waters or inability to propagate in captivity; L. niloticus requires large ponds and is sensitive to low oxygen regime; H. fasciatus is also a prolific breeder and has a poor market value (due to small adult size). African clariid catfishes (Clariasgariepinus,C.anguillaris, C.isheriensis, Heterobranchusbidorsalis, H.longifilis, H. isopterus) do not have these limitations, hence the combined production of tilapia and clariid catfishes has attracted considerable attention, particularly in west Africa (Fagbenro & Sydenham 1990; Lazard & Oswald 1995).
The hybrid clariid catfishes, H. longifilis x C. gariepinus and H. bidorsalis x C. gariepinus, and their reciprocal crosses grow faster than their parental species hence they are preferred for pond culture (Hecht & Lublinkoff 1985; Legendre et al. 1992; Oellermann & Hecht 1993; Sydenham et al. 1993). Both hybrid catfishes are carnivorous with high propensity for piscivory, which suggests that they could be used to control tilapia recruitment in ponds. This study therefore evaluates the predation efficiency of two hybrid clariid catfishes, H. longifilis x C. gariepinus and H. bidorsalis x C. gariepinus, specifically, the tilapia: hybrid catfish combination that will control tilapia recruitment and at the same time produce market-size population of Nile tilapia, Oreochromis niloticus. The results of other African clariid catfishes used as predator to control excessive reproduction and produce market-size tilapia in ponds in different west African countries are also presented and compared.
METHODS
Twelve 200 m2 earthen ponds with mean water depth of 1.4m were used in this study. Each pond was provided with water from an adjacent 0.5 ha pond through a canal. Agricultural lime was applied to the pond bottom at 300 kg/ha before commencement of fish production trial. Oreochromis niloticus fingerlings (43.22.7 g) were obtained from existing ponds on the Federal University of Technology, Akure Fish Farm, and stocked at 20,000/ha into the experimental ponds. Hybrid catfish juveniles (H. longifilis x C. gariepinus and H. bidorsalis x C. gariepinus, 151.68.2 g), obtained by hormone-induced spawning, were stocked 60 days later in order to allow the tilapia enough time to grow and breed. The experiment comprised three tilapia: hybrid catfish stocking treatments (5:1, 10:1, 20:1) and a tilapia monoculture treatment as control, each of which was replicated thrice in a randomized design. All ponds were fertilized with dry poultry manure at 60 kg/ha/day and fish were fed a 3:2 mixture of soybean meal (38.0% crude protein) and shrimp head meal (50.5% crude protein) at 2.5% body weight (bw)/day. Periodically (30-day intervals), the total weight of stocked fish was assessed (based on at least 30% of the total fish population seined from each pond) and the amount of feed adjusted to 2.5% of that weight.
At harvest (180 days after stocking hybrid catfish juveniles), ponds were drained; original stock fishes and resulting tilapia juveniles were removed and sorted according to species, counted and weighed. The preferred market weight of adult tilapia and hybrid catfishes were set at 150g and 500g respectively, as individual fish below these sizes are generally not accepted by consumers in Nigeria. Effective recruitment control was set at a tilapia AT value (% weight of market-size tilapia in the population) of 90 or above. This level was considered high enough to prevent significant food competition between the original stock tilapia and their offspring. Partial recruitment control was indicated by tilapia AT values ranging from 71 to 89 (Swingle 1950). Fish yield, extrapolated and reported as kg/ha/yr, were subjected to the one-way analysis of variance (ANOVA) test followed Duncan's multiple range test to compare the treatment means (P = 0.05).
RESULTS AND DISCUSSION
Tilapia Mortality
Post-stocking mortality occurred only in O. niloticus and dead tilapia were replaced with fish of similar size. Thereafter, throughout the production trial, mortality in O. niloticus was less than 7% of the initial stock in any of the ponds and was not related to the treatments, rather it was mainly due to handling stress during periodic weighing. All the hybrid catfish fingerlings stocked survived and were recovered at harvest.
Tilapia Recruitment
O. niloticus spawned in all the ponds in all treatments, and their fry were observed as from 90 days after stocking tilapia (30 days after stocking hybrid catfish juveniles). Tilapia recruitment control calculated for each stocking combination with hybrid catfishes and expressed as tilapia AT values are presented in Table 1. At the set tilapia AT value of 90, only the 5:1 and 10:1 combinations indicated an effective control of O. niloticus recruitment while partial recruitment control resulted from the 20:1 treatment. The tilapia AT values in all the tilapia: hybrid catfish treatments were higher (P > 0.05) than in the control treatment and was due to the consumption of pond-spawned tilapia fry by hybrid catfish. This reduced the competition between adult tilapia and pond-spawned juvenile tilapia for food, thus enabling growth of adult tilapia.
Conversely the respective contributions by weight of pond-spawned juvenile O. niloticus population to the total tilapia production were 11.13% and 47.82% in the 20:1 combination and control (tilapia monoculture) treatments. This clearly demonstrates effective reduction of juvenile O. niloticus by hybrid catfish. In tilapia monoculture, the percentage of pond-spawned tilapia in the total yields have been reported to exceed 70% in the Congo (Bardach et al. 1972) and reached 50% in high altitude ponds in Rwanda (Rurangwa 1997).
Adult Tilapia Yield
The summary of O. niloticus yield is also presented in Table 1. No significant differences (P < 0.05) occurred in adult tilapia production among the treatments, the highest being 5.6 and 5.7 t/ha/yr recorded in the 5:1 ratio treatment and was similar (P > 0.05) to production in 10:1 treatment. Mean final weights attained by original stock O. niloticus in the tilapia: hybrid catfish treatments were higher (P < 0.05) than in the control (tilapia monoculture) treatment. All the hybrid catfishes exceeded market size and there were no differences (P > 0.05) in their mean final weights among treatments.
Table 1. Tilapia yields and tilapia AT values from mixed culture of Oreochromis niloticus with hybrid clariid catfishes.
Mean stocking wt. (g) / Tilapia stocking / Mean harvest wt. (g) / Adult tilapia yield(t/ha/yr) / Tilapia AT value
(%)
Predator / Tilapia / Number/ha / Ratio / Predator / Tilapia
H. longifilis x C. gariepinus
150.5a
152.2a
151.6a
- / 44.1a
43.9a
43.7a
44.3a / 20,000
20,000
20,000
20,000 / 5:1
10:1
20:1
- / 882a
853a
845a
- / 215.5a
213.2a
195.0a
130.1b / 5.7a
5.6a
5.4a
2.6b / 98.6a
94.2a
88.7b
52.5c
H. bidorsalis x C. gariepinus
150.8a
151.4a
151.7a
- / 43.9a
44.2a
43.5a
43.6a / 20,000
20,000
20,000
20,000 / 5:1
10:1
20:1
- / 879a
858a
839a
- / 211.9a
210.6a
190.4a
123.8b / 5.6a
5.4a
5.2a
2.5b / 98.1a
95.4a
87.3b
54.8c
a, b, c - values with similar letters are not significantly different (P > 0.05)
Although this technique did not prevent adult (larger) O. niloticus from using up considerable energy in reproduction, it has improved tilapia yield, which represents an economic benefit to the farmer. Compared with the control treatment, it was obvious that the stocking of hybrid catfish had a direct effect on tilapia production. Generally, the fewer the number of catfish stocked, the lower the adult tilapia yield. The total tilapia yield, ranging from 5.2-5.7 t/ha/yr (Table 1) was high, satisfactory and comparable to production reported by various authors (Table 2) who used tilapias in combination with various clariid catfish species available in Cote d'Ivoire (Bard et al. 1976; Lazard & Oswald 1995), Nigeria (Fagbenro & Salami 1996) and Congo (de Graaf et al. 1996).
Adult O. niloticus yield in this study was higher than that obtained by Lazard (1990) in Cote d'Ivoire, Middendorp (1995) in Cameroon, Rurawanga (1997) in Rwanda; Ajayi (1998) and Sumonu-Ogunmodede (1998) in Nigeria; as well as Tilapia guineensis yield when C. gariepinus was stocked as tilapia predator (Fagbenro 1987) or C. isheriensis (Fagbenro and Sydenham 1990) in Nigeria. The disparities in equivalent yields are however accounted for by the relative variations in the quality and quantity of supplemental feed used (feeding regimens), pond fertilization, tilapia stocking density applied, tilapia: catfish stocking ratio tested, sizes of ponds used, and apparent differences in voracity/predation efficiencies or dietary habits of the clariid catfish stocked.
Table 2. Comparable tilapia yields and tilapia AT values from studies on mixed culture of tilapias with various clariid catfishes in African countries.
Tilapia stocking / Adult tilapia yield(t/ha/yr) / Tilapia AT value
(%) / Average market-size
(g)
Rate / Ratio
Tilapia guineensis &
Clarias isheriensis1 / 10,000 / 2:1-10:1 / 4.3-4.6 / 86.2-96.2 / 162-193
Tilapia guineensis &
Clarias gariepinus 2 / 6,000 / 6:1-12:1 / 3.1-4.0 / 71.5-93.5 / 200
Oreochromis niloticus &
Clarias gariepinus3 / 25,000 / 10:1 / 5.5 / - / 150
Oreochromis niloticus &
Clarias gariepinus 4 / 12,000 / 5:1 / 4.1 / - / 175
Oreochromis niloticus &
Clarias gariepinus 5 / 14,000
-19,000 / 10:1 / 3.9- 4.1 / 90.7-98.2 / 152-249
Oreochromis niloticus &
Clarias gariepinus 6 / 20,000 -23,000 / 2.7:1 / 5.6 / 99.8 / 193
Oreochromis niloticus &
Clarias gariepinus 7 / 10,000 / 3:1 / 2.9-3.6 / 71.9-76.8 / -
Oreochromis niloticus &
Clarias gariepinus 8 / 10,000 / 10:1-20:1 / 1.7-2.5 / - / <150g
Oreochromis niloticus & Heterobranchus longifilis9 / 20,000 / 22:1 / 5.2 / - / 185
Oreochromis niloticus & Heterobranchus isopterus9 / 18,000
-20,000 / 22:1-23:1 / 5.0-5.3 / - / 165-185
Oreochromis niloticus & Heterobranchus bidorsalis10 / 20,000 / 10:1-50:1 / 5.1-5.4 / 88.9-96.2 / 162-185
Oreochromis niloticus & Heterobranchus bidorsalis11 / 10,000 / 12.5:1-50:1 / 2.4-4.0 / 54.5-72.2 / <150g
Oreochromis niloticus &
H. longifilis x C. gariepinus 12 / 20,000 / 5:1-20:1 / 5.4-5.7 / 88.7-98.6 / 195-215
Oreochromis niloticus &
H. bidorsalis x C. gariepinus12 / 20,000 / 5:1-20:1 / 5.2 - 5.6 / 87.3-98.1 / 190-212
1Fagbenro & Sydenham (1990) in Nigeria; 2Fagbenro (1987) in Nigeria; 3Bard et al. (1976) in Cote d'Ivoire; 4Lazard (1990) in Cote d'Ivoire; 5Middendorp (1995) in Cameroon; 6de Graaf et al.(1996) in Congo; 7Rurangwa (1997) in Rwanda; 8Sumonu-Ogunmodede (1998) in Nigeria; 9Lazard & Oswald (1995) in Cote d'Ivoire; 10Fagbenro & Salami (1996) in Nigeria; 11Ajayi (1998) in Nigeria; 12Fagbenro (this study) in Nigeria.
CONCLUSIONS
Clariid catfishes used in African aquaculture do not have many of the limitations of other predators and except for Clarias isheriensis, they contribute a large portion to the total fish yield due to their large adult size. Differences observed in predation efficiency of catfish species were probably caused by their feeding habits and mode of predation (onset of predation). As the hybrid clariid catfishes are relatively more effective than their parental species as predators, they are therefore recommended for the control of tilapia recruitment in ponds. Based on results of this study, the recommended tilapia: hybrid catfish combination for effective recruitment control and high yield of market-size O. niloticus is between 5:1 and 10:1. The results obtained from this study affirm the suitability of hybrid clariid catfishes in solving the dual problems of tilapia stunting and overpopulation in pond culture.
ACKNOWLEDGEMENTS
Travel Grant was provided by CTA (Technical Center for Agricultural and Rural Cooperation), Wageningen, The Netherlands.
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