Georg Lambertsen

Starch as an energy source in feed for cod (Gadus morhua): Digestibility and retention

Abstract An experiment was set up to determine whether cod, Gadus morhua , could use pre-cooked potato starch as an energy source. Four energy levels (0%, 10%, 20% and 30%) of carbohydrate with a constant fat content were fed for 8 weeks. The digestion capacity for pre-cooked potato starch decreased from 40% to 26% with increasing amount of carbohydrate, the average being 33%. The digestibilities of protein and fat were independent of the starch content in the feed. The protein intake was similar for all groups. Energy intake increased when the level of carbohydrate in the feed increased. Neither growth values nor retention values for protein and fat indicated that carbohydrate was utilized to any significant degree as a source of energy. Plasma glucose increased from 350 mg/l to 800 mg/l as the carbohydrate increased from 0 to 30%, and the average was 530 mg/l. The glycogen deposition in muscle tissue seemed to reach a level of ca. 0.4% of muscle wet weight in all groups. The glycogen deposition in the liver attained a maximum of 3.5% of liver wet weight.

Fatty acid composition of glycerophospholipids in seven tissues of cod (Gadus morhua), determined by combined high-performance liquid chromatography and gas chromatography

A method for the separation from fish tissues of the four main glycerophospholipid classes, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine, using adsorption high-performance liquid chromatography with ultraviolet detection and consecutive gas chromatographic analysis, based on one injection for their fatty acid compositions, is described. Fatty acid 19:0 was used as an internal standard for the calculation of the relative concentrations of the phospholipids. The patterns of fatty acid distribution within each of the phospholipids from seven cod organs had some general similarities. Phosphatidylcholine had the highest levels of 16:0 and 18:2 n - 6, and the ratio of 20:5 to 22:6 varied between 0.5 and 0.9. Phosphatidylethanolamine had the highest total polyunsaturated fatty acids, (n -3) polyunsaturated fatty acids, and 22:6 n -3, and the ratio of 20:5 to 22:6 varied between 0.2 and 0.5. Phosphatidylinositol showed the highest level of 18:0 and 20:4 n - 6 and had the lowest ratio of (n - 3) to (n - 6). Phosphatidylserine had the highest ratio of (n - 3) to (n - 6) and the lowest ratio of 20:5 to 22:6. A generally low level (less than 1.5%) of the long-chain monoene, 22:1, was found in the phospholipids in all tissues.

Liver retention of fat and of fatty acids in cod (Gadus morhua) fed different oils

Abstract Duplicate groups of cod were fed, for 8 weeks, diets in which 48% of the available energy came from either cod liver oil, Greenland halibut oil or peanut oil. The hepatosomatic index of the fish increased from 9.5% to an average of 13%, and the liver fat content from 55% to 67–70%. The average liver retention of the absorbed fat was 60%. Corresponding fatty acid retentions were calculated for most major fatty acids, showing a general non-specific retention. Exceptions were increased values for 16:0, 18:0 and 18:1, assumed from de novo synthesis, and decreased retentions for 14:0, 22:1 and 18:4 fatty acids. The fatty acid composition of the dietary fat had a strong influence on the composition of liver triglycerides, which constitute the main fat depot in cod, and also affected the composition of polar lipid fatty acids in liver and muscle.

Feed optimization in atlantic cod (Gadus morhua): Fat versus protein content in the feed

Abstract Two feeding experiments were performed with cod. One involved 40-g fish fed for 26 days and the other 180-g fish fed for 60 days. Feeds based on squid mantle, capelin oil and dextrinized potato starch were made up to give from 75% to 27% of available protein energy, balanced with from 11% to 61% fat energy, all with 12–15% carbohydrate energy. In the second experiment, three groups of fish were fed each day, and three groups every third day, whereas in the first experiment all fish were fed five days a week. Relative growth, feed conversion, digestibilities and retentions of protein and fat were determined. Protein retentions were calculated as PER (live weight gain over protein intake) and PPV (protein gain over protein intake). The apparent digestibilities for protein and fat were above 90%, except for a diet with 61% available energy from fat. The protein-sparing effect of fat seemed to be low in cod, and 26% to 29% of protein was retained, as compared with 50% to 60% of fat, except for groups on a very low-fat diet or on reduced feeding frequency. Dietary lipid was deposited as liver fat, and a linear relation between the liver index and the fat intake was demonstrated. It was concluded that PPV is a more appropriate index for growth than PER in studies on a lean fish such as cod with a low-fat fillet and a fatty liver. A reduced feeding frequency had no effect on feed conversion and PER whereas the weight gain and PPV were reduced. Based on these experiments optimal growth for cod may be achieved with a feed giving available energy concentrations of 60%, 25% and 15% from protein, fat and carbohydrate, respectively, fed every day.

The effect of dietary carbohydrate on the stress response in cod (Gadus morhua)

Abstract 150 cod (mean weight=440 g) were divided into two groups and fed diets with or without carbohydrate for 60 days. No defferences were found in total growth during the feeding period. Both fish groups were then stressed by handling and transported for 2 h. Five fish from each dietary group were collected for analysis at different time intervals up to 96 h. In terms of serum cortisol increase, the stress response was significant in both dietary groups and reached a maximum after half an hour. No response was found in blood hemotocrit or in blood hemoglobin at any sampling time. The plasma glucose levels in resting fish reflected the dietary levels of carbohydrate. The plasma glucose response was also significantly more affected by stress in the carbohydrate-eating fish than in the fish on a carbohydrate-free diet. Blood lactate did not reflect the diet composition, while a significant increase was seen in both groups after 1.5 h of recovery. No change in muscle lactate was measured as a response to stress, but significantly higher muscle lactate levels were measured in the fish without dietary carbohydrate. Neither white muscle nor hepatic glycogen levels were affected by the diet, but a significant increase was seen in both organs in the fish on a carbohydrate feed after 3 h of recovery.

Lipid digestion in cod (gadus morhua)

Abstract 1. 1. Cod, 2.6–3.4 kg. were fed a mixed diet of sprat, capelin oil and wheat flour. 2. 2. Lipids from the feed, stomach and four intestinal segments were separated into tri-, di- and monoglycerides and free fatty acids and analysed by GLC. 3. 3. All lipolytic products were concentrated in 14:0, 16:0 and 18:0, up to 60% and extremely low in the ω-3 fatty acids. 4. 4. Residual triglycerides contained 80% of saturated and monoenoic fatty acids. 5. 5. Linoleic acid increased from 2% in feed TG to 10% in TG of the rectum.

Digestive lipolytic enzymes in cod (Gadus morrhua): Fatty acid specificity

Abstract 1. 1. Digestive juice from cod ( Gadus morrhua ) pyloric ceca and anterior ileum was tested for specificity using marine triglycerides (TG) and marine wax esters (WE) as substrates. 2. 2. The lipolysis was bile stimulated, active at 7°C, had an optimum at 37°C, hydrolysed TG faster than WE and this was not affected by mixing the substrates. 3. 3. The lipolytic activity was clearly fatty acid specific, in that short chain saturated fatty acids accumulated in the residual di- and monoglycerides whereas polyenoic fatty acids accumulated in the free fatty acid fraction and monoenoic fatty acids were evenly distributed. 4. 4. The same pattern was found for the fatty acid from the wax esters as substrate whereas no specificity was shown towards the wax alcohols.

Influence of dietary fatty acids on the glycerophospholipid composition in organs of cod (gadus morhua)

Cod (mean start weight of 26 g) were fed three diets for 15 months, each based on a dry pellet coated at a level of 9g/100 g with soybean oil, capelin oil or sardine oil. The fatty acid compositions of neutral lipids and four glycerophospholipids of white muscle, liver, gills and heart were determined. The fatty acid composition of dietary lipids influenced the composition of neutral lipids in all organs. Linoleic acid (18∶2n−6) from soybean oil was selectively incorporated into phosphatidylcholine of the four tissues. Similar levels of 20∶5n−3 and 22∶6n−3 in phosphatidylcholine and phosphatidylethanolamine were found in all organs from cod fed capelin oil and sardine oil in spite of highly differentiated feed fatty acid levels. The polyunsaturated fatty acid (PUFA) composition of phosphatidylinositol was least influenced by dietary lipids. The preferred monoenic fatty acid in phospholipids of cod was 18∶1n−9, independent of dietary intake, whereas the longer chain monoenoic acids seemed to be preferentially catabolized. The results suggest that 20∶4n−6 as well as 20∶5n−3 and 22∶6n−3 fatty acids are essential for cod.

Dietary carbohydrate utilization in cod (Gadus morhua). Hormonal response of insulin, glucagon and glucagon-like-peptide to diet and starvation.

Abstract 1. 1. Two groups of 60 cod each were fed for 8 weeks, followed by 3 weeks of starvation. The diets were equal in protein energy, while in one of the feeds 40% of the lipid energy was substituted by carbohydrate. 2. 2. Both groups showed the same weight increase. Feed consumption and feed conversion were, however, highest in the carbohydrate group reflecting equal intakes of protein energy. 3. 3. Plasma glucose, lactate, insulin and glucagon were substantially higher in fish fed dietary carbohydrate. Plasma values were significantly reduced after 3 weeks of starvation (glucagon was significantly reduced after 1 week). 4. 4. Liver glyeogen content was highest in the carbohydrate group after feeding. After starvation the liver glycogen content was equal in both groups.

Lipid digestion and absorption in cod (Gadus morhua), comparing triacylglycerols, wax esters and diacylalkylglycerols

Abstract 1. 1. Cod (Gadus morhua) were given purified triacylglycerols (TAG), wax esters (WE) and diacylalkylglycerols (DAG). 2. 2. TAG, WE, DAG, free fatty acids (FFA) and fatty alcohols (FA) were isolated from gut contents, intestinal wall and chylomicra. 3. 3. The lipolytic enzymes hydrolyse TAG, WE and DAG with specificity towards polyenoic acids. The efficiency of hydrolysis is reduced in the order: TAG: WE:DAG. 4. 4. The major part of absorbed FA was oxidized to fatty acids and reesterified to TAG in the intestinal wall. Glyceryl ethers after fatty acid hydrolysis are absorbed and reesterified to DAG. 5. 5. Chylomicra contain mainly TAG, but DAG appears in cod fed DAG.