Effects of dietary zinc intake upon copper metabolism in rainbow trout (Salmo gairdneri)

Purified diets with copper levels of 2.5 and 500 mg/kg and dietary zinc levels ranging from 34 to 1000 mg/kg were fed for 20 weeks to rainbow trout of mean initial weight 8 g. Growth and feed conversion were similar in all groups of fish and no gross pathologies were observed. Liver copper levels were greatest in trout given the high copper diets; increasing dietary zinc intake reduced these hepatic copper concentrations. Subcellular fractionation of the livers showed that in all groups of trout 70–80% of the hepatic copper was present in the nuclear and mitochondrial fractions. In contrast, the cytosol and microsomal fractions contained, on average, 73% of the liver zinc. Total liver superoxide dismutase activity was constant in all groups of fish. However, in trout fed the high copper diets the relative proportions of the copper-zinc and the manganese superoxide dismutase were correlated with the dietary zinc intake. Increasing dietary zinc reduced the activity of the manganese enzyme and increased that of the copper-zinc metalloenzyme.     

Environment-induced gill disease of cultured rainbow trout (Salmo gairdneri)

Rainbow trout from eight North German freshwater culture facilities were investigated for chronic health damage resulting from captivity. The fishes were raised under a wide variety of conditions in net cages, circulation tanks, raceways, and earthen ponds.The most obvious non-contagious health problem was gill injury. Hyperplasia of the gill filaments, leading to lamellar fusion or the development of apical caps, as well as necrotic or advanced degenerative processes were observed. In addition, the gill filaments were frequently shortened, significantly reducing the functional surface of the organ.The lesions occurred in almost the same form in all of the culture units. It is likely that they are part of a syndrome induced by the environmental conditions typical of freshwater aquaculture facilities. These are characterized by an accumulation of nitrogenous excretion and decomposition products, extreme diurnal fluctuations in the concentration of dissolved gases, and intensive feeding involving the sudden addition of large amounts of artificial products. Under such conditions even small quantities of un-ionized ammonia can be toxic for epithelial tissues and disturb the normal elimination of protein metabolites across the gills. The pathological processes may be accelerated by secondary bacterial infections.     

Comparative studies on body composition of rainbow trout (Salmo gairdneri R.) in relation to type of diet and growth rate

Three populations of rainbow trout (mean initial live weight 40 g) were fed experimentally under almost the same conditions for 49 weeks. The aim of the experiment was the examination of the changes in the relative proportions of the major whole body constituents (water, protein, fat and ash) in relation to type and amount of diet and growth rate. Two pelleted dry diets (A and B) and one mixed diet (C) were used. The amount of food given daily to the fish in the case of diets A and B was continuously based on fish body weight and water temperature. The population which received diet C (raw material and pelleted dry food) was fed on maximum ratio. Sampling was carried out approximately every two months. After 25 weeks, and besides the regular sampling, fish were sampled from each population and analyses were made on their fillets. The same analyses were also carried out. on fillets and whole body material on a sample of wild fish, of almost the same age, fed on a variety of food organisms in a stream near the experimental tanks. When the results are expressed in terms of dry weight, the analyses of whole body material showed that ash content remained fairly constant in all populations throughout the experimental time. Further, with increasing body weight and age the percentages of water and protein decreased and the percentage of fat content increased in all populations and especially in fish fed on diet C which appeared to have the maximum growth rate and final mean body weight. Similarly, fish fed on diet B, which showed the lowest growth rate and final mean body weight, had low changes in the major body constituents throughout the experimental period. The lowest and the most regular rate in the changes of these parameters appeared in fish fed on diet A which also had a sufficient growth rate and mean final body weight. Analyses of the fillets for the three different types of food used have different results. The analysed wild fish had the highest percentage of water content and, expressing the results in terms of dry weight, the highest percentage of ash and protein content, while they appeared to have the lowest percentage of fat content, on both whole body material and fillets.Since the three types of diets used in this experiment gave three different growth rates, as well as three different body compositions of the reared trout, it is suggested from the present results that the relative proportions and changes of the four body constituents and effects on the growth rate of trout are strongly affected by the type of food.     

A genetic analysis of egg,alevin and fry mortality in salmon (Salmo salar), sea trout (Salmo trutta) and rainbow trout (Salmo gairdneri)

Heritability of mortality in eggs, alevins and fry were estimated using data from salmon, sea trout and rainbow trout. The highest value (average for all species and both estimation methods) based on the sire component was obtained for the eyed egg stage, h² = 0.08, followed by the alevin stage, h² = 0.05, while estimates for fry mortality did not differ significantly from zero.The maternal effect was rather large for uneyed eggs and eyed eggs, while it was low for alevin mortality. Maternal effects were also found to have a significant influence on the mortality of salmon fry. It was, however, not possible to separate maternal effects from tank effects.     

Effects of sublethal concentrations of lignosulphonates on growth,intestinal flora and some digestive enzymes of rainbow trout (Salmo gairdneri)

Young rainbow trout (Salmo gairdneri) were exposed to lignosulphonates (LS) at concentrations of 0, 40, 80, 160, 320, 640, 1 280 and 1 920 ppm for 35 or 60 days. At concentrations of 160 ppm LS and higher the growth rates were slower. The higher concentrations had the most retarding effect on growth, but a clear general relationship between LS concentration and growth retardation was not observed.The bacterial flora in the digestive tract of the fish was examined. The predominant micro-organisms were flavobacteria, bacilli, streptococci and yeasts (Cryptococcus spp.), which were also isolated from the diet. There were about 10 000 viable aerobic and 1 000 anaerobic bacteria per gramme of intestinal contents. There was no significant difference in quantitative or qualitative composition of the intestinal flora of the different groups.The following groups of digestive enzymes were studied: proteinases, amylases, lipases and deoxyribonucleases. The activities of proteinases and nucleases were significantly impaired in fish exposed to concentrations of 1 280 ppm LS and higher, and those of amylases at concentrations of 320 ppm LS and higher. A possible connection between the reduced growth rates and depressed activities of the digestive enzymes is discussed, but no firm conclusion regarding the mechanism by which LS effects fish growth can be made on the basis of the present study.     

Effects of dietary copper and copper: Zinc ratio on rainbow trout Salmo gairdneri

Purified diets with 15 and 150 mg supplemental copper/kg with dietary copper: zinc ratios of 1:1 and 1:4 were fed for 20 weeks to rainbow trout of mean initial weight 15 g. No gross pathologies were noted in any group of fish; growth and feed conversion were the same in all groups of trout. Plasma zinc levels were positively correlated with dietary zinc intake but dietary copper level had no effect on plasma copper. Hepatic levels of copper and zinc were also related to the dietary intake of the respective minerals. The dietary copper: zinc ratio caused some small changes in the plasma and hepatic levels of a few minerals, but no evidence was found to suggest any zinc—copper antagonism in rainbow trout. The activity of the copper, zinc metalloenzyme superoxide dismutase in liver was unaffected by dietary copper or zinc intake.     

Studies on cryopreservation of eggs from rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch)

The effect of pre-freezing treatments as well as freezing of inseminated, not water-activated eggs from rainbow trout Salmo gairdneri, and coho salmon, Oncorhynchus kisutch, was investigated in relation to survival and further development.Effects above freezing temperatures included: the temperature at insemination, viability of inseminated and unactivated eggs after storage, suitability of an incubation medium and the tolerance of eggs to various levels of the cryoprotectant dimethylsulfoxide (DMSO). Freezing experiments included: investigating the action of DMSO (0, 1, 2 mole) and the tolerance of coho eggs to temperatures between ?4.6 to ?30°C. Insemination temperatures between 0.5°C and 9.8°C (coho eggs) as well as incubation in an artifical medium (1-0°C) for 80 min (rainbow trout eggs) and 170 min (coho eggs) did not influence subsequent fertility. Storage of inseminated and unactivated rainbow trout eggs for 135 min and beyond reduced egg fertility. DMSO at 2 and 4 mole was detrimental to coho eggs (1-0°C). One mole DMSO had no (coho) or reduced (rainbow trout) influence on egg fertility when it was added gradually.In the presence of 1 mole DMSO most eggs remained unfrozen (67–89%) when kept for 10 min in frozen artificial medium (?4.6%) and 27–32% subsequently reached the eyed stage (control = 100). Further cooling (0.3°C/min) to ?10°C was still tolerated (62% unfrozen, 22% eyed eggs) but not to ?20°C (6% unfrozen, no development) and ?30°C (no survival). Use of 2 mole DMSO did not improve the results.     

Effects of biotin deficiency in rainbow trout (Salmo gairdneri) fed diets of different lipid and carbohydrate content

The effects of variations in diet composition on biotin deficiency symptoms were studied in rainbow trout. Fish were fed one of six diets differing in lipid type, carbohydrate and biotin content. Fish given biotin-deficient diets gained less weight, and had inferior feed conversion ratios than the appropriate controls but did not suffer from anorexia nor were any pathological signs observed either by gross or microscopic analysis. Marked reduction in liver biotin concentration and activities of pyruvate carboxylase and acetyl CoA carboxylase, characteristic of biotin deficiency, were observed. Some less marked changes also occurred in the levels of other liver components and enzymes; these changes were influenced by diet composition as well as biotin intake. Hepatic lactate levels tended to increase in biotin deficiency when diets contained starch while the activities of citrate synthase and α-ketoglutarate dehydrogenase decreased, but these changes were reversed when diets lacked starch. Consequently, some secondary effects of biotin deficiency are related to diet composition. In certain treatments, palmitic and oleic acids in muscle triglycerides of biotin-deficient trout were significantly lower than in control fish; but there was no evidence among muscle lipids of chain elongation of linolenic acid in trout given biotin-supplemented diets.     

Accumulation of cobalt during embryonic development of rainbow trout (Salmo gairdneri Rich.)

Studies on the accumulation of cobalt by fish eggs are described. γ-Energy measurement of ⁵⁷Co and atomic absorption with the flameless technique were used for the detection of the cobalt. The cobalt level of the eggs was found to be directly proportional to the cobalt content of the aquatic medium, and its uptake decreased with increasing calcium ion concentration in the water. The accumulation of bivalent cobalt ions was found to take place on the surface of the eggs, where they are reversibly bound by the binding force of chorion-mucopolysaccharide. The present study did not show any increase in cobalt content within the larvae that hatched from the eggs.     

The nutritional properties of co-dried fish silage in rainbow trout (Salmo gairdneri) dry diets

Feed ingredients containing fish silage and liquefied fish made from ground, whole Pacific whiting and co-dried in a vacuum dryer with mixtures of soybean meal and feather meal to facilitate drying were prepared. An additional batch of fish silage was co-dried with the other dry ingredients in the diet formulation that was used, Abernathy diet S8-1. Fish meal, made by vacuum drying Pacific whiting, was used in the control diet. Co-dried fish meal was made by co-drying Pacific whiting with a soybean meal-feather meal mixture. Fish meal was entirely replaced by the co-dried products in the experimental diets, which were fed to rainbow trout (Salmo gairdneri) for 32 weeks. The best growth and food conversion values were obtained by feeding the fish meal control diet or the diet in which the fish meal was replaced with co-dried liquefied fish. No significant differences in final weights were found between trout fed diets containing co-dried fish meal or co-dried fish silage (fish products were 25% of the diet), but these fish were significantly smaller than fish fed the fish meal control or the co-dried liquefied fish diets. Reducing the fish silage to 12.5% or increasing it to 50% further reduced weight gains in the trout. Food conversion values, protein efficiency ratios, and net protein utilization values generally followed the same trends between diets as did the final weight values. Apparent digestibility coefficients for the co-dried products were lower than for the fish meal, possibly because they contained soybean meal-feather meal mixtures. Organoleptic properties of the fish were not affected by diet.     

Sperm output in rainbow trout (Salmo gairdneri) — Effect of age,timing and frequency of stripping and presence of females

An experiment was conducted to investigate the sperm production of rainbow trout. Eighty-four first-spawners were allocated randomly to three groups to be stripped at weekly, 2-weekly or 4-weekly intervals, respectively. Half of each group were exposed to females. The trial extended over two successive spawning seasons.First-season spawners were modest sperm producers. Depending on the collection frequency they produced mean stripped semen volumes of 1.17 to 1.48 ml containing 7.7 × 10⁹ to 16.8 × 10⁹ sperm. The corresponding means for the second spawning season were 3.54 to 4.59 ml and 22.2 to 35.4 × 10⁹. The spawning season extended from October to April. Production and motility increased from the beginning to mid-season, followed by a gradual decline. The effect of the presence of females was not very evident. With increased frequency of stripping, more sperm/male were obtained. Total semen volume and number of sperm/spawner obtained during the first season with weekly, 2-weekly or 4-weekly collection amounted to 24.6 ml and 160.9 × 10⁹ sperm, 13.4 ml and 135.8 × 10⁹ sperm and 8.9 ml and 101.1 × 10⁹ sperm, respectively. The corresponding values for the second season were 88.9 ml and 546.1 × 10⁹ sperm, 50.3 ml and 377.5 × 10⁹ sperm and 32.1 ml and 247.9 × 10⁹ sperm.From a practical point of view, weekly collection is feasible in second-season spawners, but a maximum of one stripping every 2 weeks appears appropriate for first-season spawners.     

Influence of the genotype and the environment on growth and survival of rainbow trout (Salmo gairdneri) in central Canadian aquaculture lakes

Strains of rainbow trout (Salmo gairdneri) were evaluated for suitability for use in extensive aquaculture operations in central Canada. Matched plantings were made of three strains of trout in a number of small, shallow, eutrophic, winterkill lakes. Growth and survival were measured at the time of harvest.There were significant effects of the genotype and the environment and significant genotype—environment interactions in the differential growth and survival of the trout.     

Biochemical changes associated with overripening of the eggs of rainbow trout Salmo gairdneri Richardson

This study of the biochemical composition of mature unfertilised eggs of rainbow trout was undertaken to investigate normal intraspecific variation in egg composition between parent females, and to describe the biochemical changes which occur after ovulation during overripening in the parental abdominal cavity. The following aspects of egg composition were measured: wet and dry weight, chorion weight, free and bound lipid, protein phosphorus, lipid phosphorus, precipitable protein, calcium, and iron. All these were determined on single eggs, and six eggs were examined from each female. Ripe eggs, defined as those stripped within 3 days of ovulation, were obtained from 7 females. Overripe eggs, defined as those stripped 30 or more days after ovulation were obtained from 8 females. Results were expressed in absolute terms (mg or μg of component per egg) and relative terms (percentage of egg dry weight). In ripe eggs, there was significant variation between females in all these aspects of egg composition when expressed absolutely, and in all except lipid phosphorus when expressed relatively. In overripe eggs, there was significant variation in all these aspects between females when egg composition was expressed either absolutely or relatively. Comparison of ripe and overripe eggs showed that overripening was accompanied by the following significant changes expressed absolutely: increase in water content, free lipid, iron, calcium; decrease in bound lipid, precipitable protein, protein phosphorus, lipid phosphorus, total lipid and chorion weight; when expressed relatively there were increases in water content, free lipid, iron, calcium, total lipid and chorion weight, and decreases in bound lipid, precipitable protein, protein phosphorus and lipid phosphorus.     

The growth of rainbow trout (Salmo gairdneri) given diets containing chitin and its relationship to chitinolytic enzymes and chitin digestibility

The growth of rainbow trout fed diets containing 4, 10 and 25% chitin, over a 12-week period, was significantly depressed (P < 0.001) when compared with controls fed diets containing 25% starch. There was no difference in growth rate between control fish and those fed diets containing 10% N-acetyl glucosamine (GlcNAc). Isotopically labelled amino sugars were shown to be oxidized when injected intraperitoneally into rainbow trout. Relatively high levels were found of chitinase activity in the stomachs and of chitobiase in the intestines. These enzyme activities were similar in all the trout, irrespective of the amount of chitin in their diets, except that chitobiase in the intestines of fish fed diets containing GlcNAc showed higher levels of activity than the controls (P < 0.05). Chitin was not significantly digested when fed at 10 and 30% of the diet but the apparent digestibility of pre-cooked starch was 50% when fed at either 15 or 25%, on the basis of the inert indicator (Cr₂O₃) method. Chitinase and chitobiase activities were not reduced in fish fed diets containing 10% chitin and an antibiotic (Tribrissen^®) although the alimentary microflora were completely eliminated. Enzyme activities were not enhanced when live chitinolytic bacteria (Vibrio alginolyticus) were incorporated into diets with 10% chitin; these bacteria were only recovered from the intestine. The evidence indicates an endogenous origin of chitinolytic enzymes in the trout gastro-intestinal tract. The presence of either antibiotic or bacteria in the diet had no effect on the digestibility of chitin.     

The influence of diet and fish density on apparent heat increment in rainbow trout, Salmo gairdneri

Rainbow trout were held in densities of 15, 35 or 50 fish per tank (2.48–8.27 kg m^?3) and fed one of six balanced diets varying in protein (34%, 48%, 58%) and lipid levels (7%, 23%). The elevation in oxygen consumption following feeding was attributed to apparent heat increment. Apparent heat increment tended to increase with dietary protein for each of the two lipid levels within each density of fish. A significant change in apparent heat increment relative to digestible energy was not demonstrable with dietary protein for each lipid level and fish density. When dietary lipid was high, the fraction of energy lost through apparent heat increment was improved and tended to decrease with dietary protein. Thus, a decrease in dietary protein with a concomitant increase in lipid provides for a more efficient utilization of dietary protein for growth. Apparent heat increment varied directly with rainbow trout density on the basis of equivalent weights and diets.     

Use of solvent extracted sunflower seed meal in complete diets for fingerling rainbow trout (Salmo gairdneri Richardson)

A preliminary 150-day feeding trial was conducted with fingerling rainbow trout to ascertain the nutritive value of solvent extracted sunflower seed meal as a dietary replacement for solvent extracted soybean meal and wheat meal (1.75–2.14 : 1) within a practical trout ration. The dietary level of soybean meal and wheat meal was reduced from 15% and 16.5% to 0% and 9.5% respectively and the level of sunflower seed meal increased from 0% to 22% with no adverse effect on overall growth performance or feed utilisation efficiency. Although growth at the highest level of sunflower seed meal tested (36.5%) was equivalent to that of fish fed the control soybean ration, supplementation of an equivalent sunflower seed meal diet with 0.2% exogenous L-methionine resulted in no beneficial effect on fish growth and feed utilisation efficiency.     

Genetic differences in lipid and dry matter content between strains of rainbow trout (Salmo gairdneri) and their hybrids

Observed phenotypic differences of lipid content between strains of rainbow trout and their hybrids cultured in small Canadian prairie lakes are related to differences in the size of fish and highly correlated with differences in growth rate. As a percent of dry matter mean lipid levels of different strains and their hybrids ranged from 32.5% to 45.9% in one experiment and from 11.6% to 24.3% in another. There were significant additive genetic differences in lipid content between strains, independent of differences in weight, and there also appeared to be significant non-additive × environment interactions.Phenotypic differences in percent dry matter were small compared to the differences in lipid content.     

The influence of changes in oxygen tension on the haematocrit value of blood samples from asphyxic rainbow trout (Salmo gairdneri)

Changes in haematocrit values were studied in vitro in blood samples of asphyxic rainbow trout (Salmo gairdneri) treated under reduced oxygen tension and with oxygen. The haematocrit value of blood kept under reduced oxygen tension increased by only about 5% during the first hour. When blood samples were oxygenated, their haematocrit value decreased by about 11% during the first hour. The MCHC value obtained for the blood directly after sampling showed that the cells were swollen in vivo. The causes of cellular swelling are discussed.     

Effect of hypervitaminosis a on the development of ascorbic acid deficiency in underyearling rainbow trout (Salmo gairdneri R.)

The effect of hypervitaminosis A on the development of ascorbic acid deficiency was investigated in rainbow trout reared on a practical diet. Excess vitamin A (124 000 I.U./kg) in the diet, as retinyl-palmitate, did not appear to interact with ascorbic acid metabolism of the trout. This dietary level of vitamin A did not affect the occurrence of the ascorbic acid deficiency symptoms, lordosis and scoliosis. Vitamin A does not appear to be toxic to rainbow trout at the level of 124 000 I.U./kg of diet and it would appear that the development of lordosis and scoliosis was due in this case to ascorbic acid deficiency.     

Effect of Geotrichum candidum protein substitution in pelleted fish feed on the growth of rainbow trout (Salmo gairdneri Rich.) and on utilization of the diet

Three experiments were conducted with rainbow trout to determine if Geotrichum candidum GC single cell protein could replace 100, 75 or 50% of fish meal in a pelleted diet. When the fish meal was completely replaced by GC the fish growth was retarded after 3 weeks of the experiment. With the larger fish (individual weight 47–54 g) in the short trial there were significant differences between fish fed the control diet (fish meal) and those fed the 75% substitution of GC diet. The most remarkable differences in fish growth appeared in a 42-day trial with small fish (5 g individual weight) when fish groups fed diets with 0.50 and 75% replacement gave significantly different results (P < 0.05), being 93,9, 46.6 and 34.2% gain, with feed coefficients of 1.49, 2.77 and 3.67, respectively. With large fish fed diets with 0,50 and 75% GC replacement, apparent digestibility of protein was 64.7, 68.2 and 37.5%, but fat digestibility was 79.5, 91.1 and 81.0%, respectively. No significant differences in amounts of free plasma amino acid (PAA) were found between rainbow trout fed diets with 0 or 50% substitution, but there was a marked decrease in PAA in the group fed the diet with 75% GC substitution. Analysis of chosen heavy metals was made on diets, fish and faeces, and Cu in particular was found not to be accumulated in the fish body.