Diets with different <i>n</i>-6/<i>n</i>-3 fatty acid ratio in diets for juvenile Atlantic salmon, effects on growth, body composition, bone development and eicosanoid production

Vegetable oils. typically high in n - 6 fatty acids, are necessary alternatives in fish feed production Such oils hive been tested in salmonid diets with good growth results, but with major changes in lipid composition. The aim of this study was to provide information regarding the effect of the higher dietary n - 6/n - 3 fatty acid ratio caused by vegetable oil on growth, chemical composition anti bone development, on eicosanoid production and on formation and mineralization of bone. A feeding experiment was carried out in juvenile Atlantic salmon (Salmo salar). Groups of fish (1.28 g) were fed diets added fish oil (FO) or soybean oil (SO) as the main lipid source through the 174 days long experimental period with sampling points at days 0, 31, 53, 96, 136 and 174 up to smoltification. Subsequently. fish performance was observed after 2, 8 and IS months in sea water. Weight was significantly higher in the fish oil group (95.4 g) than in the soybean oil group (87.4 g) after the 174 days experimental period. This difference developed during short day treatment prior to smoltification, and the fish oil group had a significantly higher growth rate (TGC) during this period (1.62 vs 1.45). Whole body mineral analysis displayed low levels of Ca (2400 and 3500 mg kg-1) and P (3200 and 3900 mg kg-1) in all samples. The corresponding Ca.P ratio ranged from 0.74 to 0.91 On day 136 the level of Ca, and Ca/P ratio. were significantly higher in the fish oil group than in the soybean oil group. There was a significant increase in n - 6 fatty acids and decrease in n - 3 fatty acids in the soybean oil group compared to the fish oil group for both TAG and PL in vertebrae. individual variation was large in plasma prostaglandin E2 (PGE2), and at day 174 the trend was towards a higher level in the soybean oil group. Radiography analyses demonstrated a distinctive pattern of development of spinal pathology with time and fish size, similar in both groups. Hyper dense vertebrae dominated at earlier stages, fusior-type malformations dominated at harvest size. The histological examination of the vertebrae revealed no differences between treatments. The results suggest that vegetable oil as a replacement for fish oil influence the arachidonic acid level in phospholipids of vertebrae, may slightly increase production of PGE2 in blood, and reduce vertebrae mineralization around the sensitive smoltification phase. These trends did not lead to any detectable skeletal malformations. Differences in growth and vertebrae mineralization observed around smoltification disappeared during the seawater phase

Digestibility of macronutrients, energy and amino acids, absorption of elements and absence of intestinal enteritis in Atlantic salmon, <i>Salmo salar</i>, fed diets with wheat gluten

Apparent digestibility coefficients (ADCs) of macronutrients and energy, and apparent absorption coefficients (AACs) of amino acids and elements were assessed in an experiment with 0.9 kg Atlantic salmon reared in saltwater tanks. Duplicate groups of fish were fed five diets, where 0, 6.25, 12.5, 25 and 50% of crude protein (CP) from fish meal (FM) was replaced with CP from wheat gluten (WG). In Experiment 2, triplicate groups of 0.9 kg salmon were fed a FM diet, a diet with 15% of CP from FM replaced with extracted, toasted soybean meal (SBM), and a diet with 35% of CP from WG, for 18 weeks. Experiment 2 was designed to determine whether WG caused pathological changes in the intestinal epithelium, and if a diet with 35% of CP from WG could support rapid growth. There was a trend toward increased ADC of fat and energy in the diets with WG, and the diet with 25% WG was ranked significantly higher than the FM control. The ADC of CP and AACs of all amino acids except alanine and lysine increased significantly with increasing proportion of dietary protein from WG, and the results indicate that absorption of individual amino acids from WG was between 94% and 100%, WG is low in lysine, but the results indicate that the requirement for lysine was nearly met and the requirement for other essential amino acids was met even with the highest WG inclusion level, due to high dietary protein concentration and the supplementary amino acid profile of FM. There was no reduced absorption of Ca, P or Mg in the salmon fed diets with WG. The absorption of Zn was higher in all the diets with WG than in the FM diet. The fish doubled their weight during Experiment 2, and there were no significant differences in growth among dietary treatments in salmon fed the WG, FM or SBM diets. No indication of intestinal pathology was seen in the salmon fed the FM or WG diets, while 60% of the examined fish fed SBM had SBM-induced changes in the mucosa of the posterior intestine