Population ecology of the paddy field‐dwelling fish Channa gachua (Günther) (Perciformes, Channidae) in Sri Lanka

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Abstract
A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m−2. The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were Lx= 179 mm total length and K=0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr−1, respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m−2, 12.06 g m−2 and 1.64, respectively.