PD/A CRSP Nineteenth Annual Technical Report
Table of Contents
Cite as: [Author(s), 2002. Title.] In: K. McElwee, K. Lewis, M. Nidiffer, and P. Buitrago (Editors), Nineteenth Annual Technical Report. Pond Dynamics/Aquaculture CRSP, Oregon State University, Corvallis, Oregon, [pp. ___.]
An experiment was conducted in eighteen 200-m2 fertilized earthen ponds at the Asian Institute of Technology, Thailand, from March through October 2000. This experiment was designed to assess the efficiency of snakehead (Channa striata) in controlling recruitment of mixed-sex Nile tilapia (Oreochromis niloticus) in ponds and to assess growth and production characteristics of Nile tilapia in monoculture and polyculture with snakehead. There were six treatments: A) monoculture of sex-reversed all-male tilapia; B) monoculture of mixed-sex tilapia; C) polyculture of snakehead and mixed-sex tilapia at 1:80 ratio; D) polyculture of snakehead and mixed-sex tilapia at 1:40 ratio; E) polyculture of snakehead and mixed-sex tilapia at 1:20 ratio; F)polyculture of snakehead and mixed-sex tilapia at 1:10 ratio. Sex-reversed and mixed-sex Nile tilapia were stocked at 2 fish m-2 at sizes of 10.5 to 11.6 g and 7.2 to 8.1 g, respectively.
Results show that snakehead were able to completely control Nile tilapia recruitment at all tested predator:stocked-prey ratios, and the best predator:stocked-prey ratio was 1:80. The addition of snakehead into Nile tilapia ponds did not result in significantly greater tilapia growth, but it significantly lowered total net and gross yields of adult plus recruited tilapia. Snakehead growth was density-dependent, decreasing significantly with increasing stocking densities. While snakehead biomass gain was not significantly different at stocking densities from 0.025 to 0.1 fish m-2, the gain was significantly lower at a stocking density of 0.2 fish m-2. The present experiment demonstrates that snakehead are able to control Nile tilapia recruitment completely and provide an alternative technique for Nile tilapia culture.
The aquaculture of species at lower trophic levels, such as tilapia, presents the greatest potential for efficiency (Welcomme, 1996). However, overpopulation of tilapia in confined ponds causes stunted growth due to shortage of natural food, particularly in semi-intensive culture. Various methods of population control have been applied (Mair and Little, 1991), such as culture in cages, culture with predators, intermittent harvesting, hybridization, induction of sterility, and production of super-male fish (YY-male). However, population control of tilapias by culture with predators has been practiced worldwide but not well studied. Various predatory fish species have been used with varying success in combination with different tilapia species depending on their availability. These species include snakehead (Channa striata or Ophiocephalus striatus) (Pongsuwana, 1956; Chimits, 1957; Tongsanga, 1962; Chen, 1976; Cruz and Shehadeh, 1980; Hopkins et al., 1982; Wee, 1982; Balasuriya, 1988); Ophiocephalus obscuris (de Graaf et al., 1996); Micropterus salmoides (Swingle, 1960; Meschkat, 1967; McGinty, 1985); Lates niloticus (Meschkat, 1967; Planquette, 1974; Lazard, 1980; Bedawi, 1985; El Gamal, 1992); Hemichromis fasciatus (Bardach et al., 1972; Lazard, 1980); Cichla ocellaris (Lovshin, 1977; McGinty, 1983; Verani et al., 1983); Clarias sp. (Meecham, 1975; Bard et al., 1976; Lazard, 1980; Janssen, 1985; de Graaf et al., 1996); Cichlasoma managuense (Dunseth and Bayne, 1978); Elops hawaiiensis (Fortes, 1980); and Megalops cyprinoides (Fortes, 1980). However, the difficulty in breeding or obtaining predators of the correct size often resulted in limited application of this population control method (Balarin and Hatton, 1979; Penman and McAndrew, 2000).
Snakehead have long been regarded as valuable food fish and widely cultured in the Far East (Wee, 1982). It was reported to be used in polyculture with tilapia to control tilapia population or with carps to keep out other extraneous pest fish in the pond system (Wee, 1982). Snakehead are highly predacious as they swallow their prey whole (Diana et al., 1985) and have been shown to effectively prey on live tilapia fry (Kaewpaitoon, 1992). A population including 5% (predator:stocked-prey ratio of 1:20) snakehead with tilapia has been demonstrated to control tilapia recruitment (Balasuriya, 1988). Negligible tilapia recruitment was generally found during harvest where snakehead existed in tilapia ponds.
The purposes of this study were to assess: