Growth, production, and demography of Moina micrura in brackish tropical fishponds (Layo, Ivory Coast)

Abstract

Sampling and experiments were performed in brackish fishponds, located near the Ebrie Lagoon, Ivory Coast. Moina developed here at salinities up to about 4 g l^-1. Mean embryonic and juvenile development times in experimental conditions were 0.82 and 0.80 day, respectively, with 2 juvenile stages at 30 °C (salinity of 3 g 1^-1; 29 μg chlorophyll-a l^-1) and 1.22 and 1.37, with 2 stages for most individuals and 3 or 4 stages for some of them at 26 °C (2 g l^-1 and 36 μg l^-1). The corresponding Q₁₀ for embryonic development was relatively high (2.7). Growth rates in weight at 30 °C were 2.11 and 1.37 μg μg ^-1 d ^-1 respectively, for the embryonic and juvenile stages, 0.21 for mean somatic growth of the five first female adult stages, and 1.00 for primipara, summed for somatic growth, production of eggs, and embryonic growth. Consequently, differences in growth rates between young and adults were small. M. micrura also was a high fecundity species according to its size, fecundity in nature varying from 2.2 to 7.7 eggs per adult female. Rates of population increase evaluated for some sequences of parthenogenetic growing periods, reached up to 0.9. Most of the daily P/B evaluated by the cumulative growth method reached values above 1.0 (28 to 31 °C), minima being about 0.7 for lower temperatures (approximatively 26 °C). Populations were also characterized by low juvenile to adult ratios (down to 0.9) and high daily birth rates (up to 1.2). Overall, M. micrura is a highly productive, opportunistic species, well adapted to the low salinities that occur during part of the year in the ponds. Biological and population characteristics of this species, and literature data on regulation mechanisms, possible use for aquaculture, and on size in tropical species are discussed.