Laboratory and field studies of mayfly growth in tropical Asia

Abstract

Growth of seven species of mayflies in three families (Baetidae, Leptophlebiidae and Heptageniidae) was investigated in the laboratory (Procloeon sp. 2 and Chopralla sp.), in the field (Cinygmina sp. and Baetiella pseudofrequenta), or both (Afronurus sp., Procloeon sp. 1 and Choroterpes spp.). Animals were reared in laboratory tanks and or in field cages at three sites in two Hong Kong (lat. 22° 17'N) streams, Tai Po Kau Forest Stream (TPKFS) and an open and shaded section of the Lam Tsuen River (LTR: LTRO and LTRS, respectively). Growth rates (mg mg -1 d -1 ) in the laboratory ranged from 0.12 (Afronurus sp.) to 0.3 (Procloeon sp. 1), and from 0.059 (Cinygmina sp.) to 0.23 (B. pseudofrequenta) in the field. All species were multivoltine. Baetids could complete more than eight generations a year, heptageniids at least four, and Choroterpes (Leptophlebiidae) up to eight. The influence of food quantity on growth was measured under laboratory and field conditions, while the effect of temperature was studied by rearing mayflies in the field throughout the year. In the laboratory, some mayfly species grew faster when reared on food collected from LTRO than from LTRS but in situ growth rates of Afronurus sp., Cinygmina sp. and Choroterpes spp. were similar in both LTR sites. No significant differences in growth rates among any sites were found for B. pseudofrequenta and Procloeon sp. 1, but growth rates at TPKFS were generally lower than at LTR for most species. Mayfly growth increased linearly with temperature, explaining 23-77 % of the total variation in field growth rates throughout the year.