The elusive copepods: their production and suitability in marine aquaculture J G Stùttrup Danish Institute for Fisheries Research, Department for Fish Biology, North Sea Centre, DK-9850 Hirtshals, Denmark Correspondence: J G Stùttrup, Danish Institute for Fisheries Research, Department of Fish Biology, North Sea Centre, Box 101, DK-9850 Hirtshals, Denmark Abstract Despite the fact that the suitability of copepods as live prey for marine ®sh larvae is now well established, their use in aquaculture remains sporadic. Although of lower nutritional value, the relative ease of production of rotifers (Brachionus spp.) and Artemia nauplii continues to ensure their predominance. Studies in the literature have highlighted differences in the levels and ratios of fatty acids, lipid classes and pigments between copepods and traditional live prey. Such differences may have important consequences for ®sh larval nutrition. The con- sequences of poor nutrition during ®sh larval development may be obvious, for example defor- mities or malpigmentation, but in many cases may be obscure, as in affects on temperature tolerance or growth during later life stages. In some aquaculture systems, copepods are cultured in large quantities in outdoor, extensive or semi- intensive units. Intensive-rearing systems for copepods require further development. However, it is now established that intensive rearing on monoalgal diets does not result in severe dete- rioration of the nutritional value of the copepods, at least in terms of their highly unsaturated fatty acid (HUFA) content. In some cases, the provision of copepods for a short period of time during the larval stage is suf®cient to ensure normal development. However, it remains to be demon- strated that the extra costs involved result in increased pro®ts as a result of higher percentages of normally pigmented juvenile ®sh, improved growth and survival and reduced incidence of disease. This paper reviews the advances in production systems for copepods, their nutritional value as live prey for ®sh and their present and potential use in aquaculture. Introduction Rearing larvae of most marine ®sh species, ranging from the coldwater species, such as cod Gadus morhua (L.) and halibut Hippoglossus hippoglossus (L.), to more temperate species, such as turbot Scophthalmus maximus (L.), and warmwater species, such as sea bass Dicentrarchus labrax (L.) and seabream Sparus auratus (L.), requires the provision of live prey for a variable period from the onset of exogenous feeding. A common feature of these species is the production of small pelagic eggs. The larvae generally hatch at an early stage in their development; many lack functional organs at the time of hatching, and they have relatively small yolk reserves. The onset of exogenous feeding is concurrent with the development of the digestive system as well as the development of organs critical for successful feeding, such as vision and motor development. In intensive-rearing systems, ®rst-feeding marine ®sh larvae are fed on rotifers Brachionus spp., with a range in lorica size from 100 mm to 340 mm (Fukusho 1989), succeeded during the later larval stages by the larger sized nauplii of the brine shrimp Artemia spp. However, some ®sh larvae, such as halibut and plaice, are large enough at ®rst feeding to attack and ingest Artemia. The brine shrimp, which can be purchased as eggs, come from a large variety of strains, varying in size and in energetic and nutritional content. Newly hatched Artemia nauplii measure 422 mm to 517 mm in length # 2000 Blackwell Science Ltd, 703 Aquaculture Research, 2000, 31, 703±711