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.     

The effect of feeding strategies and body weight on growth performance and hematological parameters of Siberian sturgeon (Acipenser baerii,Brandt 1869): Preliminary results

The purpose of present study was to investigate the growth performance and hematological parameters of Siberian sturgeon Acipenser baerii in three feeding strategies (satiation feeding, restricted feeding and starvation). We considered two body weights 465.75 ± 11.18 g and 250.40 ± 12 g for large fish and small fish, respectively. In a 45‐day experiment, eighteen fiberglass tanks were used for six triplicate treatments. In restricted feeding strategy, the fish were fed to 50% of satiation and starved treatments were an absolute feed deprivation throughout the experiment. At the end of 45‐day period, the hematological parameters were measured. The reduction of weight, condition factor and daily growth rate in the smaller fish was dramatically higher than the larger fish. Feed deprivation increased the rate of weight loss. Specific growth rate were negative in the large and small fish of starved treatments. The hematological results revealed no significant differences in except for the number of monocytes in larger fish. Large satiated fish showed the highest number of monocytes. In general, these strategies (restriction and deprivation) did not have any negative impacts on the hematological parameter in both sizes but respect to fish body weight, difference in total feed input between satiated and restricted treatments changed growth performance. It seems that restricted feeding (50% of satiation) in large fish was enough to achieve optimal growth while the amount of feed provided for small fish was not enough. Therefore; we can conclude that the restricted feeding is an effective strategy in rearing sturgeon at higher weight when the rearing condition is unsuitable.     

Effect of starvation and refeeding on digestive enzyme activities in juvenile roach, Rutilus rutilus caspicus

We evaluated the effects of starvation and refeeding on digestive enzyme activities in juvenile roach, Rutilus rutilus caspicus. Fish were divided into four feeding groups (mean mass 1.68 ± 0.12 g). The control group was fed to satiation twice a day throughout the experiment with formulated diet (SFK). The other three groups were deprived of feed for 1(S1), 2(S2), and 3(S3) weeks, respectively, and then fed to satiation during the refeeding period. The results showed that trypsin specific activity was not affected significantly either by starvation or refeeding, in all experimental groups. Chymotrypsin specific activity did not change significantly in S1 fish during the experimental period. In S2 and S3 fish no significant changes were observed during the starvation period. Upon refeeding, the activity increased in S2 fish, while it decreased in S3 fish. Amylase specific activity decreased significantly during the starvation period in all experimental groups. Upon refeeding, the activity increased. Alkaline phosphatase specific activity did not change significantly during the experiment period in S3 fish, while it showed significant changes during the starvation and refeeding period in the S1 and S2 fish. Starvation also had a significant effect on the structure of the intestine.     

Compensatory growth in juvenile roach Rutilus caspicus: effect of starvation and re‐feeding on growth and digestive surface area

The aim of this study was to investigate compensatory growth in juvenile Rutilus caspicus during starvation and re‐feeding periods. The results confirmed the existence of compensatory growth in R. caspicus which depended on the duration of food deprivation. Complete compensatory growth occurred in the fish that were food deprived for at least 3 weeks. Starvation and re‐feeding had no significant effect on the digestive somatic index and intestinal surface areas in the fish that were food deprived for 1 week, while they showed a significant decrease and increase, during starvation and re‐feeding in the fish that were food deprived for 2 and 3 weeks. This knowledge may have application in aquaculture, as appropriate exploitation of compensatory growth can give increased growth rate and feeding efficiency.     

The metabolic effects of prolonged starvation and refeeding in sturgeon and rainbow trout

The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.     

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.     

Characterization,tissue distribution of resistin gene and the effect of fasting and refeeding on resistin mRNA expression in Siberian sturgeon (Acipenser baerii)

Resistin as an adipokine identified from rodents in 2001 is involved in many biological processes. However, little is known about this gene in fish. We cloned Siberian sturgeon (Acipenser baerii) resistin cDNA of 795 base pairs, encoding 107 amino acids, which showed 38–40% identity to human and rodents. Real-time quantitative PCR showed that the resistin gene was widely distributed in tissues of Siberian sturgeon, with the highest expression in liver. After fasting for 1, 3, 6 and 10 days, the expression of the resistin gene in the liver of Siberian sturgeon decreased significantly, and after refeeding on the 10 days of fasting the resistin mRNA expression increased rapidly, suggesting that resistin may play an important role in liver in response to starvation. Taken together, these results suggest that resistin may be involved in the regulation of energy homeostasis in liver.     

The effect of energetic condition on growth dynamics and health of Atlantic cod (Gadus morhua)

Prolonged starvation resulting in sublethal condition factor values was hypothesized to have a detrimental effect on short‐term growth capacity upon refeeding. Cod (Gadus morhua) were food‐deprived and their length and mass measured before refeeding and after 3, 6, 9 and 12 weeks of ad libitum feeding. Total mass increase during the first 3 weeks of feeding was greatest in fish with a higher initial condition factor. The reverse situation was observed during the last 3 weeks of feeding. Specific growth rate peaked in the period from week 4 to week 6, except in cod with the highest condition factor for which a steady decline in specific growth rate was observed, and was not influenced by the condition factor at the start of the feeding period. Total mass increase over 12 weeks was also not influenced by initial condition factor. Thus by the end of the experiment, condition factors were lowest in fish with initially low condition factors. The hepatosomatic index and gonadosomatic index did not differ at the end of the experiment, but the proportion of mature cod increased with increasing initial condition factor. A disease outbreak caused significant mortalities among fish shortly after the start of the feeding period. Forty‐one percent of the fish had died after 84 days. No mortality was observed among fish that had started the experiment with the highest condition factor. Mortality was inversely related to initial condition factor. Growth was examined for survivors exclusively. Poor condition in wild fish may increase vulnerability to diseases and compensatory growth may not allow cod with low condition factors to fully recover unless food availability remains high over a long period of time.     

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.     

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.     

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 evidence of apelin has the bidirectional effects on feeding regulation in Siberian sturgeon (Acipenser baerii)

Apelin is a peptide, mainly produced in the brain, which participates in several physiologic effects. However, knowledge about the mechanism of appetite regulation in teleosts, including the role of apelin is not well understood. The aim of this study is to explore the effect of feeding status on the expression of apelin mRNA in the whole brain and the effects of injection of apelin on food intake in Siberian sturgeon (Acipenser baerii). In this study, we first cloned the apelin cDNA sequence of the Siberian sturgeon. We obtained a 1046-bp cDNA fragment, including a 237-bp open reading frame (ORF) that encoded 78 amino acids. Apelin was widely distributed in 11 tissues related to feeding regulation, with the highest expression in thewhole brain, followed by the spleen and trunk kidney. In addition, we measured the effects of periprandial (preprandial and postprandial) change, fasting and re-feeding on apelin mRNA expression in whole brain. The level of apelin mRNA was significantly decreased 1 h after feeding. The results of the fasting experiment showed that the expression of apelin mRNA in the brain was significantly reduced after 1 day of fasting but consistently increased throughout the 15-day food deprivation period. When the 15-day fasted fish were re-fed, apelin mRNA expression in the brain was significantly increased as compared to that of the control. These results suggest that apelin may play a bidirectional role in the regulation of food intake in the Siberian sturgeon. In order to further examine the effect of apelin on feeding regulation in Siberian sturgeons, acute and chronic intraperitoneal (i.p.) injection experiments were performed and food intakes were recorded. Results showed that acute i.p. injection of apelin-13 reduced food intake, however, chronic i.p. injection apelin-13 increased the food intake for 7 days in Siberian sturgeons. In conclusion, our results show that apelin has a bidirectional effect on feeding regulation in Siberian sturgeons by acting as a satiety factor in short-term feeding regulation and a starvation factor in long-term feeding regulation.     

Effects of temperature on growth,hematology, and immune responses of subadult Chinese sturgeon (Acipenser sinensis Gray 1835) under different ammonia nitrogen conditions in recirculating aquaculture system

The growth, hematology, and immune responses of subadult Chinese sturgeon (Acipenser sinensis) (avg. wt. 25.11 ± 3.74 kg) were determined at three water temperature levels (12, 18, and 24°C) × three concentrations of total ammonia nitrogen (TAN) (0.05 ± 0.02, 1.03 ± 0.04, and 2.03 ± 0.05 mg/L) for 90 days in recirculating aquaculture system (RAS). At the end of the experiment, all fish were weighed and serum was collected for analysis using biochemical parameters. The temperature level had significant effects on the growth and hematology responses of subadult Chinese sturgeon under the RAS conditions. The specific growth rate (SGR) of subadult Chinese sturgeon was highest at 18°C compared to other temperatures; at this temperature, the total antioxidant capacity (T‐AOC), alanine aminotransferase (ALT) and lysozyme (LZM) activities were also the highest (p < 0.05). As the temperature rose, the oxygen consumption rate and ammonia excretion rates significantly increased (p < 0.05). In addition, there was no effect of TAN level on ammonia excretion rates of subadult Chinese sturgeon, while the oxygen consumption rate was greater in the high TAN group compared with the other groups (p < 0.05). The SGR of the fish was markedly reduced when the TAN level rose, and blood urea nitrogen (BUN), blood ammonia (BA), malondialdehyde (MDA) and cortisol in the serum were significantly elevated when the fish were in high TAN water for 90 days (p < 0.05), T‐AOC and LZM activities in the serum clearly decreased, indicating that the antioxidant system and nonspecific immune mechanism of subadult Chinese sturgeon appeared to be inhibited, which could raise the sensitivity of the Chinese sturgeon to various pathogens. The results of this study indicate that subadult Chinese sturgeon could achieve normal growth in the RAS, but that growth and hematology were significantly affected when the TAN concentration in the water was higher than 2 mg/L for an extended period.     

Assessing the capacity for compensatory growth in growth‐hormone transgenic coho salmon Oncorhynchus kisutch

The effect of feed cycling (consisting of periods of starvation followed by periods of refeeding to satiation) on compensatory growth was evaluated in growth hormone transgenic and non‐transgenic wild‐type coho salmon Oncorhynchus kisutch. The specific growth rate (G_SR) of feed‐restricted non‐transgenic O. kisutch was not significantly different from the G_SR of fully‐fed non‐transgenic O. kisutch during two refeeding periods, whereas the G_SR of feed‐restricted transgenic O. kisutch was significantly higher in relation to the G_SR of fully‐fed transgenic O. kisutch during the second refeeding period, but not during the first, indicating that growth compensation mechanisms are different between non‐transgenic and growth‐hormone (GH)‐transgenic O. kisutch and may depend on life history (i.e. previous starvation). Despite the non‐significant growth rate compensation in non‐transgenic O. kisutch, these fish showed a level of body mass catch‐up growth not displayed by transgenic O. kisutch.     

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

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.     

Endocrine changes during the previtellogenic stage of the great sturgeon,Huso huso (Linnaeus, 1758)

The study aimed to investigate changes in serum concentrations of sex steroids, thyroid hormones, stress indices, cholesterol, triacylglycerol, calcium and phosphorus, as well as the growth in the 3‐year old previtellogenic stage of great sturgeon, Huso huso over a 6‐month period. Forty individually marked fish (mean weight 6913 g) were divided among three circular tanks under a natural temperature and photoperiod. Every 1.5 months fish were weighed and blood samples taken for serum analysis. Fish showed significant changes in 17β estradiol, testosterone, triiodothyronine (T₃), thyroxine (T₄), adrenocorticotropic hormone, cortisol, cholesterol, and phosphorus, but not in triacylglycerol and calcium concentrations. From the January onset of the experiment to the end of the trial in July, there was a decrease in sex steroids and cortisol concentrations as well as a decline in T₃ concentrations from March and in T₄ from February to July. The mean weight of fish increased significantly from the beginning to the end of the experiment. Although the oocyte diameter increased from 197 to 202 μm, the difference was not significant. The histological data on oocytes suggest that the great sturgeon, like the other sturgeons, has a heterogeneous asynchronous ovarian development in the early stage of reproduction. This data might be useful to the further understanding of the physiology of Huso huso and/or to improve its culture. Moreover, it leads to a general increase in the understanding of the basic reproductive biology of this valuable chondrostean species.     

The effect of fasting and refeeding on temperature preference,activity and growth of roach, <Emphasis Type="Italic">Rutilus rutilus</Emphasis>

Most fish species are regularly subjected to periods of starvation during which a reduction of energy turnover might be favourable for the animal. This reduction of energy flux may be achieved by changes in thermal behaviour and/or swimming activity. We investigated such behavioural changes during starvation and subsequent refeeding in roach, Rutilus rutilus, with respect to energetic benefits and growth maximisation. Roach, acclimated to a wide range of temperatures (4, 12, 20, 24, 27 and 30 °C), were fed to excess, subjected to 3 weeks of starvation and subsequently refed in order to determine the temperature dependence of feeding rates, growth rates and conversion efficiency (K₁) under control conditions and during compensatory growth. When exposed to a thermal gradient, control animals preferentially selected a temperature of 26.8ǂ.9 °C, which is in the range of the optimal temperatures for feeding, growth and conversion efficiency. Starving fish showed a distinct circadian pattern of the mean selected temperature (MST). They migrated to cooler water in the dark (MST_dark=22.8ǃ.1 °C) but returned to warmer water during daytime. This behaviour may be regarded as a trade-off between the potentially higher food density in warmer water areas and the energetic benefit of selecting cooler water patches. The circadian pattern of MST was gradually abandoned upon refeeding and control values were reached again after 3 weeks. Energetically more effective than behavioural hypothermia was the reduction of swimming activity. During starvation, activity peaks were slightly lower than under control conditions and mean daily activity decreased by about 50%. Swimming velocity, however, was not affected by feeding regime. After a period of starvation fish showed compensatory growth at all temperatures, even below 12 °C, where these animals normally do not grow. This suggests that after a period of starvation the critical temperature for growth shifts to lower values.     

Optimal stocking density for beluga,Huso huso,and ship sturgeon,Acipenser nudiventris during the grow‐out phase

The influence of three different initial stocking densities (SD) in flowthrough systems was evaluated on growth performance and feed utilizaition in beluga, Huso huso, and ship sturgeon, Acipenser nudiventris, juveniles in three different grow‐out phases for 228 days. In each grow‐out phase, fish were randomly distributed in 18 concrete square tanks (2.0 × 1.0 × 1.2 m³; 2 m³ of volume) according to the experimental SD. At the first phase, both fish species were subjected to three SD including 1.5, 3 and 6 kg/m² for 60 days. In the second phase, fish were submitted to three SD including 3, 6 and 9 kg/m², whereas in the third phase, beluga were stocked at 6, 9 and 12 kg/m² and ship sturgeon were stocked at 6, 8 and 10 kg/m² and each phase lasted for 12 weeks. In both species, the growth performance and feed intake (FI) significantly decreased with increasing SD at the end of the first phase (p < 0.05). In the second phase, growth performance and FI in beluga decreased with increasing SD, whereas in ship sturgeon neither growth nor FI were affected by SD. Interestingly, the growth performance and feed utilization in both species were not decreased with increasing SD in the third phase indicating adaptability of these species to high stocking density during grow‐out period. According to the result of this study, the appropriate initial SD for beluga within the range of 100–500, 500–2,000 and 1,500–3,000 g were at 1.5, 6 and 12 kg/m², respectively in an open flow‐throw system. Regarding to ship sturgeon, initial SD at 1.5 and 10 kg/m²recommended for fish within the range of 100–300 and 300–1,200 g, respectively in an open flow‐throw system.     

Effects of food deprivation on expression of growth hormone receptor and proximate composition in liver of black seabream Acanthopagrus schlegeli

The effects of food deprivation on the hepatic level growth hormone receptor (GHR) were investigated in black seabream (Acanthopagrus schlegeli) both at the protein level (by radioreceptor assay) and at the mRNA level (by ribonuclease protection assay). Serum levels of growth hormone (GH) and triiodothyronine (T₃) were also measured. Condition factor and hepatic proximate composition of the fish were also assessed. Significant decrease in hepatic GHR binding was recorded as early as on day 2 of starvation. On day 30 this decrease was even more pronounced, with the level in the starved fish reaching less than 20% the fed control level. A concomitant decrease in the hepatic GHR mRNA content was also noted during this period, with a progressive decrease from day 2 to day 30 of starvation. The extent of decrease in the mRNA content was less pronounced than the decrease in receptor binding, with the hepatic GHR mRNA content in the day 30 starved fish representing approximately 30% of the level in the fed control. In large contrast, serum GH level increased progressively during starvation. After 30 days of starvation, serum GH levels in the starved fish were more than three times the concentration found in the fed control. Serum T₃ levels, on the other hand, decreased during starvation, with the difference reaching significance on day 15 and day 30. After 30 days of starvation, serum T₃ levels in the starved fish were only approximately 40% the concentration found in the fed control. The hepatic lipid content exhibited an increasing trend during starvation. On day 30 the hepatic lipid content of the starved fish had doubled the level found in the fed control. However, the hepatic protein content did not exhibit much change during starvation. There was also a minor decrease in the moisture content of the liver during starvation, but the condition factor of the fish as a whole registered a gradual decrease during the course of food deprivation.     

Alterations in expression of genes associated with muscle metabolism and growth during nutritional restriction and refeeding in rainbow trout

Rainbow trout, as well as many other species of fish, demonstrate the ability to survive starvation for long periods of time. During starvation, growth rate is decreased and muscle exhibits signs of wasting. However, upon resumption of feeding, accelerated growth is often observed. Alterations in muscle metabolism occur during feed restriction and refeeding, although the ways in which these alterations affect the molecular pathways that control muscle growth have not been fully determined. To analyze changes in muscle metabolism and growth during starvation and refeeding, real-time PCR was used to test the expression of six metabolic-related genes and eight muscle-specific genes in rainbow trout white muscle prior to and after 30 days of starvation, and after 4 and 14 days of refeeding. The six metabolic-related genes chosen are indicative of specific metabolic pathways: glycolysis, glycogenesis, gluconeogenesis, the pentose phosphate pathway, and fatty acid formation. The eight muscle specific genes chosen are key components in muscle growth and structural integrity, i.e., MRFs, MEFs, myostatins, and myosin. Alterations in expression of the tested metabolic-related genes and muscle-specific genes suggest that during both starvation and refeeding, changes in specific metabolic pathways initiate shifts in muscle that result mainly in the modification of myotube hypertrophy. The expression levels of many of the metabolic-related genes were altered during the refeeding period compared to those observed before the starvation period began. However, the accelerated growth often observed during refeeding is likely driven by changes in normal muscle metabolism, and the altered expression observed here may be a demonstration of those changes.