Effect of starvation and re‐feeding on growth performance and content of plasma lipids,glucose and insulin in cultured juvenile Persian sturgeon (Acipenser persicus Borodin, 1897)

The effect of starvation and subsequent re‐feeding to satiation on compensatory growth performance, insulin and blood serum values were investigated in juvenile Persian sturgeon (Acipencer persicus) with an average weight 108.04 ± 0.28 g (mean ± SEM) and in the same rearing condition over an 8‐week period. Sturgeons were allocated to one of five feeding treatments: controls (C, continuous feeding), W1 (1 week starvation), W2 (2 weeks starvation), W3 (3 weeks starvation) and W4 (4 weeks starvation), followed by a single 4 weeks of re‐feeding to satiation. Changes in growth performance and blood serum indices were examined at the end of weeks 4 and 8. Body weight, specific growth rate (SGR), condition factor (CF) and weight gain were determined to have significantly decreased during starvation. Fish starved for 1 week reached the same weight as the control fish after re‐feeding for 4 weeks, indicating that complete compensatory growth occurred. Although the specific growth rate in W2, W3 and W4 fish was greater than that in the control fish after re‐feeding, W2, W3 and W4 fish did not reach the same body weight as control fish at the end of re‐feeding period, and showed partial compensation only. Blood plasma, glucose and insulin concentrations did not change significantly during starvation and re‐feeding (P > 0.05). This suggests that sturgeon are able to maintain glycaemia during starvation, probably due to their non‐carbohydrate dietary source. Plasma total lipid and triglyceride levels increased in starvation treatments, whereas the increases were significant only in W3 treatment (P < 0.05). After a 4‐week re‐feeding period, their levels decreased in comparison to the starvation periods. Increases in plasma total lipid and triglyceride levels appear to be due to their roles as preferred nutrients for mobilization in Persian sturgeon and the magnitude and duration of compensatory growth depended on the length of food deprivation.     

A comparative study of feeding methods: Effect on the growth,behaviour and biochemical performance of juvenile Beluga sturgeon (Huso huso Linnaeus, 1758)

This study compared the influence of feeding methods on growth parameters of young‐of‐year Beluga sturgeon Huso huso in a 6‐week trial. Fish with an average weight 150.3 ± 0.8 g (±SE) were stocked into nine circular concrete tanks (30 fish per tank) in an open circular system with water temperature of 18.9°C. All fish were fed by three different feeding methods: (a) hand‐fed (HF), (b) continuously available (automated feeder; AF), (c) half of daily feed provided by hand, and another half by automated feeder (combined feeding). For the hand‐feeding method, fish were fed at 09:00, 14:00, 19:00, and 24:00. The entire automatic feeding groups were fed with the same amount of feed. The mean final body weight was the highest in fish fed by AF compared to fish fed by HF. Body weight increase, condition factor, specific growth rate, and feed conversion ratio did not differ among the feeding groups. Fish fed by AF revealed higher swimming activity than the HF group. No significant changes were found in hematocrit, glucose and total protein concentrations among treatments. The results showed less dependence of growth and physiology of Beluga sturgeon on feeding method, but automated‐feeding was shown to be suitable for sturgeon rearing because of further low labour costs in rearing systems.     

The effect of feeding frequency on growth performance of juvenile cobia,Rachycentron canadum (Linnaeus, 1766)

The present study was carried out to investigate the number of daily feeding sessions that results in maximum growth of juvenile cobia under laboratory conditions. Groups of eight fish (110 g) were randomly distributed in twenty 500‐L tanks and hand‐fed a commercial diet for 60 days. The same amount of feed was offered daily, divided in 1, 2, 3, four or six meals. None of the parameters associated with growth performance (survival, weight gain, specific growth rate, feed intake, condition factor or size variation) showed any significant differences among treatments. Although under the present conditions feeding frequency had no effect on the growth performance of cobia larger than 110 g, in commercial farming operations where large numbers of fish are kept within a single rearing structure, fish may have aggressive interactions during feeding. Under these conditions, it is difficult to ensure that all cobia are fed to satiation and thus it is usual to provide two or more meals per day. The present results indicate that for an individual cobia the provision of more than one daily meal has no significant effect on growth performance.     

Growth performance and body composition in response to dietary protein and lipid levels in Nile tilapia (Oreochromis niloticus Linnaeus, 1758) subjected to normal and temporally restricted feeding regimes

A factorial experiment was designed to examine the effect on compensatory growth (CG) of Nile tilapia Oreochromis niloticus fed diets containing different protein and lipid levels under normal and temporally restricted feeding regimes. Four diets were formulated to contain either 30% or 36% crude protein, and 5% or 11% crude lipid. Triplicate replicates of each treatment were assigned to 24 150‐L tanks (20 fish/tank density). Fish (mean initial weight ± SD = 8.79 ± 0.34 g) were then fed either the normal feeding regime (thrice daily to apparent satiation) or the restricted regime (1 day feed deprivation followed by 3 days of feeding to apparent satiation) over a 44‐days study period. Fish receiving a diet under the restricted regime achieved weight gains (WG) comparable to fish consuming the diet containing 30% protein and 5% lipids under the normal feeding regime. Fish maintained on the restricted feeding regime exhibited reduced feed intake (FI), WG, feed efficiency ratio (FE), protein efficiency rate (PER) and hepatosomatic index versus fish on the normal feeding regime, except WG in fish fed the diet with 30% protein and 5% lipids. However, the resultant FI (85%~94%) was higher than the excepted 75% intake when fish were subjected to the restricted regime. Feeding 11% lipid diets led to improved FI, WG, FE, and PER compared to feeding the 5% lipid diets. Increased FI, WG, and FE, but reduced PER were observed in fish fed with 36% protein versus fish fed 30% protein. Fish receiving the 36% protein diets had lower whole‐body moisture and ash contents, but elevated whole‐body protein and lipid contents compared to those receiving the 30% protein diets. Whole‐body moisture contents were lower, but whole‐body protein, lipid and ash contents were higher in fish fed 11% lipid diets than in fish fed 5% lipid diets. There was an increase in whole‐body moisture content, but a decrease in protein and lipid content in response to the restricted feeding regime. Ash content was not affected by the feeding regime. The present study shows that Nile tilapia fed diets subjected to a restricted feeding regime exhibited growth comparable to those fed the diet at 30% protein and 5% lipid levels under a normal feeding regime. This positive effect was more pronounced in diets at a high protein level or in a combination of high protein and lipid levels.     

Compensatory growth in sub‐yearling Siberian sturgeon,Acipenser baerii Brandt, 1869: Effects of starvation and refeeding on growth,feed utilization and body composition

The capacity of sub‐yearling Siberian sturgeon (Acipenser baerii Brandt, 1869) (19.7 ± 0.8 g) to show compensatory growth was assessed for a 40‐day period for the effects of short‐term starvation and refeeding on growth, feeding performance and body composition. After acclimation, 25 experimental fish were randomly distributed among twelve 500‐L cylindrical fiberglass tanks with a flow‐through system. The fish were subjected to four different feeding regimes: control, which was fed four times daily to apparent satiation; T₁: four periods of 2 days starvation alternating with 8 days re‐feeding; T₂: two periods of 4 days starvation alternating with 16 days refeeding; T₃: an 8 days starvation period followed by 32 days refeeding. At the end of the experiment, the deprived fish attained body weights comparable to those attained by the control fish. There were no differences in growth and feeding performances between the deprived and the control fish. Total protein and lipid contents of the control fish were significantly higher than that of T₁ and T₂ fish at the end of the experiment (P < 0.05). A significant difference in the energy content was observed between T₂ and the control. Siberian sturgeon exhibited complete compensation, indicating a high ability of the deprived fish to grow sufficiently to fully compensate for weight loss during starvation. The results suggested that the feeding schedule involving starvation–refeeding cycles could be a promising feed management option for the culture of this species.     

Effects of feeding regime on food consumption, growth rates and tissue nucleic acids in juvenile Arctic charr, Salvelinm alpinus, with particular respect to compensatory growth

Juvenile Arctic charr responded to a change from restricted to satiation feeding by showing a growth spurt (compensatory growth). During this period of rapid growth the fish became hyper-phagic and in the days immediately following transfer from restricted to satiation feeding showed improved food conversion efficiency compared to their counterparts raised on a liberal feeding regime. Tissue (liver and muscle) nucleic acid concentrations were influenced by feeding regime, and RNA : DNA ratios were low in both starved fish and those fed restricted rations. Following transfer from restricted to satiation feeding, tissue RNA : DNA ratios were rapidly restored to initial levels. The uses of tissue RNA: DNA ratios both in evaluating nutritional status and as growth indices are discussed.     

西伯利亚鲟在高温下饥饿后的补偿生长

在高温(29±1)℃下将西伯利亚鲟幼鱼(21.61±0.03)g饥饿0(对照)、6、12和18d后恢复摄食3周, 研究摄食、生长和鱼体组成的变化。结果表明, 经过不同程度饥饿的鱼体重均显著低于对照组(P0.05), 而饥饿18d(S18组)的鱼体重显著低于对照(P0.05)。在饥饿过程中,鱼体脂肪含量和肝脏肝糖原含量下降的同时, 各饥饿组的灰分含量上升, 但仅S18组与对照差异显著(P0.05)。结果表明, 西伯利亚鲟在高温下表现出完全补偿现象, 且是通过同时提高摄食率和饲料效率来实现补偿生长的, 因此在夏季高温时对鲟鱼进行一段时间适度的饥饿可以在不影响生长和体成分的前提下节约饲料成本, 减少因过量投饵而引起的环境污染。       

The effects of feeding regime on proximate body composition and patterns of energy deposition in juvenile Arctic charr, Salvelinus alpinus

Juvenile Arctic charr, Salvelinus alpinus , subjected to either food deprivation or restricted feeding showed reductions in relative sizes of both liver and viscera. With food deprivation, percentage lipid decreased and percentage water increased in the eviscerated carcass, which is in agreement with findings for several other fish species. Following transfer from a restricted to a satiation feeding regime, the relative sizes of both liver and viscera increased to levels exceeding those of fish fed continuously to satiation. At the end of the experiment the percentage liver lipid content of restricted-satiation fed fish was higher than in fish fed to satiation. These differences in energy deposition patterns were, however, not sufficiently large to produce marked differences at the whole animal level, since whole body lipid energy: protein energy ratios and energy utilization efficiencies were similar for restricted-satiation and satiation fed fish.     

Effects of different food on growth and survival of first‐feeding taimen Hucho taimen (Pallas, 1773) larvae

A study was conducted to compare growth and survival of Hucho taimen larvae from 21 to 76 days after hatch (DAH) fed one of three diets: formulated feed alone (group F); a co‐feeding diet of water fleas, tubifex and formulated feed (group C); or live food of water fleas and tubifex (group L), and to investigate the potential use of dietary L‐alanyl‐L‐glutamine (L‐AG) in larval taimen for a more nutritious starter diet. Triplicate groups of 5000 fish were randomly assigned to each aquarium provided with water from a flow‐through system, and fed to apparent satiation. The results show that larvae can feed efficiently on floating crumbled particles of formulated feed. Weight gain of larvae fed only formulated feed was significantly lower than other groups at 34 DAH (P < 0.05). At the end of the experiment, weight gain reached the highest value in group F and was lowest in group L (P < 0.05). Condition factor reached the highest values in group F and lowest in group C (P < 0.05). Specific growth rate was in accordance with weight gain at 76 DAH. Survival showed no differences among the groups (P > 0.05). In conclusion, H. taimen larvae can be fed formulated feed alone and L‐AG may be used as a feeding attractant during the weaning process, which should lead to a better understanding in the rearing improvement in the feeding of larvae.     

The effect of feeding rate on growth of pectoral fin spine of juvenile great sturgeon Huso huso (Linnaeus, 1758)

The effect of two feeding rates (0.5 and 1.5% of total body weight) was assessed on the growth of pectoral fin spines of captive juvenile great sturgeon, Huso huso, after second year of life. The fish received Oxytetracycline (OTC) twice in the first and second years of their lives under basic diet. During the 5‐month experimental period, juveniles (mean 1,187.4 g, 0.1 standard deviation [SD]), n = 50) were reared with two feeding rates under similar conditions in 10 fiberglass tanks (1.5 m³). The fish were fed manually with a commercial diet twice a day (35% Biomar, Nersac, France) throughout the experiment. The OTC marks were distinguished in all pectoral fin spine sections under ultraviolet light. The means of the first and second annular radii were 806.6 µm (27.2 SD) and 2,246.5 µm (50.2 SD), respectively. The marginal increment analysis beyond the second OTC mark revealed a significantly smaller marginal increment for low feeding rate treatment (143.9, 11.2 SD) as compared to the high feeding rate one (269.0, 14.6 SD). The results indicate the slower growth rate in the fish fed the low feeding treatments seen in the pectoral fin spine formation, which can be used as an indicator of recent feeding history in sturgeon juveniles. The best daily feeding rate for great sturgeon of 2,460 g was determined to be 1.5% body weight/day in this study.     

The influence of sulphur,molybdenum and cadmium exposure on the growth of goat,cattle and pig

A three factorial designed feeding experiment with common carp (Cyprinus carpio L.) was carried out in an intensive experimental rearing system. Fish (initial body weight 200 g) were fed on two different levels of dietary energy (16 and 18 MJ DE/kg DM), two different levels of protein (320 and 420 g CP/kg DM) and also two different feeding intensities (100% and 75% of the maximum intake). The experiment was terminated when fish reached a mean body weight of 1300 g.

Growth, feed utilization and nutrient composition of the whole body and fillet were observed. The highest growth was obtained when the fish were fed on the diet containing high dietary energy and high dietary protein with satiation feeding. High dietary energy, high dietary protein and restriction of feed intake improved feed conversion ratios. High dietary energy, low dietary protein and restrictive feeding increased energy utilization. Low dietary protein and restrictive feeding resulted in better protein utilization.

Fish fed with high dietary energy contained more fat and less protein in their carcasses. A lower fat content but higher protein and higher ash content in fish carcasses was shown when fish were fed with a diet high in protein and fed restrictively.     

Effect of winter feeding and starvation on the growth performance of young‐of‐year (YOY) great sturgeon,Huso huso

The objective of this study was to evaluate the feeding rate of the great sturgeon (Huso huso) young of the year (YOY) and to investigate the effects of different feeding rates in maintaining the weight of fish during short periods of winter starvation. Six feeding rates of 0.2, 0.4, 0.6, 0.8, 1.0% body weight (BW) day^?1 and feeding to satiation were considered for the first experiment. Each feeding rate was randomly assigned to three replicate tanks, with continuous feeding throughout a 5‐week winter period of water temperatures below 10°C. Fifteen fish were held in each of 18 tanks with an average initial body weight of 219.6 ± 6.9 g. After 5 weeks of feeding, the best performance was observed in fish fed 1% BW day^?1, but negative growth was observed in fish fed 0.2% BW day^?1. In the second experiment, fish were deprived of feed for 3 weeks at winter temperatures. Weights and condition factors of all fish decreased during starvation, while the differences in mean weight before and after the starvation period were not significant in fish fed a level of 0.2% BW day^?1 and those fish fed to satiation. No mortality was recorded in either experiment. Results of this study indicate that a feeding rate of 1% BW day^?1 would be sufficient for commercial fish farming of YOY of this species to maintain them over winter. Also, to maintain fish weights and prevent weight loss in overwintering ponds, a feeding rate of around 0.3% BW day^?1 seems appropriate for hatcheries.     

Partial compensatory growth in hybrid tilapia Oreochromis mossambicus × O. niloticus following food deprivation

The capacity of hybrid tilapia Oreochromis mossambicus × O. niloticus [23.2 ± 0.2 g (mean ± SE)] to show compensatory growth was assessed in an 8‐week experiment. Fish were deprived of feed for 1, 2 and 4 weeks, and then fed to satiation for 4 weeks; fish fed to satiation during the experiment served as control. Water temperature gradually declined from 28.1 to 25.5°C throughout the experiment. Specific growth rate (SGR) decreased with progressive food deprivation. At the end of deprivation, body weight was lower in the deprived fish than in the control. Fish deprived for 4 weeks exhibited lower contents of lipids and energy in whole body, and higher moisture content and ratio of protein to energy (P/E) than those of the control; they also consumed feed faster than the control when normal feeding was resumed. All deprived fish showed higher food intake (FI) than that of the control during re‐alimentation; however, enhanced SGR was only observed in the fish deprived for 4 weeks. There were no significant differences in digestibility of protein and energy, food efficiency (FE) or energy retention efficiency between the control and deprived fish. At the end of re‐alimentation, deprived fish failed to catch up in body weight with the control, while content of moisture, lipids and energy, and P/E in whole body of the deprived fish did not significantly differ from that of the control. The results of the experiment revealed that the hybrid tilapia reared in freshwater showed partial capacity for compensatory growth following food deprivation of 4 weeks, and that growth compensation was due mainly to increased FI, rather than to improved FE.     

Effect of feeding frequency as a rearing system on biological performance,survival, body chemical composition and economic efficiency of Asian seabass Lates calcarifer (Bloch, 1790) reared under controlled environmental conditions

A 70-day rearing trial was done to determine the optimal frequency of feeding on growth performance (GP), feed conversion rate (FCR), cannibalism, survival rate (SR), body chemical composition and economic efficiency of the Asian sea bass. This study tested four different treatments of feeding frequencies (FF), once (T1), twice (T2), three times (T3), and four times (T4) per day. An average initial weight of Asian sea bass fry was 0.2 g (SD = ±0.12) were stocked 10 individuals per m³ (9.14 m × 1.82 m × 1.22 m, L × W × H; water depth 0.61 m) with two replicates per treatment (4 × 2 = 8). Fry were fed a mixture of larval commercial feed and shrimp with a pellet diet containing (46% CP). Initially, the feeding rate of 8% biomass per day was further adjusted according to fish biomass on a weekly basis. Results showed that, the FF significantly affected (p < 0.05) on growth indictors and survival rate (SR). Specifically fry fed three times a day (T3) had the best FBW, FL, SGR, ADWG and FCR followed by T4 and T2 while fry fed one time a day was the lowest in these parameters. Also, VSI, HSI and CF (k) significantly differed among the treatments. The fish whole body content of protein, moisture and ash did not significantly (p < 0.05) be affected by feeding frequency, but lipid content differed and both T3, T4 were the highest. It could be concluded that, increasing FF up to three times a day had a positive effect on weight gain, survival rate and feed utilization of Lates calcarifer. The second degree polynomial regression indicates that fed three times a day is optimum for best growth performance and survival for Asian sea bass.     

Effects of temperature and feed intake on astaxanthin digestibility and metabolism in Atlantic salmon, Salmo salar

The effects of feed intake, growth rate and temperature (8 and 12 °C) on apparent digestibility coefficients (ADC), blood uptake of individual astaxanthin E/Z isomers and metabolism of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) were determined in Atlantic salmon. Accumulation of idoxanthin (3,4,3′-trihydroxy-β,β-carotene-4-one) in plasma was used to indicate metabolic transformation of astaxanthin. Quadruplicate groups of fish were subjected to three different treatments; one treatment was kept at 12 °C and fed to satiation. Another treatment kept at 12 °C was pair-fed with fish fed to satiation at 8 °C, resulting in a restricted feeding regime for the former treatment. After 2 months of feeding, the fish were fed a single meal containing ballotini glass beads to determine individual feed intake and Y₂O₃ as an inert marker to determine ADCs. The faeces samples were pooled into 6 categories according to individual meal size (range 0.2–1.5% of body weight) and the ADCs for different meal sizes were determined. ADCs of astaxanthin ranged from 20% to 60% but were not significantly correlated with meal size. However, fish kept at 12 °C had approximately 10% higher ADC than fish kept at 8 °C (p = 0.032). Growth rate and plasma astaxanthin concentration were higher at higher temperature and higher ration. Plasma concentration of idoxanthin was not affected by temperature or by meal size. The incidence of fin erosion and non-feeding individuals was significantly higher among fish fed a restricted ration indicating more aggressive interactions. Fish with visible fin damage had a tendency for having higher idoxanthin content in plasma than fish without noticeable fin damage. It is concluded that temperature but not individual meal size affect ADC of astaxanthin, whereas both influence plasma astaxanthin levels and may therefore affect the efficiency of astaxanthin utilization.     

Effects of dietary prebiotic GroBiotic®‐A on growth performance,plasma thyroid hormones and mucosal immunity of great sturgeon,Huso huso (Linnaeus, 1758)

The present study was conducted to evaluate the effects of Grobiotic^®‐A, a commercial prebiotics, when administered in feed on the growth performance, plasma thyroid hormones and mucosal immunity of great sturgeon (Huso huso). The commercial prebiotic mixture was supplemented in the diets at four different levels (i.e. 0.0% as control, 0.5%, 1% and 2%, in three replicates, 20 fish per replicate) and fed to the fish for an 8‐week period wherein 240 fish were cultured in 1,800‐L fiberglass tanks that formed part of a flow‐through system. Water temperature was maintained at 20.4 ± 1.5°C. Significant changes in growth performance parameters were observed, but only in those groups fed with 1% and 2% prebiotics. Specifically, marked improvements relative to the control group were observed in percentage weight gain, body weight gain, feed conversion ratio and specific growth rate in prebiotic‐fed fish. The levels of plasma thyroid hormones, specifically thyroxine and thyroid stimulating hormones were significantly elevated in the group receiving 2% prebiotics. Activities of lysozyme and alkaline phosphatase in skin mucus were significantly enhanced in prebiotics‐fed groups, particularly at an inclusion level of 1% and higher (2% group compared to the control). Inhibitory activity of the skin mucus against pathogens, particularly Streptococcus iniae and Yersinia ruckeri, was significantly improved following prebiotic feeding. Taken together, dietary inclusion of GroBiotic^®‐A promoted growth, modulated thyroid hormones, and enhanced mucosal immunity of H. huso. This prebiotic mixture has the potential for use in improving the growth performance and health status of farmed great sturgeon.     

Phytase can reduce theneedfor monocalcium phosphate supplementation in soybean and rapeseed meal‐based diets of black sea bream,Acanthopagrus schlegelii (Bleeker, 1854)

A feeding trial was conducted to study the effect of partial replacement of dietary monocalcium phosphate (MCP) with phytase on growth performance, feed utilization and phosphorus discharge in black sea bream, Acanthopagrus schlegelii. In the feeding trial, the control diet (designated as P1.5) was prepared with 1.5% MCP but without phytase, and the three other diets (designated as PP1.0, PP0.5 and PP0, respectively) were supplemented with 1.0%, 0.5% and 0% MCP, respectively, along with 200 mg (400 U) phytase/kg diet in each. Each diet was tested in triplicate tanks and fish were fed twice daily to satiation. After an 8‐week feeding trial in indoor flow‐through cylindrical fibreglass tanks (25 fish per tank, initial body weight: 11.5 ± 0.12 g), fish fed with PP1.0 and PP0.5 had no significant change in weight gain (WG), specific growth rate (SGR), protein efficiency rate (PER) or feed conversion ratio (FCR) compared to the control (p > .05), whereas fish fed with PP0 showed a significantly lower growth performance in the above parameters (p < .05). The addition of phytase did not affect the body composition or muscle composition. The apparent digestibility coefficients (ADCs) of crude protein and phosphorus increased when fish were fed diets in which MCP was replaced by phytase. Phosphorus discharge was also significantly reduced in fish fed diets in which MCP was replaced by phytase (10.2 ± 0.50 to 8.01 ± 0.47 g/kg weight gain). The present study suggests that dietary MCP can be reduced when phytase is added to the black sea bream diet, with a maximum MCP reduction level of up to 1% when phytase is supplemented at 200 mg (400 U)/kg diet. Thus, phytase in the diet of black sea bream is economically and ecologically beneficial.     

The combined effect of feeding time and ration on growth performance and nitrogen metabolism of greenback flounder

Greenback flounder Rhombosolea tapirina ( c. 2 g) fed to satiation had significantly ( P <0·01) higher feed consumption in the evening than in the morning whereas there was no difference between feeding times for flounder fed restricted rations (1 or 2% body weight per day) because they consumed all of the ration. Differences in growth performance were due to feeding time and ration. Carcass moisture, lipid and energy content were significantly ( P <0·001) different between rations; length gain was significantly affected by feeding time ( P <0·05) and ration ( P <0·001); weight gain showed a significant ( P <0·001) interaction between feeding time and ration. The relationship between feed consumption and specific growth rate showed that the exponential gradient was significantly higher ( P <0·01) for the evening fed fish and indicated feed efficiency for evening fed fish increased as feed consumption increased. Urea excretion increased from 12–20 to 58–63% of total nitrogen excretion at the 1 and 3% rations, respectively. Ammonia and urea excretion were significantly affected by ration ( P <0·001) and feeding time ( P <0·05). Fish fed the 2% ration in the evening had higher growth efficiency and significantly ( P <0·01) lower rates of urea excretion than fish fed 2 or 3% ration in the morning. It is suggested that the higher energetic costs associated with differences in ammonia and urea excretion contributed to differences in growth efficiency.     

Behavioural response of Kootenai white sturgeon (Acipenser transmontanus,Richardson, 1836) early life stages to gravel,pebble, and rubble substrates: guidelines for rearing substrate size

Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programmes creating habitats for spawning and rearing of early life stages. To determine the effects of rock size on motile early life stages, experiments were conducted in artificial streams to observe the behaviour of free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus) relative to rock size. Most (≥90%) of the free embryos in replicate test streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks, with few moving downstream. There was no difference in downstream movement of free embryos among rock treatments, therefore all rock types provided cover habitat. Similarly, in rock mixture tests, with a variable percentage of pebble, small rubble, or large rubble in different tanks, even fewer free embryos moved downstream. With increasing age, larvae increasingly used the open bottom and velocity refuges downstream of or alongside rocks of any size while drift feeding. Downstream movement of larvae in both rock regime tests was affected by rock size, with significantly reduced movement relative to increasing abundance of large rock (rubble). However, in all rock mixtures, free embryos (and later, larvae when they stopped dispersing) preferred the smallest rock size available (pebble; P = 0.0001). This suggests a strong innate preference of both life stages for small substrate that is likely related to increased survival. A rock mixture of 10% gravel (16–32 mm diameter) and 30–40% pebble (diameter, 30–60 mm) should provide adequate rearing substrate for free embryos and early‐larvae. The remaining 50–60% should be mixed rubble and boulders for spawning and egg rearing.     

Compensatory growth following various time lengths of restricted feeding in rainbow trout (Oncorhynchus mykiss) under summer conditions

This study was conducted to determine the effects of various time lengths of restricted feeding at 0.5% of body weight on compensatory growth (CG) in rainbow trout under summer conditions. Seven treatments with triplicate tanks consisted of control (C) fed to satiation over 98 days and the remainder being one (R1) to six (R6) weeks of restriction and then refeeding for the remaining 8 weeks of the experiment. At the end of the experiment R1 and R2 were able to catch up with C. Repeated measures anova suggested a convergence in body mass but not in body length (structure), whereas there was an association between mass and structural CG responses. Hyperphagia and transiently better food utilisation were main mechanisms of the observed CG. Organosomatic indices of the restricted groups were significantly reduced at the end of the restriction periods, but were restored to the control fish levels by the end of the refeeding period. There was a linear increase in body moisture and a decrease in lipid and lipid/lean body mass ratio with the severity of the restriction periods, but these trends vanished by the end of refeeding. The findings of the present experiment suggest that restricted feeding and the following realimentation to elicit CG as a management tool can be used in rainbow trout, but for no more than 2 weeks under summer conditions.