168
Y. Olsen
EFA requirements have turned out to be complicated, especially for the early
stages of marine fish larvae. I suggest that the main reasons for this are that
• It took some time to realize that DHA was the most critical component in
larviculture, in part because of high larval DHA requirements and the inability
in providing sufficient analytic material.
• The ability of chain elongation and desaturation of short C 18 003 fatty acids to
DHA is inefficient, and perhaps not even possible, in many cultured marine
species. This implies that individual 003 fatty acids must be treated separately in
studies of marine larval EFA requirements.
• The live feed organisms used worldwide, and in particular the crustacean Artemia sp., are characterized by rapid DHA catabolism compared with that of the
common natural zooplankton, resulting in severe losses ofDHA in a short time.
This instability in DHA, and the fact that early stages cannot be fed formulated
feed, have made research on larval EFA requirements a challenge.
• The early experience with raising salmonid juveniles did not contribute to our
understanding of EFA requirements for larval stages of fish. Salmonids accept
formulated feed made from fish meal from the very beginning.
Although our knowledge on EFA requirements of cultured marine fish larvae is
still limited, we have learned substantial lessons through research efforts on larval
EFA metabolism and live feed production. The understanding of the structural and
metabolic functions of fatty acids has been improved, and the finding that EFA
must be treated separately and not as families is important. It is also apparent that
DHA is the most important component of the 003 family (Watanabe, 1993;
Watanabe et aI., 1989). The requirements of 006 fatty acids in marine larvae are
still unknown, but arachidonic acid (AA; 20:4(06), which is present in low proportions in marine animals, is likely to have an important metabolic role (Sargent et
aI., 1993b).
8.2.3. I. General Evaluation of EFA Requirements
The following considerations of EFA requirements are mainly restricted to 003
fatty acids and marine fish larvae. EFAs supplied in the diet and also from the
larval yolk sac in the very early larval stages play an important role in the
following physiological key processes of marine animals:
• Anabolic processes and growth-general requirements related to de novo formation of biomass, morphological development, and tissue differentiation
• Membrane transport and metabolism-inter- and intracellular membrane transports, respiration, and enzyme activity in general
• Regulation of metabolism-prostaglandins and their hormonal functions
8.2.3.2. Anabolic Processes and Growth
Most of the common marine fish species have a spawning strategy that is characteristic of r-strategists. The number of spawned eggs is high, the eggs are small
Y. Olsen
EFA requirements have turned out to be complicated, especially for the early
stages of marine fish larvae. I suggest that the main reasons for this are that
• It took some time to realize that DHA was the most critical component in
larviculture, in part because of high larval DHA requirements and the inability
in providing sufficient analytic material.
• The ability of chain elongation and desaturation of short C 18 003 fatty acids to
DHA is inefficient, and perhaps not even possible, in many cultured marine
species. This implies that individual 003 fatty acids must be treated separately in
studies of marine larval EFA requirements.
• The live feed organisms used worldwide, and in particular the crustacean Artemia sp., are characterized by rapid DHA catabolism compared with that of the
common natural zooplankton, resulting in severe losses ofDHA in a short time.
This instability in DHA, and the fact that early stages cannot be fed formulated
feed, have made research on larval EFA requirements a challenge.
• The early experience with raising salmonid juveniles did not contribute to our
understanding of EFA requirements for larval stages of fish. Salmonids accept
formulated feed made from fish meal from the very beginning.
Although our knowledge on EFA requirements of cultured marine fish larvae is
still limited, we have learned substantial lessons through research efforts on larval
EFA metabolism and live feed production. The understanding of the structural and
metabolic functions of fatty acids has been improved, and the finding that EFA
must be treated separately and not as families is important. It is also apparent that
DHA is the most important component of the 003 family (Watanabe, 1993;
Watanabe et aI., 1989). The requirements of 006 fatty acids in marine larvae are
still unknown, but arachidonic acid (AA; 20:4(06), which is present in low proportions in marine animals, is likely to have an important metabolic role (Sargent et
aI., 1993b).
8.2.3. I. General Evaluation of EFA Requirements
The following considerations of EFA requirements are mainly restricted to 003
fatty acids and marine fish larvae. EFAs supplied in the diet and also from the
larval yolk sac in the very early larval stages play an important role in the
following physiological key processes of marine animals:
• Anabolic processes and growth-general requirements related to de novo formation of biomass, morphological development, and tissue differentiation
• Membrane transport and metabolism-inter- and intracellular membrane transports, respiration, and enzyme activity in general
• Regulation of metabolism-prostaglandins and their hormonal functions
8.2.3.2. Anabolic Processes and Growth
Most of the common marine fish species have a spawning strategy that is characteristic of r-strategists. The number of spawned eggs is high, the eggs are small