Large Rainbow Trout Research Articles

The replacement of fish oil with refined coconut oil in the diet of large rainbow trout (Oncorhynchus mykiss)

Three hundred rainbow trout (242.9 ± 6.9 g) were randomly assigned to 12 fibreglass tanks (25 fish/tank). The fish were fed, for 231 days (feeding level: 0.74 % average bw), four experimental diets, containing increasing levels of coconut oil: diet A 0 %, diet B 6 %; diet C 12 % and diet D 13 %, as replacements of herring oil and cod liver oil. Weight gains of fish were > 3 g d-1 and FCR lower than 1.5, for all treatments. No significant difference was observed in the main carcass traits and whole body composition, but whole fish energy content significantly increased in fish fed diet D (10.68 KJ g-1). Different dietary fatty acid profiles had significant effects on the rainbow trout muscle contents of C10:0, C12:0, C14:0, total n-3, and the main ratios: SFA/USFA; DHA/EPA; DHA/AA, n-3/n-6, but not on total fatty acids content of the muscle.

The Effects of Whirling Disease on Growth and Survival of Snake River Cutthroat and Colorado River Rainbow Trout Fingerlings

AbstractTwo sizes of fingerling Snake River cutthroat trout Oncorhynchus clarkii behnkei and Colorado River rainbow trout O. mykiss were raised at hatcheries testing negative for Myxobolus cerebralis and stocked into the Dolores and Cache la Poudre rivers from 1999 to 2001. Populations were resampled over a 2‐year period to determine which species and size combination had the highest growth and survival rates. Fish were tested for M. cerebralis via polymerase chain reaction and pepsin−trypsin digest analyses. Growth and survival rates between the species and size groups were not significantly different in either river. In the Dolores River, annual survival for both species and sizes of fish combined ranged from 0.063 to 0.12. In the Cache la Poudre River, survival for both sizes of rainbow trout was 0.004; survival for cutthroat trout ranged from 0.182 to 0.53. Larger fish had higher growth rates than smaller fish, and cutthroat trout had higher rates than similar sizes of rainbow trout. In both rivers, a higher percentage of the rainbow trout sample was infected than in the cutthroat trout sample. Rainbow trout also had a higher mean number of spores per head than cutthroat trout, and small rainbow trout had higher spore counts than large rainbow trout. Survival rates for cutthroat trout in the Cache la Poudre River were the highest of any of the groups, suggesting a difference that is biologically significant. Raising fingerlings to sizes greater than 100 mm can improve poststocking survival. If rainbow trout are stocked into contaminated waters, raising fingerlings to a larger size does not appear to improve growth or survival rates. Stocking rainbow trout in the spring could maximize growth rates but will expose fish to greater triactinomyxon densities, resulting in higher intensities of infection.

Temperature-dependent Effects of Rainbow Trout on Growth of Atlantic Salmon Parr

Temperature may influence interactions between species by regulating energy balances of individuals. We conducted a laboratory study to determine whether temperature influenced the effects exerted by large rainbow trout on the growth of Atlantic salmon parr. Bioenergetic models were used to predict maintenance rations so that food resources were limiting over a range of temperatures; equal biomasses of rainbow trout were substituted for Atlantic salmon to evaluate the relative effect of interspecific interactions on Atlantic salmon growth. In the presence of rainbow trout, salmon growth increased as temperatures increased from 15°C to 25°C; no such temperature effect occurred for salmon maintained alone. Growth differences between salmon maintained with and without trout were highly significant at 25°C but not at 15°C. We conclude that the presence of trout depressed salmon growth at 15°C but not at higher temperatures, most likely a result of differences in thermal optima between these two species. Field data show that the proportion of stocked Atlantic salmon to wild rainbow trout coexisting in natural streams is a function of mean summer temperature. As stream temperatures increased, Atlantic salmon became increasingly favored over rainbow trout, but with a concomitant decrease in total salmonine biomass. We suggest that Atlantic salmon restoration programs focus more attention on relatively warm streams in watersheds where interactions with naturalized rainbow trout may occur.

Effect of Stocking Density on Growth, Yield, and Costs of Producing Rainbow Trout, Oncorhynchus mykiss, in Cages

Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m3) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-$3,124) and high breakeven price ($13.53/kg).

Breeding for improved appearance of large rainbow trout in two production environments

A quantitative genetic analysis was performed to study potential to breed for improved body shape, skin colour and skin spottiness of large rainbow trout in sea and fresh water production environments, and in different stages of growth. The results showed that heritabilities in both production environments were moderate for body shape and skin colour and very high for skin spots. For body shape and skin spots, genetic correlation between the two production environments was high (rA≥0.90), revealing weak genotype-by-environment interactions across the environments. For skin colour, genetic correlation between the environments was positive (0.78) but lower than for body shape and skin spots, indicating moderate genotype-by-environment interactions. Genetic correlations between 2- and 3-year-old fish were high for body shape and skin spots (rA≥0.93) and moderate for skin colour (0.85), showing that differences among families persisted strongly during growth. The positive correlations between the environments and between the ages imply that selection in fresh water environment at a single point of time should lead to favourable correlated genetic responses in the sea and at the other stages of growth.

Effect of long-term feeding with a plant protein mixture based diet on growth and body/fillet quality traits of large rainbow trout ( Oncorhynchus mykiss)

Two diets based on fish meal (FM) or on a mixture of plant protein sources supplemented with free amino acids (PP) were fed to rainbow trout having a mean initial body weight of 162.5 g reared at 17±1 °C for 24 weeks to evaluate the effect of plant protein sources on fish growth, morphological and body quality traits. At the end of the growth study, samples were withdrawn for chemical analyses as well as measurements of different parameters of quality. Compared to the FM group, the trout fed diet PP had lower growth rates (mean final body weight 663 vs. 800 g), feed efficiency (0.95 vs. 1.07) and protein efficiency ratio (1.96 vs. 2.13). Trout fed diet PP were also characterised by a lower dressed weight (89.45% vs. 91.07%), hepato-somatic index (0.92% vs. 1.01%) and fillet lipid content (5.50% vs. 6.98%), but had a higher mesenteric fat (5.65% vs. 4.08%), viscero-somatic index (10.55% vs. 8.93%) and fillet crude protein content (20.53% vs. 19.93%). The muscle fatty acid composition reflected that of the diet with a higher level of polyunsaturated (n-6) fatty acids in trout fed diet PP and a higher content in polyunsaturated n-3 fatty acids and n-3/n-6 ratio in trout fed diet FM. Sensory analysis was carried out at 5 days post-mortem on microwave-cooked dorsal portions of fillets stored at 1 °C with ice covering. The results of the triangular test showed differences between groups ( P<0.01) in organoleptic characteristics as well as in visual colour. Descriptive tests pointed out that fillets of trout fed diet PP exhibited higher hardness, less sweetness and less odour intensity than trout fed diet FM. In summary, data show that long-term feeding a diet in which fish meal was totally replaced by a mixture of plant protein sources significantly affects growth and quality criteria such as morphometric traits, fat deposits, fillet chemical composition and organoleptic characteristics of large commercial size rainbow trout.

Growth Rate, Maturation Level and Flesh Quality of Three Strains of Large Rainbow Trout (Oncorhynchus Mykiss) Reared in Estonia

Three all-female strains of large rainbow trout imported to Estonia (Danish, Finnish and Donaldson strain) were evaluated in a communal rearing experiment in tanks. The fish had been reared on different fish farms before the experiment started and they had an initial weight of 400–500 g. There were no significant genetic differences between the investigated strains on the basis of three allozyme loci. The total weight gain of the strains during the trial was similar but differences were revealed between seasons. The growth rate of the Finnish trout was high during the first autumn but decreased during the second summer of the trial, probably due to infestation by eye fluke Diplostomum sp. The strains differed in the percentage of immature fish and in the level of gonad development at the age of 2.5–3 years. The Donaldson strain had the highest number of immature fish of the studied strains. Mature females of the Finnish strain had the smallest gonads but also the lowest percentage of immature fish. The level of maturation was the main factor determining the quality – slaughter yield and flesh color.

Selection against early maturity in large rainbow trout Oncorhynchus mykiss: the quantitative genetics of sexual dimorphism and genotype-by-environment interactions

In rainbow trout Oncorhynchus mykiss, females typically mature at a later age than males, and males mature either early or late. When farmed rainbow trout is produced to obtain large fillets of high quality, especially early maturation of males reduces economical benefits. To examine whether it is possible to change the degree of this sexual dimorphism using selective breeding, we estimated sex-specific heritabilities, genetic correlations between sexes, and cross-environment correlations between two production environments for age at maturity and body weight. Extensive data set including individuals in five generations measured in brackish and fresh water in a split-family design was utilised to estimate the genetic parameters. The timing of maturity ( h 2=0.12–0.56) and body weight ( h 2=0.20–0.27) exhibited significant heritabilities, allowing genetic changes in trait means in response to selection. Genetic change in sexual dimorphism of body weight is, however, strongly constrained, as shown by the high genetic correlations between sexes ( r A≥0.95). For timing of maturity, the heritabilities of males and females differed, but the genetic correlation between sexes was high and positive ( r A=0.70). Although sexual dimorphism of age at maturity is less strongly contained than that of body weights, we conclude that no rapid genetic changes can be achieved in the sexual dimorphism of age at maturity through selective breeding. However, breeders may delay the timing of maturity in both sexes to avoid the drawbacks associated with the early maturation. Cross-environment correlations for the timing of maturity and body weight were highly positive ( r A≥0.61), indicating weak genotype-by-environment interactions and allowing parallel genetic changes in two environments where rainbow trout is farmed.

Big and beautiful? Quantitative genetic parameters for appearance of large rainbow trout

A quantitative genetic analysis of body condition, body shape, skin colour and spottiness of large, farmed rainbow trout Oncorhynchus mykiss showed that the traits can be modified through selective breeding. This was indicated by their high heritabilities (h2 = 0·46–0·61 on the underlying liability scale and 0·29–0·50 on the observed scale). Correlations calculated using linear models showed that skin colour and the amount of spots displayed positive phenotypic (rP = 0·33) and genetic correlations (rA = 0·83), the relationship being advantageous for the genetic improvement of the traits. Body shape and condition factor displayed disadvantageous correlations with body mass at both ages, the genetic correlations between the traits ranging from 0·36 to 0·57. It was concluded that there are no strong genetic constraints for the genetic improvement of appearance, the only limitation being that rapidly growing fish become rotund.

Dietary exposure of finfish to aromatic contaminants and tissue distribution.

Large rainbow trout (400 g) were exposed to food pellets spiked with four polycyclic aromatic compounds (PACs). Muscle, liver, internal organs, fatty tissue, and blood were analyzed after 5, 10, 15, and 19 weeks for PAC, lipid, and moisture content. At all collection times, concentrations expressed on a per gram basis were higher in fatty tissue and internal organs, followed by liver and muscle, and lowest levels were observed in blood. When examining the tissue burden, the highest bioaccumulations of carbazole, dibenzofuran, dibenzothiophene, and fluorene were in muscle and internal organs, intermediate in fatty tissue, and lowest in blood and liver. Carbazole with the lowest log K(OW) showed the lowest concentration within any tissue. Levels in tissues were significantly correlated to log K(OW) (> 5% level of significance), especially with longer exposure, and were more highly correlated when examining muscle, fatty tissue, and internal organs (> 0.05%). Different tissues displayed different time trends, and ratios between organs help determine the length of exposure. The most striking change in levels observed with time was in internal organs relative to other tissues, particularly when compared to daily exposure. The elimination of contaminants in feces and gallbladder bile was also compared, because they represent additional tools to assess recent exposure.

Observations of Size-related Asymmetries in Diet and Energy Intake of Rainbow Trout in a Regulated River

We examined diet and diel energy intake of rainbow trout, Oncorhynchus mykiss, of different lengths captured by electrofishing between 1991 and 1997 in the Lee's Ferry tailwater, Colorado River, below Glen Canyon Dam, Arizona. Trout diets reflected a depauperate food base and indicated limited potential of different fish size-groups to partition food resources. As evidenced by relative stomach volumes of ingested matter, mid-sized and large trout tended to consume more algae than did small fish, suggesting that they consumed diets of lower nutritional quality. An energy intake model indicated that median consumers among mid-sized and large fish generally failed annually to surpass estimated maintenance energy requirements and that median consumers among mid-sized trout failed to meet or exceed maintenance requirements during all seasons. In contrast, median consumers among small trout met or surpassed maintenance energy requirements during most years and in summer. Results support a hypothesis that larger rainbow trout in lotic systems are food-limited more often than smaller fish.

Rainbow Trout in a Regulated River below Glen Canyon Dam, Arizona, following Increased Minimum Flows and Reduced Discharge Variability

Abstract We examined the effects of dam operation on the relative abundance and relative condition of rainbow trout Oncorhynchus mykiss captured by electrofishing between 1991 and 1997 in the Lee's Ferry tailwater below Glen Canyon Dam, Arizona. Higher minimum, higher mean, and more stable flow releases from the dam after 1991 provided conditions that supported greater relative abundance of rainbow trout. Though the relative abundance of most length-classes increased following the onset of a stabilized flow regime, relative condition declined, particularly in large rainbow trout (≥305 mm). Correlation analyses suggested that the small rainbow trout (<305 mm) were more strongly influenced by physical factors (flow variation, mean discharge, and water temperature) than the large trout (≥305 mm). However, the relative condition of small trout was negatively correlated with that of all trout, and the condition of trout 305–405 mm in length was negatively correlated with the relative abundance of trout within ...

Monitoring and regulation of marine aquaculture in Denmark

Summary Marine fish farming in Denmark is completely dominated by the farming of large rainbow trout (Oncorhynchus mykiss) of 2–5 kg/piece in net cages or land-based flow-through systems, even though more species are being farmed on a small scale. The Danish production of rainbow trout in sea water reached some 8500 tonnes in 1998, and is unlikely to increase due to new restrictions imposed by the Ministry of Environment and Energy, including a provisional stop for extensions and new establishments. This prohibition was put in force in spite the fact that overall outlets are well below the frame allocated for marine fish farming. Generally, the procedures for obtaining allowances are complicated, involving regional and national institutions as well as public hearings. The procedures are described in this article.

A New Approach to Estimating the Minimum Dietary Requirement of Phosphorus for Large Rainbow Trout Based on Nonfecal Excretions of Phosphorus and Nitrogen

A new method was developed to estimate the minimum dietary requirement of phosphorus (P) for large fish for which conventional methods are not suitable. The method is based upon nonfecal (mainly urinary) excretion of inorganic P and total nitrogen from fish placed in a metabolic tank. In the first experiment, small and large rainbow trout (body wt 203 and 400 g, respectively) and, in the second experiment, P-sufficient, P-deficient and starved rainbow trout (different in diet history; body wt 349-390 g) were fed a constant amount (standard feeding rate) of semipurified diets with incremental P concentrations once daily at 15 degrees C. In all cases, there was no measurable excretion of P when dietary P concentration was low; however, beyond a specific dietary concentration, excretion of P increased rapidly. The point where the fish started to excrete P was assumed to be the minimum dietary requirement. By d 3 of consuming the experimental diets, the response of the fish to dietary P concentration stabilized, and excretion of P remained constant within dietary treatment groups for the subsequent sampling days (d 6, 9 and 12). The minimum dietary requirement of available P for fish having body wt of 203 and 400 g was estimated to be 6.62 and 5.54 g/kg dry diet, respectively, and that for P-sufficient, P-deficient and starved fish was estimated to be 4.06, 5.83 and 4.72 g/kg dry diet, respectively, when feed efficiency is 1.

Influence of dietary soy and phytase levels on performance and body composition of large rainbow trout ( Oncorhynchus mykiss) and algal availability of phosphorus load

A feeding trial was designed to evaluate the influence of partial replacement of fish meal (FM) protein for soy-derived protein in large rainbow trout fed practical, high-energy diets with and without supplemental phytase. A 2×2 factorial arrangement with two soy levels (0% and 69.4% of the dietary protein from soybeans) and two phytase levels (0 and 1200 U kg −1) was used. Soy protein was derived from soy protein concentrate (SPC) and soybean meal (SBM) with a SPC:SBM protein ratio of 4:1. Diets were formulated to contain 36% and 28% crude protein and fat, respectively, and supplemented with lysine and methionine, but not with phosphorus (P). Consequently, the dietary P contents were 10.5 and 6.9 g P kg −1 for diets without and with soy-derived proteins, respectively. Three replicate groups of fish per treatment were hand-fed once daily to apparent satiety for 24 weeks. Fish grew from 0.25 kg to an average of 2.02 kg, with soy-fed fish being significantly larger at the end of the trial. Phytase had no influence on weight gain of fish. Dietary treatments did not affect feed efficiency, which averaged 0.90. Percent bone ash was statistically significantly lower in fish fed soy diets than in fish fed FM diets (means 56.4 and 57.7), but weight performance and whole body composition analyses did not confirm the modest P deficiency in fish fed soy without supplemental phytase. Phytase supplementation did not significantly increase bone ash of fish fed soy diets. P load significantly decreased from 8.5 to 4.6 g P kg −1 weight gain due to the partial replacement of FM protein for soy protein. Algal availability of P was lower with soy-based diet than with FM-based diet (23% vs. 35%), and lower in fecal matter of fish fed soy-based diets than in fish fed FM-based diets (9% vs. 27%). Results from this study show that a significant part of FM can be replaced by soy proteins for low-pollution diets, without compromising weight gain or feed efficiency in large rainbow trout fed practical diets.

Cause for the Decline of Large Rainbow Trout in a Tailwater Fishery: Too Much Putting or Too Much Taking?

We studied causes for the decline of large (>40 cm total length, TL) rainbow trout Oncorhynchus mykiss and the transition from put–grow–take to put-and-take conditions in Lake Taneycomo, a popular tailwater in Missouri. In this fishery, rainbow trout densities have been sustained against increasing fishing pressure over the last 30 years mainly by increasing stocking rates of catchable-size fish (23–33 cm TL). Short residence times of rainbow trout resulting from heavy fishing pressure and high vulnerability to angling are generally considered the main reason for this speciesˈ limited growth after stocking in cold tailwaters. However, we found that increasing stocking rates in Lake Taneycomo have been paralleled by food base degradation, leading to submaintenance consumption rates for rainbow trout (i.e., poor growth conditions). A less prominent role of residence times was evident in the decline of poststocking growth and fewer large fish. In contrast to resident brown trout Salmo trutta, high diet similarity was observed across all sizes of rainbow trout collected during the 3-year study, hinting that this species may have a relatively limited capacity to partition food resources intraspecifically in some cold tailwaters. This limitation may contribute to the tendency of rainbow trout to fail to reach large sizes in these environments. Our findings indicate that when poststocking growth of rainbow trout is desired in cold tailwaters, greater attention to energetic conditions is warranted.

Comparison of Creel Returns from Rainbow Trout Stocked at Two Sizes

Creel returns of stocked rainbow trout Oncorhynchus mykiss are often below management objectives. In the Hoover Dam tailwater, Colorado River, predation by striped bass Morone saxatilis limits creel returns of stocked rainbow trout. On two occasions, we stocked large (33-em) and small (21–25-cm) rainbow trout into the tailwater to compare returns to the creel. Angler return rates for the two stockings were 47% and 22% for the large fish and 1 % and 2% for the small fish. Costs of large fish returned to the creel were US$6.02 and $12.86 per fish for the two stockings. Costs of small fish returned to the creel were $59.00 and $29.50 per fish for the two stockings. Annual survival of large rainbow trout did not increase compared with small fish. Stocking large rainbow trout is a cost-effective option for the Hoover Dam tailwater and may improve creel returns in other waters where predation limits survival of stocked fish.

Gradual transfer to sea water of rainbow trout: effects on liver carbohydrate metabolism

The levels of glycogen and glucose, as well as of the activities of several key enzymes of glycogenolysis, glycolysis, gluconeogenesis and the pentose phosphate shunt were assessed in livers of small (97 g) and large (166 g) rainbow trout Oncorhynchus mykiss during gradual transfer to sea water (salinities of 0, 9, 18 and 28%). Plasma glucose and protein levels were also evaluated. Liver carbohydrate metabolism changed during gradual adaptation of rainbow trout to sea water. Glucose increased with salinity in livers of both sizes of animals, as did glycogenolysis and gluconeogenesis, but this latter only in large animals, and glycolytic rates in small animals. The different responses in metabolic parameters between sizes of animals may reflect a higher stress of the small animals and/or a better adaptation of large animals to increased salinities, in a way similar to that previously suggested by other authors after evaluation of non‐metabolic parameters. The changes observed at 28% can also be the result of reduced food consumption.

RETINOIC ACID MODULATES RETINAL DEVELOPMENT IN THE JUVENILES OF A TELEOST FISH

Small (<30 g) juvenile rainbow trout (Oncorhynchus mykiss) possess retinal photoreceptor mechanisms sensitive to light in the near ultraviolet, short (blue), middle (green) and long (red) wavelengths. During normal development, the ultraviolet cone mechanism gradually disappears until, by approximately 60&shy;80 g, individuals are no longer sensitive in the ultraviolet. This shift in spectral sensitivity is associated with the loss of a single class of photoreceptor cells &shy; small accessory corner cones &shy; from the retinal photoreceptor cell mosaic. Treating small (<15 g) rainbow trout with 10(-6) mol l-1 all-trans retinoic acid (20 min exposure by immersion) induced a precocial loss of ultraviolet photosensitivity and an associated change in the retinal photoreceptor cell mosaic only 2 weeks after treatment. These changes were indistinguishable from the events that occur during normal development. Six weeks after exposure to retinoic acid, large (>90 g) rainbow trout, which had lost their ultraviolet cones during normal development, were once again ultraviolet-photosensitive and small accessory corner cones were found in their retinas. These results imply that the ultraviolet-sensitive cones, although lost at one point during development, can reappear at another time during the life history of the same individual. Retinoic acid is involved in these morphogenetic processes.

Effect of temperature and feed ration on energy utilization in large rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract In one experiment, temperature and feed ration were varied for rainbow trout, Oncorhynchus mykiss (Walbaum), with an initial size of about 1200g. In two experiments the feed ration was varied between parallel tanks, with naturally fluctuating ambient temperatures, and containing rainbow trout with an initial size of about 1000g and 400–550g, respectively. Growth and feed efficiency were measured in all experiments. An ad libitum feed ration without wastage produced the most effective energy utilization in most experimental groups. At best an average of 50% of the gross energy was utilized for growth. The relation between growth rate and feed ration was linear, and there was no optimum point for feeding below this level. The observed intake of energy is compared with growth, measurements of digestibility, feeding and starving metabolism. It is also linked to earlier observations of intake by rainbow trout fingerlings to give equations expressing the energy needs of rainbow trout of different sizes (30–1500g). These are intended to be used for efficient rearing at different temperatures (10–22°C).