Exploring the effects of dietary inulin in rainbow trout fed a high‑starch,100%plant‑based diet

Background High dietary carbohydrates can spare protein in rainbow trout(Oncorhynchus mykiss)but may affect growth and health.Inulin,a prebiotic,could have nutritional and metabolic effects,along with anti-inflammatory properties in teleosts,improving growth and welfare.We tested this hypothesis in rainbow trout by feeding them a 100%plant-based diet,which is a viable alternative to fishmeal and fish oil in aquaculture feeds.In a two-factor design,we examined the impact of inulin(2%)as well as the variation in the carbohydrates(CHO)/plant protein ratio on rainbow trout.We assessed the influence of these factors on zootechnical parameters,plasma metabolites,gut microbiota,production of short-chain fatty acids and lactic acid,as well as the expression of free-fatty acid receptor genes in the mid-intestine,intermediary liver metabolism,and immune markers in a 12-week feeding trial.Results The use of 2%inulin did not significantly change the fish intestinal microbiota,but interestingly,the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity,with 21 bacterial genera affected,including Ralstonia,Bacillus,and 11 lactic-acid producing bacteria.There were higher levels of butyric,and valeric acid in groups fed with high CHO/protein diet but not with inulin.The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines(il1b,il8,and tnfa)in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine(tjp1a and tjp3).However,the 2%inulin did not modify the expression of plasma immune markers.Finally,inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates.Conclusions With a 100%plant-based diet,inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2%inulin does not appear to improve the use of CHO when combined with a 100%plant-based diet.

Short-Term Stress Response of Juvenile Rainbow Trout Subjected to Two Different Rearing Densities

Juvenile rainbow trout Oncorhynchus mykiss were subjected to one of four treatments in a two-by-two experimental design: 1) fed at a density of 1.8 g/m3, 2) Fasted at 1.8 g/m3, 3) fed at 30.1 g/m3, and 4) fasted at 30.1 g/m3. Blood glucose and hematocrit were measured at 4, 6, 48, 168, and 336 hours after placement in one of the two rearing densities, with relative fin lengths and organosomatic indices recorded at 336 hours. Glucose levels over time were not significantly different among the density and feeding treatments. Hematocrit levels over time were also not significantly different. Total lengths, weight, hepatosomatic index, viscerosomatic index, and any of the relative fin lengths were not significantly different between the high and low densities. However, the hepatosomatic index was significantly greater in the fed fish compared to those fasted. The splenosomatic index was significantly greater in the higher density treatment. These results likely indicate no short-term stress response to the higher rearing density used in this short-term experiment and no interaction between starvation and density-related stressors.

Thermal Tempering Does Not Impact Rainbow Trout and Brown Trout Survival

Hatchery-reared fish are frequently adjusted (tempered) to the higher water temperatures present in the water bodies where they are to be stocked. This study was undertaken to determine the necessity of such tempering practices. This study used rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) reared at 11.2°C. The first two trials for each species were designed to simultaneously determine the upper incipient lethal temperature and 100% lethal temperature over a 14-day period. The third trial for each species evaluated the effects of an exaggerated 12-hour tempering regime on fish survival after placement in elevated water temperatures. After transfer from a water temperature of 11.2°C, no rainbow trout survived at 26°C, and only 50% survived at 25°C. No brown trout survived at 22°C and only 50% at 20°C. Survival of rainbow trout was not improved by the 12-hour tempering regime where water temperatures were slowly increased from 11.2°C to either 25°C or 26°C. Similarly, tempering did not improve brown trout survival at either 20°C or 22°C. These results suggest that tempering is not needed when hatchery-reared trout are reared and stocked at the water temperatures within the range of those used in this study.

An initial investigation replacing fish meal with a commercial fermented soybean meal product in the diets of juvenile rainbow trout

The inclusion of PepSoyGen (PSG), a commercially-available fermented soybean meal product, was evaluated with juvenile rainbow trout, Oncorhynchus mykiss in an initial 70-day feeding trial, with a supplemental trial involving a subset of the experimental diets continuing for an additional 40 d. Six diets containing 0%, 10%, 20%, 30%, 40%, or 50% PSG, with the PSG directly replacing fish meal, were used in the first trial. There were no significant differences in weight gain or feed conversion ratio between the fish meal-based control diet and diets containing up to 30% PSG. However, weight gain was significantly reduced and feed conversion ratio significantly increased with the 40% and 50% PSG diets. No health assessment differences were observed in fish receiving any of the diets, and no evidence of gross gut inflammation was evident. There were no significant differences in weight gain or feed conversion ratio among the four dietary treatments ranging from 0% to 30% PSG which were fed for an additional 40 d after the initial 70-d trial (110 days total). Based on these results, juvenile rainbow trout diets can contain up to 30% PSG without any loss of rearing performance, thereby replacing at least 60% of the fish meal.

Effects of full replacement of dietary fishmeal with insect meal from Tenebrio molitor on rainbow trout gut and skin microbiota

Background:Aquaculture must continue to reduce dependence on fishmeal(FM)and fishoil in feeds to ensure sustainable sector growth.Therefore,the use of novel aquaculture feed ingredients is growing.In this regard,insects can represent a new world of sustainable and protein-rich ingredients for farmed fish feeds.Accordingly,we investigated the effects of full replacement of FM with Tenebrio molitor(TM)larvae meal in the diet of rainbow trout(Oncorhynchus mykiss)on fish gut and skin microbiota.Methods:A feeding trial was conducted with 126 trout of about 80 g mean initial weight that were fed for 22 weeks with two isonitrogenous,isolipidic,and isoenergetic extruded experimental diets.Partially defatted TM meal was included in one of the diets to replace 100%(TM 100)of FM,whereas the other diet(TM 0)was without TM.To analyse the microbial communities,the Illumina MiSeq platform for sequencing of 16S rRNA gene and Qiime pipeline were used to identify bacteria in the gut and skin mucosa,and in the diets.Results:The data showed no major effects of full FM substitution with TM meal on bacterial species richness and diversity in both,gut mucosa-and skin mucus-associated microbiome.Skin microbiome was dominated by phylum Proteobacteria and especially by Gammaproteobacteria class that constituted approximately half of the bacterial taxa found.The two dietary fish groups did not display distinctive features,except for a decrease in the relative abundance of Deefgea genus(family Neisseriaceae)in trout fed with insect meal.The metagenomic analysis of the gut mucosa indicated that Tenericutes was the most abundant phylum,regardless of the diet.Specifically,within this phylum,the Mollicutes,mainly represented by Mycoplasmataceae family,were the dominant class.However,we observed only a weak dietary modulation of intestinal bacterial communities.The only changes due to full FM replacement with TM meal were a decreased number of Proteobacteria and a reduced number of taxa assigned to Ruminococcaceae and Neisseriaceae families.Conclusions:The data demonstrated that TM larvae meal is a valid alternative animal protein to replace FM in the aquafeeds.Only slight gut and skin microbiota changes occurred in rainbow trout after total FM replacement with insect meal.The mapping of the trout skin microbiota represents a novel contribution of the present study.Indeed,in contrast to the increasing knowledge on gut microbiota,the skin microbiota of major farmed fish species remains largely unmapped but it deserves thorough consideration.

GFAP expression in the optic nerve and increased Н2S generation in the integration centers of the rainbow trout（Oncorhynchus mykiss） brain after unilateral eye injury

Hydrogen sulfide(H2S)is considered as a protective factor against cardiovascular disorders.However,there are few reports on the effects of H2S in the central nervous system during stress or injury.Previous studies on goldfish have shown that astrocytic response occurs in the damaged and contralateral optic nerves.Glial fibrillary acidic protein(GFAP)concentration in the optic nerves of rainbow trout has not been measured previously.This study further characterized the astrocytic response in the optic nerve and the brain of a rainbow trout(Oncorhynchus mykiss)after unilateral eye injury and estimated the amount of H2S-producing enzyme cystathionineβ-synthase(CBS)in the brain of the rainbow trout.Within 1 week after unilateral eye injury,a protein band corresponding to a molecular weight of 50 kDa was identified in the ipsi-and contralateral optic nerves of the rainbow trout.The concentration of GFAP in the injured optic nerve increased compared to the protein concentration on the contralateral side.The results of a quantitative analysis of GFAP+cell distribution in the contralateral optic nerve showed the largest number of GFAP+cells and fibers in the optic nerve head.In the damaged optic nerve,patterns of GFAP+cell migration and large GFAP+bipolar activated astrocytes were detected at 1 week after unilateral eye injury.The study of H2S-producing system after unilateral eye injury in the rainbow trout was conducted using enzyme-linked immunosorbent assay,western blot analysis,and immunohistochemistry of polyclonal antibodies again st CBS in the integrative centers of the brain:telencephalon,optic tectum,and cerebellum.Enzyme-linked immunosorbent assay results showed a 1.7-fold increase in CBS expression in the rainbow trout brain at 1 week after unilateral eye injury compared with that in intact animals.In the ventricular and subventricular regions of the rainbow trout telencephalon,CBS+radial glia and neuroepithelial cells were identified.After unilateral eye injury,the number of CBS+neuroepithelial cells in the pallial and subpallial periventricular regions of the telencephalon increased.In the optic tectum,unilateral eye injury led to an increase in CBS expression in radial glial cells;simultaneously,the number of CBS+neuroepithelial cells decreased in intact animals.In the cerebellum of the rainbow trout,neuroglial interrelationships were revealed,where H2S was released,apparently,from astrocyte-like cells.The organization of H2S-producing cell complexes suggests that,the amount of glutamate produced in the rainbow trout cerebellum and its reuptake was controlled by astrocyte-like cells,reducing its excitotoxicity.In the dorsal matrix zone and granular eminences of the rainbow trout cerebellum,CBS was expressed in neuroepithelial cells.After unilateral eye injury,the level of CBS activity increased in all parts of the cerebellum.An increase in the number of H2S-producing cells was a response to oxidative stress after unilateral eye injury,and the overproduction of H2S in the cerebellum occurred to neutralize reactive oxygen species,providing the cells of the rainbow trout cerebellum with a protective effect.A structural reorganization in the dorsal matrix zone,associated with the appearance of an additional CBS+apical zone,and a decrease in the enzyme activity in the dorsal matrix zone,was revealed in the zones of constitutive neurogenesis.All experiments were approved by the Commission on Biomedical Ethics,A.V.Zhirmunsky National Scientific Center of Marine Biology(NSCMB),Far Eastern Branch,Russian Academy of Science(FEB RAS)(approval No.1)on July 31,2019.

Comparisons of Salinity Adaptation in Terms of Growth, Body Composition, and Energy Budget in Juveniles of Rainbow and Steelhead Trouts (Oncorhynchus mykiss)

This study examined the effect of different salinities(0, 5, 10, 15, 20, 25 and 30) on the growth performance and energy budget of juveniles of two different ecotypes of Oncorhynchus mykiss, landlocked rainbow trout and anadromous steelhead trout. In the 42 d experiment, fish were cultured in three replicate tanks per salinity treatment(eight fish per tank). At the end of the experiment, the growth of rainbow and steelhead trouts was significantly higher at salinities of 5 and 10, respectively, than at all other salinities. The protein, lipid and energy content of both ecotypes declined with the increase of salinity. Based on their energy budgets, the percentage of energy consumed for growth by rainbow and steelhead trouts were significantly higher at salinities of 5(34.00% ±1.69%) and 10(43.76% ± 1.29%), respectively, than at all other salinities. The percentage of energy consumed for respiration by rainbow and steelhead trouts was lower at salinities of 5(54.90% ± 1.77%) and 10(46.73% ± 0.62%), respectively, than at all other salinities. Our results indicated that the salinity adaptation ability of juvenile steelhead trout was slightly better than that of juvenile rainbow trout, and salinities of 10 and 5, respectively, were most suitable for growth of these two fishes.

Temperature-Dependent Fatty Acid Composition Change of Phospholipid in Steelhead Trout (Oncorhynchus mykiss) Tissues

In this study, the changes of the fatty acid composition of phospholipid in different tissues(muscle, heart, brain and spleen) of steelhead trout(Oncorhynchus mykiss) were analyzed when the water temperature decreased gradually from 16 to 12℃℃, 8℃, 6℃, 4℃, 2 and 1℃℃. Three fish individuals each tank(average weight 70.32 g ± 9.12 g) were collected and used to analysis at each designed temperatures. At normal temperature(16℃), the fatty acid composition of phospholipid of muscle and heart was similar each other. The highest concentration of saturate fatty acids(SFA) was found in the phospholipid of spleen. The brain phospholipid contained higher oleic acid(18:1 n9) than the phospholipid of other tissues at 16℃. When the environmental temperature decreased, the concentration of unsaturated fatty acids of phospholipids in all tissues increased, and accordingly the ratio pf the unsaturated to saturated fatty acids(U/S) and unsaturation index(UI) increased, indicating that steelhead trout can compensate temperature-dependent changes in membrane fluidity by remodeling the fatty acid composition of phospholipids. The changes in the fatty acid composition of phospholipid were tissue-specific. At the early stages of the experiment(16 to 8℃℃), the fatty acid composition of phospholipid changed remarkably in muscle, heart, and spleen. When temperature decreased to less than 8℃, an obvious response of phospholipid fatty acid was observed in all tissues. The change of phospholipid composition of steelhead trout tissues may be affected by both cold stress and starvation when the temperature decreased to 2℃, and the change of phospholipid composition of muscle was very obvious.

Effect of Stocking Density on Water Quality and(Growth, Body Composition and Plasma Cortisol Content) Performance of Pen-Reared Rainbow Trout(Oncorhynchus mykiss)

The goal of the study was to examine the effect of stocking density on the water quality of culture area, as well as the growth, body composition and cortisol content of rainbow trout(Oncorhynchus mykiss). Pen-reared trout were stocked in densities of 40, 60, 80 fish individuals m^(-3)(4.6, 6.6, 8.6 kg m^(-3), SD1, SD2 and SD3 groups, respectively) for 300 days. Compared to the water from SD1 and SD2, that from SD3 exhibited significantly higher NH_4^+-N content and COD(chemical-oxygen-demand), and a significant reduction of dissolved oxygen in day 180(40.6 kg m^(-3)). Stocking density was significantly associated with body weight, standard length, VSI(viscerosomatic index), CF(condition factor) and FC(food coefficient) in group SD3, particularly in day 240 and day 300(45 or 49.3 kg m^(-3)). Increased crude fat and decreased crude protein were displayed in high density group when the density reached to 36 kg m^(-3). As a cumulative effect of density-related stress, VSI, CF, FC, moisture, and crude protein content varied over time in each density group(SD1, SD2, and SD3). In summary, trout exhibited a better growth performance in low density(26.3 kg m^(-3)) than those reared in high densities(36 and 45 kg m^(-3)). The results indicate that rainbow trout(114.44 g ± 6.21 g, 19.69 cm ± 0.31 cm) initially stocked in 6.6 or 8.6 kg m^(-3) should be lightened to less than 36 kg m^(-3) after an intensive rearing for 240 days.

An Effective Method of Prompting Juvenile Rainbow Trout (Oncorhynchus mykiss) to Cope with Heat Stress

In the present study,juvenile rainbow trout(Oncorhynchus mykiss)were acclimated at 5 temperatures.Fish in the control group(C0)were reared at a constant temperature(16℃);trout in four other treatments(A0,A3,A6,and A9)were acclimated to a high temperature(22℃)for 0,3,6,and 9 d,respectively,and then returned to normal temperature(16℃)for 7d.The temperature was then raised to 20℃and the fish were cultured for 40 d.The results showed that the growth rates of A3,A6,and A9 were higher than that of A0 but lower than that of C0.The growth rate of A9 was the highest among the 4 acclimation groups.The activities of serum transaminase and liver antioxidant enzyme significantly increased during acclimation.At the beginning of growth,the activities of enzymes were lower in A3,A6,and A9 with the lowest in A9.In addition,the transcript abundance of heat shock protein(HSP)60 gene in A9 was not significantly different from that of C0 during growth.HSP70 in A9 significantly increased at the beginning and returned to that of C0 at the end.Our findings indicated that pre-acclimation improved the high temperature tolerance with the best effectiveness observed at 22℃for 9 d.A possible mechanism underlining such phenomenon is the improvement of antioxidant defense system.

Effect of micro-algae Schizochytrium sp.supplementation in plant diet on reproduction of female rainbow trout(Oncorhynchus mykiss):maternal programming impact of progeny

Background:The broodstock diet,and in particular the lipid and fatty acid composition of the diet,is known to play a key role in reproductive efficiency and survival of the progeny in fish.A major problem when replacing both fish meal and fish oil by plant sources is the lack of n-3 long chain polyunsaturated fatty acids,such as eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA).To address this problem,we studied the effect of the plant-based diet supplemented with Schizochytrium sp.microalgae,source of DHA,compared to a conventional commercial diet rich in fish meal and fish oil on reproductive performance and egg quality and the consequences on progeny,in female rainbow trout broodstock.Results:The results demonstrated that DHA-rich microalgae supplementation in a plant-based diet allowed for the maintenance of reproductive performance and egg quality comparable to a conventional commercial feed rich in fish meal and fish oil and led to an increased significant fry survival after resorption.Moreover,when females were fed a plant-based diet supplemented with micro-algae,the 4-month-old progenies showed a significant higher growth when they were challenged with a similar diet as broodstock during 1 month.We provide evidence for metabolic programming in which the maternal dietary induced significant protracted effects on lipid metabolism of progeny.Conclusions:The present study demonstrates that supplementation of a plant-based diet with DHA-rich microalgae can be an effective alternative to fish meal and fish oil in rainbow trout broodstock aquafeed.

Influence of Maternal and Larval Immunisation against <i>Lactococcus garviae</i>Infection in Rainbow Trout <i>Oncorhynchus mykiss</i>(Walaum) Lysozyme Activity and IgM Level

This study evaluated efficacy of maternal and larval immunisation against Lactococcus garviae infection and on the lysozyme and immunoglobulin (IgM) levels in rainbow trout Oncorhynchus mykiss (Walaum). Forty-eight-day-old larvae (mean weight 96 mg) originating from injected weekly with letrozole and immunised, only immunised and non-immunised parents were experimentally infected with the L. garvieae, and the mortality rate was recorded daily. Larvae were vaccinated by immersion at 58 days post hatch with live L. garvieae (109 cells/mL) for 15 min. Every third day post larvae vaccination, two larvae from each group were collected for analysis lysozyme (by a method based on the ability of lysozyme to lyse the bacterium Micrococcus lysodeikticus) and IgM (by enzyme-linked immunosorbent assay (ELISA)) parameters. Vaccinated and control larvae were tested for protection against L. garvieae 30 days post larvae immunization when the larvae were 88 days old. Larvae were challenged by bath exposure with live L. garvieae (109 cells/mL) for 2 min and monitored for mortality for at least 10 days following challenge. The challenge experiment with L. garvieae showed a significant reduction in larvae from immunised (54.44% ± 0.64%) and injected weekly with letrozole and immunised fish (52.96% ± 0.97%) compared to larvae from control fish (62.96% ± 2.22%). Vaccinated larvae originated from injected weekly with letrozole and immunised parents showed significantly higher lysozyme activity compared to other fish groups. Vaccinated larvae showed significantly less mortality compared to controls. The relative percent survival (RPS) values of larvae from only immunised, injected weekly with letrozole and immunised and non-immunised parents vaccinated with L. garvieae were 67.36% ± 0.9%, 68.05% ± 0.66% and 48.27% ± 2.79% respectively. The results indicate that the effect of maternal immunization rainbow trout against L. garvieae infection by eliciting the immune responses as indicated by an increase in the IgM level and lysozyme activity.

Rearing Performance of Juvenile Brown Trout (<i>Salmo trutta</i>) Subjected to Exercise and Dietary Bioprocessed Soybean Meal

This 121-day experiment evaluated the rearing performance of brown trout Salmo trutta fed one of two isonitrogenous and isocaloric diets and reared at velocities of either 2.8 or 16.1 cm/s. Fishmeal was the primary protein source for the reference diet, and bioprocessed soybean meal replaced approximately 67% of the fishmeal in the experimental diet. At the end of the experiment, there were no significant differences in gain, percent gain, feed conversion rates, or specific growth rates between the dietary treatments. There were also no significant differences in intestinal morphology, splenosomatic, hepatosomatic, and viscerosomatic indices related to diet composition. However, gain, percent gain, feed fed, and specific growth rate were all significantly greater in brown trout reared at the higher velocity. No significant differences in any of the other variables measured were observed between the velocity treatments. There were no significant interactions between diet and velocity in any of the variables. Based on the results of this study, bioprocessed soybean meal can replace at least 67% of the fishmeal in brown trout diets, regardless of the rearing velocities used in this study. However, higher rearing velocities are recommended to maximize juvenile brown trout growth rates.

Brown Trout Spawn Timing, Redd Locations, and Stream Characteristics in Spearfish Creek within Spearfish, South Dakota, USA

This study documented brown trout (Salmo trutta) spawning locations, redd construction timing, and associated environmental variables in an 850-m long mainstem section and a 400-m long diversion channel of Spearfish Creek within the city limits of Spearfish, South Dakota, USA in 2019. The first redds were observed on October 15, with no new redds observed after November 12. Redd construction peaked during the first week of November, when 23 redds were observed in the mainstem section and 50 in the diversion channel. Substrate size was significantly smaller, water temperatures significantly higher, and water velocities significantly greater in redd versus non-redd locations in both the mainstem reach and the diversion channel (P &#730;C), but significant, increase in water temperature from the rest of the channel locations. This is the first study to document redd locations in Spearfish Creek and will provide a baseline to evaluate future spawning activity, particularly as it may be affected by likely future anthropogenic changes potentially affecting the stream environment.

Trout Redd Locations in Two Streams in the Black Hills, South Dakota, USA

This study examined the spatial and temporal characteristics of brook trout Salvelinus fontinalis and brown trout Salmo trutta redds in two sites from two creeks in the Black Hills of South Dakota, USA. Spawning began in both streams in early October and continued through mid-November. Significant spatial clustering was only observed on both Rapid Creek sites, where-as random redd development was observed in both of the sites on Box Elder Creek. Based on visual observations, brown trout redds were more abundant in Rapid Creek, where-as brook trout redds were more abundant in Box Elder Creek. Differences in redd clustering could be due to species-specific, geological, or hydrological differences between the

Novel Surgical Technique for Acoustic Transmitter Insertion in Rainbow Trout Reduces the Need for Surgical Training

The implantation of acoustic transmitters into the peritoneal cavity of fish is typically performed by experienced surgeons. This study compared the effectiveness of an experienced and inexperienced surgeon performing two different types of transmitter insertion techniques on rainbow trout (Oncorhynchus mykiss). The methods used were either a traditional sutured ventral incision or a novel unsutured lateral incision. There was no significant difference in surgical duration, tag retention, or fish survival between the experienced and naïve surgeon. The time to complete surgical wound closure was not significantly different between the fish operated on by an experienced or naïve surgeon, and surgeon experience had no significant effect on the duration of inflammation. However, there were significant differences between the two surgical techniques, regardless of surgeon experience. The ventral incision with sutures method took approximately three times longer to complete than the lateral incision-only method. However, complete wound closure was significantly faster in the sutured ventral incision treatment compared to the unsutured lateral treatment. Post-surgery inflammation was over seven times longer in the fish with sutures compared to those only receiving a lateral incision. Tag retention was not significantly different between the two surgical methods. The results of this study indicate that the unsutured lateral surgical technique used in this experiment can be completed with minimal training and surgical experience in contrast to the standard technique requiring sutures. These results also provide additional support to the use of sutureless surgical techniques for acoustic transmitter implantation.

Effect of Temperature on the Carbon, Nitrogen, and Phosphorus Nutrient Budgets of Steelhead Trout (Oncorhynchus mykiss) with Different Sizes

This study was performed to evaluate the effect of temperature on the carbon(C),nitrogen(N),and phosphorus(P)nu-trient budgets of adult steelhead trout(Oncorhynchus mykiss)with different body sizes.A complete two-factor experiment was con-ducted at four temperatures,i.e.,9(T9),13(T13),16(T1℃℃℃6),and 19(T19);and three body sizes,℃i.e.,0.65 kg±0.02 kg(S1),1.22 kg±0.06 kg(S2),and 2.05 kg±0.09 kg(S3).The following properties of steelhead trout were determined:C,N,and P nutrient budgets;feed intake rate;fecal production rate;oxygen consumption rate;ammonia excretion rate;phosphorus excretion rate;scope of the growth of C,N,and P;and absorption efficiency of C,N,and P.Results showed no significant interaction between temperature and body size in terms of the nutrient budgets of steelhead trout.However,temperature and body size played important separate roles in the nutrient budgets except for the absorption efficiency of nitrogen.The feed intake rate,fecal production rate,ammonia excretion rate,phosphorus excretion rate,and scope of the growth of C,N,and P were the highest in the T16 treatments.The absorption effi-ciency of C and P decreased as temperature increased.Nonlinear multiple regression results indicated that 15 was the approximate℃optimal temperature for the feeding and growth of steelhead trout.The feed intake rate,fecal production rate,oxygen consumption rate,ammonia excretion rate,phosphorus excretion rate,and scope of the growth of C,N,and P per unit of the body weight of fish decreased as body size increased.The absorption efficiency of C increased as body weight increased,and the absorption efficiencies of P in the S2 and S3 treatments were significantly higher than those in the S1 treatment.During the culture of steelhead trout,the daily ratio should be adjusted with changes in the temperature and body size of fish.Furthermore,managers should focus on the risk of hypoxia at high water temperatures.

Fatty Acid Composition and Digestive Enzyme Activities of Rainbow Trout in Response to Dietary Docosahexaenoic Acid(DHA)and Eicosapentaenoic Acid(EPA)During Salinity Acclimation

This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)on the fatty acid composition and digestive enzyme activities of rainbow trout(Oncorhynchus mykiss)during salinity acclimation.Rainbow trout with an average initial weight of 90.61 g±9.25 g were fed diets with the quantities of DHA and EPA equaling to 0.54%,0.95%,1.40%and 1.79%(abbreviated as DE-0.54,DE-0.95,DE-1.40,and DE-1.79,respectively)for eight weeks,after which the gastric and intestinal fatty acids composition were analyzed.Subsequently,the fish underwent salinity acclimation.On days 1,4,7,and 14 after the freshwater was replaced by seawater and at the end of the 8-week period,gastric and intestinal digestive enzyme activities were determined.The results showed that the gastric and intestinal DHA and EPA contents of the fish were positively correlated to their dietary DHA and EPA levels.Low dietary DHA and EPA levels inhibited the protease activity of rainbow trout.Fish in the DE-0.54 group increased the lipase activity to enhance the utilization of lipids maybe due to the inadequate essential fatty acids for fish in this group.Hence,rainbow trout in the DE-0.54 group failed to maintain suitable activities of digestive enzymes after salinity acclimation.Therefore,a diet with minimum 0.95%DHA and EPA levels is necessary for rainbow trout during salinity acclimation.

Juvenile rainbow trout responses to diets containing distillers dried grain with solubles, phytase, and amino acid supplements

Distillers dried grain with solubles (DDGS) was evaluated in juvenile Shasta-strain rainbow trout Oncorhynchus mykiss diets during a 36-day feeding trial. Two experimental diets containing either 10% or 20% DDGS with supplemented amino acids (lysine, methionine, isoleucine, and his-tidine) and phytase were compared to a fish meal-only control diet. Tanks of trout receiving diets containing either concentration of DDGS weighed significantly less at the end of the trial and had significantly poorer feed conversion ratios than tanks of fish being fed the fish meal- only control. There was no significant difference in individual fish length, weight, condition factor, or any fish health measurements among diet treatments. Both the hepatosomatic index and viscerosomatic index were significantly less in the fish fed 10% DDGS than those fed the control diet. Body fat was significantly greater in the fish receiving 20% DDGS compared to fish fed either of the other two diets. Fillet composition, as determined by crude protein, crude lipid, ash, and water, was not significantly different among fish reared on any of the diets. There was also no significant difference in estimated protein digestibility coefficients among fish receiving any of the diets. The results suggest that DDGS, even if supplemented with essential amino acids and phytase, will lead to decreased juvenile rainbow trout growth at dietary concentrations of at 10% or greater.

The Effects of Letrozole in Transfer of Maternal Immunity against Lactococcosis to Eggs and Larvae in Rainbow Trout (<i>Oncorhynchus mykiss</i>, Walbaum)

This study evaluated transfer of maternal lysozyme and immunoglobulin (IgM) against Lactococcus garviea, the causative agent of lactococcosis to eggs and larvae in rainbow trout. Changes in circulating lysozyme and IgM during development of eggs and larvae were measured by a method based on the ability of lysozyme to lyse the bacterium Micrococcus lysodeikticus and enzyme-linked immunosorbent assay (ELISA) respectively. For doing this, twelve broodstocks were injected weekly with 2.5 mg&middotkg-1 letrozole (an endocrine disrupter component) two months before spawning season and vaccinated intraperitoneally (i.p) with a bacterin (inactivated L. garviae) one month before spawning. Twelve broodstocks for vaccination and twelve female rainbow trouts as control group were also immiunised (i.p) with the bacterin and injected (i.p) with PBS respectively. Results showed that at day 8 after hatching, lysozyme and IgM levels during pre-larval stages decreased gradually, as yolks were absorbed. Lysozyme and IgM levels were significantly higher in the letrozole injected immiunised parents 30 days after immunisation as well as their larvae compared to the control group (p L. garviae) (one month before spawning) in maternal transfer of lysozyme and IgM levels to eggs and larvae.