Erland Austreng

Digestibility determination in fish using chromic oxide marking and analysis of contents from different segments of the gastrointestinal tract

Methods of feed digestibility determination in fish were reviewed. The indicator method, using chromic oxide, was judged most suitable, but the best method of sampling faeces was uncertain. Rainbow trout (Salmo gairdneri, Richardson) were fed an experimental diet containing 1% chromic oxide. Faeces were collected by two stripping methods, and gut contents were obtained by dissection from five zones of the alimentary canal. Analyses of feed, faeces, and gut contents were made, and digestibility of protein, fat, carbohydrate, ash and gross energy calculated. It was concluded that absorption occurs in all parts of the alimentary tract, and that it is important to limit the stripping of faeces for analysis in digestibility studies to the hindmost part of rectum, i.e. from the ventral fin to anus.

Growth rate estimates for cultured Atlantic salmon and rainbow trout

Abstract The growth rate (% wt/day), depending on fish size (g) and water temperature (°C), has been estimated from a series of full-scale feeding experiments with Atlantic salmon ( Salmo salar L.) and rainbow trout ( Salmo gairdneri Richardson). The experiments were conducted with fish sizes between start feeding and 5 kg at temperatures from 2 to 16°C in fresh-water tanks and sea cages. The results are presented in three tables which may be helpful for the calculation of daily feed rations.

Carotenoids in diets for salmonids: I. Pigmentation of rainbow trout with the individual optical isomers of astaxanthin in comparison with canthaxanthin

Abstract Visual and chemical determinations revealed that the individual optical isomers of astaxanthin were more efficacious than canthaxanthin in pigmenting the flesh of rainbow trout ( Salmo gairdneri , Richardson). The visual assessment of the astaxanthin pigmentation by means of a colour scale correlated well with the chemical determination. The same utilization was found for all three astaxanthin isomers, ( 3S, 3′S )-, ( 3R, 3′S )-, ( 3R, 3′R )-astaxanthin and a 1 : 2 : 1 mixture of the three isomers. No epimerization took place at the chiral centres of C-3 and C-3′ in astaxanthin. Astaxanthin and canthaxanthin were not interconverted. No metabolites were detected in the flesh.

Evaluation of selected trivalent metal oxides as inert markers used to estimate apparent digestibility in salmonids

Abstract Trivalent oxides of yttrium and rare earth metals were evaluated as inert markers in apparent digestibility studies with salmonids in four experiments. In Experiment 1, 100 mg kg−1 of each of 15 oxides (Dy2O3, Er2O3, Eu2O3, Gd2O3, Ho2O3, La2O3, Lu2O3, Nd2O3, Pr2O3, Sc2O3, Sm2O3, Tb(III and IV) oxide, Tm2O3, Y2O3 and Yb2O3) were included in a feed fed to rainbow trout. The ratio between each marker and Yb2O3 in stripped faeces was used as an indicator of recovery. Only Er2O3, Ho2O3 and Tm2O3 had lower recoveries than the other markers. Experiment 2 compared the excretion rates of Cr2O3 and of the selected alternative markers (La2O3, Y2O3 and Yb2O3). A feed with 7.5 g kg−1 of Cr2O3 and 750 mg kg−1 of each of the other markers was fed to Atlantic salmon for a period of 1 week. Thereafter, the fish were fed with a marker-free feed, and gastro-intestinal evacuation was evaluated by comparing the marker ratios in the feed and in the faeces sieved from the outlet water of the tanks. The results did not reveal any systematic differences in evacuation among the various markers. Experiment 3 compared in vitro solubility of Cr2O3, Dy2O3, La2O3, Y2O3 and Yb2O3 in weak acid (HCl, pH 3 as in stomach contents of Atlantic salmon), weak acid neutralised with NaOH, and in water. Cr2O3 was not dissolved. Only 1.3% of Yb2O3, 22% of Y2O3, 31% of Dy2O3, and 96% of La2O3 was soluble in weak acid, but more than 99% of the dissolved markers precipitated when neutralised, and none of the markers were soluble in water. Experiment 4 compared the estimates of apparent digestibility coefficients (ADCs) of nitrogen and fat in rainbow trout when using Cr2O3, La2O3, Y2O3 and Yb2O3 as markers. The feed contained 10 g kg−1 Cr2O3 and 100 mg kg−1 of each of the other markers. Markers in feeds and stripped faeces were dissolved for the analysis with both HCl:HNO3 and H3PO4:MnSO4. Except for Cr2O3, the markers gave similar ADCs within each acid solubilisation procedure. The ADCs of fat were similar with both procedures, but the ADCs of nitrogen were 0.2% lower with HCl:HNO3 than with H3PO4. Cr2O3 was incompletely dissolved in HCl:HNO3, resulting in low ADCs. With H3PO4, no differences were seen among the ADCs obtained with Cr2O3 and the other markers. In conclusion, trivalent metal oxides, such as La2O3, Y2O3 and Yb2O3, can substitute Cr2O3 in digestibility studies with salmonids, and can be used at lower concentrations without affecting accuracy.

Ration level for salmonids: I. Growth, survival, body composition, and feed conversion in Atlantic salmon fry and fingerlings

Abstract Twelve groups of Atlantic salmon (Salmo salar L.), raised in fibre-glass tanks, were fed at 12 ration levels for 7 periods, each period lasting 28 days. The basic ration level was calculated from an expected maximum growth rate, depending on fish size and water temperature. This level was defined as “level 1.00”. The experimental ration levels varied from 0.50 to 3.25 in intervals of 0.25. During the start-feeding period there was an average survival rate of 95%. After the remaining 6 periods the group which was fed least had a survival rate of 48%. The other groups had an average survival rate of 81%. In all 7 periods, increasing the ration levels from 0.50 to 1.00 resulted in increased growth. A further increase in ration level did not result in extra growth. The weight distribution of the fingerlings was bimodal, with the majority of fish in the scantiest fed groups being in the lower mode. The majority of the fish in the adequately fed groups were distributed in the upper mode. The water temperature varied from 10 to 17°C, and the thermal sum was 2430 day-degrees. The average final weight of the fish which received ration levels from 1.00 to 3.25 was 28.3 g, while the fish on the scantiest ration weighed only 9.6 g at the end of the study. The feed conversion rate, which was 0.9–1.0 kg dry feed/kg growth for the two underfed groups, ranged from 1.0 to 3.0 in the other groups. The chemical composition of the fish varied according to fish size and ration level.

Ration Level for Salmonids II. Growth, Feed Intake, Protein Digestibility, Body Composition, and Feed Conversion in Rainbow Trout Weighing 0.5-1.0 kg

Storebakken, T. and Austreng, E., 1987. Ration level for salmonids. II. Growth, feed intake, protein digestibility, body composition, and feed conversion in rainbow trout weighing 0.5-1.0 kg. Aquaculture, 60: 207-221. Six groups of rainbow trout (Salmo gairdneri Richardson), raised in fibre-glass tanks, were fed at six different ration levels for two periods of 21 days each. Each tank contained 20 individually tagged fish with a mean initial weight of 415 g. The water temperature averaged 8.4” C and 10.2 o C in the two periods. The basic ration level was calculated from an expected maximum growth rate, depending on fish size and water temperature. This level was defined as “level 1.000”. The other experimental levels were 0.125,0.250,0.500,2.000, and 4.000 relative to this, respectively. No fish died during the experiment. The growth of the fish increased significantly with increasing rations up to the level 2.000. The fish lost weight at the ration level 0.125. The growth rate was near zero at the ration level 0.250. The growth of the fish receiving the highest ration level was 1.72% of their weight per day. The variation in growth of the fish within various weight classes was influenced by the ration level so that the growth distribution of the scantiest fed groups was skewed to the left. There was no skewness in the distribution of the most plentifully fed groups. The ration level had no significant effect on the apparent protein digestibility. Measurements of the feed intake using a radioactive isotope in a 6-h meal showed that the fish ingested all the feed at the ration levels from 0.125 to 1.000. The feed intake recorded was equivalent to the requirements for fish growth at the ration level 2.000, while it was lower at the ration level 4.000. The liver weight percentage increased with increasing ration while the dressed-out carcass percentage decreased. The chemical composition of the carcass was influenced to a greater extent by the feeding than that of the intestines. The feed conversion efficiency (FCE) and the productive protein value (PPV) of the feed were highest at the ration level 1.000. The values obtained were an FCE of 1.0 kg growth per kg dry feed ingredients and a PPV of 41%.

Carotenoids in diets for salmonids: IV. Pigmentation of Atlantic salmon with astaxanthin, astaxanthin dipalmitate and canthaxanthin

Abstract Diets supplemented with synthetic astaxanthin, astaxanthin dipalmitate and canthaxanthin at concentrations of 0, 30, 60 and 90 mg/kg, as carotenoid equivalents, were fed to groups of Atlantic salmon (Salmo salar L.) for 56 weeks. The mean initial and final fish weights were 62 and 406 g respectively. There was a tendency for astaxanthin to be more efficiently utilized than canthaxanthin, which in turn was more efficiently utilized than astaxanthin dipalmitate, for flesh pigmentation. These differences were partly explained by differences in the apparent digestibility of the carotenoids. The flesh pigmentation increased with increasing dietary carotenoid concentration. The visual assessments of flesh colour by means of a colour scale correlated well with the chemical determination. The carotenoid content of the skin was higher for the fish fed diets containing carotenoids than for the control groups, but there was no significant difference in the carotenoid concentration in the skin of the fish fed the different carotenoids.

Carotenoids in diets for salmonids: V. Pigmentation of rainbow trout and sea trout with astaxanthin and astaxanthin dipalmitate in comparison with canthaxanthin

Abstract Rainbow trout ( Salmo gairdneri Richardson) and sea trout ( Salmo trutta L.), kept in fresh water, were fed diets containing either 30 mg synthetic astaxanthin (a 1:1:2 mixture of the three optical isomers 3 S , 3′ S , 3 R , 3′ S ) plus 30 mg cantaxanthin/kg (diet i) or 30 mg synthetic astaxanthin dipalmitate (as astaxanthin equivalents) plus 30 mg canthaxanthin/kg (diet ii). The flesh was more efficiently pigmented in rainbow trout than in sea trout. Astaxanthin and canthaxanthin were deposited to the same extent when fed in a mixture. Astaxanthin dipalmitate was deposited in the flesh as free astaxanthin and more slowly than canthaxanthin, resulting in enhanced canthaxanthin deposition with diet ii. High values for apparent digestibility of the carotenoids were found but this was partly ascribed to breakdown of the carotenoids in the intestine or faeces. Analysis of the optical isomers of astaxanthin in the flesh demonstrated an increased level of (3 R ,3′ R )-astaxanthin and a reduced level of (3 S ,3′ S )-astaxanthin in both rainbow trout and sea trout fed the diet containing astaxanthin dipalmitate.

Effect of varying dietary protein level in different families of rainbow trout

Groups of rainbow trout (Salmo gairdneri) fingerlings from five different families and five inbred groups were fed for 153 days on each of four diets similar in energy content, but differing in their percentage of protein. The protein contents were 24, 33, 42 and 51%, respectively. Significant differences between fish families were found for growth, condition factor, chemical composition of the carcass, and digestibility of protein. At the end of the experiment, interaction between diet fed and family was found close to significance for weight and relative growth rate, and significant for length and condition factor. This interaction indicates that prospects for selectively breeding strains of rainbow trout specifically better able to utilize protein are promising. Fish growth rate increased with increasing dietary protein content. The corresponding condition factor, content of dry matter and energy in the carcass decreased. The high protein diets gave more protein in the carcass and a more discoloured liver than the low protein diets. Apparent protein digestibility increased with increasing protein level.

Carbohydrate in rainbow trout diets. III. Growth and chemical composition of fish from different families fed four levels of carbohydrate in the diet

Abstract Groups of rainbow trout ( Salmo gairdneri ) from five different families and five inbred groups were fed four diets similar in protein and energy content but differing in the percentage of metabolizable energy present as carbohydrate. The percentage of metabolizable energy from carbohydrate was 15, 26, 37 and 49%, respectively. Significant differences between fish families were found for growth, condition factor, chemical composition of the fish, relative liver wight, liver colour, digestibility of energy and N-free extracts, dressing percentage amount of intestinal fat and flesh colour. Interaction between diet and family was significant for relative liver weight and liver colour. There was no interaction between diet and family for growth, indicating that the prospects for selectively breeding a strain of rainbow trout specifically better able to utilize carbohydrate are not promising. Growth rate and condition factor increased with decreasing carbohydrate level in diet. The fish fed high levels of carbohydrate had less dry matter, fat and ash in the body, and higher percentage carbohydrate in the liver. They also had higher relative liver weights and more discoloured livers. The fish fed high levels of carbohydrate had significantly better apparent digestibility of energy and protein. There were no significant differences in mortality rate between the groups, and veterinary examination did not reveal any pathological differences in the fish fed different feeding regimes.