Culture of fish food organisms

Unit 4 - Copepods

4.3.Biology and life cycle of copepods
Most adult copepods have a length between 1 and 5 mm. The body of most copepods is cylindriconical in shape, with a wider anterior part. The trunk consists of two distinct parts, the cephalothorax (the head being fused with the first of the six thoracic segments) and the abdomen, which is narrower than the cephalothorax. The head has a central naupliar eye and unirameous first antennae that are generally very long. Planktonic copepods are mainly suspension feeders on phytoplankton and/or bacteria; the food items being collected by the second maxillae. The male copepods are commonly smaller than the females and appear in lower abundance than the latter. The eggs hatch as nauplii and after five to six naupliar stages (moltings), the larvae become copepodites. After five copepodite moltings the adult stage is reached and molting is ceased. A diapause stage is present in the development of the copepods so as to survive adverse environmental conditions, such as freezing. The major diapause habitat is the sediment, although a minor part of the diapausing individuals may stay in the planktonic fraction, the so-called “active diapause”. Harpacticoid copepods are less sensitive and more tolerant to extreme changes in environmental conditions (i.e. salinity: 15-70 g/l; temperature: 17-30°C) than calanoids and thus are easier to rear under intensive conditions. Moreover, harpacticoids have a higher productivity than calanoids and can be fed on a wide variety of food items, such as microalgae, bacteria, detritus and even artificial diets. However, as mentioned previously, care should be taken in this respect as the lipid and (n-3) HUFA composition of the copepods is largely dependent on that of the diet fed.