J.G. Stottrup, R. Sheilds, M. Gillespie, M.B. Gara, J.R. Sargent, J.G. Bell, R.J. Henderson, D.R. Tocher, R. Sutherland, T. Naess, A. Mangor Jensen, K. Naas, T. van der Meeren, T. Harboe, F.J. Sanchez, P. Sorgeloos, P. Dhert, R. Fitzgerald
Abstract:
This papers deals with the results from a 2 year Concerted Action financed by the European Union comprising reviews on several major topics ranging from copepod production and nutritional value to an economic review on the culture of halibut.
The work was focused on rearing methods for 3 species of marine fish; turbot Scophthalmus maximus, cod Gadus morhua and halibut Hippoglossus hippoglossus. Except for one farm in Denmark, turbot hatcheries depend on rotifers and Artemia nauplii as live prey. The Danish farm depends on copepods for providing the correct nutritional diet and relies on Artemia nauplii as an indispensable energetic supplement. For cod and halibut, rearing systems have to date been copepod-based using natural zooplankton. In terms of their nutritional value, copepods remain unquestionably the superior live prey. In particular, their content of essential fatty acids such as 20:5n-3 (EPA), 22:6n-3 (DHA) and 20:4n6 which have been recognized as crucial for normal development in several marine species and more recently the ratio of DHA:EPA.
However, the problems associated with obtaining sufficient numbers of the right size at the right time will continue to ensure the use of rotifers and Artemia nauplii despite their inherent deficiencies. The provision of copepods for a short duration is the compromise many hatcheries depend on to supply essential nutrients. This has been shown to be particularly important for obtaining high survival rates of naturally pigmented juvenile halibut. Artemia on the other hand, are particularly useful in supplying the necessary energy input in the form of triacylglycerol to ensure high growth rates in the rapidly developing fish larvae as demonstrated in the Danish outdoor copepod-based system used for turbot.
The development of the commercial rearing for halibut is dependent on the rearing strategy followed, because the type of live prey used will have an impact on the profitability of the rearing system. Copepods are required for high survival of normally-pigmented juveniles, yet Artemia nauplii are by far the cheapest and more stable source of live prey. Thus substantial improvements in the nutritional value of Artemia nauplii will provide the required impetus for investors in this sector. Techniques for the provision of all-female stocks for halibut rearing would also improve the economic balance.
(Danish Institute for Fisheries Research, Dept. of Fish Biology, Box 101, DK-9850 Hirtshals, Denmark)