Growth Of Trout Research Articles

Calcifediol is a safe and effective metabolite for raising vitamin D status and improving growth and feed conversion in rainbow trout

The vitamin D endocrine system is required for the transcriptional regulation of a myriad of vertebrate genes including those involved in bone health, growth, nutrient metabolism and immunity. The requirements of salmonids for vitamin D are amongst the highest for any aquaculture species. With nuances, the metabolism of the pre-vitamin cholecalciferol (D3) via calcifediol (25-OH-D3), required to produce the physiologically active hormone calcitriol (1,25-OH-D3) is conserved in fish. The composition of modern aquafeeds, growth in seawater and production challenges, such as disease, may result in the suboptimal biochemical activation of vitamin D hormone in fish.A 91-day experimental feeding trial was used to test the safety and efficacy of calcifediol for the supply of vitamin D to rainbow trout with an initial body weight of 57.6 g. A practical diet containing cholecalciferol within recommended levels (5240 IU) was supplemented with either 69.8, 687 or 6854 μg/kg calcifediol. The efficacy of calcifediol was determined by the assessment of zootechnical performance and the appearance of vitamin D metabolites in the blood. The safety of the dietary interventions was assessed from generic health indices, examination of gross pathologies, hematology, and blood chemistry.Test fish increased body weight at least 5.6-fold to 323.5 g over the experimental feeding period. The supplementation of 687 or 6854 μg/kg calcifediol resulted in significant improvements in growth rate and feed conversion (FCR). Whilst not detectable in control fish, calcifediol increased linearly according to dietary levels in the blood and to a lesser extent in the white muscle. The increases of calcifediol in the blood were accompanied by saturable increases of circulating active vitamin D. At the end of the 91-day feeding period, survival was 100%, no gross pathologies relating to the diets were observed, and health indices, hematology, and blood chemistry, including calcium and phosphorus, were not significantly altered.The supplementation of calcifediol to practical diets containing recommended levels of cholecalciferol improves zootechnical performance and ensures that maximal levels of active vitamin D are present in the blood to meet physiological demands. With a lack of significant effects on health indices, hematology, and blood chemistry, including calcium and phosphorus, the tested high doses of calcifediol are concluded to be safe for salmonids.

Influence of daily rhythmic light spectra and intensity changes on the growth and physiological status of juvenile steelhead trout (Oncorhynchus mykiss)

The objective of this study was to investigate the effects of different rhythmic light spectra and intensities on growth performance and physiological and biochemical parameters of juvenile steelhead trout (Oncorhynchus mykiss). Seven treatments were randomly assigned to 21 tanks using a single-flow system for 13 weeks (N = 3), namely blue–purple–red light (BPR), red–purple–blue light (RPB), blue light (VB), and red light (VR). These light treatments alternated at 300, 900, and 1,200 lx, as well as a constant 900 lx of blue light (CB), red light (CR), and white light (CW). Results showed that the highest feed intake (FI), final body weight (FBW), and specific growth rate (SGR) were observed in the BPR treatment, which were significantly higher than those in the CW, CR, CB, and VB treatments. BPR treatment resulted in higher levels of insulin-like growth factor 1 (IGF-1), free triiodothyronine (FT3) and thyroxine (FT4), superoxide dismutase (SOD), and catalase (CAT), and total antioxidant capacity (T-AOC) activities were found. Fish exposed to BPR showed significantly enhanced lipase (LPS) and trypsin (Trp) activity in the stomach and gut tissues which promoted digestion. Trout exposed to a constant light spectra and intensity environment showed decreased activities of antioxidant and gastrointestinal digestive enzymes. Our results indicate the positive influence of BPR light conditions on the growth, stress response, digestion, and metabolism of juvenile steelhead trout, which is likely related to its similarity to the light rhythm in natural water environments, and can be used to improve growth and physiological status in the aquaculture trout.

Study of the effectiveness of using the antioxidant astaxanthin in the composition of feeds for valuable aquaculture objects

The “Enzymsporin” is one of these preparations, which is a probiotic feed additive for optimizing digestion processes, increasing the productivity and safety of fish. Second year rainbow trout grown in cages at the cooling pond of the Smolensk NPP were used as the objects of study. Specialized domestic feed “Trout growth 44/23” was used as the main diet (MD) for feeding the fish. The main diet with the addition of 0,5 g of “Enzymsporin” per 1 kg of feed was used as an experimental variation. An increase of the body girth index (66,7% versus 61,9% at p < 0,05) in the experimental group of the trout was founded. A tendency to increase the coefficient of fatness and the relative length of the stomach and intestines were noted, but the difference was not significant. The relative weight of fish without chyme (gastric and intestinal contents) in the control (without the use of the preparation) was significantly higher by 2,6% (p < 0,05), that indicates its lower nutritional activity. Significant differences in the content of moisture and minerals in the experimental and control groups won’t founded, but the fat content in the body of fish when using a probiotic was 1,5% higher then in control. Therefore, trout meat in this variant was more nutritious. An improvement in rearing results was achieved in the experimental group, especially the average daily growth gain increased by 6,8%, survival — by 6,7%, standing crop of the fish per unit area in a body water — by 9,2%, with a reduction of feed conversion ratio by 10,2%. The trout meat of the experimental group after heat treatment had a more pleasant taste, juiciness and tender texture. The average score of its overall average degustation evaluation significantly exceeded the control (8,0 versus 7,5 at p < 0,05). An economic effect in the experimental variant of feeding was 98257,5 rubles for the 80 m2 cage.

Changes in Juvenile Rainbow Trout (Oncorhynchus mykiss) Growth Performance, Digestive Enzyme Activity, Hematological Profile and Serum Biochemical Markers After Dietary Administration of γ-irradiated Cinnamon (Cinnamomum verum) Ethanolic Extract

The aim of this study was to investigate the effects of dietary supplementation of γ-irradiated cinnamon ethanolic extract on the growth performance, digestive enzymes, lysozyme activity level and hematological factors in the juvenile rainbow trout. The fish were divided into five groups, including control group and four experimental groups (received diets enriched with 10 g/kg of non-irradiated or irradiated CEE at the radiation doses of 10, 20 and 40 KGy. At the end of the feeding trial (60` days), 10 fish were sampled from each tank after 12 h of feed deprivation. The results showed that the fish dietary irradiated CEE at doses of 10 KGy and 20 KGy had significantly higher final weights, weight gain, specific growth rates and growth hormone levels, and lower feed conversion ratios compared to the other groups (P≤0.05). The blood glucose level significantly lowered in the fish group fed with dietary γ-irradiated CEE, and increased the activity of lysozyme activity level and digestive enzymes compared to the control group (P≤0.05). In conclusion, dietary supplementation of γ-irradiated CEE at a dose of 10 KGy can enhance the positive effects of cinnamon extract and improve the growth performance, digestion and lysozyme activity in juvenile rainbow trout.

Stress response of juvenile rainbow trout reared at three densities

High rearing densities (kg of fish per rearing unit volume) can impact fish health and growth. This study evaluated the stress levels (as indicated by blood glucose) and growth of juvenile Shasta strain rainbow trout (Oncorhynchus mykiss) reared at three densities in 1.8-m diameter circular tanks for 111 days. Initial and final rearing densities for each treatment were: low (4.48 and 47.56 kg/m3), medium (5.96 and 60.60 kg/m3), and high (7.49 and 72.42 kg/m3). Throughout the experiment, blood glucose levels from individual fish were not significantly different among the three density treatments. At the end of the experiment, total tank weights and gain were significantly greater in the high-density treatment than the medium-density treatment, which in turn was significantly greater than the low-density treatment. However, percent gain was significantly greater in the low-density treatment. Feed conversion ratio was significantly lower in the high-density treatment compared to the low-density treatment, with the ratio in the medium-density treatment similar to the other two treatments. The results of this study indicate that higher rearing densities do not negatively impact juvenile Shasta strain rainbow trout stress or hatchery rearing performance.

GROWTH OF RAINBOW TROUT FINGERLING AT DIFFERENT LEVELS AND RATIOS OF LYSINE AND ARGININE IN COMBINED FEED

The article highlights the results of research on the influence of different levels and ratios of the amino acids lysine and arginine in compound feed and the growth and feed consumption of rainbow trout fingerling. For research, 6 groups were formed, 1 control and 5 experimental, each with 500 samples. Combined feed, which differed only in the content of lysine and arginine, was distributed 4 times a day at the rate of 3% of the weight of the fish. In the main period lasting 40 days, the level of arginine changed from 2.00 to 3.60% in compound feed against the background of 2 levels of lysine of 3.00 (groups 1–3) and 3.20% (groups 4–6). If the content of lysine in compound feed is taken as 100%, then the content of arginine varied from 62.50 to 120.00%. We determined the mass of trout, calculated absolute, average daily and relative growth, feed consumption per 1 kg of growth. With an increase in the level of arginine from 2.00 to 3.60% against the background of an effective level of lysine - 3.00% in the combined feed of rainbow trout fingerling, the weight of fish increases by 2.47-2.71% (р˂0.05), absolute, average daily and relative increases, respectively, by 3.04–3.24% (р˂0.05); 3.85% (р˂0.05) and 14.52–15.62 (р˂0.05)%, feed costs per 1 kg of growth decreased by 2.91–3.02%. An increase in the level of arginine from 2.00 to 3.60% against the background of an increased level of lysine - 3.20% in the combined feed of rainbow trout this summer led to an increase in the weight of fish by 2.71-4.30% (р˂0.001), an absolute increase - by 3.14–5.14% (р˂0.001), average daily growth – by 3.85–7.69% (р˂0.001), relative growth – by 12.69–26.49 (р˂0.001) %, combined feed costs per 1 kg of growth decreased by 3.02–4.85%. An increase in the level of lysine in the combined feed from 3.00 to 3.20% against the background of the basic level of arginine - 2.00% in the combined feed of trout this summer probably did not affect the weight and intensity of fish growth. In our studies, no antagonism phenomena between lysine and arginine were established. A one-sided increase in the content of lysine in compound feed did not lead to a decrease in the growth of rainbow trout fingerling. The high rate of growth of rainbow trout this summer was obtained with a ratio between lysine and arginine in compound feed of 1.05–1.20:1. The most effective ratio was 1.13:1.

Effect of Dietary Origanum onites on Growth, Non Specific Immunity and Resistance against Yersinia ruckeri of Rainbow Trout ( Oncorhynchus mykiss).

Natural substances has been identified to maintain health and improve growth performance in the aquaculture. The effect of Origanum onites on growth and immune response of rainbow trout was investigated. Experimental groups (A and B) of 70 fish were separated into 10 different treatments. A groups were fed with dietary administration of O. onites essential oil (0.5 mL kg-1 and 3.0 mL kg-1) and crude powder (1.0 g kg-1 and 10.0 g kg-1) for a period of 8 weeks. Other groups (B) were vaccinated against Yersinia ruckeri at the beginning of experiment and then fed the same diets described above. Results showed that feed conversion ratio in fish fed a combination of O. onites and vaccine was statistically better than the control. NBT-positive cells, phagocytic activity, serum lysozyme activity and immunoglobulin M level were stimulated in both non vaccinated and vaccinated fish (p<0.05). Cumulative mortality in fish fed O. onites was lower than controls following challenge with Y. ruckeri. No mortality was observed in vaccinated fish fed with 0.5 mL kg-1 of O. onites. These results indicated that dietary administration of O. onites could act as an enhanced non specific immune response, growth performance and resistance to Y. ruckeri.

Factors Influencing Early Growth of Juvenile Tiger Trout Stocked into Subalpine Lakes as Biocontrol and to Enhance Recreational Angling

Tiger trout (Salmo trutta × Salvelinus fontinalis) are sterile hybrids often stocked as a biocontrol agent for undesirable fishes and to enhance recreational angling. Yet, how different ecological processes affect their post-stocking performance remain poorly understood. Rapid growth early in life can foster rapid transitions to piscivory, and improve survival. Identifying factors that benefit early growth can help managers optimize tiger trout stocking for meeting multiple fisheries management objectives. Here, we characterized the trophic ecology and growth of tiger trout stocked at varying densities into seven lentic subalpine systems in Colorado, USA. Study systems supported different species of undesirable fish (e.g., minnows or suckers). We used stable isotopes of carbon and nitrogen to quantify trophic relationships among tiger trout and other fishes in each system. We then evaluated several system-specific attributes as predictors for the size of tiger trout at age-1 using a Random Forest model. Stable isotopes demonstrated the potential for resource competition among tiger trout and other fishes, but potential varied by system. Indices of resource competition ranked highest in the Random Forest model, but the stocking density of tiger trout was most important, suggesting that intraspecific competition outweighed interspecific competition in driving early growth. These processes were mediated by system productivity. Thus, stocking density in combination with the realized carrying capacities of systems should be considered when making management decisions for tiger trout.

Protective Effect of [Cu(NN1)2](ClO4) Complex in Rainbow Trout Challenged against Flavobacterium psychrophilum.

Previously, we reported an in vitro evaluation regarding antibacterial effects against F. psychrophilum by a new Cu (I) complex, [Cu(NN1)2](ClO4). This study presents the results of an in vivo evaluation of [Cu(NN1)2](ClO4) added as a dietary supplement against F. psychrophilum in rainbow trout. The results showed that the administration of [Cu(NN1)2](ClO4) at 29 and 58 µg/g of fish for 15 days does not affect the growth of rainbow trout. On the other hand, the amount of copper present in the liver, intestine, and muscle of rainbow trout was determined. The results showed that the amount of copper in the liver, when compared between treated fish and control fish, does not change. While, in the intestine, an increase in the fish fed at 58 µg/g of fish was observed. In muscle, a slight decrease at 29 µg/g was obtained. Additionally, copper concentrations in the pond water after 15 days of feeding with the [Cu(NN1)2](ClO4) complex showed the highest levels of copper. Finally, the effect of the administration of [Cu(NN1)2](ClO4) for 15 days at 58 µg/g of fish was evaluated against F. psychrophilum, where a 75% survival was obtained during 20 days of challenge.

Growth, Health and Fillet Quality of Rainbow Trout (Oncorhynchus mykiss) Fed Directly with Black Soldier Fly (Hermetia illucens) Prepupae

Black soldier fly (BSF; Hermetia illucens) has received growing attention as an alternative sustainable ingredient for aquafeeds. This study aimed to investigate the effects of direct BSF feeding on growth, health, and filet quality of rainbow trout. Fish were fed with dried black soldier fly (BSF) prepupae for one, two, or three meals a day. After 90 days of feeding, a substantial reduction in growth was found in dried BSF fed groups as daily dried BSF meal increased. Rejection and reduction in feed intake were only observed in the fish group that was fed with dried BSF 3 times a day. Amino acid content of BSF prepupae was significantly higher than that of commercial diet and some of the fatty acid contents were similar toor higher than commercial diet. When fish were fed with dried BSF 2 or 3 times a day, chitin accumulated in the fish's gut, causing constipation and leading to a decreased or rejected feed intake. A substantial decreasing trend was detected in arginine, histidine, and threonine with the increase in the number of dried BSF meals, while isoleucine, leucine, tryptophan, and alanine levels were considerably increased. Inclusion of one dried BSF meal in a daily feeding resulted in improvements in fish PUFAn-3, PUFAn-6, and DPA fatty acid levels.

Drought-related changes in water quality surpass effects of experimental flows on trout growth downstream of Lake Powell reservoir

Flows released from reservoirs are often modified to mitigate the negative ecosystem effects of dams. We estimated the effects of two experimental flows, fall-timed floods and elimination of sub-daily variation in flows on weekends, on growth rates of rainbow trout ( Oncorhynchus mykiss) in the Colorado River downstream from Glen Canyon Dam. Experimental flow effects were compared to effects of water temperature, phosphorous concentration, solar insolation, and competition, by fitting mixed effect von Bertalanffy models to ∼ 10 000 observations of growth from mark-recapture between 2012 and 2021. There was strong support for models predicting faster growth during intervals with higher solar insolation, and lower water temperature and competition for prey. Effects of phosphorus and experimental flows were small and uncertain. Drought-related increases in dam release temperatures during summer and fall were predicted to result in severe weight loss for larger trout and could eventually threaten the viability of the population and the fishery it supports. The effects of water temperature and competition on fish growth substantially exceeded the effects of controlled floods and steadier flows.

Identifying mechanisms underlying individual body size increases in a changing, highly seasonal environment: The growing trout of West brook.

As air temperature increases, it has been suggested that smaller individual body size may be a general response to climate warming. However, for ectotherms inhabiting cold, highly seasonal environments, warming temperatures may increase the scope for growth and result in larger body size. In a long-term study of individual brook trout Salvelinus fontinalis and brown trout Salmo trutta inhabiting a small stream network, individual lengths increased over the course of 15 years. As size-selective gains and losses to the population acted to reduce body sizes and mean body size at first tagging in the autumn (<60 mm) were not observed to change substantially over time, the increase in body size was best explained by higher individual growth rates. For brook trout, increasing water temperatures during the spring (when both trout species accomplish most of their total annual growth) was the primary driver of growth rate for juvenile fish and the environmental factor which best explained increases in individual body size over time. For brown trout, by contrast, reduction in and subsequent elimination of juvenile Atlantic salmon Salmo salar midway through the study period explained most of the increases in juvenile growth and body size. In addition to these major trends, a considerable amount of interannual variation in trout growth and body size was explained by other abiotic (stream flow) and biotic (population density) factors with the direction and magnitude of these effects differing by season, age-class and species. For example, stream flow was the dominant growth rate driver for adult fish with strong positive effects in the summer and autumn, but flow variation could not explain increases in body size as we observed no trend in flow. Overall, our work supports the general contention that for high-latitude ectotherms, increasing spring temperatures associated with a warming climate can result in increased growth and individual body size (up to a point), but context-dependent change in other factors can substantially contribute to both interannual variation and longer-term effects.

Fish feeds supplemented with calcium-based buffering minerals decrease stomach acidity, increase the blood alkaline tide and cost more to digest

Predatory fish in the wild consume whole prey including hard skeletal parts like shell and bone. Shell and bone are made up of the buffering minerals calcium carbonate (CaCO3) and calcium phosphate (Ca3(PO4)2). These minerals resist changes in pH, meaning they could have physiological consequences for gastric acidity, digestion and metabolism in fish. Using isocaloric diets supplemented with either CaCO3, Ca3(PO4)2 or CaCl2 as non-buffering control, we investigated the impacts of dietary buffering on the energetic cost of digestion (i.e. specific dynamic action or SDA), gastric pH, the postprandial blood alkalosis (the “alkaline tide”) and growth in juvenile rainbow trout (Oncorhynchus mykiss). Increases in dietary buffering were significantly associated with increased stomach chyme pH, postprandial blood HCO3−, net base excretion, the total SDA and peak SDA but did not influence growth efficiency in a 21 day trial. This result shows that aspects of a meal that have no nutritional value can influence the physiological and energetic costs associated with digestion in fish, but that a reduction in the SDA will not always lead to improvements in growth efficiency. We discuss the broader implications of these findings for the gastrointestinal physiology of fishes, trade-offs in prey choice in the wild, anthropogenic warming and feed formulation in aquaculture.

Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows

AbstractSub‐daily fluctuations in streamflow may have adverse effects on the biota downstream of dams in hydropeaking‐regulated rivers. Although the stranding of salmonid fry is one documented effect of hydropeaking, little is known about the species‐specific behavioural and subsequent growth effects of sub‐daily flow fluctuations. We investigated the effects of sub‐daily flow fluctuation on growth, mortality and behaviour of sympatric Atlantic salmon (Salmo salar) and brown trout (S. trutta) fry (29–34 mm) in a laboratory experiment. The fluctuating flow treatment negatively affected growth and increased mortality for trout but not for salmon. The level of aggressive behaviour was similar in the fluctuating‐ and stable‐flow treatments. Within the fluctuating flow treatment, there was a trend that more fishes were visibly active above the substrate during low than high flow. These findings suggest that hydropeaking‐induced flow fluctuations may affect fry of different salmonid species in different ways and that brown trout fry may be more vulnerable to hydropeaking effects than Atlantic salmon fry. It can therefore be important to consider the possibility of divergent reactions by different fish species under hydropeaking situations and to incorporate species‐specific strategies to conserve culturally and economically relevant riverine fish species.

Photoperiod-independent diurnal feeding improved the growth and feed utilization of juvenile rainbow trout (Oncorhynchus mykiss) by inducing food anticipatory activity

A three-month culture experiment was designed to assess the effects of photoperiod and feeding regime on growth, feed utilization, and food anticipatory activity (FAA) of juvenile rainbow trout. The experiment included two photoperiods: 24L:0D (LL) and 12L:12D (LD); three feeding regimes: random feeding (R), mid-dark stage feeding (D), and mid-light stage feeding (L). A total of six treatment groups (R-LL, D-LL, L-LL, R-LD, D-LD, L-LD) were defined. The experimental results showed that the growth and feed utilization of the scheduled feeding groups (D and L groups) were significantly higher than those of the R group under both photoperiods, and there was no statistical difference between the D and L groups. A typical FAA was observed in the L group, independent of the photoperiod. Also, the digestive enzyme activity of the L group was synchronized by the feeding time under both photoperiods. There were rhythms in serum levels of glucose (GLU), triglyceride (TG), and total-cholesterol (T-CHO) in the D and L groups. Serum GLU also had a rhythm in the R group, but the peaks occurred at the feeding point (LL group) or after the feeding point (LD group), reflecting a possible passive rise in GLU after feeding. Serum cortisol was higher in the R group than in the scheduled feeding group, indicating that random feeding caused stress to juvenile rainbow trout. Serum insulin levels were found to increase before feeding in all three feeding regimes, probably reflecting the anticipation of food induced by the last meal. Serum melatonin levels were suppressed by the LL group. Serum 5-HT levels were synchronized by meal time in the R and L groups. Finally, rhythms of appetite-related genes were observed under all three feeding regimes, and more genes were rhythmic under LL, suggesting that food can strongly synchronize the feeding rhythm of juvenile rainbow trout when lacking light zeitgeber. In summary, this study concluded that diurnal feeding (L group) independent of photoperiod induced typical FAA in juvenile rainbow trout and that the LD (12L:12D) photoperiod and L (mid-light phase) feeding were recommended in the juvenile rainbow trout aquaculture.

Contemporary Growth and Survival of Stocked and Wild Lake Trout in Lake Champlain Evaluated Using Maxillary Age Estimates

AbstractThe population of Lake Trout Salvelinus namaycush in Lake Champlain has been sustained by stocking since 1973, but natural recruitment of wild fish has been observed since 2012. By 2020, continued recruitment and maturation of wild year‐classes indicated that updated population parameters were needed to assess and adjust management practices. Age estimation from historical methods (fin clips and scales) was undependable due to crowding of annuli in older fish and the inability to verify uncertain age estimates using a 5‐year fin clip rotation for older fish. We used maxillary bones to obtain precise and accurate age estimates for adult wild and stocked fish. In combination with preadult ages derived from fin clips and length–frequency analysis, we estimated the contemporary survival and growth of juvenile (age 2–3), early‐adult (age 3–4), and adult (age 5+) Lake Trout in Lake Champlain. The precision and accuracy of our maxillary age estimates were greater than or comparable to the precision and accuracy of otolith and maxillary age estimates of Lake Trout populations in the Great Lakes. Estimates of Lake Trout growth suggested that stocked and wild fish grew at different rates, with stocked fish having an early size advantage but ultimately reaching a similar maximum size. There were no significant differences in length–weight relationships between stocked and wild fish. Estimates of adult survival were slightly greater than range‐wide averages and well above recent estimates for stocked populations in the Great Lakes. Juvenile and early‐adult survival estimates were similar to each other and both far lower than adult estimates. Stocked and wild fish had similar survival rates in all age‐classes. Ultimately, the use of maxillary bones allowed us to make better estimates of contemporary population parameters necessary for informing management decisions.

Effects of white mustard (Sinapis alba) oil on growth performance, immune response, blood parameters, digestive and antioxidant enzyme activities in rainbow trout (Oncorhynchusmykiss)

A study was conducted to evaluate the effects of dietary supplementation of white mustard (Sinapis alba) oil (WMO) on growth performance, immune responses, digestive and antioxidant enzyme activities in juvenile rainbow trout (Oncorhynchus mykiss). For this purpose, fish (initial weight: 25.77 ± 0.13 g) were divided into four experimental groups in triplicate and fed ad libitum twice a day with diets containing WMO at 0 (control), 0.5, 1, and 1.5% of diet for 9 weeks. Three fish from each tank (n:9 per treatment) were sampled on 21st, 42nd, and 63rd days for further analyses. At the end of the feeding period, fish were challenged with Aeromonas hydrophila and Yersinia ruckeri in two separate experimental setups. Results showed that final weight, weight gain, and specific growth rate were significantly increased in all experimental groups compared to the control. Feed conversion ratio was similar among treatments. Respiratory burst and potential killing activity decreased in all experimental groups compared to the control (P < 0.05). Lysozyme and myeloperoxidase activities were elevated in all experimental groups at the end of the experiment compared to the control (P < 0.05). Cytokine gene expressions in the head kidney and intestine were elevated in all experimental groups compared to that of the control in general (P < 0.05). Hematological responses of the experimental fish groups were similar to that of the control (P > 0.05). Pepsin and trypsin levels decreased in all experimental groups (P < 0.05). In terms of antioxidant enzyme activities, significant improvement in liver superoxide dismutase, catalase, and glutathione s-transferase activities in all treatment groups were determined (P < 0.05). In addition, a significant decline in liver lipid peroxidation levels was recorded in all treated groups at all sampling times compared to the control (P < 0.05). At the end of this feeding trial, no significant differences (P > 0.05) were observed in survival against A. hydrophila among experimental groups compared to the control (P > 0.05). However, increased survival against Y. ruckeri was determined in experimental fish groups (P < 0.05). This study suggests that white mustard oil had a favorable effect on the overall health and growth of rainbow trout.

Investigation of somatic and gonadal growth of female rainbow trout (Oncorhynchus mykiss) reared in cage in the Caspian Sea

Investigation of somatic and gonadal growth of female rainbow trout (Oncorhynchus mykiss) reared in cage in the Caspian Sea

Environmental estrogens inhibit insulin-like growth factor (IGF) receptor mRNA expression, IGF binding, and IGF signaling ex vivo in rainbow trout (Oncorhynchus mykiss)

In this study, we used juvenile rainbow trout to examine the direct effects of selected environmental estrogens (EE), specifically, 17 β-estradiol (E2), β-sitosterol (βS), and 4-n-nonylphenol (NP), on target tissue sensitivity to insulin-like growth factor (IGF) as assessed by expression of IGF receptor type 1 (IGFR1) mRNAs and IGF-1 binding capacity, as well as on the cell signaling pathways through which EE exert their effects. E2 and NP inhibited IGFR1A and IGFR1B mRNA expression in a time- and concentration-related manner in gill and muscle; however, βS had no effect on expression of IGFR1 mRNAs in either tissue. NP reduced 125I-IGF binding in gill and E2 and NP reduced 125I-IGF in white muscle; βS had no effect on 125I-IGF binding in either gill or white muscle. Treatment of gill filaments with either E2 or NP rapidly deactivated (via reduced proportion of phosphorylation) JAK2, STAT5, Akt, and ERK; βS had no effect on the activation state of any cell signaling elements tested. The effects of EE on IGFR mRNA expression in gill were estrogen receptor (ER) dependent as the inhibitory effects were rescued by the ER antagonist, ICI 182,780. All EE tested blocked growth hormone (GH)-stimulated IGFR mRNA expression in gill filaments. GH-stimulated activation of JAK2, STAT5, Akt, and ERK were blocked by E2, βS, and NP. Lastly, E2 and NP stimulated suppressor of cytokine signaling 2 (SOCS-2) mRNA expression, an effect that also was ER dependent. These results indicate that EE directly reduce the sensitivity of peripheral tissues to IGF by reducing mRNA and functional expression of IGFRs. Such inhibitory actions of EE are mediated, at least in part, by ER-dependent mechanisms that deactivate JAK, STAT, Akt, and ERK and enhance expression of SOCS-2. These findings together with our previous results show that EE retard growth of post-embryonic rainbow trout through widespread direct effects on the GH-IGF system, specifically, by reducing tissue sensitivity to GH, inhibiting IGF production, reducing tissue sensitivity to IGF, and by deactivating post-receptor IGF cell signaling pathways.

Lake trout (Salvelinus namaycush) otoliths indicate effects of climate and lake morphology on growth patterns in Arctic lakes

AbstractClimate change is occurring rapidly in the Arctic, and an improved understanding of the response of aquatic biota and ecosystems will be important for this data‐limited region. Here, we applied biochronology techniques and mixed‐effects modelling to assess relationships among growth increments found on lake trout (Salvelinus namaycush) otoliths (N = 49) captured from 13 lakes on the Arctic Coastal Plain of northern Alaska, observed and modelled climate patterns, and individual‐level fish and lake characteristics. We found that annual growth varied by year, fish growth slowed significantly as individuals aged, and females grew faster than males. Lake trout had higher growth in flow‐through lakes relative to lakes that were perennially or seasonally connected. Annual growth was positively correlated with observed air temperature measurements from a local weather station for the period 1998–2014, but no clear warming trend was evident for this period. Modelled August air temperatures from 1978–2014 predicted lake trout annual growth (root mean squared error = 0.045 mm) and indicated increasing temperatures and annual lake trout growth over the period 1950–2014. This study demonstrated that biochronology techniques can reconstruct recent climate patterns and provide a better understanding of trends in Arctic lake ecosystems under a changing climate.