Post-embryonic developmental rates as a function of food type in the cyclopoid copepod, Mesocyclops thermocyclopoides Harada

Abstract

We studied under laboratory conditions the post-embryonic developmental rates (from nauplii to adult stage) of Mesocyclops therrnocyclopoides, commonly found in the eutrophic and hypertrophic local ponds, in relation to different food types. Nauplii hatched from the eggs collected from laboratory-maintained mass cultures were reared at 25 ± 1.5°C, using the following test diets: bacteria (Klebsiella aerogenes), cyanobacteria (Microcystis aeruginosa, as single cells and in the form of colonies), green algae (Chlorella, Scenedesmus and Chlorogonium), ciliates (Tetrahymena) and rotifers (Brachionus angularis). The developmental rates were fastest, and the proportion of nauplii reaching the copepodid stage and that of copepodiris reaching the adults stage the highest, with Chlorogonium, followed by ciliates and rotifers. Development was incomplete with bacteria and Microcystis. The algae Chlorella and Scenedesmus supported complete post-embryonic development only when cultured in media enriched with beef extract, bactotryptone and yeast extract. With rotifers as the exclusive food, >70% of the nauplii reached the copepodid stage, and >85% of the copepodids the adult stage. The ratio (D(c)/D(n)) of copepodid duration (D(c)) and naupliar duration (D(n)) was significantly different from 1.0, indicating the absence of isochronal development in M. therrnocyclopoides. Our results show that post-embryonic development in this species is not possible with certain algal diets, probably because of nutritional deficiencies, and that the later stage nauplii are capable of capturing rotifers and utilizing them as food to complete their development to the adult stage.