Cost estimates of hatchery production of marine fish in Norway.
The marine species cultivated in hatcheries in Norway are Atlantic halibut (Hippoglossus hippoglossus), turbot (Scophthalmus maximus) and Atlantic cod (Gadus morhua). Fry of halibut are presently produced in a few commercial farms, turbot is produced in one, and cod is cultivated for research purposes only.
The costs in juvenile production have been evaluated in various feasibility studies made for alternative production methods, ranging from pure extensive to intensive methods. Some studies assume theoretical optimum production conditions whereas others are based on practical production tests, including commercial production. The approximate ranges of total costs derived for juveniles of the three species are 1.5-6 ECU/juvenile for halibut, 1-2 ECU/juvenile for turbot and 0.5-2 ECU/juvenile for cod.
The cases yielding lowest cost estimates involve photo-manipulation of brood fish and egg production all through the year. The fixed costs tend to be the major cost component in both theoretical and practical feasibility studies, constituting some 30-50% of the total costs. The costs of eggs are significant for halibut and turbot (>10%), but is not that important for cod. The relative costs for larval feeds (5-20%) tend to be much lower than for larger fish, but are closely related to larval feed technology and the survival of fish larvae during the later stages of first feeding, which is important for all cost components.
(Trondhjem Biological Station, University of Trondheim, Bynesveien 46, N-7018 Trondheim, Norway)
Priorities during growth of fish larvae.
The small and numerous eggs of teleosts supply the free-swimming larvae with little yolk to construct their body systems. Swimming, feeding and ventilation belong to the first functional priorities because they determine the chances to find and use external sources of energy for development and growth. In this contribution we will summarize available and add new data on the sequence and intensity of growth of functional components in the body of the larva. Does this pattern of growth reflect deductions about the successive needs of the larva in its changing environment?
In order to test such questions we studied the development of mechanical functions e.g. suction feeding, swimming and ventilation during the transition from a viscosity-dominated towards an inertia-dominated flow of water. The relative importance of these forces is expressed in the dimensionless Reynolds (Re) number. It increases rapidly with the increase of velocity and body length of the growing larva. Roughly speaking, this transition domain lies in fish larvae between a total body length of 2.5 to 10 mm. Examples taken from experiments with larvae of the carp and the African catfish show that several features of the actual pattern of their allometric growth can be correlated with changing Re-number.
The importance and relevance of such data for the culture of fish larvae will be discussed.
(Department of Experimental Animal Morphology and Cell Biology, Agricultural University, P.O. Box 338, NL-6700 AH Wageningen, The Netherlands)
