Juvenile Oncorhynchus Mykiss Research Articles

Performance, immune response, disease resistance, and gut microbiota of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) juveniles fed ground leonardite with a high humic substance content

In the present study, the effects of feeding ground leonardite (LE), which contained 68% of humic substances, to juvenile Oncorhynchus mykiss were examined on overall growth and production performance, feed nutrient digestibility, gut microbiota, health condition, antioxidant status, immune response, and disease resistance. During two consecutive experiments, fish were fed four experimental diets with different LE supplementary levels: 0, 0.5, 1, and 3% of feed mass (LE0, LE0.5, LE1, and LE3, respectively). Firstly, the fish were tested in a growing experiment (GE, n = 300 fish/group, body weight 15.4 ± 2.5 g) for 56 days. Thereafter, these fish (n = 75 fish/group, body weight 51.9 ± 8.7 g) were exposed to an intraperitoneal infection challenge experiment (IC) with Aeromonas salmonicida subsp. salmonicida for 28 days.In the GE, dietary LE did not affect the growth, production, or health performance of O. mykiss juveniles, although the fish more than tripled their initial body weight. The LE dose had an impact on the digestibility of feed nutrients (dry matter, gross energy, and ash), but not on the protein and lipid digestibility or solid waste outputs. The gut microbial communities were highly diverse across the experimental groups and remained distinct between the control and LE groups. The LE had a dose-dependent effect on the cell composition of the head kidney and peripheral blood leukocytes. The highest LE addition exerted the immune suppressive effect, and a decreased count of immune cells was observed in the LE3.The peritoneal cavity infection in the IC trial induced the rapid recruitment of myeloid cells in all groups shortly after the infection, except for the LE3, which had an apparent delayed response. The cumulative mortality and specific trout antibody levels against A. salmonicida did not significantly vary among tested groups, although their average initial level dropped by half at 3 days post-infection (dpi), and subsequently doubled at 28 dpi. The plasma biochemical parameters (TP, TAG, and CHOL) showed an overall decrease at 0–3 dpi, while increasing back to the initial levels at 3–6 dpi. Only LDH negatively correlated with LE inclusion, this can reflect the oxidative stress in the highest LE inclusion.Overall, our results support that there is a dose-dependent effect that should be optimised for ground LE dietary use in aquaculture.

Laboratory studies of fish entrainment sampling using a screw centrifugal impeller pump

AbstractObjectiveRegulatory legislation in both the United States and Canada requires water users with medium to high intake volumes to monitor entrainment losses to determine effects and to assess potential mitigation strategies to reduce harm to fish. Recent studies have recommended the use of both increased sampling frequency and sampling volume to characterize fish entrainment for large power plants on the Great Lakes. There is little doubt that increasing the flow rate and volume of water collected for sampling reduces the uncertainty in estimates of annual entrainment. Depending on the type of pump and the pumping flow rate used for entrainment sampling, considerable damage to fish larvae can occur. A screw‐type centrifugal pump has many qualities that make it ideal for entrainment sampling, but it has not yet been used as a sampling device for fish entrainment applications at power plants or other large industrial water users. The objective of this study was to determine mortality of entrainable fish eggs and larvae due to passage through a screw‐type centrifugal pump.MethodsIn a laboratory setting, Lake Trout Salvelinus namaycush eggs and larvae, Lake Whitefish Coregonus clupeaformis eggs, and Rainbow Trout Oncorhynchus mykiss juveniles were passed through a screw‐type centrifugal pump at three treatment flow rates: 39.5, 47.3, and 59.1 m3/h. Fish and eggs were monitored for mortality posttreatment and again at 24 and 48 h.ResultAcross treatments, very few mortalities were observed. Species specific moralities were four larval Lake Trout, one Lake Whitefish egg, and one juvenile Rainbow Trout. No mortality was observed for Lake Trout eggs.ConclusionThe present study identified high egg and larval survival (≥99%) after passage through a screw‐type centrifugal pump. High survival reduces error associated with identification and counting of entrained organisms, which provides more accurate estimates of annual entrainment losses.

Dietary Sodium Butyrate Improves Intestinal Health of Triploid Oncorhynchus mykiss Fed a Low Fish Meal Diet

This study aimed to determine the effects of dietary sodium butyrate (NaB) on the growth and gut health of triploid Oncorhynchus mykiss juveniles (8.86 ± 0.36 g) fed a low fish meal diet for 8 weeks, including the inflammatory response, histomorphology, and the composition and functional prediction of microbiota. Five isonitrogenous and isoenergetic practical diets (15.00% fish meal and 21.60% soybean meal) were supplemented with 0.00% (G1), 0.10% (G2), 0.20% (G3), 0.30% (G4), and 0.40% NaB (G5), respectively. After the feeding trial, the mortality for G3 challenged with Aeromonas salmonicida for 7 days was lower than that for G1 and G5. The optimal NaB requirement for triploid O. mykiss based on weight gain rate (WGR) and the specific growth rate (SGR) was estimated to be 0.22% and 0.20%, respectively. The activities of intestinal digestive enzymes increased in fish fed a NaB diet compared to G1 (p < 0.05). G1 also showed obvious signs of inflammation, but this inflammation was significantly alleviated with dietary NaB supplementation. In comparison, G3 exhibited a more complete intestinal mucosal morphology. Dietary 0.20% NaB may play an anti-inflammatory role by inhibiting the NF-κB-P65 inflammatory signaling pathway. Additionally, the relative abundance of probiotics was altered by dietary NaB. In conclusion, dietary 0.20% NaB improved the intestinal health of triploid O. mykiss fed a low fish meal diet.

Effects of an Enzyme Complex-Treated Rice Protein Concentrate on Growth Performance and Feed Utilization of Rainbow Trout Oncorhynchus mykiss Juveniles

This study investigated the effect of the inclusion of an enzyme complex-treated rice protein concentrate (RPC) in an extruded diet of juvenile rainbow trout (Oncorhynchus mykiss). A mixture of RPC, corn gluten and soybean meal was pretreated with an enzyme complex before extrusion processing of the diets. An enzyme complex-pretreated RPC (5, 10 and 15%) was formulated with 20% fish meal. A diet without RPC was used as a control. A total of 240 rainbow trouts with an average body weight of 6.04 g were placed in 12 rectangular glass aquaria and fed one of the experimental diets at apparent satiation for 12 weeks. There were no significant differences in growth, feed intake and survival among the groups. Slightly inferior weight gain and specific growth rate were observed in the RPC15E group compared to those in the other groups. The protein and ash contents of the whole body of the final fish were not significantly different among all groups, but the lipid content was significantly lower than that of the control when the dietary RPC level was &gt;10%. Protein digestibility was negatively affected by increased RPC levels in diet. Significantly lower phosphorus digestibility was observed in fish fed the diet containing 5% enzyme-treated RPC than the control. Although there was no significant difference in lipid digestibility in all groups, significantly lower lipid retention was observed in fish fed a diet formulated with more than 10% RPC. These results suggest that the inclusion of RPC in the diet affects lipid retention and the content of rainbow trout. It also decreased protein digestibility. In conclusion, rainbow trout can be fed an extruded diet formulated with 20% fishmeal and 10% enzyme-treated RPC without negative effects on fish growth.

Seasonal growth potential of Oncorhynchus mykiss in streams with contrasting prey phenology and streamflow

AbstractThe growth of any organism depends on habitat conditions, food availability, and their seasonal interactions. Yet in the vast literature on Pacific salmon (Oncorhynchus), the seasonal interaction between habitat conditions and food availability has received relatively little attention. We examined juvenile Oncorhynchus mykiss rearing, physical habitat, and resource phenologies in two Mediterranean coastal streams—one perennial, cool, and shaded and the other intermittent, seasonally warm, and sunny. We used a bioenergetic model to investigate the timing and magnitude of growth potential for drift‐foraging O. mykiss during the spring and summer in both systems. Growth potential peaked at least 2 months earlier in the intermittent stream than in the perennial stream. By early summer (June), growth potential had declined in the intermittent stream, whereas growth rates were peaking in the perennial stream. However, the mid‐July lipid content of juvenile O. mykiss in the intermittent stream was nearly twice that of fish in the perennial stream. By late summer (August), foraging profitability declined in both streams, as abiotic conditions in the intermittent stream approached lethal. In contrast, the perennial stream maintained suitable abiotic conditions even though the growth rate was low. We suggest that the divergent resource phenologies and seasonal mortality risks experienced by anadromous O. mykiss rearing in these streams could drive diversification of traits governing size, age, and timing of outmigration.

Analysis of Muscle Lipidome in Juvenile Rainbow Trout Fed Rapeseed Oil and Cochayuyo Meal.

This study aimed to analyze the effects on the lipidome of juvenile Oncorhynchus mykiss muscle fed 90% Brassica napus “rapeseed” oil and different amounts of Durvillaea antarctica “Cochayuyo” meal (1.5, 3 and 6%) as a replacement for cellulose. The analysis allowed for the identification of 329 lipids, mainly represented by phospholipids and fatty esters. The inclusion of Brassica napus oil significantly increased the levels of C18:2 species and fatty esters of hydroxylated fatty acids, which could play a bioactive role in human health. One of the most abundant lipids in all fillets was Phosphatidylcholine 33:6, which, according to the literature, could be considered a biomarker for the identification of Oncorhynchus mykiss. In all experimental diets, the species Phosphatidylethanolamine 15:1-18:24 showed four-fold higher levels than the control; increments of n-3- and n-6-rich phospholipids were also observed. Diets containing Durvillaea antarctica meal did not generate more significant variation in fish muscle phospholipids relative to the muscle of the rapeseed-oil-only group. These lipid species consist of medium- and long-chain fatty acids with different degrees of unsaturation. Still, it appears that the rapeseed oil masks the lipid contribution of the meal, possibly due to the low levels of total lipids in the macroalgae.

Effects of Dietary Arginine on Growth Performance, Digestion, Absorption Ability, Antioxidant Capability, Gene Expression of Intestinal Protein Synthesis, and Inflammation-Related Genes of Triploid Juvenile Oncorhynchus mykiss Fed a Low-Fishmeal Diet

In this study, the effects of arginine on growth, serum antioxidant levels, intestinal digestion physiology, intestinal protein synthesis, and expression of inflammatory-related genes of triploid juvenile rainbow trout (Oncorhynchus mykiss) were investigated. Five diets containing 0.86%, 1.65%, 2.10%, 2.85%, and 3.50% arginine were fed to satiation to triplicate groups of 30 fish per tank for 8 weeks. The results showed that the weight gain rate, specific growth rate, and protein efficiency ratio significantly increased. The optimal dietary arginine requirement was 2.48% (5.97% of dietary protein) based on quadratic regression analysis between specific growth rate and dietary arginine content. There were no significant differences in crude lipid and ash content. Moisture significantly decreased, and crude protein content significantly increased ( P &lt; 0.05 ). Superoxide dismutase, catalase, and lysozyme levels in serum and the liver first significantly increased and then decreased with the level of arginine compared to the control group ( P &lt; 0.05 ), while the malondialdehyde level significantly decreased. Intestinal lipase and amylase levels significantly increased, but there was no significant difference in trypsin level ( P &gt; 0.05 ). The muscular layer thickness and villus width foregut in the 2.85% group were significantly increased. TOR at 2.86% and IGF-1 and S6K1 at 2.11% reached the maximum level, and IL-1β, IL-6, and IL-8 showed a decreasing trend with their lowest levels in the 3.50% and 2.85% groups. The expression of TNF-α first decreased and then increased with the arginine level. Both TGF-β and IL-10 expression first decreased and then increased with the level of arginine and reached the maximum value in the 2.85% group. NF-κB showed an opposite trend and reached the lowest value in the 3.50% group. In conclusion, dietary arginine has a significant effect on growth, serum antioxidant capability, digestion physiology, immunity, digestion, and absorption of nutrients in triploid O. mykiss, and the optimum requirement is 2.48% fed a low-fishmeal diet.

Oncorhynchus mykiss’te Subakut Clothianidin Uygulamasının Doku Spesifik Yanıtlarının Histopatolojik Değerlendirmesi

Clothianidin, one of the latest members of neonicotinoids, is a systemic insecticide of the neonicotinoid group that affects the central nervous system by acting as a nicotinic acetylcholine receptor agonist. Although it is stated that it has no dangerous potential for aquatic organisms, accumulation in water basins is important in terms of environmental toxicity. In this study, the histopathological changes caused by clothianidin applied in subacute application (7 days) form and in environmental doses (3, 15 and 30 µg/L) in the brain, kidney, muscle and gill tissue of juvenile Oncorhynchus mykiss were determined. Parallel to the administration of increasing doses of clothianidin, an increase in the severity of pathological lesions is observed in the brain, muscle, kidney and gill tissue. In particular, it shows that as a result of the accumulation of pesticides in aquatic organisms, lesions may develop as tissue-specific responses, thus leading to tissue dysfunction.

The influence of probiotics of different microbiological composition on histology of the gastrointestinal tract of juvenile Oncorhynchus mykiss.

This article presents results of the influence of three probiotic feed additive of various microbiological composition: Bacillus subtilis (VKPM B-2335); B. subtilis (OZ-2 VKPM-11966) + Bacillus amyloliquefaciens (OZ-3 VKPM-11967); Lactobacillus acidophilus (VKPM B-3235) on the growth and histology of the organs of the gastrointestinal tract of juvenile Oncorhynchus mykiss by morphometric parameters. These probiotic bacteria are the most commonly used in aquaculture. The effect of the probiotic feed additive led to the increase in fish growth and influenced different sections of the gastrointestinal tract. The biggest change was found in the mid intestine and the reliable difference compared with the control diet was obtained at the following parameters: lamina propria width, intraepithelial lymphocytes number of prismatic epithelium and goblet cells area. The changes in the pyloric appendages were less obvious but reported as playing an important functional role in digestion. The liver preserved normal functional structure in all series of the experiment except for the group with L. acidophilus, where hepatocyte small-drop vacuolization was observed. That might be connected with the change of the digest activity resulting from a decrease in secretory activity of the intestinal exocrinocytes. The use of all probiotic feed additives led to a similar change in morphometric parameters in all groups, which suggests a decrease in the immune response.

Toxicity and biochemical responses induced by phosmet in rainbow trout (Oncorhynchus mykiss).

Phosmet is a non-systemic organophosphorus insecticide exerting its toxicity by inhibiting acetylcholinesterase upon entering the body via contact, ingestion and inhalation. Data regarding its sublethal effects on fish are limited, and therefore, with this study it was aimed to investigate the effects of phosmet on liver and brain tissues of juvenile Oncorhynchus mykiss following 24, 48, 72 and 96h of exposure to 5, 25 and 50μg/l concentrations. Pesticide treatment caused notable decrease in the levels of serum glucose, protein and cholesterol, whereas there was prominent elevation in the activities of alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase. Anticholinesterase activity of phosmet was observed in brain tissue reaching maximum of 46%. In both tissues, increase in the activities of superoxide dismutase, catalase and glutathione peroxidase and level of glutathione was accompanied by elevated thiobarbituric acid reactive substances level. Our results clearly indicate the modulatory effect of phosmet on acetylcholinesterase activity and its potency to provoke oxidative stress condition. The determined alteration in alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities indicates hepatotoxic potential of pesticide; meanwhile, obtained hypoglycaemia and hypoproteinaemia are evaluated as adaptive responses to handle the stress to survive.

Manifestations of oxidative stress and liver injury in clothianidin exposed Oncorhynchus mykiss.

This investigation was conducted to evaluate the effects of clothianidin, a neonicotinoid insecticide, on hepatic oxidative stress biomarkers, biochemical indices of blood serum and liver integrity in juvenile Oncorhynchus mykiss following 7, 14 and 21days of application to environmentally relevant concentrations of 3, 15 and 30μg/l. The observed hypertrophy caused elevation in hepatosomatic index, a significant increase in serum glucose and a decrease in tissue protein level with extended period of exposure were determined. The treatment resulted in a marked induction in the activities of antioxidant enzymes which were accompanied with simultaneous elevation in MDA and protein carbonyl level reflecting loss of membrane integrity and protein function. Histopathological examination showed liver injury manifested as hepatocellular degeneration, fibrosis, vacuolation, congestion, necrosis, steatosis and pyknosis proceding with the concentration. The stressful condition triggered hyperglycemic and hypoproteinemic conditions which might be proposed as general adaptive response. Moreover, altered liver histology reveals the hepatotoxic potential of clothianidin via oxidative stress as a common pathological mechanism leading to liver injury.

Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos‎

Microplastic (MP) sorption and transfer of chemical contaminants has been widely reported, yet few studies have investigated combined effects of contaminant-loaded MPs on organisms. This study examined effects of pristine or chlorpyrifos (CPF)-loaded polystyrene (PS)‎ fragments on histopathological and histomorphometrical biomarkers in rainbow trout (Onchorhynchus mykiss)‎. In laboratory, O. mykiss were exposed for 96 h to pristine PS-MPs concentrations (30 or 300 µg/L), concentrations of CPF ‎alone (2 or ‎‎6 µg/L), and the same concentrations of CPF in the presence of PS-MPs in aquaria‎. Results showed the highest histopathological alterations in both CPF concentrations and when combined with PS-MPs in fish gills. Alternatively, high histopathological lesions including massive necrosis, infiltration of inflammatory cells, and shed of villi tips were observed in fish gut in high CPF concentrations combined with high PS-MP concentrations of ‎(6 μg/L CPF+300 μg/L PS-‎MPs). Individual CPF and PS-MP concentrations or combined together showed significant changes in histomorphometrical biomarkers in fish gills, gut and skin. Findings highlight that pristine PS-MPs cause toxicity and increase adverse effects of CPF in O. mykiss, especially in gill tissue. We present evidence that pristine short-term exposure to even low concentrations of PS-MPs has a significant impact on biomarker responses in O. mykiss.

Dietary inorganic monophosphates in high plant ingredient‐based diets influence nutrient digestibility, postprandial macro‐mineral status and immune functions of juvenile rainbow trout,Oncorhynchus mykiss

Inorganic monophosphates supplementation effects in high plant ingredient‐based diets of juvenile Oncorhynchus mykiss were evaluated by feeding four experimental diets supplemented with 11.4, 10.0, 11.5 and 10.0 g/kg of monocalcium phosphate (MCP), monoammonium phosphate (MAP), monopotassium phosphate (MKP) and monosodium phosphate (MSP), respectively. After 60 days, MAP and MKP supplemented groups showed improved growth and feed intake (p > .05). Apparent digestibility coefficient of dry matter (ADCDM) was significantly higher in MSP diet followed by MKP, MCP; MAP diet showed significantly lower ADCDM. MAP and MSP diets showed significantly higher mineral digestibility. The postprandial plasma P levels were significantly influenced by the dietary treatments and the period after a single meal. MAP, MKP and MSP groups showed significantly higher baseline P concentration than MCP. The other macro‐minerals (Ca, Mg, K and Na) were significantly influenced by the postprandial time. MSP and MKP diets showed significantly higher lysozyme activity. Total immunoglobulin was significantly higher in MSP group. MKP diet showed significantly higher expression of cd4‐2β genes compared with MCP. Significantly higher lysozyme gene expression observed in MSP diet followed by MKP; MAP and MCP groups showed significantly lower value. Finally, MAP, MKP and MSP significantly improved nutrient digestibility, mineral bioavailability and immune functions of rainbow trout compared with MCP in high plant ingredient‐based diets.

The adverse effects of selenomethionine on skeletal muscle, liver, and brain in the steelhead trout (Oncorhynchus mykiss)

Juvenile Oncorhynchus mykiss (average weight: 22.3 g) were fed one of five selenomethionine diets (1.09, 8.79, 15.37, 30.79, or 61.58 mg Se/kg diet). After 4 weeks, hepatic catalase activity over 15.37 mg Se/kg diets was significantly decreased, and the glutathione peroxidase activity over 30.79 mg Se/kg diets was elevated compared to the controls. In the brain, the dopamine levels at 61.58 mg Se/kg diet and the serotonin levels over 15.37 mg Se/kg diets were significantly increased, whereas the 3,4-dihydroxyphenylacetic acid, homovanillic acid, and dopamine turnover, and the 5-hydroxyindoleacetic acid and serotonin turnover over 30.79 mg Se/kg diets were decreased. In muscle, the 3-nitrotyrosine level over 15.37 mg Se/kg diets, acetylcholine esterase activity over 30.79 mg Se/kg diets, and histological alterations over 8.79 mg Se/kg diets were increased. Our current results showed that selenomethionine disrupted dopamine and serotonin metabolism in the brain and damaged the neuromuscular system in skeletal muscle.

Trans-cinnamic acid application for rainbow trout (Oncorhynchus mykiss): I. Effects on haematological, serum biochemical, non-specific immune and head kidney gene expression responses

The present study investigated the effects of dietary trans-cinnamic acid (CA) on pre- and post-challenge haematological, serum biochemical, non-specific immune and head kidney gene expression responses of rainbow trout, Oncorhynchus mykiss juveniles. In this regard, fish with an average weight of 17.01 ± 0.05 g were divided into five groups, and fed daily with an additive free basal diet (control); 250, 500, 750 or 1500 mg kg−1 CA for a 60-day period. Fish were sampled every 20 days during the experiment. On days 20, 40 and 60 (the pre-challenge period), the dietary CA especially at 250 and/or 500 mg kg−1 significantly increased blood granulocyte percentage, and serum total protein, globulin, lysozyme and total immunoglobulin values. Furthermore, dietary CA increased activities of phagocytic activity, respiratory burst and potential killing, and increased the expression levels of immune related genes [serum amyloid A (SAA), interleukin 8 (IL-8), interleukin 1, beta (IL-1β), transforming growth factor beta (TGF-β), tumor necrosis factor (TNF-α), and immunoglobulin T (IgT)] in the head kidney of fish fed with 250 and/or 500 mg kg−1 CA. Following 60 days of feeding, fish were challenged with Yersinia ruckeri and mortality was recorded for 20 days. Highest percentage survival (%) rate was found in the 250 and/or 500 mg kg−1 CA-supplemented feeding groups. During the post-challenge period, red blood cell (RBC) count, hematocrit (%), respiratory burst activity, and total antiprotease activity increased in fish fed with feed containing 500 mg kg−1 content. Moreover, markedly up-regulated the expression of related genes (SAA, IL-8, IL-1β, TGF-β, TNF-α, IFN-γ and IgM) in fish fed 250, 500 and/or 750 mg kg−1 CA. Therefore, feeding O. mykiss for 60 days with dietary CA at 250–500 mg kg−1 CA incorporation levels can be suggested as optimal to enhance the immunity and disease resistance against Y. ruckeri.

Effects of grapeVitis viniferaseed oil supplementation on growth, survival, fatty acid profiles, antioxidant contents and blood parameters in rainbow troutOncorhynchus mykiss

In this study, effects of grape Vitis vinifera seed oil supplementation (0, 250 mg, 500 mg, 1,000 mg/kg feed) for 60 days on rainbow trout Oncorhynchus mykiss juveniles were investigated. The average final fish weights were not different between the control group and 500 mg/kg feed group (p > .05), but 250 mg/kg feed group were lower than those of the control group, and 1,000 mg/kg feed group were higher than those of the control group. Although the SFA, MUFA and n3 ratios of the control group were higher than that of the other groups, no statistical difference was found. The highest fatty acids in the fish were palmitic acid C 16: 0 in the SFA group and C 18: 1n-9 and docosahexaenoic acid C 22: 6n-3 in the PUFA group. The EPA ratio was significantly increased in all groups compared with the control group. The DHA ratio was significantly higher in the control group than in the experimental groups, and there was no difference between the experimental groups. Urea were significantly lower in the 250 mg/kg feed group. Total protein and aspartate aminotransferase were significantly increased in the 1,000 mg/kg feed group. Only the 1,000 mg/kg feed group showed an increase in antioxidant activities, and this concentration also yielded positive results in terms of growth performance, survival rates, fatty acid composition and antioxidant enzyme activities in rainbow trout juvenile and can be used as a natural feed additive.

Rainbow trout personality: individual behavioural variation in juvenile Oncorhynchus mykiss

Abstract We evaluated the variation in dispersal, exploration, and aggression across time in juvenile progeny produced from wild caught rainbow trout (Oncorhynchus mykiss) at a critical developmental shift associated with the highest mortality in fish. By testing multiple ecologically relevant behaviours repeatedly in the same individuals, we simultaneously tested multiple hypotheses regarding personality, plasticity, and behavioural syndromes to better understand the innate behavioural variation in a population containing both migratory and resident life histories. There were consistent behavioural differences, or personality, between individuals across time, for dispersal, aggression, and exploration, unrelated to size or sex. The significant repeatabilities (0.10–0.46) indicate that these traits are potentially heritable. Also, we found both habituation in all behaviours and significant differences between individuals in the rate of that habituation, despite no evidence of a behavioural syndrome. The identification of this individual level variation is a step towards understanding which heritable traits selection could influence.

Life History Diversity of Steelhead in Two Coastal Washington Watersheds

AbstractWe used PIT tags implanted in juvenile Oncorhynchus mykiss to monitor movement into and out of two coastal Washington State rivers, East Twin River and West Twin River. Movement patterns revealed at least 18 life histories of steelhead O. mykiss with variations in age and seasonal migration of juveniles, juvenile use of the ocean prior to migration, years spent in the ocean, season of adult return, and iteroparity. While most migrants left the river in their first fall or winter, we did not detect any returning adults from these age‐0 migrants. Adults were only produced from age‐1 and older migrants, of which most were age‐2 spring migrants that returned after two summers in the ocean. Our results indicated a positive relationship between fish length at tagging and the probability of being detected as a migrant, while the probability of a migrant leaving at age 1 and older decreased with increasing length at tagging among fish that were detected as migrants. We hypothesize that fish attaining a large enough size early in life to survive over the winter but not big enough to trigger migration at age 0 were more likely to remain in the river to become age‐1 migrants, which were more likely to produce a returning adult steelhead. We also found evidence that density‐dependent growth may influence juvenile steelhead migration patterns and production of migrants as evidenced by increasing contributing‐adult steelhead escapement being negatively related to average cohort body size, probabilities of fish being detected as migrants, and production of age‐1 and older migrants. We anticipate that the findings of this study can be used to inform the development of steelhead recovery strategies for East Twin and West Twin rivers, which have experienced recent declines in adult returns much like other North Pacific Ocean stocks.Received January 20, 2016; accepted May 18, 2016 Published online August 5, 2016

Seasonal changes in spatial patterns of Oncorhynchus mykiss growth require year‐round monitoring

AbstractGrowth and movement of juvenile salmonids influence the expression of individual life history traits and production of adults at the population scale. We individually marked and recaptured juvenile Oncorhynchus mykiss over the course of a year in Murderers Creek, a semi‐arid tributary to the South Fork John Day River in Northeast Oregon. We tagged O. mykiss in three reaches with differing stream gradient, stream temperature and fish density. Mean growth rates differed significantly among reaches and seasons with a significant interaction between reach and season. Reaches with high growth rates shifted across Murderers Creek among seasons. Stream reaches with high growth during the winter had low growth during summer and vice‐versa. The proportion of individuals moving at the reach scale during summer was low (≤2.6%), suggesting that individuals did not track resources at the reach scale. The spatio‐temporal variation in growth indicates that monitoring stream salmonids across multiple seasons is necessary to accurately characterise the production of different stream reaches.

The effects of different cycles of starvation and re-feeding on growth and body composition in rainbow trout (Oncorhynchus mykiss , Walbaum, 1792)

Summary This study was designed to investigate the effects of starvation and re-feeding cycles on the growth performance and body chemical composition of Oncorhynchus mykiss juveniles. A total of 360 juveniles with initial mean weights (IW) of 8.46 ± 0.07 g (n = 360) were stocked into 400-L tanks in triplicate for each group, with 30 juveniles per tanks. The control group received regular feed, as is the common practice. The three other groups were periodically starved: 1 day starvation followed by 6 days re-feeding (S1), 2 days starvation followed by 5 days re-feeding (S2) and 3 days starvation followed by 4 days re-feeding (S3). The experiment lasted for 10 weeks, over the course of which the water flow rate was 4 L min−1 and the water quality parameters determined as: temperature 14.4 ± 1.1°C, oxygen 8.2 ± 0.4 mg L−1 and pH 7.5 ± 0.2. At the end of the study, S1 had the best growth performance (final weight, specific growth rate, average daily growth) of all test groups (P < 0.05). The lowest daily feed intake (DFI) and growth performance parameters were observed in S3 (P < 0.05), while protein efficiency ratio (PER), net protein utilization (NPU) and lipid efficiency ratio (LER) were higher in the S3 fish group than in the other groups (P < 0.05). Whole body protein and lipid contents were highest in S1 fish. The hepatosomatic index (HSI) and viscerosomatic index (VSI) were significantly different among groups (P < 0.05). Feed conversion ratio (FCR) was significantly lower in starvation groups S1, S2 and S3 than in the control (P < 0.05). Compensation coefficient (CC) values were higher than 1 in all starvation groups. The concluding indicate that rainbow trout exposed to 1 and 2 days of starvation in week cycles could achieve over compensation compared to the control. Additionally, partial growth compensation and improved feed utilization could be achieved in a starvation group within 3 days in a week, by beginning with the juvenile size over a 10-week experimental period.