Nitrogen and phosphorus digestibility and excretion of different-sized groups of milkfish (Chanos chanos Forsskal) fed formulated and natural food-based diets

This study determined the digestibility of nitrogen and phosphorus, and the excretion rate of different‐sized groups of milkfish fed a commercial diet, a SEAFDEC formulated diet or lab‐lab (natural food‐based diet). Fish (31.2–263.0 g) were stocked in 12 units of 300‐L fibreglass tanks filled with aerated seawater. The postprandial total ammonia‐nitrogen (TAN) and phosphate (PO₄‐P) excretion of fish were estimated from changes in TAN and PO₄‐P concentrations in water for 24 h. Digestibility was determined from the nitrogen, phosphorus and Cr₂O₃ content of the diets, and pooled faeces after the fish had been fed diets marked with chromic oxide. TAN excretion rate (mg TAN kg^?1 fish day^?1) was significantly lowest (P < 0.05) in medium to very big fish fed the lab‐lab diet (60.8–124.4) and highest in small and medium fish fed the SEAFDEC diet (333.3–331.6) and small fish fed the commercial diet (280.1). Regardless of size, fish fed lab‐lab excreted (mg PO₄‐P kg^?1 fish day^?1) significantly lower PO₄‐P (36.2) but did not differ with fish fed the commercial diet (64.8). Excretion rates decreased exponentially as fish weight increased but positively increased with feed ration. Excretion pattern of milkfish revealed two peaks: the first peak occurred 6 h after feeding and the second peak at 18 h for TAN and 21 h for PO₄‐P, coinciding with the start of the daylight hours. TAN and PO₄‐P excretion accounted for 20.5–34.6% of total N consumed and 18.7–42.6% of P consumed respectively. Approximately 27.9–42.5% of N consumed and 47.2–58.5% of P consumed were lost as faeces. Total nutrient losses were lower using the lab‐lab diet (0.31 g N and 0.14 g P kg^?1 fish) compared with the formulated diets (0.47–0.48 g N and 0.17–0.19 g P kg^?1 fish); the losses decreased per kg of fish as fish size increased. Results suggest that the diet and size of fish influence wastage of N and P to the environment with greater losses in small fish and when artificial diets are used. Such measurements will provide valuable information for the preparation of N and P budgets for milkfish in grow‐out systems.     

The influence of body size, habitat and diet concentration on feeding of Laternula marilina Reeve

A Chinese duckbilled marine clam (Laternula marilina Reeve) was cultured in a simulated natural culture system for the preliminary determination of its physiological energetics. The results showed that both clearance rate (CR) and ingestion rate (IR) were related exponentially to body size (flesh dry weight, W) as described by the equations CR=0.49W^0.65, IR=0.96W^0.57. Body size had no effect on assimilation efficiency (AE) at water temperatures of 10°C, 16°C and 23°C, but within this range AE significantly increased with increasing water temperature. It was found that L. marilina performed in feeding behaviour far better when natural substrates conditions were provided. On a sand or silt substrate both CR and IR were two times higher than on an uncovered tank bottom. AE was also improved when sand (13.12% increase) or silt (14.19% increase) was provided. It is evident in our results that within the range of diet (as particulate organic matter, POM) concentration of 2.30±0.21 to 6.20±0.13 mg POM L^?1 the relationships between POM and CR and IR were exponential and as described by the equations CR=0.29 [POM]^0.75, IR=0.33 [POM]^1.34. In these experiments, the diet concentration threshold of pseudofaecal excretion was found to be 3.05 mg POM L^?1. There was no marked influence of diet concentration on AE, which was consistently about 60%.     

低温对菲律宾蛤仔能量收支的影响

在实验室内采用静水法，测定了在315和8℃下，菲律宾蛤仔的耗氧率和排氨率与体重的关系及其能量收支情况。实验数据显示，在实验的温度范围内，菲律宾蛤仔的耗氧率和排氨率都与体重负相关；温度对耗氧率的影响与体重有关。摄食率、生长率（净生长率、毛生长率）与温度正相关。温度对能量分配影响较大，代谢分配率、排粪分配率随温度的升高而降低，且变化极其显著（P＜0.01)；生长分配率随温度的升高而增大。在能量收支方程中，排粪能所占比例较大，在41.131%-60.69%之间，代谢能在23.37%－32.73%之间，生长能在6.13%-34.63%之间，排泄能所占的比例最小，低于3％。     

The effect of temperature on the energy budget of the Manila clam, <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>

In this study, the energy budget of the Manila clam, Ruditapes philippinarum, was evaluated after one-week acclimation periods at 5, 10, 15, 20, and 25°C. Small clams (151 ± 12 mg DW) and large clams (353 ± 16 mg DW) were fed with the microalgae, Isochrysis galbana. Filtration rate, ingestion rate, assimilation efficiency, oxygen-consumption rate, and ammonia excretion rate were measured. Both filtration rate and ingestion rate of small and large clams were found to be related to temperature. The highest Q ₁₀ values were measured in the range 15–20°C for both small and large clams. Assimilation efficiency of both small and large clams was not significantly influenced by temperature, although the maximum mean values were detected at 20°C. Oxygen consumption rate and ammonia excretion rate of small and large clams were found to be related directly to temperature over the entire range, with a maximum being detected at 25°C. The highest Q ₁₀ value was estimated in the range 10–15°C with regard to oxygen consumption rate, and in the range of 15–20°C with regard to ammonia excretion rate. Scope for growth (SFG) was positive at all temperatures, achieving a maximum value at 20°C in both small and large clams, primarily as a consequence of the enhanced ingestion rate which offset the concomitant elevation in the metabolic rate. In this study we have estimated the thermal optimum for this species at 20°C.     

Ecological consequences of variation in standard metabolism and dominance among salmon parr

Abstract – Standard metabolic rate (SMR, closely related to basal and resting metabolism) varies by up to threefold among juvenile Atlantic salmon, Salmo salar L., of similar size at common temperature. Here, consequences of this variation are predicted by combining empirically derived relationships between SMR, specific dynamic action, energy budgets, water velocity, food level in the environment and food availability to fish. The range of velocities across which growth is predicted to occur is inversely related to a fish’s SMR. Growth is positively related to SMR at high but negatively related to it at low‐food levels. The relationship between food level and the range of velocities over which lower SMR fish can grow but higher SMR fish cannot is asymmetrically bi‐phasic and peaked. It is predicted that maternal manipulation of offspring SMR would generate fitness benefits through bet‐hedging against unpredictability in food level and increases in the overall range of velocities that the family of offspring can occupy and thrive in.     

Effects of temperature,salinity and body size on the physiological responses of the Iwagaki oyster Crassostrea nippona

The physiological responses of the juvenile Crassostrea nippona in terms of filtration, oxygen consumption and ammonia excretion to changes in temperature (16–32°C), salinity (15–35 psu) and body size (small, medium and large) were investigated. In this study, the values of filtration rate (FR), oxygen consumption rate (OCR) and ammonia excretion rate (AER) increased with temperature rising from 16°C to 24°C, reaching the highest values at 24°C and 28°C; with any further increase in temperature above this limit, these values decrease drastically (p < .05). The highest Q₁₀ coefficients were 2.75 for large, 3.54 for medium at 16–20 and 3.47 for small size at 20–24°C respectively. Moreover, the responses of FR and OCR were found to be influenced significantly by salinity, tending to increase concomitantly with salinity up to 25–30 psu, though the values of these parameters were diminished dramatically (p < .05) above this level, showing a reverse pattern from that observed in AER, which firstly decreased to the lowest level at 25 and 30 psu, and then severely (p < .05) increased to the highest level at 35 psu. In addition, the low O:N ratios of all sizes of C. nippona at 16°C and 30–35 psu were indicative of a protein‐dominated catabolism, whereas the O:N ratios of large size at 20–32°C and all sizes at 20–30 psu, indicating that the metabolic energy from protein diminished and lipid and carbohydrate were used as the energy substrates. Physiological rates of C. nippona were well correlated with its size. The average values of mass exponents (b‐values) estimated in the present study were 0.657 for OCR and 0.776 for AER at different temperatures, and 0.647 for OCR and 0.767 for AER at varying salinities, signifying that physiological process of C. nippona becomes relatively slower with increasing body size regardless of temperature or salinity. Finally, our results confirm that the optimal temperature and salinity for juvenile C. nippona lie within 24–28°C and 25–30 psu respectively. The results of physiological traits in response to environmental factors of this species are informative in site selection for the cultivation.     

盐度胁迫对泥蚶能量代谢的影响

在水温(26.4±0.79)℃、盐度11、14.5、18、21.5、25和28.5下,将壳长27~28mm泥蚶饲养在流水系统中24h,每一盐度梯度设置3个平行和3个空白对照,以研究盐度对泥蚶摄食、代谢、碳收支及能量代谢的影响。试验结果显示,随着盐度的升高,泥蚶的滤水率、摄食率、吸收率和O∶N均先升后降,而耗氧率与排氨率先降后升,在盐度18~21.5时显著达到极值(P0.05),但盐度对泥蚶的耗氧率、排氨率和O∶N影响不显著(P0.05)。泥蚶代谢所需要的能量主要由脂肪和碳水化合物提供,盐度18~21.5为泥蚶的适宜盐度范围,此时的能量代谢方程分别为:100C=26.12F+30.75R+5.78U+37.35P;100C=25.06F+32.03R+5.15U+37.76P。     

Oxygen consumption of the ascidian Styela clava in relation to body mass,temperature and salinity

The metabolic physiological response to body mass, temperature (12–28 °C) and salinity (20–36 g L^?1) was examined in this paper. Oxygen consumption rate, which is dependent on environmental conditions, was exponentially related to body mass and varied from 0.045 to 1.11 mg h^?1 g^?1. Oxygen consumption rate increased as salinity increased from 20 to 36 g L^?1, and increased with increasing temperature. The effect of temperature gradient between experimental treatments on oxygen consumption rate was evaluated by calculating Q₁₀ (the Arrehenius relationship for increase with temperature). The Q₁₀ value within the temperature range from 12 to 16 °C was much higher than the value within the temperature range from 16 to 20 °C, 20 to 24 °C and 24 to 28 °C, indicating a reduced temperature dependence of ascidian metabolism at a high temperature.     

Effects of body size and water temperature on food consumption and growth in the sea cucumber Apostichopus japonicus (Selenka) with special reference to aestivation

To investigate the effects of body size and water temperature on feeding and growth in the sea cucumber Apostichopus japonicus (Selenka), the maximum rate of food consumption in terms of energy (C_maxe; J day^?1) and the specific growth rate in terms of energy (SGRe; % day^?1) in animals of three body sizes (mean±SE) – large (134.0±3.5 g), medium (73.6±2.2 g) and small (36.5±1.2 g) – were determined at water temperatures of 10, 15, 20, 25 and 30°C. Maximum rate of food consumption in terms of energy increased and SGRe decreased with increasing body weight at 10, 15 and 20°C. This trend, however, was not apparent at 25 and 30°C, which could be influenced by aestivation. High water temperatures (above 20°C) were disadvantageous to feeding and growth of this animal; SGRe of A. japonicus during aestivation was negative. The optimum temperatures for food consumption and for growth were similar and were between 14 and 15°C, and body size seemed to have a slight effect on the optimal temperature for food consumption or growth. Because aestivation of A. japonicus was temperature dependent, the present paper also documented the threshold temperatures to aestivation as indicated by feeding cessation. Deduced from daily food consumption of individuals, the threshold temperature to aestivation for large and medium animals (73.3–139.3 g) was 24.5?25.5°C, while that for small animals (28.9–40.7 g) was between 25.5 and 30.5°C. These values are higher than previous reports; differences in sign of aestivation, experimental condition and dwelling district of test animals could be the reasons.     

Interactions between body mass and water temperature cause energetic bottlenecks in juvenile steelhead

Across taxa, it is generally accepted that there are fitness advantages to rapid growth early in life. For stream‐dwelling salmonids, however, high temperatures and associated energetic costs during the summer growing season might offset or even prevent the competitive advantage of large body size. Our overall objective was to understand the relative importance of factors that can cause variation in growth rates in an age‐0 cohort of wild steelhead (Oncorhynchus mykiss) in Idaho, USA, where temperatures approach, and temporarily exceed, their tolerance level. For individually tagged fish inhabiting the same stream reach, we found that growth rates were negatively related to fish mass (slopes of the two best approximating models were both ?0.024). Comparing growth rates from 16 different stream reaches throughout the watershed, we found that temperature‐induced metabolic cost was the single best approximating model (AIC w_i = 1.0) of the variation in individual growth rates. The bioenergetic model showed that mass‐specific metabolic costs decreased with mass, but the absolute energetic demands increased over the same size range. Because temperature had a multiplicative effect on metabolic cost, our results suggest that the effect of food limitation increased with fish size. We conclude that high water temperatures pose energetic bottlenecks and can be a potentially strong mechanism limiting growth in juvenile salmonids in summer, particularly as streams in the region experience warming trends.     

Patterns of growth and nutrient deposition in lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis) and their hybrid, F1 splake (Salvelinus namaycush × Salvelinus fontinalis) as a function of water temperature

Several fish species of the genus Salvelinus are used for stocking freshwaters in North and South America and much of Europe but there is little information about their growth and carcass composition. Lake trout (S. namaycush), brook trout (S. fontinalis) and their hybrid F₁ splake (S. namaycush × S. fontinalis) (initial body weight ca. 2–4 g) were raised at 6.4, 10.6 and 14.9 °C to examine growth and nutrient deposition as a function of water temperature. In all species, weight gain and feed intake increased significantly with water temperature and feed efficiency was significantly lower at 6.4 than at 10.6 and 14.9 °C. In brook trout, Thermal‐unit Growth Coefficient (TGC) growth rate was significantly lower at 6.4 than at 10.6 and 14.9 °C, while in F₁ splake TGC was only lower at 6.4 than 10.6 °C. Expressed in terms of relative composition a significant effect of temperature was observed. In all species, moisture content decreased while crude protein, lipid, ash and energy contents increased with increased temperature. Expressed in absolute terms, however, a significant effect of temperature was not observed. In all species carcass contents increased significantly with increased live body weight and were best described by simple linear equations. Gross energy concentration was significantly affected by both water temperature and body weight. These data indicate that the growth of these species is a function of water temperature and, in absolute terms, carcass composition is mainly a function of body weight and not water temperature. Also, such simple linear equations bode well for modification of existing feed requirement and waste outputs models; improving their applicability to these species.     

Polyculture of milkfish Chanos chanos (Forsskal) and the red seaweed Gracilariopsis bailinae (Zhang et Xia) in brackish water earthen ponds

Growth, net production, and survival rates of milkfish cultured with Gracilariopsis bailinae at two stocking density combinations (T₁– 30 fingerlings 100‐m^?2 pond+1‐kg G. bailinae 4‐m^?2 net cage, T₂– 30 fingerlings 100‐m^?2 pond+2‐kg G. bailinae 4‐m^?2 net cage) in brackish water earthen ponds over four culture periods were determined. The control (T₃) was stocked at 30 fingerlings 100‐m^?2 pond. Specific growth and production rates of G. bailinae were also calculated. There were no significant differences in mean growth, survival, and net production rates of milkfish between the three treatments. Irrespective of stocking singly or in combination with G. bailinae, significantly higher mean growth and mean production rates for milkfish were obtained during the third culture period of year 1 than those obtained from the other culture periods. Survival rates were not significantly different among the four culture periods. There were no significant differences in mean specific growth and mean net production rates between the two stocking densities of G. bailinae. Significantly higher mean specific growth and mean net production rates of red seaweed were also obtained during the third culture period of year 1 than those obtained from other culture periods. The production of milkfish and red seaweed was higher during the dry season. Growth rates of milkfish was positively correlated with temperature and salinity, while net production rates were positively correlated with temperature and total rainfall, but was inversely correlated with dissolved oxygen. G. bailinae growth and net production rates were positively correlated with water temperature and salinity. Results show that milkfish can be polycultured with G. bailinae grown in net cages in brackish water ponds at stocking density combination of 30 fingerlings 100‐m^?2 pond+1‐kg G. bailinae 4‐m^?2 net cage.     

Effect of food amount and temperature on growth rate and aerobic scope of juvenile chum salmon

Offshore migration of Pacific salmon Oncorhynchus spp. is partly triggered by increasing body size and high motility in the early stages of life. The survival of juvenile salmon may depend on their growth rate during the first few months in the sea, and this factor partly regulates the dynamics of adult populations. Here, we assessed the effects of water temperature and food availability on the growth of juvenile chum salmon O. keta. In addition, by combining the measurements of metabolic performance for growth and activity (Absolute Aerobic Scope: AAS) with a bioenergetics model, we estimated the energy allocation for different activities in the juveniles. Under high temperatures (14 °C), juveniles reared at low food levels (1% body weight) allocated less than half their energy for growth than those reared at high food levels (4% body weight). These findings suggest that high temperature and low food level constrain the growth of juveniles, providing an insight into the effect of the recent increase in warm and low-nutrient water masses on survival of juveniles and catches of adult chum salmon on the Pacific side of Honshu Island, Japan.

     

Effect of ration size on growth, conversion efficiency and body composition of fingerling mrigal, Cirrhinus mrigala (Hamilton)

Optimum ration size of Indian major carp, Cirrhinus mrigala fingerlings was determined by feeding purified diet (40% crude protein (CP); 3.61 kcal g^?1) at five ration sizes (2%, 4%, 6%, 8% and 10% of body weight per day) for 6 weeks. Feeding trial was conducted in triplicate. Fishes were randomly stocked at the rate of 20 fish per trough fitted with water flow‐through system. The best feed conversion ratio (FCR), specific growth rate (%) and protein efficiency ratio (PER) were evident at the ration size of 4–6% body weight. Second‐degree polynomial regression analysis of the FCR, PER, and protein and energy retention data indicated the breakpoints at ration size of 5.16%, 5.24%, 5.52% and 5.42% body weight per day. Carcass composition of fish fed different ration sizes varied significantly. Maximum carcass protein and minimum moisture content were noticed at 4% and 6% ration levels. A linear increase in fat content was evident with increasing ration levels up to 6% body weight. Ash content remained insignificantly different among various ration levels except at 2%, showing the significantly highest value. Water temperature, dissolved oxygen, free carbon dioxide, pH and total alkalinity were recorded regularly during the length of the experiment. No mortality was observed during the feeding trial. Based on the above results, it is recommended that feeding in the range of 5–5.5% body weight per day corresponding to 20 g protein and 181 kcal energy to 22 g protein and 199 kcal energy per kg of the diet per day is optimum for the growth and efficient feed utilization of C. mrigala.     

Effect of water temperature on energy budget of Nile tilapia,Oreochromis niloticus

A 21‐day growth trial was undertaken to investigate the effect of water temperature (25, 28, 31, 34, 37 °C) on growth, feed utilization and energy budget of juvenile Nile tilapia (Oreochromis niloticus) (initial body weight around 12 g) with four replicates at each temperature. Feed intake energy (IE), recovered energy (RE), faecal energy (FE), excretory energy (UE + ZE) and heat energy (HE) were calculated to obtain the energy budget. The results showed that feeding rate and ammonia excretion were not significantly affected by water temperature. Specific growth rate in wet weight (SGRw) and FE was significantly lower in the fish reared at 37 °C while no significant difference was observed between the fish reared at 25–34 °C. Protein retention efficiency was highest at 28 °C and lowest at 37 °C. The proportion of IE channelled into RE and UE + ZE was lower while those lost in HE was higher in the fish reared at 37 °C. The optimal growth temperature was estimated as 30.1 °C based on the regression of SGR and water temperature. Energy budget at maximum growth (34 °C) was: 100 IE = 27.0 RE + 1.1 (ZE + UE) + 10.6 FE + 59.2 HE. HE accounted for 69.3% and RE for 30.7% of metabolizable energy.     

Global drivers of reef fish growth

Few studies have attempted to understand how fish growth scales at community and macroecological levels. This study evaluated the drivers of reef fish growth across a large gradient of environmental variables and a range of morphological and behavioural traits. We compiled Von Bertalanffy Growth parameters for reef fishes and standardized K relative to species maximum sizes, obtaining K_max. We then modelled the response of K_max to body size, diet, body shape, position relative to the reef, schooling behaviour, sea surface temperature, pelagic net primary productivity and ageing method, while accounting for phylogenetic structure in the data. The final model explained 61.5% of the variation in K_max and contained size, temperature, diet, method and position. Body size explained 64% of the modelled K_max variability, while the other variables explained between 6% (temperature) and 2.5% (position). K_max steadily decreased with body size and increased with temperature. All else being equal, herbivores/macroalgivores and pelagic reef fishes had higher growth rates than the other groups. Moreover, length–frequency ageing tended to overestimate K_max compared to other methods (e.g. otolith's rings). Our results are consistent with (a) metabolic theory that predicts body size and temperature dependence of physiological rates; and (b) ecological theory that implies influence of resource availability and acquisition on growth. At last, we use machine learning to accurately predict growth coefficients for combinations of traits and environmental settings. Our study helps to bridge the gap between individual and community growth patterns, providing insights into the role of fish growth in the ecosystem process of biomass accumulation.     

Interactions between temperature and size on the growth,size heterogeneity,mortality and cannibalism in cultured larvae and juveniles of the Asian catfish,Pangasianodon hypophthalmus (Sauvage)

Temperature effects vary throughout the ontogeny, but are proportionally more variable during the early life stages than in older fish. The larvae of a few species have been studied but contrasting trajectories were observed, thereby making it difficult to predict how temperature impacts on the growth, survival and size heterogeneity in a particular species. This study examined these interactions in young [0.9 mg–1 g wet mass (WM)] Pangasianodon hypophthalmus, one of the most extensively cultured tropical fish. Fish were raised at five temperatures from 23 to 33 °C in a recirculated water system, fed in excess with a high‐energy feed (Artemia then a formulated feed, >50% protein), and examined at 1‐day (first feeding days) or 4‐day intervals (older fish). The temperature that produced the fastest growth (T°_opt) was 31 °C at the start of exogenous feeding (0.9 mg); it increased to 32.7 °C at 8 mg then decreased by 0.7 °C for each 10‐fold increase of WM. Size heterogeneity was lower and survival was higher (70–85% from 0.9 mg to 1 g) when the temperature was close to T°_opt. Comparisons with other species suggest that the slope of the relationship between T°_opt and fish size has a strong latitudinal component, and may also reflect the fish sensitivity to oxygen.     

Feeding,body condition and reproductive investment of Astyanax intermedius (Characiformes,Characidae) in relation to rainfall and temperature in a Brazilian Atlantic Forest stream

Life history theory seeks to explain how environmental variation selects for patterns of investment in growth and survival relative to production and survival of offspring. Seasonal variations in rainfall and temperature provide environmental cues for spawning by many tropical freshwater fishes. To investigate environment–life history associations, we conducted a one‐year study of Astyanax intermedius in an Atlantic Forest stream of southeastern Brazil. Our analysis focused on temporal variation in feeding, body condition and reproduction in relation to rainfall and water temperature. For mature females, food intake was not significantly correlated with rainfall or temperature; however, body condition was negatively correlated with rainfall and water temperature. Female reproductive effort was positively correlated with water temperature, but did not vary with rainfall. For males and juveniles, there was no significant relationship between food intake or body condition and either environmental variable. Testis weight was negatively correlated with rainfall, but was not significantly correlated with water temperature. We detected a negative correlation between gonad mass with body condition and food intake for females but not for males. Our results differed from other studies in tropical and subtropical areas where rainfall has been shown to be positively correlated with fish reproductive effort. Our results indicate that reproductive effort of males is relatively constant throughout the year, whereas for females, it increases with increasing water temperature. This increase in reproductive investment in concert with an increasing temperature and metabolic rate may incur a trade‐off with somatic growth and survival for this small stream fish.     

Nutritive value of partially dehulled and extruded sunflower meal for post-smolt Atlantic salmon (Salmo salar L.) in sea water

This study determined the digestibility of protein in partially dehulled sunflower meal (SFM) and then, as the main goal, the nutritive value of high‐temperature extruded (≤149°C) partially dehulled SFM (SFM_EX) for post‐smolt Atlantic salmon Salmo salar in sea water. The digestibility study was conducted using the settling column approach (‘Guelph system’) for faeces collection as described by Hajen, Higgs, Beames and Dosanjh. In the nutritive value study, triplicate groups of 50 salmon (mean weight ～116 g) in 4000‐L outdoor fibreglass tanks supplied with 25–40 L min^?1, filtered, oxygenated (dissolved oxygen, 7.0–8.5 mg L^?1), 11–12°C sea water (salinity, 29–31 g L^?1), were fed twice daily to satiation one of five steam‐pelleted dry diets that contained 422 g of digestible protein (DP) kg^?1 and ～16.4 MJ of digestible energy (DE) kg^?1 on a dry weight basis for 84 days. Low‐temperature‐dried anchovy meal (LT‐AM) comprised 68.2% of the basal diet protein whereas in four test diets, SFM_EX progressively replaced up to 33.0% of the DP provided by LT‐AM in the basal diet (SFM_EX≤271 g kg^?1 of dry matter). Sunflower meal had 87.9% DP. Diet treatment did not significantly affect specific growth rate (1.39–1.45% day^?1), feed efficiency (1.19–1.26), percentage of dietary protein retained (45.8–47.5), gross energy utilization (46.5–49.4%), per cent survival (96.0–99.3) or terminal whole body and muscle proximate compositions. We conclude that SFM_EX can comprise ≥271 g kg^?1 of the dry diet or ≥22.7% of the digestible dietary protein of post‐smolt Atlantic salmon in seawater without any adverse effects on their performance.     

Anticipating climate change impacts on Mongolian salmonids: bioenergetics models for lenok and Baikal grayling

The Eg–Uur River ecosystem in north‐central Mongolia provides an opportunity to study salmonid species in a system that has already experienced significant climate change. These species are currently imperilled in Mongolian waters, with Baikal grayling (Thymallus arcticus baicalensis) listed as near‐threatened and lenok (Brachymystax lenok) listed as vulnerable on the Mongolian red list. Air temperature records demonstrate that in the last 40 years Northern Mongolia's rate of warming has been three times greater than the northern hemisphere average. Despite alarming trends in air temperatures, little is known of the thermal ecology of these species. Due to the threat of climate change to these species, the objective of our study was to quantify metabolic costs for these species from streamside routine metabolic measures and derive bioenergetics models that we used to assess potential climate change response. Streamside measurements of metabolism were remarkably consistent with expectations from measures of other salmonids gathered under more closely controlled laboratory conditions. Metabolism increased exponentially with temperature for both species. The resulting preliminary bioenergetics models suggest these species are already experiencing temperatures near their upper levels for growth during summer and conditions are expected to deteriorate with warming. Even a modest 2 °C increase in water temperatures during ice out would result in a 59% reduction in growth of lenok, and an inability of Baikal grayling to grow (if food levels remained unchanged) or a 14–23% increase in consumption in order to maintain current growth rates.