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A 9‐week feeding trial was conducted to evaluate one custom formulation and six commercially available diets when fed to juveniles of the endangered Lost River Sucker Deltistes luxatus. The seven treatments included the following: two catfish Ictalurusspp. diets, a tilapia Oreochromisspp. diet, a shrimp diet, a general warmwater fish diet, a general fish diet, and a feed formulated at the Abernathy Fish Technology Center (Abernathy sucker diet). The general fish diet produced fish that were significantly larger than the fish fed the other diets. The Lost River Suckers fed the general fish diet or the Abernathy sucker diet averaged 99.0% survival for the duration of the trial, which was significantly higher than in Lost River Suckers fed all other diets except for one catfish diet. Spinal deformities were significantly less frequent in fish fed the general fish diet and the Abernathy sucker diet. Whole‐body proximate and fatty acid composition were affected by diet. Whole‐body fatty acid profiles generally mirrored the diet profiles. The general fish diet appears to be an effective diet for juvenile Lost River Suckers, although the Abernathy sucker diet should be considered for further development as it yielded high survival and no incidence of spinal deformity.

Impacts of plant-based ingredients and temperatures on energy metabolism in rainbow trout was investigated. A total of 288 fish (mean body weight: 45.6 g) were fed four isocaloric, isolipidic, and isonitrogenous diets containing 40% protein and 20% lipid and formulated as 100% animal-based protein (AP) and a blend of 50% fish oil (FO) and 50% camelina oil (CO); 100% AP and100% CO; 100% plant-based protein (PP) and a blend of 50% FO and 50% CO or 100% PP and 100% CO at 14 or 18 °C for 150 d. Diet did not significantly affect weight gain (WG) (P= 0.1902), condition factor (CF) (P= 0.0833) or specific growth rate (SGR) (P= 0.1511), but diet significantly impacted both feed efficiency (FE) (P= 0.0076) and feed intake (FI) (P= 0.0076). Temperature did not significantly affect WG (P= 0.1231), FE (P= 0.0634), FI (P= 0.0879), CF (P= 0.8277), or SGR (P= 0.1232). The diet × temperature interaction did not significantly affect WG (P= 0.7203), FE (P= 0.4799), FI (P= 0.2783), CF (P= 0.5071), or SGR (P= 0.7429). Furthermore, temperature did not influence protein efficiency ratio (P= 0.0633), lipid efficiency ratio (P= 0.0630), protein productive value (P= 0.0756), energy productive value (P= 0.1048), and lipid productive value (P= 0.1386); however, diet had significant main effects on PER (P= 0.0076), LPV (P= 0.0075), and PPV (P= 0.0138). Temperature regimens induced increased activities of mitochondrial complexes I (P= 0.0120), II (P= 0.0008), III (P= 0.0010), IV (P< 0.0001), V (P< 0.0001), and citrate synthase (CS) (P< 0.0001) in the intestine; complexes I (P< 0.0001), II (P< 0.0001), and CS (P= 0.0122) in the muscle; and complexes I (P< 0.0001), II (P< 0.0001), and III (P< 0.0001) in the liver. Similarly, dietary composition significantly affected complexes I (P< 0.0001), II (P< 0.0001), IV (P< 0.0001), V (P< 0.0001), and CS (P< 0.0001) in the intestine; complexes I (P< 0.0001), II (P< 0.0001), III (P= 0.0002), IV (P< 0.0001), V (P= 0.0060), and CS (P< 0.0001) in the muscle; and complexes I (P< 0.0001), II (P< 0.0001), IV (P< 0.0001), V (P< 0.0001), and CS (P< 0.0001) in the liver activities except complex III activities in intestine (P= 0.0817) and liver (P= 0.4662). The diet × temperature interaction impacted CS activity in the intestine (P= 0.0010), complex II in the muscle (P= 0.0079), and complexes I (P= 0.0009) and II (P= 0.0348) in the liver. Overall, comparing partial to full dietary substitution of FO with CO, partial dietary replacement showed similar effects on complex activities.Based on the results, vegetable-based ingredient sources could replace 100% of dietary fishmeal and oil without negative effects on rainbow trout grown at 18 °C or below. Plant-based protein and camelina oil have the potential to replace fishmeal and fish oil in trout feeds.Diets are one of the most important consideration in aquaculture production as more than 50% of production costs are incurred in raising cultured fish to market size. As the price of FM and FO continues to increase, it is necessary to seek alternative sources of proteins and oils for sustainable aquaculture development. Plant-based ingredient sources have appeared as sustainable alternatives; however, it is uncertain whether the uses of plant-based alternatives will be appropriate in securing the production of carnivorous aquaculture species in the context of global warming, with studies postulating on the potential effects of climate change on fish growth and health. A study was conducted to examine how the replacement of FM and FO with sustainable plant-based protein and camelina oil (CO) as ingredient sources at 14 or 18 °C would affect the growth performance, nutrient utilization efficiencies, and mitochondrial enzyme activity in rainbow trout. Based on the results, mitochondrial enzyme activities were generally higher at 18 °C and CO could replace 50% dietary FO without negative effects on rainbow trout. Overall, our study demonstrated that animal-based protein with CO is as good as animal-based with FO for growth and health, thus providing potentially sustainable diet options for aquaculture.

Transition diets, often supplemented with salt and other additives, have been used to prepare Pacific salmon Oncorhynchusspp. being moved directly from freshwater to saltwater net pens for aquaculture production. However, the use of transition diets to prepare hatchery-reared salmon released into freshwater prior to out-migration to the ocean has shown mixed results. We compared the physiological (size, condition factor, Na+,K+-ATPase [NKA] enzyme activity, survival during a saltwater challenge) and nutritional (proximate composition, fatty acid profile) condition of juvenile Chinook Salmon O. tshawytschathat were fed either a standard hatchery feed or a commercially available transition diet for the final 6 weeks of hatchery rearing to determine whether the transition diet altered smolt condition. At release, NKA activity of fish fed the transition diet was higher than that of fish fed the control diet, though survival during a saltwater challenge was similar between groups. Differences were seen in the proximate composition of the fish, with increased total body moisture and decreased lipid in the fish fed the transition diet relative to fish fed the control diet. Whole-body fatty acid composition of fish was similar to the fatty acid composition of the feeds in both groups, though some key whole-body fatty acids did not follow this trend. Palmitic acid (16:0), linoleic acid (18:2[n-6]), eicosapentaenoic acid (20:5[n-3]), and docosahexaenoic acid (22:6[n-3]) varied between prefeeding trial samples and fish fed the two diets. Further research is required to determine whether the physiological changes that occurred are related to smoltification or the maintenance of osmotic balance while fish are fed additional salt.

AbstractTransition diets, often supplemented with salt and other additives, have been used to prepare Pacific salmon Oncorhynchusspp. being moved directly from freshwater to saltwater net pens for aquaculture production. However, the use of transition diets to prepare hatchery-reared salmon released into freshwater prior to out-migration to the ocean has shown mixed results. We compared the physiological (size, condition factor, Na+,K+-ATPase [NKA] enzyme activity, survival during a saltwater challenge) and nutritional (proximate composition, fatty acid profile) condition of juvenile Chinook Salmon O. tshawytschathat were fed either a standard hatchery feed or a commercially available transition diet for the final 6 weeks of hatchery rearing to determine whether the transition diet altered smolt condition. At release, NKA activity of fish fed the transition diet was higher than that of fish fed the control diet, though survival during a saltwater challenge was similar between groups. Differences were seen in the proximate composition of the fish, with increased total body moisture and decreased lipid in the fish fed the transition diet relative to fish fed the control diet. Whole-body fatty acid composition of fish was similar to the fatty acid composition of the feeds in both groups, though some key whole-body fatty acids did not follow this trend. Palmitic acid (16:0), linoleic acid (18:2[n-6]), eicosapentaenoic acid (20:5[n-3]), and docosahexaenoic acid (22:6[n-3]) varied between prefeeding trial samples and fish fed the two diets. Further research is required to determine whether the physiological changes that occurred are related to smoltification or the maintenance of osmotic balance while fish are fed additional salt.Received October 13, 2015; accepted April 3, 2016

AbstractThe establishment of a propagation program is among the recommended actions of the U.S. Fish and Wildlife Service recovery plan for the endangered Lost River Sucker Deltistes luxatus. As an initial step in diet development, a feeding trial was conducted to identify appropriate dietary lipid sources to feed juvenile Lost River Suckers at a rate of 0.47 g/fish. Six dietary treatments were produced by adding the following to a basal diet: (1) marine fish oil (Fish) as a control, (2) flaxseed oil (Flax), (3) soybean oil (Soy), or a 1:1 mixture of (4) fish and flax oil (Fish/Flax), (5) fish and soy oil (Fish/Soy), or (6) flax and soy oil (Flax/Soy). At the conclusion of the feeding trial weight gain of fish fed the control diet (Fish) was not significantly different than that of fish fed the other dietary treatments. However, weight gain of fish fed Soy was significantly higher than that of fish fed Fish/Flax. Whole-body lipid was significantly higher in fish fed Soy than in fish fed Fish, Flax, Fish/Flax, or Fish/Soy, but not significantly different than that in fish fed Flax/Soy. Generally, whole body fatty acid profiles reflected the fatty acid profiles of their respective dietary treatments. These results suggest soybean oil is an appropriate dietary lipid source for the Lost River Sucker, but more research on quantitative dietary requirements is needed for successful propagation of this species.Received November 20, 2015; accepted March 4, 2016 Published online June 15, 2016

The establishment of a propagation program is among the recommended actions of the U.S. Fish and Wildlife Service recovery plan for the endangered Lost River Sucker Deltistes luxatus. As an initial step in diet development, a feeding trial was conducted to identify appropriate dietary lipid sources to feed juvenile Lost River Suckers at a rate of 0.47 g/fish. Six dietary treatments were produced by adding the following to a basal diet: (1) marine fish oil (Fish) as a control, (2) flaxseed oil (Flax), (3) soybean oil (Soy), or a 1:1 mixture of (4) fish and flax oil (Fish/Flax), (5) fish and soy oil (Fish/Soy), or (6) flax and soy oil (Flax/Soy). At the conclusion of the feeding trial weight gain of fish fed the control diet (Fish) was not significantly different than that of fish fed the other dietary treatments. However, weight gain of fish fed Soy was significantly higher than that of fish fed Fish/Flax. Whole-body lipid was significantly higher in fish fed Soy than in fish fed Fish, Flax, Fish/Flax, or Fish/Soy, but not significantly different than that in fish fed Flax/Soy. Generally, whole body fatty acid profiles reflected the fatty acid profiles of their respective dietary treatments. These results suggest soybean oil is an appropriate dietary lipid source for the Lost River Sucker, but more research on quantitative dietary requirements is needed for successful propagation of this species.

AbstractThe Lost River Sucker Deltistes luxatusis endemic to the Klamath Basin in southern Oregon and northern California. Population declines led to listing this species as endangered in 1988. Its native habitat has been greatly reduced and degraded putting their future in question. If this species is to be reared in captivity to prevent extinction, the development of culture methodologies is necessary. Successful initial feeding methods are one of the first areas of culture that need to be developed. Lost River Suckers begin feeding during the larval life stage. Larval fish often require live prey at the onset of feeding; however, it may be possible to start larvae on formulated microdiets. We investigated the use of live Artemiaand two commercial microdiets (Hikari and Otohime brands) as first feeds over the course of a 41-d feeding trial. Starting on day 21 of the trial, feed sizes were increased, and the Artemia-fed fish were offered a commercial microdiet (Otohime) while being co-fed Artemiathrough day 26 of the trial (6 d cofeeding). After day 26 the Artemia-fed fish were only offered the microdiet. The response variables of total length, weight, survival, whole-body lipid content, and whole-body fatty acid profile were measured during and at termination of the trial. Fish grew significantly faster when started on Artemiaand also displayed significantly higher survival compared with fish fed only commercial microdiets. Fish started on Artemiatransitioned well to Otohime B1, and maintained 95.2% (SD, 2.2) survival over the 41-d feeding trial. The fatty acid profiles of the fish generally reflected the profiles of the diets they were fed. This study demonstrated that live Artemiafollowed by a transition to Otohime commercial feed is an effective feeding regimen for the duration of the larval phase of this species.Received April 10, 2015; accepted October 2, 2015

The Lost River Sucker Deltistes luxatusis endemic to the Klamath Basin in southern Oregon and northern California. Population declines led to listing this species as endangered in 1988. Its native habitat has been greatly reduced and degraded putting their future in question. If this species is to be reared in captivity to prevent extinction, the development of culture methodologies is necessary. Successful initial feeding methods are one of the first areas of culture that need to be developed. Lost River Suckers begin feeding during the larval life stage. Larval fish often require live prey at the onset of feeding; however, it may be possible to start larvae on formulated microdiets. We investigated the use of live Artemiaand two commercial microdiets (Hikari and Otohime brands) as first feeds over the course of a 41-d feeding trial. Starting on day 21 of the trial, feed sizes were increased, and the Artemia-fed fish were offered a commercial microdiet (Otohime) while being co-fed Artemiathrough day 26 of the trial (6 d cofeeding). After day 26 the Artemia-fed fish were only offered the microdiet. The response variables of total length, weight, survival, whole-body lipid content, and whole-body fatty acid profile were measured during and at termination of the trial. Fish grew significantly faster when started on Artemiaand also displayed significantly higher survival compared with fish fed only commercial microdiets. Fish started on Artemiatransitioned well to Otohime B1, and maintained 95.2% (SD, 2.2) survival over the 41-d feeding trial. The fatty acid profiles of the fish generally reflected the profiles of the diets they were fed. This study demonstrated that live Artemiafollowed by a transition to Otohime commercial feed is an effective feeding regimen for the duration of the larval phase of this species.

AbstractRosemary Rosmarinus officinalisoil has shown potential for use as a phytobiotic fish feed supplement with antioxidant properties that can inhibit the growth of Flavobacterium psychrophilum, the pathogen that causes bacterial cold-water disease (BCWD). To determine the in vivo effectiveness of rosemary oil in preventing or minimizing BCWD, Rainbow Trout Oncorhynchus mykisswere fed commercial feed top-coated with one of two concentrations of rosemary oil (1% or 3% of the feed) or a control diet for 14 d. Fish from each feed treatment were then challenged with one of two doses of F. psychrophilumvia subcutaneous injection, and mortality was monitored for 28 d. In both F. psychrophilumchallenges, fish treated with feed coated with rosemary oil at the 1% and 3% levels experienced significantly higher mortality than fish treated with only soybean oil–coated feed. While the use of rosemary oil as a top-coat on feed increased mortality among Rainbow Trout subjected to a disease challenge in the current study, the mechanism for this result has not been established.Received January 22, 2014; accepted April 18, 2014

Rosemary Rosmarinus officinalisoil has shown potential for use as a phytobiotic fish feed supplement with antioxidant properties that can inhibit the growth of Flavobacterium psychrophilum, the pathogen that causes bacterial cold-water disease (BCWD). To determine the in vivo effectiveness of rosemary oil in preventing or minimizing BCWD, Rainbow Trout Oncorhynchus mykisswere fed commercial feed top-coated with one of two concentrations of rosemary oil (1% or 3% of the feed) or a control diet for 14 d. Fish from each feed treatment were then challenged with one of two doses of F. psychrophilumvia subcutaneous injection, and mortality was monitored for 28 d. In both F. psychrophilumchallenges, fish treated with feed coated with rosemary oil at the 1% and 3% levels experienced significantly higher mortality than fish treated with only soybean oil–coated feed. While the use of rosemary oil as a top-coat on feed increased mortality among Rainbow Trout subjected to a disease challenge in the current study, the mechanism for this result has not been established.

Fish meal (FM) is the main protein source in aquaculture diets owing to its palatability and quality. Available quantities of FM have remained constant for the past several decades; however, demand has dramatically increased due to its inclusion in diets used for the global aquaculture industry. There are various alternative protein sources that can be used in aquaculture diets, with soyabean meal (SBM) being the most widely used plant protein ingredient; however, use of SBM as the sole protein source has often resulted in reduced fish growth. There is a growing segment of consumers who desire organically grown foods, and since Nile tilapia is one of the most-cultured fish in the world and has herbivorous/omnivorous feeding habits, Nile tilapia fed an organic diet may allow producers to enter this rapidly developing market. A feeding experiment was conducted to evaluate the combination of organic SBM and an organic yeast extract (YE) as complete replacements for FM. Five isonitrogenous, isocaloric diets were fed to small (0.1 g) Nile tilapia, Oreochromis niloticus, for 6 weeks. Diets contained various percentages (0%, 10%, 20%, 30% and 40%) of YE, with Diet 1 formulated to be similar to a high-quality commercial diet containing 0% YE and 20% FM. At the conclusion of the feeding trial, fish fed Diet 1 had statistically significantly (p < 0.05) higher mean final weight (3.99 g) and specific growth rate (8.48% day− 1), and a lower feed conversion ratio (1.40) than fish fed all other diets. Based upon the data, an organic diet which replaces FM with a combination of SBM and YE appears promising but further research is needed to refine formulation so as to have similar growth performance with a FM-based diet.

Successful reproduction of captive-reared fishes depends on hatchery practices and proper broodstock nutrition. Nutrient requirements and environmental conditions stimulating reproductive development are unknown for many threatened and endangered species and may differ between lineages within species. Accordingly, prior to spawning, Main Diamond Gila Trout Oncorhynchus gilaebroodstock were exposed to different thermal cycles and hormonal injection to improve reproductive success. Additionally, egg fatty acid composition and hatching success of Main and South Diamond Gila Trout were evaluated to determine the extent of phenotypic differences between lineages. Thermal conditioning of broodstock accompanied with injections of exogenous luteinizing hormone releasing hormone analog (LHRHa) prior to spawning improved progeny survival over historic hatchery means as well as means for broodstock reared in raceways at constant temperatures without LHRHa. Egg n-6 fatty acid content appears to be associated with this improvement. Eggs from Main and South Diamond broodstock fed the same feeds had similar hatch rates but could be differentiated on the basis of fatty acid profile. Future trials should further evaluate the influence of dietary fatty acids on egg deposition and hatch rate, while acknowledging that changes in reproductive performance may differ across lineages. Broodstocks should continue to be conditioned with thermal cycling and use of LHRHa to induce ovulation, as these techniques resulted in significantly better hatch rates in the current study than use of only photoperiod manipulation to stimulate reproductive development.

AbstractSuccessful reproduction of captive-reared fishes depends on hatchery practices and proper broodstock nutrition. Nutrient requirements and environmental conditions stimulating reproductive development are unknown for many threatened and endangered species and may differ between lineages within species. Accordingly, prior to spawning, Main Diamond Gila Trout Oncorhynchus gilaebroodstock were exposed to different thermal cycles and hormonal injection to improve reproductive success. Additionally, egg fatty acid composition and hatching success of Main and South Diamond Gila Trout were evaluated to determine the extent of phenotypic differences between lineages. Thermal conditioning of broodstock accompanied with injections of exogenous luteinizing hormone releasing hormone analog (LHRHa) prior to spawning improved progeny survival over historic hatchery means as well as means for broodstock reared in raceways at constant temperatures without LHRHa. Egg n-6 fatty acid content appears to be associated with this improvement. Eggs from Main and South Diamond broodstock fed the same feeds had similar hatch rates but could be differentiated on the basis of fatty acid profile. Future trials should further evaluate the influence of dietary fatty acids on egg deposition and hatch rate, while acknowledging that changes in reproductive performance may differ across lineages. Broodstocks should continue to be conditioned with thermal cycling and use of LHRHa to induce ovulation, as these techniques resulted in significantly better hatch rates in the current study than use of only photoperiod manipulation to stimulate reproductive development.Received September 11, 2012; accepted March 14, 2013

Juvenile Atlantic cod Gadus morhua(initial weight = 24.1 ± 1.4 g [mean ± SE) were fed diets in which fish meal (FM) was replaced with soy protein concentrate (SPC) and soybean meal (SBM) in isonitrogenous, isocaloric diets for 84 d. A standard marine finfish diet (3 mm, 54% protein, 14% fat) was modified to produce four experimental diets in which 50% of FM was replaced with soy at 0:1, 1:1, or 1:2 ratios of SPC:SBM and 100% FM replacement with a 1:1 ratio of SPC:SBM. No differences in mortality or feed intake were detected among treatments, and fish fed the 50% FM replacement diets, in any combination, grew as well or better than the control for all variables investigated. Cod fed the 100% FM replacement diet exhibited the lowest growth and differed from the control with respect to final body weight, growth, specific growth rate, and thermal-unit growth coefficient. No enteritis was observed in histological sections. These results indicate that 100% fish meal replacement is not recommended, but 50% replacement can be used without significant reductions in growth or condition indices.

Two feeding trials were conducted in a closed system with Nile tilapia Oreochromis niloticusfry (mean weight, 0.10 g; experiment 1) and juveniles (mean weight, 2.84 g; experiment 2) to examine the effects of total replacement of fish meal (FM), with and without supplementation of dl-methionine (Met) and l-lysine (Lys), by plant protein sources. In experiment 1, fry were fed nine isoenergetic (available energy [AE] = 4.0 kcal/g of diet) and isoproteic (40% protein as fed basis) practical diets containing protein primarily from soybean meal (SBM), with and without essential Met and Lys. After 5 weeks, final individual weight (FW; g/fish) and percent weight gain (PWG) of fry fed diet 1 (control with 20% FM) was significantly higher (P< 0.05) compared with fry fed all other diets, while fry fed diet 9 containing 46% SBM and 22% feed-grade poultry by-product meal PBM) was significantly higher than all other diets (diets 2–8). Quantity of diet fed and percent survival did not differ significantly (P> 0.05) among all diets. In experiment 2, juveniles were fed six isoenergetic (AE = 4.0 kcal/g of diet) and isoproteic (35% protein as fed basis) practical diets containing protein primarily from SBM, soybean protein concentrate (SPC), feed-grade PBM, or combinations of those. After 7 weeks, mean FW, PWG, and amount of diet fed for fish fed diets 1 (control with 20% FM) and 6 (with 20% SPC and 20% PBM) were significantly higher (P< 0.05) compared with juveniles fed all other diets. Feed conversion ratio (FCR) was similar among treatments, but fish fed diet 5 (with 36% SPC and 0% FM) recorded the highest FCR value. Likewise, protein efficiency ratio (PER) was similar among treatments; however, PER in juveniles fed diets 3 (with 52% SBM and 0% FM) and 5 were significantly lower than in fish fed all other diets. Overall, no significant (P> 0.05) difference was found in percent survival, which averaged 92.6% among all diets fed. These data suggest that Nile tilapia fry cannot utilize diets containing high levels (>75%) of SBM when no animal protein ingredient is added, even with supplemental Met and Lys. However, a diet containing 20% SPC and 20% feed-grade PBM appears to be suitable for juvenile Nile tilapia, which may help reduce diet costs and allow for sustainable production.

Additives are commonly used in feed to enhance fish performance, health, and well-being. In recent years, antibiotics have received increased scrutiny owing to concerns about overuse and their environmental impact. These concerns have generated a desire for naturally derived alternatives for the aquafeed industry. For screening purposes, we examined the in vitro effects of an essential oil on bacteria commonly associated with fish diseases. Six concentrations of rosemary Rosmarinus officinalisoil (0.1, 0.3, 0.5, 0.7, and 0.9 µL/µL of 1% Tween-20 and pure rosemary oil [1.0]) were used against Flavobacterium psychrophilum, Yersinia ruckeri, Aeromonas salmonicida, and three warmwater bacterial pathogens, A. hydrophila, Edwardsiella ictaluri, and E. tarda, along with a control treatment (1% Tween-20 only). After incubation, the mean zone of inhibition around the disks was measured. While most concentrations were found to inhibit pathogen growth, a concentration of 50% or more was found to have significantly higher effects on most of the pathogens tested. Rosemary oil was found to inhibit the growth of F. psychrophilumto the greatest extent and had a limited effect on the other fish pathogens. Although rosemary oil was shown to inhibit the growth of some bacterial fish pathogens in experimental trials, further laboratory and field studies are required to determine whether rosemary oil as a feed additive has any application as part of an integrated fish health management strategy.

A 12-week feeding trial was conducted to evaluate a fish-meal-free, fish-oil-free diet for use with first-feeding steelhead Oncorhynchus mykiss. The marine-based control diet (marine diet) contained sardine (Sardinopsspp.) meal and pollock (Pollachius virens) liver oil as the primary sources of protein and lipid, respectively. The experimental diet (terrestrial diet) contained only terrestrial sources of protein (poultry by-product meal, blood meal, canola, corn gluten, and wheat gluten) and lipid (canola oil and flaxseed oil). Each diet was administered to five replicate groups of first-feeding fry. At the conclusion of the feeding trial, fish that were fed the marine diet exhibited significantly higher weight gain and feed efficiency than fish that were given the terrestrial diet. Survival was not significantly affected by dietary treatment. However, fish that received the terrestrial diet exhibited significantly lower hemoglobin concentration and percent packed cell volume. Histological examination indicated that in comparison with control fish, steelhead that were fed the terrestrial diet exhibited a lesser degree of vacuolation in hepatocytes, mild hypertrophy and hyperplasia of the nephron tubular epithelium, and intracellular vacuolation in epithelium of the pyloric caeca. Carcass crude protein concentration was significantly higher in fish that were fed the marine diet than in fish that were fed the terrestrial diet. After 2 weeks of feeding, steelhead that received the marine diet exhibited significantly higher carcass concentrations of 14:0, 16:0, 16:1, 20:1, 20:5(n-3), 22:5(n-3), and 22:6(n-3) fatty acids but significantly lower carcass concentrations of 18:1, 18:2(n-6), 18:3(n-6), 18:3(n-3), and 20:4(n-6) relative to fish that were given the terrestrial diet. These differences in carcass fatty acid concentrations persisted throughout the feeding trial. Results of this study indicate that the current terrestrial-based diet is not a satisfactory replacement for the standard marine-based diet used with first-feeding steelhead. Received January 21, 2010; accepted January 22, 2011

In 2006, Bio-Oregon, Inc., the only commercial producer of cold-extruded moist diets (~20–27% moisture) formulated for salmonids, announced that it would discontinue production of this diet line. One of these diets, BioDiet starter (19.5–21.5% moisture) was the primary feed used in many hatcheries that produce Chinook salmon Oncorhynchus tshawytscha. Thus, a feeding trial was conducted to identify an alternative starter diet for spring Chinook salmon. Five commercial diets were evaluated: Skretting BioVita (<10% moisture), EWOS Micro (<10% moisture), Rangen Starter (<10% moisture), Rangen Soft-Moist (14–17% moisture), and Silver Cup Soft-Moist (<13% moisture). Each dietary treatment was fed to quadruplicate groups of 200 randomly selected first-feeding fry reared in fiberglass tanks. Initial weight of the fish averaged 0.34 g/fish. The flow-through water supply was 12°C throughout the 8-week feeding trial. At the end of the study, fish fed Skretting BioVita exhibited significantly higher (P< 0.05) weight gain (3.4 g/fish) and feed efficiency (1.9 g gain/g feed) than fish fed the other diets. Fish fed Rangen Soft-Moist exhibited significantly lower (P< 0.05) weight gain (1.6 g/fish) and feed efficiency (1.2 g gain/g feed) than fish fed the other commercial diets. Survival rates were high (97–99%) and not significantly (P> 0.05) affected by dietary treatment. Carcass moisture and fat concentrations were significantly (P< 0.05) affected by the various diets. Carcass fat concentrations were significantly higher and carcass moisture concentrations were significantly lower in fish fed Skretting BioVita than in fish fed Rangen Starter, Rangen Soft-Moist, or Silver Cup Soft-Moist. Results of this study indicate that a moist starter diet is not required for rapid weight gain and high survival rates of first-feeding spring Chinook salmon.

The bonytail Gila elegansis a critically endangered cyprinid that is endemic to the southwestern United States, where it is cultured in ponds and water reuse systems as part of recovery efforts. Unlike in extensive outdoor pond culture, where natural food productivity plays a primary nutritional role, manufactured feed must provide complete nourishment for fish reared indoors in recirculating systems. The objective of this study was to determine the effects of diet on the growth and survival of juvenile bonytails fed four commercially available feeds over a 120-d period. The four treatment diets were identified as a catfish diet, a trout diet, a high-protein shrimp diet, and a low-protein shrimp diet. Significant (P< 0.05) differences in growth among treatments were observed on sampling day 102. By day 120, the average weight of fish fed the high-protein shrimp diet (36.3 g) was significantly higher than the weights of fish fed the catfish (26.6 g), trout (24.7 g), and low-protein shrimp diets (24.2 g). The specific growth rates measured on days 102 and 120 were significantly greater for bonytails fed the high-protein shrimp diet than for fish fed the other treatments. The feed conversion ratio of fish fed the high-protein shrimp diet was significantly better than those of fish fed the trout and low-protein shrimp diets, while the protein efficiency ratio and apparent net protein retention were generally higher in the high- and low-protein shrimp diet treatment groups than in the other two treatment groups. Overall survival was high (93.5%) and did not differ significantly among treatment groups (P= 0.05) through 120 d.

At two Washington State hatcheries in August 1999–2002, juvenile steelhead Oncorhynchus mykisswere size-graded and the largest fish (4.8–9.2% of the population) were coded-wire-tagged and mixed with small fish to determine whether the large fish were those that became precocious males. The results showed that the large fish in August at Merwin Hatchery tended to become precocious, although the mean lengths of the precocious and nonprecocious fish were similar at their time of release in April. At Abernathy Fish Technology Center (FTC), the large fish in August did not disproportionately become precocious, and the nonprecocious fish were significantly larger than the precocious fish at release. We suggest that precocious fish at Abernathy FTC may have committed to precocity before August whereas fish at Merwin Hatchery committed to precocity in August. Because only 0.82% of the large fish became precocious, removing the 5–10% largest fish in August at the Merwin Hatchery would be marginally successful in reducing the number of precocious males.