15 JULY 1999
LIPIDS IN COD (GADUS MORHUA L.) AND ATLANTIC SALMON (SALMO SALAR L.) EGGS, WITH SPECIAL EMPHASIS ON REPRODUCTION AND QUALITY
J. Pickova-1998
Doctorate, Swedish University of Agricultural Sciences, Uppsala
Abstract:
Throughout the world, fish provide a source of animal protein and oil. Therefore the dwindling world fisheries are of great concern. Reproduction is probably the most important issue in this respect, and factors affecting reproductive success are of utmost importance to assure sustainable fish populations for future generations.
This study focused on comparing Baltic and Atlantic populations of cod and salmon. Landlocked salmon, which has a limnic diet, was also included. The objective of this work was to compare lipid composition of eggs from these three environments and relate it to egg quality. Since the Baltic Sea is heavily polluted, the relation between xenobiotics, and reproductive success was studied. To elucidate the effect of spawning environment on the lipid composition of salmon eggs, river stocks were compared. Dietary effects were studied by feeding females from one environment with food from another. We focus on results related to the biologically important fatty acids docosahexaenoic, 22:6n-3 (DHA) and arachidoic, 20An-6 (AA), as well as cholesterol and its oxidation products (C0Ps). We found: 1. DHA content in cod egg phospholipids was slightly (at least one gonadal cycle) affected by diet. For salmon, egg DHA remained stable in spite a change of diet. Further, its content was inversely related to river winter-temperature. 2. AA content was related to egg quality in cod and salmon. In landlocked salmon the importance of AA was greater. 3. Salmon eggs exhibiting the pollution-related syndrome M74 had elevated levels of both DHA and COPs, whereas levels of AA and cholesterol were unaffected. These eggs also had a lower level of the astaxanthin, a potent antioxidant.
Based on our findings we suggest that i) the DHA level is genetically determined and that the difference between salmon stocks is an adaptation to temperature. This is supported by studies on importance of DHA in regulating membrane fluidity at low temperatures. ii) AA, being a precursor of prostaglandins, is essential for the development of physiological functions in eggs and larvae. This should be considered when feeding broodstock and juvenile fish. iii) Elevated levels of DHA in M74-affected salmon may be related to exposure to xenobiotics, which increase COPs contents and decrease antioxidant levels.
(Swedish University of Agricultural Sciences, Department of Food Science, P.O. Box 7051, 750 07 Uppsala, Sweden)