The effect of abiotic factors on the hatching of Moina micrura Kurz, 1874 (Crustacea: Cladocera) ephippial eggs

Many zooplankton taxa produce encysted embryos, usually resulting from sexual reproduction. Such resting stages form a key part of aquaculture, and the mastering of both acquisition and hatching techniques of such cysts and ephippia is crucial for larviculture of fish and crustaceans. Moina micrura is a common species found throughout South America. This genus is important as food for fish larvae, such as pacu (Piaractus mesopotamicus) and tambaqui (Colossoma macropomum) which are commonly utilized in Brazilian aquaculture. The goal of this work was to examine the relationship between pH (3 to 12), concentration of dissolved ions (from deionized water to 800 mg times l super(-1) of selected salts), temperature (10 to 40 degree C), photoperiod (0 to 24 hours) and light intensity (0 to 2000 lux) and the hatching of Moina micrura ephippial eggs, in an effort to define optimum hatching techniques. The populations were kept in laboratory aquaria with 30-40 l of water, maintained at a temperature of 25 plus or minus 2 degree C, with a photoperiod of 14 hours light at an intensity of 500 lux. The Moina were fed "ad libitum" twice a day, in the morning with Baker's yeast (Saccharomyces cerevisiae) and, at the end of the afternoon, with algae (Chlorella homosphaera, Scenedesmus ecornis, Kirchneriella lunaris, Chlamydomonas sp. and Nephrocylium lunatium). Each experiment was replicated, while each treatment of each experiment had ten repetitions, using ten eggs in each. For each experimental replicate, all eggs used were produced by the same population and at the same period. The data were examined using Analysis of Variance (ANOVA), experimental replicates being combined; treatment means were compared with the Tukey complementary test (p < 0.05).